V. B. Bhatkar et al. / (IJAEST) INTERNATIONAL JOURNAL OF ADVANCED ENGINEERING SCIENCES AND TECHNOLOGIES Vol No. 5, Issue No. 2, 236 - 238
Synthesis and Luminescence Properties of Sr5(PO4)3Cl:Eu2+ V. B. Bhatkar
D. S. Thakare
Department of Physics Shri Shivaji College AKOT (MS) 444101 India bhatkar_vinod@yahoo.com
S. K. Omanwar
Department of Physics Shri Shivaji College AKOT (MS) 444101 India
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stable during lamp fabrication and also unaffected by high energy radiation and Hg vapor. For optimum brightness and effective coating of lamp phosphors, phosphor hosts should be single phase crystalline compounds with narrow particle size distribution (particle size 5 µm) and large surface area. The wet-chemical methods such as co-precipitation, sol-gel, evaporative decomposition, hydrothermal etc. produce phosphor hosts with desired properties. The dependence of the lamp efficacy and the colour rendering index on the position of the blue emission band has been studied extensively [6]. The performance of the tricolour lamp depends critically on the position of the blue emission band. The optimum efficacy corresponds to a peak wavelength of 450 nm. Colour rendering indices well above 90 are feasible when the blue emission is located at 480 nm, this however, occurs at the expense of the lamp efficacy. So, only phosphors emitting from 440-460 nm, are of any practical use. This can be realized using BaMgAl10O17:Eu2+, Sr3(PO4)5Cl:Eu2+, 2+ 2+ Sr2Al6O11:Eu and BaAl12O19:Eu phosphors all exhibiting a quantum yield of about 90%. Apatite material of M5(PO4)3X type are well known for their applications as phosphor materials [7], laser host [8] and biocompatible materials [9]. The recently synthesized alkaline earth chloroapatites activated with divalent europium are efficient phosphor materials, which are extensively used as the blue component in high-efficiency trichromatic fluorescent lamps [10, 11].
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Abstract— In the lamp industry white light is obtained by blending blue (10%), green (30%) and red (60%) phosphors. The narrow band emitter tricolor lamp phosphors with proper colour coordinates are of much importance for the preparation of the white light emitting blend. Theoretically, it is predicted that good Colour Rendering Index (CRI) can be obtained if three narrow band emissions centered on 450, 540 and 610 nm are combined. It is known that the characteristic rare earth (RE) emission is in the form of narrow bands. Particularly Eu2+ (blue), Tb3+ (green) and Eu3+ (red) emission are suitable for tri-colour lamps. The emission of Sr5(PO4)3Cl : Eu2+ is around 445 nm for the 254 nm excitation. We report the optimized synthesis method for the synthesis of this phosphor. The photoluminescence (PL) study of Sr4.95Eu0.05(PO4)3Cl prepared phosphors shows the PL emission at 445 nm in the blue region of the spectrum when excited by 254 nm emission of mercury discharge.. The excitation spectrum is characterized by peaks around 275 nm and 360 nm attributable to effective absorption by Eu2+. Spectrum consists of a broad band indicating appreciable response throughout the entire UV region. Sr4.95 Eu0.05 (PO4)3Cl possesses comparable PL intensity with that of commercial blue phosphor. Hence, Sr4.95 Eu0.05 (PO4)3Cl can be used in lamp industry as a blue component of tri-colour lamp.
Department of Physics SGB Amravati University Amravati (MS) India
Keywords- Photoluminescence, chloroapatite, Europium.
I.
Lamp-Phosphors,
Strontium
INTRODUCTION
Research on lamp phosphors noticed a spurt in activity with the prediction of tri-colour lamp [1, 2]. Haft and Thornton [3] developed the tri-colour lamp based on 1971 predictions. Theoretically, it is predicted that good CRI (close to 100%) can be obtained if three narrow band emission centered on 450, 540 and 610 nm are combined. Haft and Thornton used Eu3+ doped yttrium oxide for red, Eu2+ for strontium chloroapatite for blue and Mn doped zinc silicate for green emission. It is known that the characteristic rare earth (RE) emission is in form of narrow bands. Particularly Eu 2+ (blue), Tb3+ (green) and Eu3+ (red) emission are suitable for tri-colur lamps. Opstelten et al [4] reviewed materials for tricolour lamp. Verstegen [5] described a large number of suitable phosphors. White light can be obtained by blending blue (10%), green (30%) and red (60%) phosphors and widely used phosphors are Y2O3 : Eu3+ (red), BaMgAl10O17 : Eu2+ (blue) and CeMgAl11O19 (green). The phosphor has to be
ISSN: 2230-7818
II.
MATERIALS AND METHODS
All the ingredients used were of GR grade from Loba Chemie India. Sr4.95Eu0.05(PO4)3Cl was prepared by two methods: In the first method, SrHPO4 was prepared by precipitation method. Sr(NO3)2 was mixed in double distilled (DD) water and its clear aqueous solution was obtained. Similarly (NH4)2HPO4 was mixed in DD water and its clear aqueous solution was obtained. The solution of (NH4)2HPO4 was added drop by drop to Sr(NO3)2 and stirred continuously. The SrHPO4 precipitates, which is then filtered. The so obtained precipitate was washed thoroughly by DD water and dried at 50°C. EuCl2 was obtained by dissolving Eu2O3 in concentrated HCl. Then the solution of was mixed with SrCl2. The mixture was evaporated to dryness. Dried powder was then mixed with
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V. B. Bhatkar et al. / (IJAEST) INTERNATIONAL JOURNAL OF ADVANCED ENGINEERING SCIENCES AND TECHNOLOGIES Vol No. 5, Issue No. 2, 236 - 238
SrCO3 and lab synthesized SrHPO4 Mixture was fired at 400°C for 12 hours and then at 800°C for 12 hours in the reducing atmosphere with subsequent grindings. 6SrHPO4 + 2.9 SrCO3 + 0.9 SrCl2 + 0.05 Eu2O3 2Sr4.95 Eu0.05(PO4)3Cl In the second method all the weighed constituents i.e. mixture of EuCl3 and SrCl2 as prepared in method A, and (NH4)2HPO4 was mixed in a mortar for ½ an hour. The powder was put in a packed crucible with a lead. The mixture was annealed in two steps at 400°C for 12 hours and at 800°C for 12 hours. Annealing was performed in burning charcoal. The photoluminescence emission and excitation spectra were recorded on Hitachi F-4000 spectrophotometer in the wavelength region of 200-800 nm at room temperature with spectral width of 1.5 mm. The structure of the phosphor was confirmed by XRD analysis. RESULTS AND DISCUSSION
Figure 1. Excitation and Emission spectra of Sr5(PO4)3Cl : Eu2+ a) Excitation spectra at λem=445 nm b) Emission spectra at λex=254 nm
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The ground state of Eu2+ is 8S7/2, corresponding to the halffilled 4f7 configuration. On excitation with UV, two types of lowest excited states are possible, namely 6Pj (f-f) or 4f6, 5d(fd) depending on the host matrix [12]. The nature of Eu2+ emission, namely either an intra-configurational (f-f) line or inter-configurational (f-d) band emission from Eu2+ luminescent centre(s) in a given host, is mainly decided by the effect of the crystal field on the Eu2+ energy level. In the case of M5(PO4)3X apetites, the anions constituted by the PO4 network offer a strong nephelauxetic effect and hence the 6 2+ level, leading to narrow-band 4f 5d level is the lowest Eu emission. It should be noted that the local site symmetry of the eccentric sites occupied by Eu2+ will be highly favourable for observing the 4f65d 8S electric dipole transition. Emission spectra of Eu2+ in strontium chloroapatites shows only one emission band with maximum intensity at 445 nm.
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III.
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The Fig. 1(a) shows the excitation spectrum of Sr4.95Eu0.05(PO4)3Cl phosphor. The excitation spectrum is characterized by peaks around 275 nm and 360 nm attributable to effective absorption by Eu2+. Spectrum consists of a broad band indicating appreciable response throughout the entire UV region. Consequently the utility of the material in lamp application is established.
Fig. 1(b) shows the Emission spectra with strong emission peaking at 445 nm (λex = 254 nm). These emissions correspond to transition 6Pj 8S7/2 levels of Eu2+ such emission have also been observed by previous workers [13, 14]. In pure Sr5(PO4)3Cl sample, the 445 nm PL emission peak is not seen. The emission maximum is highly dependent on the type of X ion that constitutes the system and the spectral position of the Eu2+ emission band depends on the crystal field splitting of the 5d level and the energy gap between the 8S7/2 ground state and the 5d level. The excitation spectra of Eu2+ emission shows
some interesting results that is the presence of fine structure due to various interactions is observed with more clarity than for the other systems. The fine structure superimposed on the broad excitation band due to the 5d electron can arise from an exchange interaction between 4f6 (7fj) and 5d electrons of Eu2+ leading to the "stair-case" like feature as reported.[15] . IV.
CONCLUSIONS
Prepared Sr4.95 Eu0.05 (PO4)3Cl phosphor shows the PL emission at 445 nm in the blue region of the spectrum after excitation of 254 nm of emission of Hg vapour. Sr4.95 Eu0.05 (PO4)3Cl possesses comparable PL intensity with that of commercial leader blue phosphor. Hence, Sr4.95 Eu0.05 (PO4)3Cl can be used in lamp industry as a blue component of tri-colour lamp. The excitation spectra of Sr 4.95 Eu0.05 (PO4)3Cl has shows good absorption at 380 nm and therefore can be used as a blue emitter in solid state lighting. Also phosphor Sr5 (PO4 )3 Cl, doped with Eu2+ is reported to be at least twice as sensitive as the conventional CaSO4 :Dy phosphor used in thermoluminescence dosimetry of ionizing radiations. It has a linear response, simple glow curve, emission peaking at 456 nm, negligible fading and excellent reusability [16]. Therefore it can be used in the TL dosimetry. REFERENCES [1]
M. Koedam and J. J. Opstelen, “Measurement
and computeraided optimization of spectral power distributions”, Light Res. Technol. 3, 205, 1971.
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K. Kaniya , M. Tanahashi, T. Suzuki and K. Tanaka, “Effects of the addition of F− ions on the properties of fibrous hydroxyapatite grown in the gel system”, Mater. Res. Bull. 25, 63, 1990. B. Smets, J. Rutten, G. Hoeks and J. Verlijsdonk, “2SrO.3Al2O3:Eu2+ and 1.29(BaCa)O.6 Al2O3:Eu2+ “, J. Electrochem. Soc. 136, 2119, 1989. M. Nakamoto, T. Nishimura and H. Kohmoto, “Three-Narrow-Band de Luxe Fluorescent Lamp with Newly Developed Phosphors”, Toshiba Corp. Prospectus No. 15 (Narra/Ed UC 1133), 1982. G. Blasse, “On the Nature of the Eu2+ Luminescence”, Phys. Status Solidi b 55, 131, 1973). M. Hirano and S. Shionoya, “Luminescence of Eu3+ Ion in Antiferromagnetic KMnF3 Crystals”, J. Phys. Soc. Japan 28, 926, 1970. D. K. Sardar, W. A. Sibley and R. Akala, “Optical absorption and emission from irradiated RbMgF3:Eu2+ and KMgF3:Eu2+”, Journal of Luminescence. 27(4), 401-11, 1982. F. M. Ryan, W. Lehman, D. W. Feldman and S. W. Murphy, “Fine structure in the optical spectra of divalent Europium in the alkaline earth sulphates”, .J. Electrochem. Soc. 121, 1475, 1974. S. J. Dhoble, “Preparation and characterization of the Sr5(PO4)3Cl:Eu2+ phosphor”, Journal of Physics D, 33 ( 2) 158, 2000.
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C. Feldmann, T. Jüstel, C. R. Ronda, P. J. Schmidt, “Inorganic Luminescent Materials: 100 Years of Research and Application”, Adv. Func. Mater., 13(7) 511, 2003. H. H. Haft and W. A. Thornton, "High Performance Fluorescent Lamps." Journal of the Illuminating Engineering Society 2(1), 29, 1972. J. J. Opstelten, W. A. Radielovic and W. .L. Wanmaker, “The choice and evaluation of phosphors for application to lamps with improved color rendition”, J. Electrochem. Soc. 120, 1400, 1973. J. M. P. Verstegen, D. Radielovic and L. E. Vrenken, “A new generation of „Delux‟ fluorescent lamps, combining an efficacy of 80 lumen/watt, or more with acolor rendering index of approximately 85”, J. Electrochem. Soc., 121, 1627, 1974. B. M. J. Smets, “Phosphors based on rare-earths, a new era in fluorescent lighting”, Materials Chemistry and Physics, 16(3-4) 283299, 1987. K. H. Butler, “Fluorescent Lamp Phosphor, technology and theory”, Pennsylvania State University Press Park Penn State, PA : Univ. Press. 1986 J. P. Budin, J. C. Michel and F. Auzel, “Oscillator strengths and laser effect in Na2Nd2Pb6(PO4)6Cl2 (chloroapatite), a new high-Ndconcentration laser material”, J. appl. Phys. 50, 641, 1979.
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