Luminescence Properties of Eu 2+ Doped Ca-α-SiAlON Phosphor. Li Li 1,a, Zhang Cheng 2,b, Feng Tao 3, Xu Haifeng 3, Li Qiang 1,c

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1 Advanced Materials Research Online: ISSN: , Vol. 177, pp doi: / Trans Tech Publications, Switzerland Luminescence Properties of Eu 2+ Doped Ca-α-SiAlON Phosphor Li Li 1,a, Zhang Cheng 2,b, Feng Tao 3, Xu Haifeng 3, Li Qiang 1,c 1 Depratment of Chemistry, East China Normal University, Shanghai , China 2 Department of Materials Science and Engineering, Shanghai Institute of Technology, Shanghai , China 3 Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai, , China a @ecnu.cn, b czhang@sit.edu.cn, c qli@chem.ecnu.edu.cn Keywords: Ca-α-SiAlON; Phosphor, Luminescence; LED Abstract. Eu 2+ Doped Ca-α-SiAlON phosphor have been synthesized from SiO 2, Al 2 O 3, CaCO 3, Eu(NO 3 ) 3,carbon powders by carbothermal reduction nitridation (CRN). Using X-ray Diffractometer (XRD) and fluorescent spectrophotometer, the influences of the phase content of the sintered samples after different soaking time at 1390 C and their luminescence properties were studied. The pure Ca-α-SiAlON:Eu 2+ were prepared at processing temperatures of 1390 C in a holding time of 8 h. Ca-α-SiAlON:Eu 2+ had high adsorption in the UV visible spectral region. Two bands were observed in the emission spectrum centered at about 459 and 545 nm exited at 290nm. And two excitation bands located at about 297nm, nm were observed in the excitation spectrum with monitored at emission wavelength of 469nm or 550nm respectively. The morphology of the samples was examined via SEM, TEM. Ca/Eu co-doped α-sialon powders had hollow sphere morphology and it is composed of large numbers of very fine particles of around 30 to 70 nm in diameter. Elemental distribution was investigated using an EDS attached to a scanning electron microscopy (SEM). The sintered sample has a composition commonly seen for α-sialon. Introduction White light-emitting diodes (LEDs) are attracting significant attention in recent years because they are a new, ultra efficient, low energy and environment friendly lighting system [1]. Currently, LEDs are widely used as indicators, rear lamps for vehicles, decorated lamps, backlights for cellular phones, liquid crystal displays, and small-area lighting. With advances in the brightness and color-rendering properties of LEDs, it is generally accepted that they will replace conventional lamps for general lighting in the near future. To date, rare-earth-doped oxynitride or nitride compounds have been reported to be luminescent and may then serve as new phosphors with good thermal and chemical stabilities [2 5]. In this work, we will report the photoluminescence (PL) spectra of europium-doped Ca-α-SiAlON ceramics. Ca-α-SiAlON powder was synthesized by CRN of a SiO 2 Al 2 O 3 CaCO 3 mixture. Experimental Section The composition of europium-doped Ca-α-SiAlON used is located on the α-plane in the system Ca-Si-Al-O-N with m=2.0 and n=1.0, according to the formula (Ca 1-x RE x ) m/2 Si 12-(m+n) Al m+n O n N 16-n (x=0.05). The starting powders were SiO 2 (99.99%), Al 2 O 3 (99.99%), CaCO 3 (99.8%), Eu(NO 3 ) 3,and carbon (99.97%, H260). CaCO 3 in the mixture decomposes above ~900 C, producing CaO and CO 2. The carbon content in all samples was fixed at 1.2 times the required stoichiometric value. The mixtures were milled with ethanol in an agate mortar for 1 h. The dried powders were subsequently ground and passed through a sieve with 300 µm holes. The mixed powder was then put into a graphite boat. Firing was performed in a horizontal electrical furnace at 1390 C for various holding times. A constant nitrogen gas flow of 0.45L/min through the furnace was used during the whole heating cycle. The residual carbon was removed by burning the synthesized powder at 800 C for 2 h in air. Materials All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications, (ID: , Pennsylvania State University, University Park, USA-09/04/16,14:02:36)

2 278 Testing and Evaluation of Inorganic Materials I were characterized with an X-ray diffractometer system (XRD, Rigaku).Luminescence spectra were measured using a F-4500 fluorescent spectrophotometer at room temperature. The morphology of the synthesized samples was examined via scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The elemental distribution was investigated using an energy dispersive X-ray spectrometer (EDS) attached to a scanning electron microscopy (SEM). Result and Discussion Figure 1(a), (b), (c) shows XRD patterns of the sintered samples of various holding times at 1390 C. The sintered sample holding time for 2h contained the major phase of Si 2 N 2 O and no SiAlON had Fig.1. XRD patterns of the sintered samples for various holding times at 1390 C (a) the holding time for 2h (b) the holding time for 3-8h (c) the holding time for 10h Fig.2 Photoluminescence emission spectra (a) and excitation spectra(b) (c) of the Ca/Eu co-doped α-sialon powders, as a function of various holding times at 1390 C.

3 Advanced Materials Research Vol been formed. When the sintering time was prolonged to 3h, the β-sialon phase had appeared. With longer time for 4h, the α-sialon had begun to be shaped. By extending the holding time at 1390 C, the phase will change another one. when the holding time was up to 8h, α-sialon phase have dominated the content of the as-prepared specimen and a bit of remanent β-sialon phase have co-existed. Furthermore, the pure α-sialon phase was present without any other material in the sample for 10h, and by extending the time, the structure was hardly changed. By the ananlysis of the above results, it indicated that the holding time played an important role in the formation of α-sialon. The longer time, the more content of α-sialon were within 10h. Figure 2(a), (b), (c) shows the emission and excitation spectra of Ca/Eu co-doped α-sialon ceramics at room temperature. The results in Fig. 2(a) illustrated that two bands centered at λ values of ~459nm and ~545 nm were observed for all sintered samples of various holding times at 1390 C and monitored at 290nm. Ca/Eu co-doped α-sialon ceramics had high adsorption in the UV visible spectral region. The excitation spectrum centered at about 297nm and monitored at 469nm, Fig. 2(b). Another excitation spectrum centered at about nm and monitored at 550nm, Fig. 2(c). Apparently, the luminescent intensity increased with the increase of the holding time, this was possibly caused by the enhanced grain crystallinity and the decline of defect in the powder. The morphology of the synthesized powders holding time for 10h at 1390 C was examined using SEM (Fig. 3) and TEM (Fig. 4). It was found that the synthesized Ca/Eu co-doped α-sialon powders had a beadlike texture (Fig. 3), the SiAlON beads were actually hollow spheres and composed of large numbers of very fine particles of around 30 to 70 nm in diameter, which could be detected by the higher resolusion TEM Image (Fig. 4). The bonding between the nanograins in the hollow beads did not seem very strong because the hollow beads could be broken down into nanoparticles by ultrasonic Fig. 3. SEM image of Ca/Eu co-doped α-sialon Fig.4. TEM image of Ca/Eu co-doped α-sialon powders powders Fig.5. EDS spectra of Ca/Eu co-doped α-sialon powders

4 280 Testing and Evaluation of Inorganic Materials I vibration. The EDS spectra for Ca/Eu co-doped α-sialon powders holding time for 10h at 1390 C are shown in Figs.5. As can be seen in Fig.5, the powders contained visible signals of calcium and silicon, aluminium, oxygen, and nitrogen. It has a composition commonly seen for α-sialon. Conclusions Ca/Eu co-doped α-sialon powders can be produced by CRN of SiO 2 Al 2 O 3 CaCO 3 and carbon black powder mixtures at 1390 C for 8 h. Ca/Eu co-doped α-sialon powders had a beadlike morphology. The beads were actually hollow spheres and composed of large numbers of very fine particles of around 30 to 70 nm in diameter. Ca/Eu co-doped α-sialon powders had high adsorption in the UV visible spectral region. Two broad bands were observed in the emission spectrum centered at about 459nm, 550 nm, and monitored at 290nm. That excitation band centered at about 250 ~ 400 nm.the emission intensity of Ca/Eu co-doped α-sialon powders increased by increasing holding time at 1390 C.This novel Ca/Eu co-doped α-sialon phosphor is expected to be used for phosphor converted white LEDs. References [1] S. Nakamura, G. Fasol: The Blue Laser Diode (Springer, Berlin, Germany, 1997) [2] R.J. Xie, M. Mitomo, et al. : J. Am. Ceram. Soc. Vol. 85(2002),p.1229 [3] T. Suehiro, H. Onuma, et al.: J. Phys. Chem. C. Vol.114(2010),p [4] P. Bo: Master Degree Thesis (Harbin Institute of Technology, Harbin, China, 2007) [5] R.J. Xie, N. Hirosaki: Science and Technology of Advanced Materials. Vol.8 (2007),p.588

5 Testing and Evaluation of Inorganic Materials I / Luminescence Properties of Eu 2+ Doped Ca-α-SiAlON Phosphor / DOI References [1] S. Nakamura, G. Fasol: The Blue Laser Diode (Springer, Berlin, Germany, 1997) /