Research article Received: 10 May 2014,
Revised: 27 July 2014,
Accepted: 30 November 2014
Published online in Wiley Online Library
(wileyonlinelibrary.com) DOI 10.1002/bio.2840
Photoluminescence enhancement in Na3SO4Cl: X (X=Ce3+, Eu3+ or Dy3+) material Nita Shinde,a N. S. Dhoble,b S. C. Gedamc* and S. J. Dhoblea ABSTRACT: The compound Na3SO4Cl X (X = Ce3+, Eu3+ or Dy3+) prepared by the wet chemical method was studied for its photoluminescence (PL) and energy transfer characteristics. The PL from Na3SO4Cl:Ce3+ shows strong emission at 322 nm at an excitation of 272 nm. Therefore, an efficient Ce3+ → Dy3+, Eu2+ → Dy3+ and Eu2+ → Eu3+ energy transfer had taken place in this host. The Dy3+ emission caused by Ce3+ → Dy3+ energy transfer under ultraviolet (UV) wavelengths peaked at around 477 nm and 572 nm due to 4 F9/2 → 6H15/2 and 6H13/2 transitions with yellow–orange emission in the Na3SO4Cl lattice. An intense Dy3+ emission was observed at 482 and 576 nm caused by the Eu2+ → Dy3+ energy transfer process and due to 4 F9/2 → 6H15/2 and 4 F9/2 → 6H13/2 transitions respectively. The Eu3+ blue to red light emission caused by the Eu2+ → Eu3+ energy transfer peaked at 593 nm and 617 nm due to 5D0 → 5D3 transitions. The presence of trivalent Eu in Na3SO4Cl suggested the presence of Eu3+ in the host compound that occupied two different lattice sites and that peaked at 593 and 617 nm due to 5D0 → 7 F1 and 5D0 → 7 F2 transitions respectively. The trivalent europium ion is very useful for studying the nature of metal coordination in various systems due to its non-degenerate emitting 5D0 state. The present paper discusses the photoluminescence characteristics of Eu2+ → Dy3+ and Eu2+ → Eu3+ energy transfer. This compound may be useful as a lamp phosphor. Copyright © 2015 John Wiley & Sons, Ltd. Keywords: photoluminescence; wet chemical method; optical material; lamp phosphor; rare earths
Introduction Chlorosulphate phosphors activated with rare earth ions are known to be luminescent materials and have been used particularly in photoluminescence (PL) and thermoluminescence (TL) studies. Chloride substituted for a large number of sulphates has several interesting optical properties. There has been recent increased interest in chloride-based materials because of their wide ranging applications (1–6). Recently, Gedam et al. have reported on KZnSO4Cl, KMgSO4Cl, KCaSO4Cl Na3SO4Cl, Na6(SO4) 2FCl, Na6Pb4(SO4)6Cl2 and CeSO4Cl chlorosulphates that were activated with different rare earths and inner transition elements (7–12). Energy transfer phenomena have lead to the development of new and efficient photoluminescence materials. By using the wet chemical method (WCM), significant results in photoluminescence have been observed in the Na3(SO4)Cl host. Efforts have also been made towards finding new sulphate phosphors that could be used for PL. Sulphate materials such as europium-doped fluoride (13), borophosphate (14) and halosulphate (15), have been used in tricolor fluorescent lamps (16), electroluminescent lamps and display devices (17). Ce3+ is a low cost material that can provide strong absorption of UV light and an efficient conversion to longer wavelengths. Halosulphate phosphors can be easily prepared by the WCM and large numbers of sulphates with a well characterized structure are known, therefore it was decided to study the emission of Ce3+ in halosulphate materials. The luminescence properties of Ce3+ compounds have been of considerable interest in recent years. Ce-activated phosphors can be widely used in scintillation detectors (18), and detectors for X-ray imaging (19–21). Dy3+ emission falls mainly into two bands in the visible region, arising from 4 F9/2 → 6H15/2 (470–500 nm) and 4 F9/2 → 6H13/2 (570 nm) transitions. The relative intensities of the two bands
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depend on local symmetry (22). When the ratio of blue to green emission is appropriate, one can obtain white emission using Dy3+. This property has generated some interest in Dy3+ luminescence. Ultraviolet light cannot efficiently excite Dy3+ because its charge transfer (CT) state as well as the 5d levels are situated above 50,000 cm1. Dy3+ can be sensitized by Bi3+ (23), Gd3+, Ce3+, Pb2+ and vanadate (24–26) ions. GdAl3B4O12 doped with Bi3+ and Dy3+ is an efficient lamp phosphor. YVO4:Dy3+ is another lamp phosphor. From our previous work (27) on this phosphor, it is clear that the phosphor is quite suitable to give luminescence following different methods of synthesis. We had previously used the solid-state diffusion method for the preparation of this phosphor. We had observed that an excitation band was located at around 232 nm (λem = 341 nm). In the PL emission spectra of Ce3+ ions with different concentration under excitation of 232 nm, the peaks were observed at 335 nm, which are assigned to the 5d → 4f transition of Ce3+ ions. It was observed that with increasing concentration of Ce3+ ions the peak intensity (at
* Correspondence to: S. C. Gedam, Department of Physics, KZS Science College, Kalmeshwar, Nagpur-441501, India. E-mail: [email protected] a
Department of Physics, RTM Nagpur University, Nagpur 440033, India
b
Department of Chemistry, Sevadal Mahila Mahavidyalaya, Nagpur 440018, India
c
Department of Physics, KZS Science College, Kalmeshwar, Nagpur 441501, India Abbreviations: PL, photoluminescence; TL, thermoluminescence; UV, ultraviolet; WCM, wet chemical method; XRD, X-ray diffraction.
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341 nm) increases. Similarly, in Na3(SO4)Cl:Ce, Dy phosphor, PL emission of Dy3+ ions was observed at 482 and 571 nm (for 340 nm of excitation ) due to presence of Ce3+ ion, as a sensitizer. Dy3+ emission at 482 and 571 nm was observed due to the 4 F9/2 → 6H15/2 and 4 F9/2 → 6H13/2 transitions of the Dy3+ ion, respectively. Compared with this method, the results obtained by WCM show that, according to PL (excitation and emission) spectra, the method of preparation not only affected the peak height but also the peak profile. Comparatively, the WCM was quite suitable and a simple option for the synthesis of this phosphor.
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Na3SO4Cl host doped by Ce; Dy and Eu as well as co-doped by Ce, Dy; and Eu, Dy phosphors were synthesized by a WCM taking into account the following reaction:
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Wavelength (nm) Figure 1. PL excitation spectra of Na3SO4Cl:Ce.
Na2 SO4 þ NaCl→Na3 SO4 Cl
Results and discussion PL in Na3SO4Cl:Ce The XRD pattern and PL characterization of the Na3SO4Cl:Ce sample (solid state diffusion method) has performed previously (27). Figure 1 shows the excitation spectra peaked at λex = 272 nm when monitoring at 322 nm emission. In this figure some selected emission spectra with various Ce3+ contents are shown. The emission peak wavelength and its relative intensity are shown for different contents (0.2 mol% to 0.5 mol%) of the Ce3+ ion in Fig. 2. It was clear that with increase in Ce3+ content, the emission intensity increased relatively. Curves (a) and (b) represent the emission spectra for 0.5 mol% and 0.2 mol% concentrations of Ce3+ respectively and show its broad band nature. The well known UV emission of Ce3+ ions in these phosphors was around 322 and 342 nm. This band is due to the allowed transition from 5d → 4f of Ce3+ ions, giving maximum intensity for the excitation wavelength of 272 nm. The excitation energy
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For preparation of Na3(SO4)Cl:Ce the starting materials, NaCl, Na2SO4 and cerium sulphate salt were of analytical grade and were taken at a stoichiometric ratio. These materials were weighed in the proper molar ratio and then dissolved separately in double-distilled de-ionized water and then mixed, resulting in a solution of Na3SO4Cl:Ce and confirming that no undissolved constituents were left behind and all the salts had completely dissolved in the water. Then, this homogeneous mixture was heated at 80 °C for 12 h in an oven, resulting in the formation of the Na3SO4Cl:Ce compound in powder form. The samples were then slowly cooled at room temperature. The resultant polycrystalline mass was crushed to fine particles in a crucible, this powder form was used for further study. The same process was adopted for the rest of the samples such as Na3SO4Cl:Dy; Na3SO4Cl:Ce, Dy; Na3SO4Cl:Eu and Na3SO4Cl:Eu, Dy (here sulphate salts of dysprosium and europium were used).The prepared host lattice was characterized for its phase purity and crystallinity by X-ray powder diffraction (XRD). The PL emission spectra of the samples were recorded using a fluorescence spectrometer (Shimatzu RF-5301). The same amount of sample was used in each case. Emission and excitation spectra were recorded using a spectral slit width of 1.5 nm.
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Wavelength (nm) Figure 2. PL emission spectra of Na3SO4Cl:Ce: (a) 0.5 mol%; (b) 0.2 mol %.
matched the energy separation between the ground state and lowest state of the 5d level of the ion. This situation populates the lowest 5d level to the maximum and favours maximum emission intensity. The characteristic feature of the emission band is the absence of the expected doublet arising due to the transition from 5d → 2 F5/2 and 2 F7/2 levels due to spin orbit splitting of the 4f1 ground state of Ce3+ ions.
PL in Na3SO4Cl:Dy3+and Ce3+ → Dy3+ energy transfer The emission of Dy3+ originates from the 4 F9/2 level. The transitions to 6H15/2 (~475 nm) and 6H13/2 (~570 nm) dominate. The latter has ΔJ = 2 and is hypersensitive. The emission has a whitish to yellow colour in host lattices where hypersensitivity is pronounced. There is a Ce3+ ion as a possible sensitizer of the halosulphates lattice and Dy3+ as activator. Dy3+ can be excited by neither low nor high pressure mercury discharges (> 40,000 cm1) because the charge transfer level and also the lowest 5d level of Dy3+ are situated at energies >50,000 cm1. The excitation can occur only by the parity forbidden f → f transition,
Copyright © 2015 John Wiley & Sons, Ltd.
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Photoluminescence in Na3SO4Cl: X (X = Ce3+, Eu3+ or Dy3+) 304
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leading to weak absorption by Dy3+ from the radiation of mercury discharge. The excitation spectra of the Dy-doped ions in the Na3SO4Cl host are shown in Fig. 3. In this figure the excitation spectrum was recorded and plotted, monitoring at 474 nm emission. At this wavelength the emission spectra for different concentrations (0.05 mol% and 0.1 mol%) were observed. The most intense broad excitation band with maximum at 357 nm was observed. Selecting the 357 nm excitation wavelength, the emission spectra for the same samples was recorded. A strong PL emission of Dy3+ ions was observed at 474 and 576 nm in Na3SO4Cl:Dy phosphor. The Dy3+ emission at 474 and 576 nm was observed due to 4 F9/2 → 6H15/2 and 4 F9/2 → 6H13/2 transitions respectively (under excitation wavelength at 357 nm (Fig. 4). Energy transfer from donor to acceptor plays an important role in luminescence and solid state lasers. In this study, we used the Na3SO4Cl halosulphate as host for the luminescence and energy transfer process for Ce → Dy ions. The excitation and emission spectra of the co-doped Ce → Dy ions in the Na3SO4Cl halosulphate host are shown in Figs 5 and 6. In this figure the
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Wavelength (nm) Figure 5. PL excitation in Na3SO4Cl:Ce,Dy.
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Wavelength (nm) Figure 6. PL emission spectra of Na3SO4Cl:Ce 5 mol%, Dy: (a) 0.2 mol%; (b) 0.1 mol%; (c) 0.05 mol%.
Figure 3. PL excitation spectra of Na3SO4Cl:Dy.
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Wavelength (nm) Figure 4. PL emission spectra of Na3SO4Cl:Dy: (a) 0.05 mol%; (b) 0.1 mol%.
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excitation spectrum was recorded and plotted, monitoring at 474 nm emission. The excitation spectra showed the maximum position at 304 nm and a faint shoulder at about 273 nm. Selecting 304 nm excitation wavelengths, the emission spectra were recorded for Ce5mole% and Dy0.1mole% contents in this sample. The emission spectra show the two prominent peaks at 477 nm and 572 nm with sharp and high intensity. As Ce3+ and Dy3+ ions were co-doped to the system, the Ce3+ emission nearly disappeared with corresponding intense emission lines of Dy3+ observed at 477 nm and 572 nm. The Dy3+ emission was due to transition of 4 F9/2 → 6H15/2 at 477 nm and 4 F9/ 6 2 → H13/2 at 572 nm, respectively. These results indicates that very efficient energy transfer from Ce3+ to Dy3+ takes place in the Na3SO4Cl halosulphate lattice. This result occurred due to energy transfer from Ce3+ to Dy3+ ions. Figure 7 shows the Ce3 + → Dy3+ energy transfer mechanism in Na3SO4Cl halosulphate material. The emission in Dy3+ comes via a non-radiative transition to the 4 F9/2 level followed by radiative transitions to 6H15/2 and 6H13/2 levels.
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Figure 7. Ce → Dy halosulphate material.
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energy transfer mechanism in Na3SO4Cl:Ce5 mol%, Dy
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Wavelength (nm) Figure 9. PL emission spectra of Na3SO4Cl:Eu: (a) 0.5 mol%; (b) 0.2 mol%.
Eu2+ → Eu3+ and Eu2+ → Dy3+ energy transfer 2+
Eu emission results from two types of transitions. The most common is that due to 4f 65d → 4f 6 (8S7/2) transition. As the position of the band corresponding to 4f 65d configuration is strongly influenced by the host, the emission can be any where from 365 nm (e.g. in BaSO4) to 650 nm. As the 4f → 5d transition is an allowed electrostatic dipole transition, the absorption and emission of Eu2+ is very efficient in many hosts, which makes the Eu2+-doped phosphors of practical importance. Figure 8 shows an excitation spectra that peaked at 396 nm and had the two small peaks at 382 nm and 387 nm. The emission spectra of Na3SO4Cl:Eu2+ (0.2 and 0.5 mol%) phosphors are shown in Fig. 9. As can be seen in the figure, the emission of the material has a prominent peak at around 425 nm having a number of small peaks around this wavelength that can be well assigned to Eu2+ emission arising from transitions of the 4f65d configuration to the 8S7/2 level of the 4f7 configuration. The result illustrated that the main emission peaks of this phosphor are at about 593 nm and 617 nm, which indicated that Eu2+ ions have been shifted to Eu3+ completely in the Na3SO4Cl:Eu phosphor. For 0.5 mole% of concentration for Eu there were two intense peaks observed at 593 nm and 617 nm, which showed
the Eu3+ emission. The PL emission spectrum of Na3SO4Cl:Eu chlorosulfate phosphor showed an Eu2+ emission due to the 4f → 5d transition at the 425 nm wavelength and was the basic characteristic of the Eu2+ emission in the blue region. The PL emission showed there was transfer of energy from Eu2+ to Eu3+ ions. Eu3+ PL emission was also observed in the presence of Eu2+ due to 5Do → 7 F1 and 5Do → 7 F2 transition of Eu3+ ions. Figure 9 shows that the Eu2+ emission gets less suppressed and enhances the Eu3+ PL emission in the red region at the same excitation wavelength. The Eu3+ emission reached the characteristics of the red region, i.e. 611 nm wavelengths. This showed that the Eu2+ emission as well as the Eu3+ emission is possible in this lattice. The induced luminescence of Eu3+ via the radiative energy transfer is shown in Fig. 10. The population at the 5D3 level of Eu3+ increased via the radiative energy transfer from Eu2+ to Eu3+. Finally, the population arrived at the emitting 5D0 level via non-radiative transitions from the upper levels. The trivalent europium ion is very useful for studying the nature of metal coordination in various systems, owing to its non-degenerate emitting 5D0 state. It is possible that in Na3SO4Cl:Eu, Dy some form of energy transfer takes place with the Eu2+ ions acting
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Figure 10. The induced luminescence of Eu Na3SO4Cl:Eu.
Copyright © 2015 John Wiley & Sons, Ltd.
3+
via the radiative energy transfer in
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Photoluminescence in Na3SO4Cl: X (X = Ce3+, Eu3+ or Dy3+) as sensitizers and Dy3+ ions as activators. Figures 11 and 12 show the PL emission spectra of Na3SO4Cl:Eu, Dy for 394 nm excitation. Three peaks were obtained, one at around 329, 348 and 394 nm and in emission spectra the other two at around 482 and 576 nm. The peak 394 nm is characteristic of the Eu2+ emission arising from transitions of the 4f 65d configuration to the 8S7/2 level of the 4f7 configuration; the next two peaks (Fig. 12) could be assigned to the Dy3+ emission due to the transitions 4 F9/2 → 6H15/2 and 4 F9/2 → 6H13/2 respectively (28–30). It can be seen in Fig. 11 that the excitation spectrum of the Dy3+ emission (482 nm 576 nm) contains not only a band corresponding to excitation of theDy3+ ion itself but also a band that corresponds to excitation of the Eu2+ ion, giving evidence for the occurrence of energy transfer from the Eu2+ to the Dy3+ ion. Figure 13 shows the Eu2+ → Dy3+ energy transfer mechanism in Na3SO4Cl halosulphate material. The emission in Dy3+ comes via a non-radiative transition to the 4 F9/2 level followed by radiative transitions to 6H15/2 and 6H13/2 levels. Excellent results have been observed in the presented host (31,32). Emission of europium in the visible blue and red regions has found important industrial applications as the 20
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materials for mercury-free fluorescence lamps and colour plasma display panels. The concentration dependence
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Wavelength (nm) Figure 11. PL excitation spectra of Na3SO4Cl:Eu,Dy.
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Figure 13. Eu material.
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Wavelength (nm) Figure 12. PL emission spectra of Na3SO4Cl:Eu,Dy (Eu 0.1 mol%; Dy: (a) 0.2 mol%; (b) 0.5 mol%).
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In Fig. 2 the peaks of emission spectra of Ce3+ for 0.5 mol% at 322 and 342 nm in the Na3SO4Cl host is much stronger than the peak of Ce for 0.2 mol %. The intensity ratio (I1/I2) of these peaks is increased by 1.2. In PL emission spectra for Na3SO4Cl: Dy (Fig. 4) for 0.05 mol% and 0.1 mol% concentrations of Dy, intensity was found to increase with increase in concentration. The intensity ratio (I1/I2) of these peaks was increased by 1.3. Figure 6 shows the PL emission spectra of Na3SO4Cl:Ce5 mol%, Dy 0.2 mol%, 0.1 mol% and 0.05 mol% peaking at 572 nm. Here the intensity ratio (I1/I2) of these peaks was increased by 2.1. The emission intensity at 477 and 572 nm excited by 304 nm increased linearly as the concentration increases. In Fig. 9, PL emission spectra of Na3SO4Cl:Eu (a) 0.5 mol%, (b) 0.2 mol% the intensity ratio (I1/I2) of these peaks was increased by 15.1, whereas in PL emission spectra of Na3SO4Cl:Eu, Dy, the intensity ratio (I1/I2) is 2.2. From results mentioned above, it can be concluded that the increase in ratio I1/I2 with the increase in concentrations of the activator. This result showed that the host Na3SO4Cl is strongly concentration dependent.
The Na3SO4Cl host is suitable for Ce3+ emission, which peaked at 322 and 342 nm for the excitation of 272 nm due to the 5d → 4f transition. Ce3+ and Eu2+ play an important role in PL emission and it is due to the transfer of energy from these to the Dy3+ and Eu3+ centers in the host lattice. Individual Dy3+ emission at 474 and 576 nm is observed due to 4 F9/2 → 6H15/2 and 4 F9/ 6 2 → H13/2 transitions respectively, whereas the energy transfer process from Ce to Dy took place in Na3SO4Cl in which the Dy3 + emission was observed at 477 and 572 nm. Eu2+ as well as Eu3+ emissions is also possible in this lattice in the blue–red region of the visible spectrum. The occurrence of energy transfer from Eu2+ to Dy3+ ion is efficiently peaked at 482 and 576 nm due to the transitions 4 F9/2 → 6H15/2 and 4 F9/2 → 6H13/2 respectively. There is a difference in the peak positions observed in the individual Dy emission and co-doped by Ce and Eu. This may be due to the sensitization effect on the host lattice.
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N. Shinde et al.
Acknowledgments NSD wishes to thank the University Grants Commission, New Delhi, Govt. of India, for providing financial assistance.
References 1. Lopez FL, Martin A. EPR and optical absorption of a self-trapped hole in Rb2ZnCl4 crystals. Phys Rev B 1988;38:6392–97. 2. Papavassiliou G, Milia F, Giannakopoulos E. 35Cl spin-spin relaxation time T2 in Rb2ZnCl4 studied by nuclear quadrupole resonance. Phys Rev B 1990;41:6213–19. 3. Meeks H, Janner A. High accuracy polarimetry and its application. Phys Rev B II 1988;28:8075. 4. Wahlstrom G, Chao K. Surface Chemistry of Catalysis by Gold. Phys Rev B 1987;36:9573–78. 5. Jeong SY, Jang MS, Han SK, Haussuhl S. Physical Properties of K2ZnCl4. Cryst Res Tech 1992;27:883–8. 3+ 6. Annapurna K, Dwivedi RN, Buddhudu S. Emission properties of Eu ions in ZnCl2 -BaCl2 -KCl glass. Mater Lett 2002;53:359–65. 3+ 7. Gedam SC, Dhoble SJ, Moharil SV. Synthesis and effect of Ce co-doping on photoluminescence characteristics of KZnSO4Cl: 3+ 2+ M (M = Dy or Mn ) new phosphors. J Lumin 2006;121:450–55. 3+ 2+ 8. Gedam SC, Dhoble SJ, Moharil SV. Dy and Mn emission in KMgSO4Cl phosphor. J Lumin 2007;124:120–6. 9. Thakre PS, Gedam SC, Dhoble SJ. Evaluation of trapping parameters in KCaSO4Cl: X (X = Ce, Dy, Mn or Pb) phosphor. J Mater Sci 2012;47:1860–64. 3+ 10. Gedam SC, Dhoble SJ, Moharil SV. Luminescence in Ce doped mixed sulphate fluoride phosphors [NaMgSO4F and Na3SO4F]. Eur Phys J Appl Phys 2007;37:73–8. 11. Thakre PS, Gedam SC, Dhoble SJ, Atram RG. Luminescence of KCaSO4Cl:X, Y (X = Eu or Ce; Y = Dy or Mn) halosulfate material. J Lumin 2011;131:1612–16. 12. Gedam SC, Dhoble SJ. Energy transfer in Na6Pb4(SO4)6Cl2: X, Y (X = Ce or Eu; Y = Dy or Tb). J Curr Inorg Chem 2012;2:248–52. 13. Shionoya S, Yen WM. SrAl2O4:Eu, Dy in vacuum ultraviolet region. Phosphor handbook. Boca Raton: CRC, 2000. 14. Liang H, Zeng Q, Tao Y, Wang S, Su Q. VUV-UV excited luminescent properties of calcium borophosphate doped with rare earth ions. Mater Sci Eng B 2003;98:213–19.
wileyonlinelibrary.com/journal/luminescence
15. Dhoble SJ, Gedam SC, Nagpure IM, Godbole SV, Bhide MK. Photoluminescence and thermoluminescence characteristics of KXSO4Cl:Eu (X = Zn or Mg) halosulfate phosphor. J Phys D Appl Phys 2007;40:1. 16. Vollkommer F, Hitzschke L. Energy conversion and the reduction of costs and production effort. Phys Lett 1997;53:887. 17. Welker T. Recent developments on phosphors for fluorescent lamps and cathode-ray tubes. J Lumin 1991;48–9. 18. Miejerink A, Blasse G. New inorganic scintillators and storage phosphors for detection ofthermal neutrons. J Phys D 1991;24:626. 19. Crawford MK, Brixner LH. Photostimulable phosphors for X-ray imaging: applications and mechanism. J Lumin 1991;48:37–42. 20. Von Saggern J. X-Ray Imaging with Photo- stimulable Phosphors. Cryst Lattice Defects Amorphic Mater 1989;18:399. 21. Rossner W, Grabmainer BC. Phosphors for X-ray detectors in computed tomography. J Lumin 1991;48–49:29–36. 3+ 22. Yokomo S, Abe T, Hoshine T. Red luminescence of Ce due to the large stokes shifts in Y2O2S and Lu2O2S. J Lumin 1981;24–25:309–12. 23. Morgan GP, Yen WM. Laser Spectroscopy of Solids [M]. Topics in Applied Physics. Springer, 1989;65:77–122. 3+ 24. Blasse G, Brill A. Investigation of some Ce activated phosphors. J Chem Phys 1967;47:5139. 3+ 25. Blasse G, Brill A. Energy Transfer in Tb -Activated Cerium(III). J Chem Phys 1969;51:3252–54. 26. Su Q, Pei Z, Chi L, Zhang H, Zhang Z, Zou F. The yellow-to-blue inten3+ sity ratio (Y/B) of Dy emission. J Alloy Comp 1993;192:25–7. 2+ 27. Gedam SC, Dhoble SJ, Moharil SV. Dy3+ and Mn emission in fluoride- and chloride-based Na3(SO4)X (X = F or Cl) phosphors. Luminescence 2012;27:441–6. 28. Blasse G, Brill A. The absorption and emission spectra of some important activators. Tech Rev 1970;31:304–10. 29. Blasse G. In: Di Bartolo B, Optical Spectroscopy of Inorganic Solid. Luminescence in inorganic solids. New York: Plenum Press, 1978; 457–469. 30. Matthews RJ, Stoebe TG. Thermoluminescent spectra and optical absorption in CaSO4:Dy. J Phys C: Solid State Phys 1982;15:6271–76. 31. Shinde N, Dhoble NS, Gedam SC, Dhoble SJ. Thermoluminescence cha. of Na3SO4 Cl:X (X = Ce, Dy, Mn) phosphor. Radiat Eff Defect in solids 2014;169:361–7. 3+ 2+ 32. Gedam SC, Dhoble SJ, Moharil SV. Dy and Mn emission in fluoride- and chloride-based Na3(SO4)X (X = F or Cl) phosphors. Luminescence 2012;27:441–6.
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Luminescence 2015
Revised: 27 July 2014,
Accepted: 30 November 2014
Published online in Wiley Online Library
(wileyonlinelibrary.com) DOI 10.1002/bio.2840
Photoluminescence enhancement in Na3SO4Cl: X (X=Ce3+, Eu3+ or Dy3+) material Nita Shinde,a N. S. Dhoble,b S. C. Gedamc* and S. J. Dhoblea ABSTRACT: The compound Na3SO4Cl X (X = Ce3+, Eu3+ or Dy3+) prepared by the wet chemical method was studied for its photoluminescence (PL) and energy transfer characteristics. The PL from Na3SO4Cl:Ce3+ shows strong emission at 322 nm at an excitation of 272 nm. Therefore, an efficient Ce3+ → Dy3+, Eu2+ → Dy3+ and Eu2+ → Eu3+ energy transfer had taken place in this host. The Dy3+ emission caused by Ce3+ → Dy3+ energy transfer under ultraviolet (UV) wavelengths peaked at around 477 nm and 572 nm due to 4 F9/2 → 6H15/2 and 6H13/2 transitions with yellow–orange emission in the Na3SO4Cl lattice. An intense Dy3+ emission was observed at 482 and 576 nm caused by the Eu2+ → Dy3+ energy transfer process and due to 4 F9/2 → 6H15/2 and 4 F9/2 → 6H13/2 transitions respectively. The Eu3+ blue to red light emission caused by the Eu2+ → Eu3+ energy transfer peaked at 593 nm and 617 nm due to 5D0 → 5D3 transitions. The presence of trivalent Eu in Na3SO4Cl suggested the presence of Eu3+ in the host compound that occupied two different lattice sites and that peaked at 593 and 617 nm due to 5D0 → 7 F1 and 5D0 → 7 F2 transitions respectively. The trivalent europium ion is very useful for studying the nature of metal coordination in various systems due to its non-degenerate emitting 5D0 state. The present paper discusses the photoluminescence characteristics of Eu2+ → Dy3+ and Eu2+ → Eu3+ energy transfer. This compound may be useful as a lamp phosphor. Copyright © 2015 John Wiley & Sons, Ltd. Keywords: photoluminescence; wet chemical method; optical material; lamp phosphor; rare earths
Introduction Chlorosulphate phosphors activated with rare earth ions are known to be luminescent materials and have been used particularly in photoluminescence (PL) and thermoluminescence (TL) studies. Chloride substituted for a large number of sulphates has several interesting optical properties. There has been recent increased interest in chloride-based materials because of their wide ranging applications (1–6). Recently, Gedam et al. have reported on KZnSO4Cl, KMgSO4Cl, KCaSO4Cl Na3SO4Cl, Na6(SO4) 2FCl, Na6Pb4(SO4)6Cl2 and CeSO4Cl chlorosulphates that were activated with different rare earths and inner transition elements (7–12). Energy transfer phenomena have lead to the development of new and efficient photoluminescence materials. By using the wet chemical method (WCM), significant results in photoluminescence have been observed in the Na3(SO4)Cl host. Efforts have also been made towards finding new sulphate phosphors that could be used for PL. Sulphate materials such as europium-doped fluoride (13), borophosphate (14) and halosulphate (15), have been used in tricolor fluorescent lamps (16), electroluminescent lamps and display devices (17). Ce3+ is a low cost material that can provide strong absorption of UV light and an efficient conversion to longer wavelengths. Halosulphate phosphors can be easily prepared by the WCM and large numbers of sulphates with a well characterized structure are known, therefore it was decided to study the emission of Ce3+ in halosulphate materials. The luminescence properties of Ce3+ compounds have been of considerable interest in recent years. Ce-activated phosphors can be widely used in scintillation detectors (18), and detectors for X-ray imaging (19–21). Dy3+ emission falls mainly into two bands in the visible region, arising from 4 F9/2 → 6H15/2 (470–500 nm) and 4 F9/2 → 6H13/2 (570 nm) transitions. The relative intensities of the two bands
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depend on local symmetry (22). When the ratio of blue to green emission is appropriate, one can obtain white emission using Dy3+. This property has generated some interest in Dy3+ luminescence. Ultraviolet light cannot efficiently excite Dy3+ because its charge transfer (CT) state as well as the 5d levels are situated above 50,000 cm1. Dy3+ can be sensitized by Bi3+ (23), Gd3+, Ce3+, Pb2+ and vanadate (24–26) ions. GdAl3B4O12 doped with Bi3+ and Dy3+ is an efficient lamp phosphor. YVO4:Dy3+ is another lamp phosphor. From our previous work (27) on this phosphor, it is clear that the phosphor is quite suitable to give luminescence following different methods of synthesis. We had previously used the solid-state diffusion method for the preparation of this phosphor. We had observed that an excitation band was located at around 232 nm (λem = 341 nm). In the PL emission spectra of Ce3+ ions with different concentration under excitation of 232 nm, the peaks were observed at 335 nm, which are assigned to the 5d → 4f transition of Ce3+ ions. It was observed that with increasing concentration of Ce3+ ions the peak intensity (at
* Correspondence to: S. C. Gedam, Department of Physics, KZS Science College, Kalmeshwar, Nagpur-441501, India. E-mail: [email protected] a
Department of Physics, RTM Nagpur University, Nagpur 440033, India
b
Department of Chemistry, Sevadal Mahila Mahavidyalaya, Nagpur 440018, India
c
Department of Physics, KZS Science College, Kalmeshwar, Nagpur 441501, India Abbreviations: PL, photoluminescence; TL, thermoluminescence; UV, ultraviolet; WCM, wet chemical method; XRD, X-ray diffraction.
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341 nm) increases. Similarly, in Na3(SO4)Cl:Ce, Dy phosphor, PL emission of Dy3+ ions was observed at 482 and 571 nm (for 340 nm of excitation ) due to presence of Ce3+ ion, as a sensitizer. Dy3+ emission at 482 and 571 nm was observed due to the 4 F9/2 → 6H15/2 and 4 F9/2 → 6H13/2 transitions of the Dy3+ ion, respectively. Compared with this method, the results obtained by WCM show that, according to PL (excitation and emission) spectra, the method of preparation not only affected the peak height but also the peak profile. Comparatively, the WCM was quite suitable and a simple option for the synthesis of this phosphor.
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Na3SO4Cl host doped by Ce; Dy and Eu as well as co-doped by Ce, Dy; and Eu, Dy phosphors were synthesized by a WCM taking into account the following reaction:
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Wavelength (nm) Figure 1. PL excitation spectra of Na3SO4Cl:Ce.
Na2 SO4 þ NaCl→Na3 SO4 Cl
Results and discussion PL in Na3SO4Cl:Ce The XRD pattern and PL characterization of the Na3SO4Cl:Ce sample (solid state diffusion method) has performed previously (27). Figure 1 shows the excitation spectra peaked at λex = 272 nm when monitoring at 322 nm emission. In this figure some selected emission spectra with various Ce3+ contents are shown. The emission peak wavelength and its relative intensity are shown for different contents (0.2 mol% to 0.5 mol%) of the Ce3+ ion in Fig. 2. It was clear that with increase in Ce3+ content, the emission intensity increased relatively. Curves (a) and (b) represent the emission spectra for 0.5 mol% and 0.2 mol% concentrations of Ce3+ respectively and show its broad band nature. The well known UV emission of Ce3+ ions in these phosphors was around 322 and 342 nm. This band is due to the allowed transition from 5d → 4f of Ce3+ ions, giving maximum intensity for the excitation wavelength of 272 nm. The excitation energy
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For preparation of Na3(SO4)Cl:Ce the starting materials, NaCl, Na2SO4 and cerium sulphate salt were of analytical grade and were taken at a stoichiometric ratio. These materials were weighed in the proper molar ratio and then dissolved separately in double-distilled de-ionized water and then mixed, resulting in a solution of Na3SO4Cl:Ce and confirming that no undissolved constituents were left behind and all the salts had completely dissolved in the water. Then, this homogeneous mixture was heated at 80 °C for 12 h in an oven, resulting in the formation of the Na3SO4Cl:Ce compound in powder form. The samples were then slowly cooled at room temperature. The resultant polycrystalline mass was crushed to fine particles in a crucible, this powder form was used for further study. The same process was adopted for the rest of the samples such as Na3SO4Cl:Dy; Na3SO4Cl:Ce, Dy; Na3SO4Cl:Eu and Na3SO4Cl:Eu, Dy (here sulphate salts of dysprosium and europium were used).The prepared host lattice was characterized for its phase purity and crystallinity by X-ray powder diffraction (XRD). The PL emission spectra of the samples were recorded using a fluorescence spectrometer (Shimatzu RF-5301). The same amount of sample was used in each case. Emission and excitation spectra were recorded using a spectral slit width of 1.5 nm.
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Wavelength (nm) Figure 2. PL emission spectra of Na3SO4Cl:Ce: (a) 0.5 mol%; (b) 0.2 mol %.
matched the energy separation between the ground state and lowest state of the 5d level of the ion. This situation populates the lowest 5d level to the maximum and favours maximum emission intensity. The characteristic feature of the emission band is the absence of the expected doublet arising due to the transition from 5d → 2 F5/2 and 2 F7/2 levels due to spin orbit splitting of the 4f1 ground state of Ce3+ ions.
PL in Na3SO4Cl:Dy3+and Ce3+ → Dy3+ energy transfer The emission of Dy3+ originates from the 4 F9/2 level. The transitions to 6H15/2 (~475 nm) and 6H13/2 (~570 nm) dominate. The latter has ΔJ = 2 and is hypersensitive. The emission has a whitish to yellow colour in host lattices where hypersensitivity is pronounced. There is a Ce3+ ion as a possible sensitizer of the halosulphates lattice and Dy3+ as activator. Dy3+ can be excited by neither low nor high pressure mercury discharges (> 40,000 cm1) because the charge transfer level and also the lowest 5d level of Dy3+ are situated at energies >50,000 cm1. The excitation can occur only by the parity forbidden f → f transition,
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Photoluminescence in Na3SO4Cl: X (X = Ce3+, Eu3+ or Dy3+) 304
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leading to weak absorption by Dy3+ from the radiation of mercury discharge. The excitation spectra of the Dy-doped ions in the Na3SO4Cl host are shown in Fig. 3. In this figure the excitation spectrum was recorded and plotted, monitoring at 474 nm emission. At this wavelength the emission spectra for different concentrations (0.05 mol% and 0.1 mol%) were observed. The most intense broad excitation band with maximum at 357 nm was observed. Selecting the 357 nm excitation wavelength, the emission spectra for the same samples was recorded. A strong PL emission of Dy3+ ions was observed at 474 and 576 nm in Na3SO4Cl:Dy phosphor. The Dy3+ emission at 474 and 576 nm was observed due to 4 F9/2 → 6H15/2 and 4 F9/2 → 6H13/2 transitions respectively (under excitation wavelength at 357 nm (Fig. 4). Energy transfer from donor to acceptor plays an important role in luminescence and solid state lasers. In this study, we used the Na3SO4Cl halosulphate as host for the luminescence and energy transfer process for Ce → Dy ions. The excitation and emission spectra of the co-doped Ce → Dy ions in the Na3SO4Cl halosulphate host are shown in Figs 5 and 6. In this figure the
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Wavelength (nm) Figure 5. PL excitation in Na3SO4Cl:Ce,Dy.
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Wavelength (nm) Figure 6. PL emission spectra of Na3SO4Cl:Ce 5 mol%, Dy: (a) 0.2 mol%; (b) 0.1 mol%; (c) 0.05 mol%.
Figure 3. PL excitation spectra of Na3SO4Cl:Dy.
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Wavelength (nm) Figure 4. PL emission spectra of Na3SO4Cl:Dy: (a) 0.05 mol%; (b) 0.1 mol%.
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excitation spectrum was recorded and plotted, monitoring at 474 nm emission. The excitation spectra showed the maximum position at 304 nm and a faint shoulder at about 273 nm. Selecting 304 nm excitation wavelengths, the emission spectra were recorded for Ce5mole% and Dy0.1mole% contents in this sample. The emission spectra show the two prominent peaks at 477 nm and 572 nm with sharp and high intensity. As Ce3+ and Dy3+ ions were co-doped to the system, the Ce3+ emission nearly disappeared with corresponding intense emission lines of Dy3+ observed at 477 nm and 572 nm. The Dy3+ emission was due to transition of 4 F9/2 → 6H15/2 at 477 nm and 4 F9/ 6 2 → H13/2 at 572 nm, respectively. These results indicates that very efficient energy transfer from Ce3+ to Dy3+ takes place in the Na3SO4Cl halosulphate lattice. This result occurred due to energy transfer from Ce3+ to Dy3+ ions. Figure 7 shows the Ce3 + → Dy3+ energy transfer mechanism in Na3SO4Cl halosulphate material. The emission in Dy3+ comes via a non-radiative transition to the 4 F9/2 level followed by radiative transitions to 6H15/2 and 6H13/2 levels.
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Figure 7. Ce → Dy halosulphate material.
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energy transfer mechanism in Na3SO4Cl:Ce5 mol%, Dy
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Wavelength (nm) Figure 9. PL emission spectra of Na3SO4Cl:Eu: (a) 0.5 mol%; (b) 0.2 mol%.
Eu2+ → Eu3+ and Eu2+ → Dy3+ energy transfer 2+
Eu emission results from two types of transitions. The most common is that due to 4f 65d → 4f 6 (8S7/2) transition. As the position of the band corresponding to 4f 65d configuration is strongly influenced by the host, the emission can be any where from 365 nm (e.g. in BaSO4) to 650 nm. As the 4f → 5d transition is an allowed electrostatic dipole transition, the absorption and emission of Eu2+ is very efficient in many hosts, which makes the Eu2+-doped phosphors of practical importance. Figure 8 shows an excitation spectra that peaked at 396 nm and had the two small peaks at 382 nm and 387 nm. The emission spectra of Na3SO4Cl:Eu2+ (0.2 and 0.5 mol%) phosphors are shown in Fig. 9. As can be seen in the figure, the emission of the material has a prominent peak at around 425 nm having a number of small peaks around this wavelength that can be well assigned to Eu2+ emission arising from transitions of the 4f65d configuration to the 8S7/2 level of the 4f7 configuration. The result illustrated that the main emission peaks of this phosphor are at about 593 nm and 617 nm, which indicated that Eu2+ ions have been shifted to Eu3+ completely in the Na3SO4Cl:Eu phosphor. For 0.5 mole% of concentration for Eu there were two intense peaks observed at 593 nm and 617 nm, which showed
the Eu3+ emission. The PL emission spectrum of Na3SO4Cl:Eu chlorosulfate phosphor showed an Eu2+ emission due to the 4f → 5d transition at the 425 nm wavelength and was the basic characteristic of the Eu2+ emission in the blue region. The PL emission showed there was transfer of energy from Eu2+ to Eu3+ ions. Eu3+ PL emission was also observed in the presence of Eu2+ due to 5Do → 7 F1 and 5Do → 7 F2 transition of Eu3+ ions. Figure 9 shows that the Eu2+ emission gets less suppressed and enhances the Eu3+ PL emission in the red region at the same excitation wavelength. The Eu3+ emission reached the characteristics of the red region, i.e. 611 nm wavelengths. This showed that the Eu2+ emission as well as the Eu3+ emission is possible in this lattice. The induced luminescence of Eu3+ via the radiative energy transfer is shown in Fig. 10. The population at the 5D3 level of Eu3+ increased via the radiative energy transfer from Eu2+ to Eu3+. Finally, the population arrived at the emitting 5D0 level via non-radiative transitions from the upper levels. The trivalent europium ion is very useful for studying the nature of metal coordination in various systems, owing to its non-degenerate emitting 5D0 state. It is possible that in Na3SO4Cl:Eu, Dy some form of energy transfer takes place with the Eu2+ ions acting
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Figure 10. The induced luminescence of Eu Na3SO4Cl:Eu.
Copyright © 2015 John Wiley & Sons, Ltd.
3+
via the radiative energy transfer in
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Photoluminescence in Na3SO4Cl: X (X = Ce3+, Eu3+ or Dy3+) as sensitizers and Dy3+ ions as activators. Figures 11 and 12 show the PL emission spectra of Na3SO4Cl:Eu, Dy for 394 nm excitation. Three peaks were obtained, one at around 329, 348 and 394 nm and in emission spectra the other two at around 482 and 576 nm. The peak 394 nm is characteristic of the Eu2+ emission arising from transitions of the 4f 65d configuration to the 8S7/2 level of the 4f7 configuration; the next two peaks (Fig. 12) could be assigned to the Dy3+ emission due to the transitions 4 F9/2 → 6H15/2 and 4 F9/2 → 6H13/2 respectively (28–30). It can be seen in Fig. 11 that the excitation spectrum of the Dy3+ emission (482 nm 576 nm) contains not only a band corresponding to excitation of theDy3+ ion itself but also a band that corresponds to excitation of the Eu2+ ion, giving evidence for the occurrence of energy transfer from the Eu2+ to the Dy3+ ion. Figure 13 shows the Eu2+ → Dy3+ energy transfer mechanism in Na3SO4Cl halosulphate material. The emission in Dy3+ comes via a non-radiative transition to the 4 F9/2 level followed by radiative transitions to 6H15/2 and 6H13/2 levels. Excellent results have been observed in the presented host (31,32). Emission of europium in the visible blue and red regions has found important industrial applications as the 20
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materials for mercury-free fluorescence lamps and colour plasma display panels. The concentration dependence
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Wavelength (nm) Figure 12. PL emission spectra of Na3SO4Cl:Eu,Dy (Eu 0.1 mol%; Dy: (a) 0.2 mol%; (b) 0.5 mol%).
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In Fig. 2 the peaks of emission spectra of Ce3+ for 0.5 mol% at 322 and 342 nm in the Na3SO4Cl host is much stronger than the peak of Ce for 0.2 mol %. The intensity ratio (I1/I2) of these peaks is increased by 1.2. In PL emission spectra for Na3SO4Cl: Dy (Fig. 4) for 0.05 mol% and 0.1 mol% concentrations of Dy, intensity was found to increase with increase in concentration. The intensity ratio (I1/I2) of these peaks was increased by 1.3. Figure 6 shows the PL emission spectra of Na3SO4Cl:Ce5 mol%, Dy 0.2 mol%, 0.1 mol% and 0.05 mol% peaking at 572 nm. Here the intensity ratio (I1/I2) of these peaks was increased by 2.1. The emission intensity at 477 and 572 nm excited by 304 nm increased linearly as the concentration increases. In Fig. 9, PL emission spectra of Na3SO4Cl:Eu (a) 0.5 mol%, (b) 0.2 mol% the intensity ratio (I1/I2) of these peaks was increased by 15.1, whereas in PL emission spectra of Na3SO4Cl:Eu, Dy, the intensity ratio (I1/I2) is 2.2. From results mentioned above, it can be concluded that the increase in ratio I1/I2 with the increase in concentrations of the activator. This result showed that the host Na3SO4Cl is strongly concentration dependent.
The Na3SO4Cl host is suitable for Ce3+ emission, which peaked at 322 and 342 nm for the excitation of 272 nm due to the 5d → 4f transition. Ce3+ and Eu2+ play an important role in PL emission and it is due to the transfer of energy from these to the Dy3+ and Eu3+ centers in the host lattice. Individual Dy3+ emission at 474 and 576 nm is observed due to 4 F9/2 → 6H15/2 and 4 F9/ 6 2 → H13/2 transitions respectively, whereas the energy transfer process from Ce to Dy took place in Na3SO4Cl in which the Dy3 + emission was observed at 477 and 572 nm. Eu2+ as well as Eu3+ emissions is also possible in this lattice in the blue–red region of the visible spectrum. The occurrence of energy transfer from Eu2+ to Dy3+ ion is efficiently peaked at 482 and 576 nm due to the transitions 4 F9/2 → 6H15/2 and 4 F9/2 → 6H13/2 respectively. There is a difference in the peak positions observed in the individual Dy emission and co-doped by Ce and Eu. This may be due to the sensitization effect on the host lattice.
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Acknowledgments NSD wishes to thank the University Grants Commission, New Delhi, Govt. of India, for providing financial assistance.
References 1. Lopez FL, Martin A. EPR and optical absorption of a self-trapped hole in Rb2ZnCl4 crystals. Phys Rev B 1988;38:6392–97. 2. Papavassiliou G, Milia F, Giannakopoulos E. 35Cl spin-spin relaxation time T2 in Rb2ZnCl4 studied by nuclear quadrupole resonance. Phys Rev B 1990;41:6213–19. 3. Meeks H, Janner A. High accuracy polarimetry and its application. Phys Rev B II 1988;28:8075. 4. Wahlstrom G, Chao K. Surface Chemistry of Catalysis by Gold. Phys Rev B 1987;36:9573–78. 5. Jeong SY, Jang MS, Han SK, Haussuhl S. Physical Properties of K2ZnCl4. Cryst Res Tech 1992;27:883–8. 3+ 6. Annapurna K, Dwivedi RN, Buddhudu S. Emission properties of Eu ions in ZnCl2 -BaCl2 -KCl glass. Mater Lett 2002;53:359–65. 3+ 7. Gedam SC, Dhoble SJ, Moharil SV. Synthesis and effect of Ce co-doping on photoluminescence characteristics of KZnSO4Cl: 3+ 2+ M (M = Dy or Mn ) new phosphors. J Lumin 2006;121:450–55. 3+ 2+ 8. Gedam SC, Dhoble SJ, Moharil SV. Dy and Mn emission in KMgSO4Cl phosphor. J Lumin 2007;124:120–6. 9. Thakre PS, Gedam SC, Dhoble SJ. Evaluation of trapping parameters in KCaSO4Cl: X (X = Ce, Dy, Mn or Pb) phosphor. J Mater Sci 2012;47:1860–64. 3+ 10. Gedam SC, Dhoble SJ, Moharil SV. Luminescence in Ce doped mixed sulphate fluoride phosphors [NaMgSO4F and Na3SO4F]. Eur Phys J Appl Phys 2007;37:73–8. 11. Thakre PS, Gedam SC, Dhoble SJ, Atram RG. Luminescence of KCaSO4Cl:X, Y (X = Eu or Ce; Y = Dy or Mn) halosulfate material. J Lumin 2011;131:1612–16. 12. Gedam SC, Dhoble SJ. Energy transfer in Na6Pb4(SO4)6Cl2: X, Y (X = Ce or Eu; Y = Dy or Tb). J Curr Inorg Chem 2012;2:248–52. 13. Shionoya S, Yen WM. SrAl2O4:Eu, Dy in vacuum ultraviolet region. Phosphor handbook. Boca Raton: CRC, 2000. 14. Liang H, Zeng Q, Tao Y, Wang S, Su Q. VUV-UV excited luminescent properties of calcium borophosphate doped with rare earth ions. Mater Sci Eng B 2003;98:213–19.
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15. Dhoble SJ, Gedam SC, Nagpure IM, Godbole SV, Bhide MK. Photoluminescence and thermoluminescence characteristics of KXSO4Cl:Eu (X = Zn or Mg) halosulfate phosphor. J Phys D Appl Phys 2007;40:1. 16. Vollkommer F, Hitzschke L. Energy conversion and the reduction of costs and production effort. Phys Lett 1997;53:887. 17. Welker T. Recent developments on phosphors for fluorescent lamps and cathode-ray tubes. J Lumin 1991;48–9. 18. Miejerink A, Blasse G. New inorganic scintillators and storage phosphors for detection ofthermal neutrons. J Phys D 1991;24:626. 19. Crawford MK, Brixner LH. Photostimulable phosphors for X-ray imaging: applications and mechanism. J Lumin 1991;48:37–42. 20. Von Saggern J. X-Ray Imaging with Photo- stimulable Phosphors. Cryst Lattice Defects Amorphic Mater 1989;18:399. 21. Rossner W, Grabmainer BC. Phosphors for X-ray detectors in computed tomography. J Lumin 1991;48–49:29–36. 3+ 22. Yokomo S, Abe T, Hoshine T. Red luminescence of Ce due to the large stokes shifts in Y2O2S and Lu2O2S. J Lumin 1981;24–25:309–12. 23. Morgan GP, Yen WM. Laser Spectroscopy of Solids [M]. Topics in Applied Physics. Springer, 1989;65:77–122. 3+ 24. Blasse G, Brill A. Investigation of some Ce activated phosphors. J Chem Phys 1967;47:5139. 3+ 25. Blasse G, Brill A. Energy Transfer in Tb -Activated Cerium(III). J Chem Phys 1969;51:3252–54. 26. Su Q, Pei Z, Chi L, Zhang H, Zhang Z, Zou F. The yellow-to-blue inten3+ sity ratio (Y/B) of Dy emission. J Alloy Comp 1993;192:25–7. 2+ 27. Gedam SC, Dhoble SJ, Moharil SV. Dy3+ and Mn emission in fluoride- and chloride-based Na3(SO4)X (X = F or Cl) phosphors. Luminescence 2012;27:441–6. 28. Blasse G, Brill A. The absorption and emission spectra of some important activators. Tech Rev 1970;31:304–10. 29. Blasse G. In: Di Bartolo B, Optical Spectroscopy of Inorganic Solid. Luminescence in inorganic solids. New York: Plenum Press, 1978; 457–469. 30. Matthews RJ, Stoebe TG. Thermoluminescent spectra and optical absorption in CaSO4:Dy. J Phys C: Solid State Phys 1982;15:6271–76. 31. Shinde N, Dhoble NS, Gedam SC, Dhoble SJ. Thermoluminescence cha. of Na3SO4 Cl:X (X = Ce, Dy, Mn) phosphor. Radiat Eff Defect in solids 2014;169:361–7. 3+ 2+ 32. Gedam SC, Dhoble SJ, Moharil SV. Dy and Mn emission in fluoride- and chloride-based Na3(SO4)X (X = F or Cl) phosphors. Luminescence 2012;27:441–6.
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