Luminescent Properties of B-Sialon:Eu2＋ Green Phosphors Synthesized by Gas Pressured Sintering

Journal of the Ceramic Society of Japan 116 [3] 389-394 2008 Paper

Luminescent properties of b-SiAlON:Eu2＋ green phosphors synthesized by gas pressured sintering

JeongHoRYU,† Youn­Gon PARK, Hyong Sik WON, Hideo SUZUKI, Sang Hyun KIM and Chulsoo YOON

Corporate R&D Institute, Samsung Electro­Mechanics Co., LTD., 314, Maetan 3­Dong, Yeongtong­Gu, Suwon, Guunggi­Do 443–743, South Korea

2＋ b-SiAlON: Eu oxynitride green phosphors with compositions of EuxSi6－zAlzOzN8－z (x＝0.0065 －0.0390, z＝0.231) were successfully prepared using GPS (gas pressured sintering) method. The phase purity, microstructure, luminescent and thermal quenching properties for the prepared b-SiAlON:Eu2＋ phosphors were investigated in detail. The prepared b-SiAlON:Eu2＋ phosphor samples with Eu2＋ doping concentration of x＜0.0238 showed pure single b-SiAlON phase. The prepared b-SiAlON: Eu2＋ phosphors absorbed UV-visible spectral region, and showed a single intense broadband emission in a range from 525 to 540nm.TheeffectsoftheEu2＋ doping concentration on the optical properties for the b-SiAlON: Eu2＋ phosphors were dis- cussed under consideration of concentration quenching. The temperature dependence of photoluminescence (PL) properties was investigated from 25 to 300°C, and the activation energies (DE) for thermal quenching of the prepared b-SiAlON:Eu2＋ phosphors were determined by Arrhenius fitting. The experimental results clearly indicates that the prepared b-SiAlON:Eu2＋ has great potentials as a down-conversion green phosphor for white light emitting diodes (LEDs) utilizing near UV or blue LEDs as the primary light source.  2008 The Ceramic Society of Japan. All rights reserved.

Key-words : b-SiAlON:Eu2＋,GPS(gas pressured sintering), Photoluminescence, Concentration quenching, Temperature depen- dence, Activation energy for thermal quenching

[Received November 13, 2007; Accepted January 17, 2008]

1. Introduction red colors, and were not accepted for general illuminations. The white LEDs (light-emitting diodes) are promising To improve the color-rendering properties of LEDs for new-generation light source which can replace conventional general illumination, appropriate green and red phosphors incandescent and fluorescent lamps due to their reliability should be incorporated simultaneously. Therefore, it is thus and low energy consumption.1),2) At the present time, the necessary to develop highly efficient green or red lumines- commercial white LEDs comprising a blue LED chip and cent nitride or oxynitride materials that are suitable for white YAG:Ce3＋ yellow phosphor are widely used as outdoor LEDs. 3) lighting sources. However, these white LEDs are not b-SiAlON has a hexagonal crystal structure (P63 or P63/m applicable for indoor lighting purpose due to their less red space group), which is derived structure from b-Si3N4 by luminescence and relatively lower color rendering index equivalent substitution of Al–O for Si–N, and its chemical

(CRI75) value. Improvement of CRI is possible by doping compositioncanbewrittenasSi6－zAlzOzN8－z (z represents ionsthatcanemitinorange/red region or by mixing of the number of Al–O pairs substituting for Si–N pairs and another orange/red phosphor.4) 0＜Z4.2).10) Previously, Hirosaki research group already In recent times, rare-earth-doped oxynitride or nitride reported a green emitting property of Eu2＋-doped b-SiAlON compounds have been reported to be photoluminescent and with a composition of Eu0.00296Si0.41395Al0.01334O0.0044N0.56528 may then serve as new phosphors because of their good ther- under the near UV or blue light excitation.11) Recently, mal and chemical stabilities.5)–7) Their luminescent property extensive and detailed experimental results for b-SiAlON: is attributable to the strong nephelauxetic effect and large Eu2＋ were reported with dopant concentration varying in a crystal field splitting as activator ions are coordinated to range of 0.02–1.5 mol and z value from 0.1 to 2.0 by same nitrogen. Besides this, the oxynitride or nitride phosphors research group.12) In that report, it was found that Eu2＋ are expected to have high thermal and chemical stabilities solubility go down with increasing z value (z＞0.5). Besides, because the crystal structure of the host lattice is built on the powders coarsened and platelike SiAlON polytypoids stiff frameworks consisting of Si–N or Al–N tetrahedra. were detected in high z value samples. Hirosaki et al.8),9) have developed a yellow oxynitride phos- In a viewpoint of application to LEDs, phosphors with phor based on Eu2＋-doped Ca-a-SiAlON which absorbs high phase purity, fine particle size, uniform particle size strongly over a broad range from UV to blue spectral region, distribution and high dopant solubility are recommended. and reported white LED devices using the yellow phosphor In this work, therefore, Eu2＋ activated b-SiAlON phosphors with a blue LED chip. However, the white LEDs using a with compositions of EuxSi6－zAlzOzN8－z (x＝0.0065– single Eu2＋-doped Ca-a-SiAlON presented relatively low 0.0390) at low z value (z＝0.231) were prepared using GPS color-rendering properties due to lack of enough green and (gas pressured sintering) method, and effects of the Eu2＋ doping concentration on their optical characteristics were † Corresponding author: Jeong Ho RYU; E-mail: jimihen.ryu＠ investigated in detail. A relative high emission efficiency was samsung.com foundinhighEu2＋ doping concentration region (x＞0.015),

 2008 The Ceramic Society of Japan 389 JCS­Japan Ryu et al.: Luminescent properties of b-SiAlON:Eu2＋ green phosphors synthesized by gas pressured sintering

which were not investigated in the previous works.11),12) Fur- thermore, the b-SiAlON:Eu2＋ is thought to be promising for high-temperature application due to its thermal and chemical stability. However, its luminescent property in elevated tem- perature ranges was not systematically studied. In this report, temperature dependence on luminescent properties was analyzed in a temperature range from room temperature to 300°C and activation energy for thermal quenching was measured.

2. Experimental procedures 2＋ b-SiAlON:Eu phosphors with compositions of EuxSi6－z AlzOzN8－z were synthesized from a-Si3N4 (Ube Industries LTD., Japan),AlN(Tokuyama Corp., Japan) and Eu2O3 (Shin-Etsu Chemical Co., Ltd., Japan) powders. The Eu2＋ doping concentration (x) varied in a range from 0.0065 to 0.039 with a fixed z value of 0.231. The raw powder mixtures were prepared using a Si3N4 ball milling in n-hexane. After drying in vacuum oven, the powder mixture was granulated using a test sieve, and then loaded into a BN crucible. Calci- nation was carried out at 2000°Cfor2hin0.92MPaofN2 atmosphere using GPS (gas pressured sintering) furnace. After heating, the power was shut off and the samples were cooled down in the GPS furnace. The crystalline phase of the synthesized powders were identified by X-ray powder diffraction (XRD, Rigaku, Japan), operating at 40 kV using Cu Ka radiation (l＝0.15406 nm). The data were collected in the continuous scan mode at the speed of 3°at 2u/min with step size of 0.014°from 20 to 60°. The powder mor- phology was investigated by scanning electron microscopy Fig. 1. (a) Schematic projection of 56-atomic supercell in (SEM, JEOL, JSM 5900 LV, Japan). The photolumines- b-SiAlON structure onto the (001) plane. (b) X-ray diffraction cence (PL) properties of the prepared phosphor samples patterns for the EuxSi6－zAlzOzN8－z (x＝0.0065–0.0390, z＝0.231) were measured using a spectrofluorometer (Fluorolog phosphors prepared at 2000°Cfor2hwithvaryingEu2＋ doping con- Tau-3, Horiba, USA) in a temperature range of 25 and centration. 300°C with a 450 W xenon lamp as an excitation source. The excitation wavelength used for measuring PL emission was 460 nm, and the excitation spectra were measured at emis- sion maxima x＝0.0217, whereas a secondary low-temperature phase of a-SiAlON is observed in samples with composition of x 3. Results and discussion 0.0238. The remain of a-SiAlON phase in the highly Eu2＋ It is well known that b-SiAlON comprises a three-dimen- doped samples can be explained by stabilization effect of 2＋ sional network structure of corner sharing (Si, Al)(O, N)4 doped rare earth metal (Eu ) ions. It has previously been tetrahedra with a continuous channel along [001] direc- stated that the transformation between a-andb-Silicon tion13) as represented in Fig. 1(a). Unlike a-SiAlON, it is nitride, which occurs at temperatures exceeding 1350°C, is a not essential for b-SiAlON to accommodate metal ions for reconstructive polymorphic transformation, whereas the charge compensation. It means that metal ions such as transformation between a-andb-SiAlON is essentially rare-earth ions could not enter into the crystal structure of chemically controlled.15) Accordingly, the phase assemblage b-SiAlON or occupy any sites in the b-SiAlON structure. obtained in the final product is mainly determined by the This was verified by previous study that metal ions were overall composition of the starting materials. It is well located in the glass phase connecting the b-SiAlON known also that the metal cation (M) doped a-SiAlON, particles.14) However, the strong green emission from Eu2＋ where M is Li, Mg, Ca, Y and the rare-earth metals, is more clearly indicated that Eu2＋ was located somewhere in the stable at high temperatures due to incorporation of Mp＋ structure of b-SiAlON.11) This conflicting result imply that metal ions into vacant network sites, and that the ease with the solubility of metal ions in b-SiAlON is still debatable and which this transformation proceeds decreases as the atomic needs to be clearly researched through various analyses. number of the metal cation increases.16),17) The XRD results Here, we used XRD technique to roughly outline the doping in Fig. 1(b) indicate that, with the above-described 2＋ 2＋ limit of Eu into single b-SiAlON (EuxSi6－zAlzOzN8－z, z＝ approach, the solubility of Eu into single b-SiAlON 0.231) phase. (EuxSi6－zAlzOzN8－z, z＝0.231) phase in 2000°C is limited Figure 1(b) shows XRD patterns of the prepared b- under lower than x＝0.0238. SiAlON:Eu2＋(z＝0.231) phosphor samples with varying The microstructural observations for the prepared b- Eu2＋ doping concentration. It reveals that the samples con- SiAlON:Eu2＋ (x＝0.0065–0.0390) were carried out using sist of a single b-SiAlON crystalline phase (JSPDScardNo. SEM. Typical SEM images of the microstructure for x＝ 48–1615) when the Eu2＋ doping concentration is less than 0.0130, 0.0195 and 0.0260 samples are presented in Figs. 2

390 Journal of the Ceramic Society of Japan 116 [3] 389-394 2008 JCS­Japan

Fig. 2 SEM photographs of the prepared EuxSi6－zAlzOzN8－z (z＝0.231) phosphors with x value of (a) 0.0130, (b) 0.0195 and (c) 0.0260, respectively.

(a–c), respectively. As seen, all the prepared b-SiAlON: Eu2＋ powder samples had a rod-like morphology which have a uniform size of 3–5 mminlengthand0.5–1mmindiameter. In addition, the b-SiAlON samples with low Eu2＋ doping concentrations were soft and easy to pulverize, whereas the highly Eu2＋ doped samples (x0.0238) were hard and the particles were easily damaged. Figure 3 represents the excitation and emission spectra of the prepared b-SiAlON (EuxSi6－zAlzOzN8－z, z＝0.231) phosphor powders with varying Eu2＋ doping concentration (x) at room temperature. In excitation spectra of Fig. 3(a), two broad bands centered at about 355 and 406 nm were observed for all x valued samples. The first peak was assigned to absorption of the host lattice (b-SiAlON) and the second one corresponded to 4f7 → 4f65d1 absorption of the Eu2＋ cations.18) The absorption peak intensity increased when the Eu2＋ doping amount increased, and a maximum value was found in the sample of x＝0.0195. The emission spectra of the prepared b-SiAlON:Eu2＋ samples, as shown in Fig. 3(b), exhibited a single broad band peaking at 525–540 nm. From Fig. 3(a–b), it can be confirmed that the PL properties of Eu2＋ doped b-SiAlON:Eu2＋ phosphors depend strongly on the Eu2＋ doping concentration. No spe- cial emission peaks of Eu3＋ (sharplinesbetween580and650 nm) were observed in the spectra, suggesting that Eu3＋ was reduced to Eu2＋ in a reducing nitrogen atmosphere. This was also verified in other studies.19),20) Table 1 summarizes the luminescent emission properties of the prepared b-SiAlON: Eu2＋ phosphor samples, i.e. CIE (Commission Internation- al del'Eclairge) 1931 chromatic coordination values, emis- sion peak intensity, integral emission intensity, peak center position and full width of half maximum (FWHM) values. The energy level scheme of Eu2＋ has been known for a long time.21),22) In the emission spectra, either sharp 4f → 4f transitions or very broad band emissions because of 5d → 4f transitions are usually observed depending on how large is Fig. 3. Room temperature (a) excitation and (b) emission spectra the ligand field splitting of the 5d levels because the 4f levels of the prepared EuxSi6－zAlzOzN8－z (x＝0.0065–0.0390, z＝0.231) remain unaffected.23) The emission and excitation spectra of phosphors with Eu2＋ doping conc entrations. the Eu2＋ ions in the present b-SiAlON lattice, which exhibit- ed broad bands, were thus ascribed to transitions between 8 7 6 1 the S7/2 (4f ) ground state and the lowest level of the 4f 5d configuration as excited state. Figure 4(a) schematically The present b-SiAlON:Eu2＋ phosphors had emission spec- shows the configurational coordinate model for Eu2＋ in b- tra peaking at about 525–540 nm, and thus gave a green SiAlON lattice. The absorption of blue or near UV photons color. It has been known that the emission of Eu2＋ vary by the host matrix was followed by a nonradiative transfer to from near UV to red color, depending on the host the Eu2＋ ions, and these latter came back to the ground state lattice.24)–26) It was suggested that the preferential orienta- through a radiative transition. tion of a d-orbital or low-lying states of the conduction band

391 JCS­Japan Ryu et al.: Luminescent properties of b-SiAlON:Eu2＋ green phosphors synthesized by gas pressured sintering

Table 1. Summarized PL Emission Data for the EuxSi6－zAlzOzN8－z (x＝0.0065–0.0390, z＝0.231) Phosphors Calcined at 2000°Cfor2h

als that the emission occurred at longer wavelengths as the nitrogen concentration increased.27) This color tuning of Eu2＋ in nitride or oxynitride host lattice is attributed to the fact that the higher formal charge of N3－ in respect to O2－ and the nephelauxetic effect caused the ligand-field splitting of the 5d levels to be larger and the center of gravity of the 5d states to occur at lower energies than in an analogous oxygen environment as shown in Fig 4(b).28) Figure 5(a–b) shows the dependence of luminescent properties, i.e. emission peak intensity, integral emission intensity, peak position and FWHM of the respective emis- sion bands as a function of Eu2＋ doping concentration. The highest PL intensity is found in the sample with composition of x＝0.0195, and concentration quenching occurs when the Eu2＋ concentration is beyond x＝0.0195. This concentration quenching is mainly caused by the energy transfer among Eu2＋ ions, the probability of which increases as the concen- tration of Eu2＋ increases.24) Since 4f → 5d transition of Eu2＋ is allowed in the present material and the luminescence spectra overlaps at 520–540 nm, the nonradiative energy transfer among Eu2＋ ions take places as a result of an electric multipolar interaction and radiation re-absorption. When the concentration of Eu2＋ increases, the distance between Eu2＋ ions becomes small, and thus the probability of energy transfer increases. Furthermore, the spectral overlap at the emission and excitation spectra means that interaction leads to energy migration, which also results in concentration quenching. Another phenomena relating to the increase of Eu2＋ dop- ing concentration is the red-shift of the emission peak posi- tion and broadening of bandwidth as conformed in Fig. 5 Fig. 4. (a) Schematic illustration of a configurational coordinate model for excitation by blue light. The vertical arrows indicate the (b). This may be due to some changes produced in the 2＋ absorption of blue light and the emission of visible lights, respective- crystal field around Eu which causes the splitting of 5d ly. (b) Schematic diagram for splitting of energy levels of Eu2＋ due electrons. As mentioned earlier, the probability of the energy to the crystal field in b-SiAlON host. transfer from the Eu2＋ ions at higher levels of 5d to those at the lower levels of 5d increases with an increase of Eu2＋ con- centration. This makes it possible that higher Eu2＋ concen- shifted the emission to longer wavelengths. Furthermore, it tration lowers the emission energy for transfer from the low was shown in Eu2＋ doped oxynitride or nitride host materi- 5d excited state to the 4f ground state, and hence increases

392 Journal of the Ceramic Society of Japan 116 [3] 389-394 2008 JCS­Japan

Fig. 5. (a) Normalized PL peak intensity and integral emission intensity of the prepared EuxSi6－zAlzOzN8－z (x＝0.0065–0.0390, z＝0.231) phosphors with Eu2＋ doping concentration. (b) The dependence of emission peak position and FWHM of the prepared Fig. 6. (a) Emission spectra measured with increasing temperature b-SiAlON:Eu2＋ powders with Eu2＋ doping concentration. The from 25 to 300°CfortheEuxSi6－zAlzOzN8－z (x＝0.0195, z＝0.231) graph reveals obviously red-shift of emission bands and bandwidths phosphor sample. Inset graph shows PL emission spectra of broadening, which is due to the concentration quenching. 2＋ SrBaSiO4:Eu green phosphor measured at 25, 150 and 300°C. (b) Temperature dependence of emission peak intensity and integral emission intensity in the temperature range of 25 and 300°C. The graph in inset depicts an Arrhenius fitting of the emission intensity the bandwidth (fullwidthofhalfmaximum) and shifts in the measuring temperature range, and calculated activation emission band to long wavelength as well as shown in Fig. 5 energy for thermal quenching (DE) is shown. (b). Thermal quenching property is one of the most important technological parameters for phosphors applied in white LEDs. The temperature dependent PL properties of the pre- the thermal quenching of the emission intensity.29) And also, pared b-SiAlON:Eu2＋ phosphors were investigated in a tem- the electron-phonon interaction resulted from increased perature range from 25 to 300°C, and a typical result for b- population density of phonon broadens FWHM of emission SiAlON:Eu2＋ with composition of x＝0.0195 is shown in spectra at high temperature.30) Fig. 6(a). Upon heating the phosphor samples, the decrease Figure 6(b) displays decrease of the normalized emission in emission intensity and broadening of bandwidths peak intensity and integral emission intensity for the pre- (FWHM) are apparent, which can be explained by the ther- pared b-SiAlON:Eu2＋ (x＝0.0195) as a function of measur- mal quenching in the configuratinal coordinate model for ing temperature. The integral PL emission intensity which is Eu2＋ asshowninFig.4(a). The lower potential curve and proportional to the quantum efficiency decreased slightly the higher one represent the total energy of the ground state less than the emission peak intensity as shown in Fig. 6(b). 7 8 6 1 of 4f ( S7/2 ) and the excited state of 4f 5d , respectively. At 150°C, the integral emission intensity and peak intensity The equilibrium positions of the two states are different were about 74 and 65 of those measured at room tempera- from each other because of the spatial distribution of the ture. This thermal quenching result is slightly inferior to electron orbitals. The excited luminescent center is thermally those (about 85) of Xie et al., which is considered to be activated through phonon interaction, and then thermally originated by high Eu2＋ doping concentration (x＝0.0195) released through the crossing point between the excited state compared to the case of Xie et al. (x＜0.015), because ther- and the ground state in the configurational coordinate dia- mal quenching becomes larger generally as dopant concen- gram. This non-radiative transition induced by thermal acti- tration increases.12) In order to evaluate thermal quenching vation is strongly dependent on temperature, which results in quality comparing with other green phosphor compounds,

393 JCS­Japan Ryu et al.: Luminescent properties of b-SiAlON:Eu2＋ green phosphors synthesized by gas pressured sintering

thermal degradation of PL emission for silicate green phos- References 2＋ phor (SrBaSiO4:Eu ) being used commercially was meas- 1) E.F.Schubert,J.K.Kim,H.LuoandJ-Q.Xi,Rep. Prog. ured and presented in inset of Fig. 6(a). Integral emission Phys., 69, 3069–3099 (2006). and peak intensity measured at 150°Cwere35and33 of 2) H. Luo, J. K. Kim, E. F. Schubert, J. Cho, C. Sone and Y. those measured at room temperature, respectively, which Park, Appl. Phys. Lett., 86, 243505 (2005). 3) Y.Narukawa,J.Narita,T.Sakamoto,K.Deguchi,T. are no more than half values of the prepared b-SiAlON:Eu2＋ Yamada and T. Mukai, Jpn. J. Appl. Phys., 45, L1084–L1086 (x＝0.0195) sample. For applying to LEDs, phosphors must (2006). sustain efficiency at temperatures of about 150°Coveralong 4) R-J. Xie, N. Hirosaki, N. Kimura, K. Sakuma and M. term. It is thus required that the thermal quenching of phos- Mitomo, Appl. Phys. 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Yamamoto and M. dependent emission peak intensity can be described by the Mitomo, Appl. Phys. Lett., 84, 5404–5406 (2004). expression,31) 10) V. A. Izhevskiy, L. A. Genova, J. C. Bressiani and F. Aldinger, J. Eur. Ceram. Soc., 20, 2275–2295 (2000). I I(T)＝ 0 (1) 11) N.Hirosaki,R.-J.Xie,K.Kimoto,T.Sekiguchi,Y. －DE Yamamoto, T. Suehiro and M. Mitomo, Appl. Phys. Lett., 1＋A exp ( k T ) 86, 211905 (2005). B 12) R.-J.Xie,N.Hirosaki,H.-L.Li,Y.Q.LiandM.Mitomo,J. where I is the initial intensity, I(T) is the intensity at a given 0 Electrochem. Soc., 154, J314–J319 (2007). temperature T, A is a constant, DE is the activation energy 13) S. V. Okatov and A. L. Ivanovskii, Phys. Stat. Sol. B, 231, for thermal quenching, and kB is Boltzmann's constant. The R11–R13 (2002). graph in inset of Fig. 6(b) plots ln [(I0/I)－1] vs 1/(kBT) 14) T. Ekstrom and Mats Nygren, J. Am. Ceram. Soc., 75, and gives a straight line up to T＝300°C. The best fit follow- 259–276 (1992). ing Eq. (1) gives activation energy (DE) of 0.234 eV, which 15) A. Rosenflanz and I.-W. Chen, J. Eur. Ceram. Soc., 19, is comparable to the reported value (0.23 eV) in Ca-a- 2325–2335 (1999). SiAlON:Yb2＋ phosphor.4) 16) H.MandalandM.J.Hoffmann,J. Am. Ceram. Soc., 82, 229–232 (1999). 17) A. Rosenflanz and I.-W. Chen, J. Am. Ceram. Soc., , 4. Conclusion 82 1025–1036 (1999). In this work, green emitting Eu Si Al O N (x＝ x 6－z z z 8－z 18) S. H. M. Poort, H. M. Reijnhoudt, H. O. T. van der Kuip and 0.0065–0.0390, z＝0.231) phosphors were successfully pre- G. Blasse, J. Alloys Compd., 241, 75–81 (1996). pared by gas pressure sintering and their photoluminescence 19) K. Uheda, H. Takizawa, T. Endo, H. Yamane, M. Shimada, properties were studied in detail. The phase pure, fine, and C. M. Wang and M. Mitomo, J. Lumin., 87/89, 967–969 uniform b-SiAlON:Eu2＋ phosphors were obtained at 2000°C (2000). under a nitrogen gas pressure of 0.92 MPa and in doping 20) H. A. Hoppe, H. Lutz, P. Morys, W. Schnick and A. concentration range lower than x＝0.0238. The obtained b- Seilmeier, J. Phys. Chem. Solids, 61, 2001–2006 (2000). SiAlON:Eu2＋ phosphor samples had rod-like morphology 21) P. Dorenbos, J. Lumin., 104, 239–260 (2003). with a uniform size of 3–5 mm in length and 0.5–1 mmin 22) H.N.Russell,W.AlbertsonandD.N.Davis,Phys. Rev., 60, diameter. The highest PL emission intensity was found in the 641–656 (1941). 23) G. Blasse, Phys. Status. Solidi B, , K131–K134 (1973). sample with x＝0.0195. Concentration quenching occurred 55 24) J. Qiu, K. Miura, N. Sugimoto and K. Hirao, J. Non-Cryst. when the Eu2＋ concentration is beyond the x＝0.0195. A sys- Solids, 213/214, 266–270 (1997). tematic red-shift and broadening of the emission bandwidths 25) N. Yamashita, J. Lumin., 59, 195–199 (1994). 2＋ were observed as the Eu doping concentration increases, 26) H.Liang,Q.Su,Y.Tao,T.HuandT.Liu,J. Alloys ＋ which were explained by the energy transfer between Eu2 Compd., 334, 293–298 (2002). ions and the splitting of 5d electrons of Eu2＋ caused by 27) J.W.H.vanKrevel,H.T.Hintzen,R.MetselaarandA. changes in crystal field. Temperature dependence for PL Meijerink, J. Alloys Compd., 268, 272–277 (1998). 28) R.-S. Liu, Proc. Phosphor Global Summit 2007, March 5–7, property of the prepared EuxSi6－zAlzOzN8－z (x＝0.019, z＝ 0.231) was investigated from 25 to 300°C and showed a Seoul, South Korea (2007). superior thermal quenching property to commercially used 29) S. Shionoya and W. M. Yen,“Phosphor Handbook, Laser & Optical Science & Technology Series”, CRC, New York silicate green phosphor, which means b-SiAlON:Eu2＋ phos- (1998) pp. 35–48. phors are promising for high-power LED applications. By 30) J.S.Kim,Y.H.Park,S.M.Kim,J.C.ChoiandH.L.Park, fitting the temperature dependent PL data based on the clas- Solid State Commun., 133, 445–448 (2005). sical thermal quenching theory, the activation energy (DE) 31) Y.Chen,B.Liu,C.Shi,G.RenandG.Zimmerer,Nucl. for thermal quenching were determined to be 0.234 eV. Instr. And Meth. A, 537, 31–35 (2005).

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