CC BY
27
DOI: 10.5862/JPM.237.4 UDC: 535.37
D.N. Game1, N.B. Ingale2, S.K.Omanwar1
1 Sant Gadge Baba Amravati University, Amravati, India 2 Prof. Ram Meghe Institute of Technology and Research, Amravati, India
SYNTHESIS AND LUMINESCENCE PROPERTIES OF Ca5(PO4)3Cl:Eu2+ phosphor FOR SOLID STATE Lighting
A novel method to prepare Eu2+ doped chlorapatite phosphor Ca5(PO4)3Cl useful
for solid state lighting has been given in this paper. The phosphor was synthesized
by the Pechini (citrate gel) method which turned out to be more efficient than the
conventional high temperature solid state reaction. The results of the photoluminescence
(PL) investigation revealed that it was possible to efficiently excite the phosphor by a
UV-visible light from 220 to 430 nm; the phosphor exhibited a bright blue emission
at the wavelength X = 456 nm for the excitation wavelength X = 350 nm of near° em 4=3 ex
ultraviolet light. The developed phosphor emits in blue and, hence, could provide one of the three (RGB) primary color components in a phosphor-converted LED-producing white light.
SOLID STATE LIGHTING, PECHINI (CITRATE GEL) METHOD, BLUE PHOSPHOR, PHOTOLUMINESCENCE.
1. Introduction
White-light emitting diodes (W-LEDs) are one of the most promising eco- friendly light sources due to their low energy consumption [1]. W-LEDs offer benefits in terms of reliability, energy saving, and safety and therefore have drawn much attention in recent years [2, 3]. To increase the efficiency of W-LEDs, special attention has recently been paid to the development of new phosphors with good luminescence properties that can be excited in the long-UV range (300 - 420 nm). Blue phosphors are an important part in those new phosphors. Recently, W-LEDs have been used in many applications due to the developments in GaN-based chips and phosphor technology. The most popular products in the market are obtained by the combination of a blue-emitting phosphor (YAG:Ce3+), which suffer from the low color rendering index(CRI) and high color temperature T (usually above 5500 K). These drawbacks can be overcome by the use of triband W-LED, utilizing RGB (red, green and blue) tricolor phosphor coatings on the near ultraviolet (near-UV) LED chip. Blue phosphor BaMgAl10O17: Eu2+ (BAM:Eu2+) has been intensively studied [4, 5]. However,
BAM:Eu2+ has two major drawbacks: thermal degradation and UV damage, which lead to a color shift and loss of brightness [6, 7]. Apatite phosphors, which are naturally occurring materials, have recently been used for fieldemission displays (FEDs) and would be suitable for white LEDs in the near future because of their low price, environmental friendliness, thermal stability and good photoluminescence properties [8]. W.N. Wang, et al. [8] reported synthesis of a chloroapatite blue phosphor (Ca,Mg)5(PO4)3Cl:Eu with high quantum efficiency using a spray pyrolysis method. The color of the present W-LED depends completely on phosphors because the eyes are not sensitive to the UV output from the W-LED. The market share of the three-band W-LEDs based on near-UV chips has been steadily increasing. Eu2+ ions doped alkaline earth halophosphates are efficient blue-emitting phosphors used for triband W-LEDs. The hosts have been paid more attention in many studies because of their high quantum efficiencies and the excellent physical and chemical stabilities [9, 10]. At the time they show very interesting physical, and, in particular, optical properties [11, 12]. Several solid solutions of alkaline earth halophosphates like Ca5(PO4)3Cl, Sr5(PO4)3Cl and Ba5(PO4)3Cl
are known [13]. The substitution of Eu2+ for Ca2+ is facilitated by the similarity in ionic radii. These phosphors are normally synthesized by solid state reaction which requires very high temperature and it is time consuming also. This prompted us to go for alternative method for the synthesis of such phosphors which would be easy, needs low temperature and less time consuming than solid state reaction.
The present work reports for the first time the synthesis of Ca5(PO4)3Cl:Eu2+ phosphor via the Pechini (citrate gel) method and the investigation of its photoluminescent properties.
2. Experimental
For synthesis of Eu2+ activated chlorapatite phosphor Ca5(PO4)3Cl stoichiometric amount of the precursors Ca(NO3)2'4H2O, converted to Eu(N03)3>6H20, and (NH4)H2PO4 were taken in a china clay basins and dried in a desiccator. All the dried precursors were then finely milled and mixed together. Stoichiometric amount of Citric monohydrated and Ethylene glycol along with 2 drops of Glacial acetic acid were added to
2-, Eu2O3 CaCl2 • 2H20
dried precursors and stirred continuously.
On slow heating up to 140 °C for ~1 h, the solution boils with the evolution of pale yellowish brown fumes and the process of gelation started. The mixture was then allowed to cool leading to a thick pale yellow gel. The gel was further heated slowly up to 350 °C in air. The polymerization took place and a pale yellow resin/foam was formed and was pyrolysed into stunning black foam at 450 °C, which started burning at 600 oC. The complete pyrolysis took place at 750 °C for 2 h. The white powder so obtained was slowly reduced first at 600 °C for 1 h and then at 970 °C for 3 h in presence of charcoal in order to reduce the trivalent activator to divalent state. Thus white crystalline Ca5(PO4)3Cl:Eu2+ phosphor was prepared.
3. Results and discussion
XRD-Studies.
pattern of as
x-ray diffraction (xRD) prepared Ca5(PO4)3Cl:Eu2+ phosphor obtained using Rikagu Meniflex II x-ray diffractometer is shown in Fig. 1. The xRD pattern of calcium apatite suggests the formation of a crystalline Ca5(PO4)3Cl:Eu2+
Fig. 1. x-ray diffraction pattern of Ca5(PO4)3Cl:Eu2+ phosphor
matrix. The results of the xRD analysis indicate that almost all diffraction peaks can be indexed to a pure hexagonal Ca5(PO4)3Cl in JCPDS file with file No. JCPDS 33-02741.
Surface Morphology. The phosphor surface morphology was investigated using a Hitachi S-520 scanning electron microscope (SEM). Fig. 2 presents the SEM image of as prepared Ca5(PO4)3Cl:Eu2+ phosphor. It can be seen that the particles have some irregular shape and the particle size lies in the range from 5 to 10 ^m.
Photoluminescence (PL) study. PL measurements were performed at room temperature, using a Hitachi F-7000 Spectrofluorimeter equipped with a 450 W xenon lamp, in the range from 200 to 700 nm, with spectral width of 2.5 nm. Spectra were corrected using Rhodamine B standard by following the procedure prescribed by Hitachi. Prepared phosphors for W-LED meet the basic requirement that exhibits a bright emission under the excitation of near-UV light. Thus, the excitation and emission spectra of the prepared phosphors Ca5(PO4)3Cl:Eu2+ were studied in order to assess their potential to be used for near-UV LED based W-LEDs. The photoluminescence (PL) and photoluminescence excitation (PLE)
Wavelength, nm
Fig. 3. Photoluminescence emission (1) and excitation (2) spectra of Eu2+ activated Ca5(PO4)3Cl
phosphor; X = 456 nm, X = 350 nm
" em ' ex
550
Wavelength, nm
650
Fig. 4. Photoluminescence emission spectrum of Ca5(PO4)3Cl with different concentration of Eu2+, mol: 0.001 (1), 0.002 (2), 0.0055 (3), 0.010 (4), 0.020 (5)
spectra of phosphor prepared are shown in Fig. 3. There are two broad bands in the PLE (Xem = 456 nm) spectra of phosphors, which are due to the transition from 8S7/2 (4/) ground state of Eu2+ to the 4f 65d excited state. The weaker band is located at about 299 nm, and the stronger one is located at around 350 nm with shoulders at 386 nm, which matches well with the emission of commercially available near-UV LED chips. The bright blue emission band with peak at about 456 nm is observed in the PL (lex = 350 nm) spectra of this phosphors, which could be attributed to the typical 4f65d (t2g) - 4f7 (8S7/2) transition of Eu2+ [14].
The concentration of the activator has an impact on the performance of a phosphor. Therefore, it is important to determine the composition of the Ca5(PO4)3Cl:Eu2+ phosphor with optimal PL emission intensity. A series of Ca5-x(PO4)3Cl : xEu2+ phosphors with various Eu2+ content x was prepared and studied for the effect of activator concentration. The emission spectra of Ca5(PO4)3Cl:Eu2+ phosphor (lex = 350 nm) with different activator concentration are shown in Fig. 4. No obvious changes were observed for all the samples in our experimental wavelength range,
except the fact that the emission intensity of phosphor increases with the increase in Eu2+ concentration and reaches the maximum at x = 0.01 then concentration quenching occurs as the concentration of Eu2+ increased above 1 %. This type of quenching may be attributed to the fact that energy transfer between two identical ions occurs because the average distance between the activator ions becomes short enough for the energy to migrate and for the killers to reach [15].
CIE color coordinates. Fig. 5 shows color coordinates CIE (Commission internationale de l'éclairage) 1931 as (0.1551, 0.0849) for Ca5(PO4)3Cl : 0.01 Eu2+ where as the commercial blue phosphor BaMgAl10O17: Eu2+ (BAM:Eu2+) has color coordinates as (0.1417, 0.1072 ) thus showing better purity of Ca5(PO4)3Cl : 0.01 Eu2+ as compared to BAM:Eu2+ phosphor. Moreover, the color coordinates of the above synthesized phosphor are nearer to those for blue color suggested by the color system EBUPAL/ESCAM, RGBs Blue as well as Adobe blue (0.15, 0.06). Thus the synthesized phosphor is a potential candidate for blue emitting phosphor for solid state lighting using near-UV based W-LEDs.
4. Conclusions
For the first time Eu2+ doped chlorapatite
phosphor Ca5(PO4)3Cl
was
synthesized
by novel Pechini (citrate gel) method. Photoluminescence measurements showed that Eu2+ doped chlorapatite phosphor Ca5(PO4)3Cl synthesized by this method exhibits intensive blue wide-band emission with maximum intensity at 456 nm under near-UV excitation. Both blue and white LEDs can be fabricated by pre-coating the above synthesized phosphors onto 395 nm-emitting InGaN chips. Moreover, the strong absorption of phosphor in the range of 300 nm to 410 nm makes this Eu2+-activated
chlorapatite phosphor a potential candidate as a blue component (one of the three primary color components) for fabrication near-UV based phosphor converted white LEDs.
Acknowledgements
The author D.N. Game is thankful to the Head of the Department of Physics, Sant Gadge Baba Amravati University, Amravati, for providing all the necessary research facilities and also to the Principal, Deccan Education Society's Technical Institute, Fergusson College Campus, Pune for constant encouragement and guidance.
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^ Научно-технические ведомости СПбГПУ. Физико-математические науки № 1(237) 2016
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THE AUTHORS
GAME Deorao N.
Sant Gadge Baba Amravati University
Camp Area, Near Tapovan Road, Amravati, Maharashtra 444602, India [email protected]
INGALE Nitin B.
Prof. Ram Meghe Institute of Technology and Research
Anjangaon Bari Road, Badnera, Amravati, Maharashtra 444701, India
OMANWAR Shreeniwas Kerba
Sant Gadge Baba Amravati University
Camp Area, Near Tapovan Road, Amravati, Maharashtra 444602, India [email protected]
Гейм Д.Н., Ингале Н.Б., Оманвар Ш.К. СИНТЕЗ И ЛЮМИНЕСЦЕНТНЫЕ СВОЙСТВА СОЕДИНЕНИЯ Ca5(PO4)3Cl:Eu2+, ПЕРСПЕКТИВНОГО ДЛЯ СОЗДАНИЯ ТВЕРДОТЕЛЬНОГО ИСТОЧНИКА ОСВЕЩЕНИЯ.
В статье представлен новый метод приготовления люминофора на основе хлорапатита Ca5(PO4)3Cl, активированного Eu2+, который можно применять как твердотельный источник освещения. Люминофор был синтезирован методом Печини (цитратный метод), который оказался более эффективным, чем традиционный метод высокотемпературной твердотельной реакции. Изучение люминофора показало, что его фотолюминесценцию можно возбуждать источником света в диапазоне 220 — 430 нм, что вызывает ярко-синее свечение на длине волны Xem = 456 nm (длина волны возбуждения = 350 nm лежит в ближней УФ-области). Предлагаемый люминофор испускает синий цвет и, следовательно, может служить одним из трех исходных цветовых компонентов (RGB — красный, зеленый, синий) светодиода, дающего белый свет.
ТВЕРДОТЕЛЬНЫЙ ИСТОЧНИК ОСВЕЩЕНИЯ, МЕТОД ПЕЧИНИ (ЦИТРАТНЫЙ МЕТОД), СИНИЙ ЛЮМИНОФОР, ФОТОЛЮМИНЕСЦЕНЦИЯ.
список литературы
[1] Mikami M., Watanabe H., Uheda K., et al.,
New phosphors for white LEDs: Material design concepts // IOP Conf. Ser. Mater. Sci. Eng. 2009. Vol. 1. No. 1. P. 012002.
[2] Bredol M., Kynast U., Ronda C. Designing luminescent materials // Adv. Mater. 1991. Vol. 3. No. 7-8. Pp. 361-367.
[3] Yen W.M., Shionoya S., Yamamoto H. Phosphor Handbook. New York: CRC Press, 2007.
[4] Ekambaram S., Patil K.C. Synthesis and properties of Eu2+ activated blue phosphors // J. Alloys Compd. 1997. Vol. 248. No. 1-2. Pp. 7-12.
[5] Rao R.P., Devine D.J. RE-activated lanthanide phosphate phosphors for PDP applications // J. Lumin. 2000. Vol. 87-89. Pp. 1260-1263.
[6] Wu Z., Dong Y., Jiang J. Thermal treatment effects on degradation of BaMgAl10O17:Eu2+ phosphor for PDP // Mater. Sci. Eng. B. 27008. Vol. 150. No. 3. Pp. 151-156.
[7] Zhu P., Zhu Q., Zhu H., et al., Effect of SiO2 coating on photoluminescence and thermal stability of BaMgAl10O17: Eu2+ under VUV and UV excitation // Opt. Mater. (Amst). 2008. Vol. 30. No. 6. Pp. 930-934.
[8] Wang W.-N., Iskandar F., Okuyama K., Shinomiya Y. Rapid synthesis of non-aggregated fine chloroapatite blue phosphor powders with high quantum efficiency // Adv. Mater. 2008. Vol. 20. No. 18. Pp. 3422-3426.
[9] Kottaisamy M., Jagannathan R., Jeyagopal
P., Rao R.P., Narayanan R. Eu2+ luminescence in M5(PO4)3X apatites, where M is Ca2+, Sr2+ and Ba2+, and X is F-, Cl- , Br- and OH- // J. Phys. D. Appl. Phys. 1994. Vol. 27. No. 10. Pp. 2210-2215.
[10] Zhang Z., Wang J., Zhang M., Zhang Q., Su Q. The energy transfer from Eu2+ to Tb3+ in calcium chlorapatite phosphor and its potential application in LEDs // Appl. Phys. B. 2008. Vol. 91. No. 3-4. Pp. 529-537.
[11] Parreu R., Carvajal J.J., Solans X., DHaz F., Aguily M. Crystal structure and optical characterization of pure and Nd-substituted type III KGd(PO3)4 // Chem. Mater. 2006. Vol. 18. No. 1. Pp. 221-228.
[12] Parreu R., Solfi R., Gavalda J., et al., Crystallization region, crystal growth, and phase transitions of KNd(PO3)4 // Chem. Mater. 2003. Vol. 15. No. 26. Pp. 505394-5064.
[13] Gahane D.H., Mungmode C.D., Moharil S.V. Development of blue phosphor for white light emitting diode // Bionano Front. 2013. Special Issue. Pp. 38-40.
[14] Yu J., Guo C., Ren Z., Bai J. Photoluminescence of double-color-emitting phosphor Ca5(PO4)3Cl:Eu2+, Mn2+ for near-UV LED // Opt. Laser Technol. 2011. Vol. 43. No. 4. Pp. 762-766.
[15] Blasse G., Grabmaier B.C. Luminescent Materials. Berlin: Springer Science & Business Media. 2012.
СВЕДЕНИЯ ОБ АВТОРАх
ГЕЙМ Деорао Н. — сотрудник кафедры физики университета Сант Гадж Баба Амравати, Индия.
Camp Area, Near Tapovan Road, Amravati, Maharashtra 444602, India [email protected]
ИНГАЛЕ Нитин Б. — сотрудник Института технологии и исследований Проф. Рама Мегхе, Амравати, Индия.
Anjangaon Bari Road, Badnera, Amravati, Maharashtra 444701, India [email protected]
ОМАНВАР Шринивас Керба — Ph.D., профессор, заведующий кафедрой физики университета Сант Гадж Баба Амравати, Индия.
Camp Area, Near Tapovan Road, Amravati, Maharashtra 444602, India [email protected]
© Санкт-Петербургский политехнический университет Петра Великого, 2016
