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北京化工大学：《材料导论》课程阅读材料（无极非金属）Silicon-based_oxynitride_and_nitride_phosphors_for_white_LEDs_review

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Science and Technology of Advanced Materials ] (]]]]) ]]]–]]] Review Silicon-based oxynitride and nitride phosphors for white LEDs—A review Rong-Jun Xie, Naoto Hirosaki Nitride Particle Group, Nano Ceramics Center, National Institute for Materials Science, Namiki 1-1, Tsukuba, Ibaraki 305-0044, Japan Received 11 June 2007; received in revised form 25 July 2007; accepted 27 August 2007 Abstract As a novel class of inorganic phosphors, oxynitride and nitride luminescent materials have received considerable attention because of their potential applications in solid-state lightings and displays. In this review we focus on recent developments in the preparation, crystal structure, luminescence and applications of silicon-based oxynitride and nitride phosphors for white light-emitting diodes (LEDs). The structures of silicon-based oxynitrides and nitrides (i.e., nitridosilicates, nitridoaluminosilicates, oxonitridosilicates, oxonitridoaluminosilicates, and sialons) are generally built up of networks of crosslinking SiN4 tetrahedra. This is anticipated to significantly lower the excited state of the 5d electrons of doped rare-earth elements due to large crystal-field splitting and a strong nephelauxetic effect. This enables the silicon-based oxynitride and nitride phosphors to have a broad excitation band extending from the ultraviolet to visible-light range, and thus strongly absorb blue-to-green light. The structural versatility of oxynitride and nitride phosphors makes it possible to attain all the emission colors of blue, green, yellow, and red; thus, they are suitable for use in white LEDs. This novel class of phosphors has demonstrated its superior suitability for use in white LEDs and can be used in bichromatic or multichromatic LEDs with excellent properties of high luminous efficacy, high chromatic stability, a wide range of white light with adjustable correlated color temperatures (CCTs), and brilliant color-rendering properties. r 2007 NIMS and Elsevier Ltd. All rights reserved. Keywords: Oxynitride; Nitride; Phosphor; Luminescence; White LEDs; Sialon Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Classification and crystal chemistry of nitride compounds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 3. Structure and luminescence of silicon-based oxynitride and nitride phosphors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 3.1. Blue-emitting phosphors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 3.2. Green-emitting phosphors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 3.3. Yellow-emitting phosphors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 3.4. Red-emitting phosphors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 4. Synthesis of silicon-based oxynitride and nitride phosphors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 4.1. Solid-state reaction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 4.2. Gas-reduction nitridation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 4.3. Carbothermal reduction and nitridation (CRN) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 5. Applications of oxynitride and nitride phosphors in white LEDs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 6. Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 ARTICLE IN PRESS www.elsevier.com/locate/stam 1468-6996/$ - see front matter r 2007 NIMS and Elsevier Ltd. All rights reserved. doi:10.1016/j.stam.2007.08.005 Corresponding author. Tel.: +81 29 860 4312; fax: +81 29 851 3613. E-mail address: Xie.Rong-Jun@nims.go.jp (R.-J. Xie). Please cite this article as: R.-J. Xie, N. Hirosaki, Sci. Technol. Adv. Mater. (2007), doi:10.1016/j.stam.2007.08.005

ARTICLE IN PRESS 1.Introduction phosphors for LEDs,it is essential to modify existing on phosphors or to explore new host crystals for phosphors nitrid earth-doped III-V g nitride ena are associated with large energy losses that occu such as AIN,GaN, large Stokes shifts ntensively i operation of LEDs is based on spontaneous light emissior the luminescence of silicon-based oxynitride and nitride in semiconductors,which is due to the radiative recombi nation of excess el tron and [that are produce con N2 pres sure,an Sub the ly,the radi that they used as As a high-temperature structural materials;and (iv)the limited with conventional lamp dersta struct ures as a resul of th hav nsumption and pollution from fossil fuel power plants recent vears becar of their enc raging luminescent ]Currently,LEDs are widely used ndicators. rea properties (excitability blue light,high conversion quid de hts Io the of ful in the brighu and high otential for use i yhite I ED it is generally accepted that they [11-14.In this review,we discuss recent developments in replace conventional lamps for general lighting in the rare-earth-activated oxynitrid and nitride ding th phosphor ral ther are three methods of creating light in LEDs:(i)using three individual monochromatic green and red colors;(ii)combining an olet (UV) and red pho 2.Cla sification and crystal chemistry of nitride compound nhosnhors 2 In the latter two case Nitride compounds are a large family of nitrogen- phosphorsre used as downconversion luminescent mat containing that are formed by combining sourc hors in ED electro J:0 for pho for p e in I EDs ar (in chemical characteristics of the bonds between nitr en and c phosphors in cathode-ray Meta llic nitrides. such as TiN 254 aps are are u by the form of M-N.with M being an alkali-.alkaline- addition,they should also have the following ch cte metal,and/or rare arth metal;examples include Li; stabilit n as B. AIN.GaN y thermal a ith IB-VB om the size(5-20um片and(w）appr phor ut white be co ed as host lattices for phosphors because the (Y1 ol an mn orthosilicates 3.aluminates 5 and sulfides 5.6]have either electrical or ionic conductors and both have narrow d in white LEDs.How band the gaps.Furthermore,the covalent chemical bonding low a nit to a ene hlue i EDs On the other hand sulfide-hased phosphors e cited of the sd electrons of the activato thermally unstable and very sensitive to moisture,and thei (e.g..Eu Ce )[16-20].This results in long excitation/ nce degrades significantly unde ambient emi wave engths and low therma in conventiona ors usec nd CRTs Please cite this article as:R.Xie,N.Hirosaki Sci.Technol Adv.Mater.(2)doi:.1016/.00

1. Introduction Conventional incandescent or fluorescent lamps rely on either incandescence or discharge in gases. Both phenomena are associated with large energy losses that occur because of the high temperatures and large Stokes shifts involved. Light-emitting diodes (LEDs) using semiconductors offer an alternative method of illumination. The operation of LEDs is based on spontaneous light emission in semiconductors, which is due to the radiative recombination of excess electrons and holes [1] that are produced by the injection of current with small energy losses. Subsequently, the radiative recombination of the injected carriers may attain quantum yields close to unity. As a result, compared with conventional lamps, LED-based light sources have superior lifetime, efficiency, and reliability, which promise significant reductions in power consumption and pollution from fossil fuel power plants [1]. Currently, LEDs are widely used as indicators, rear lamps for vehicles, decorated lamps, backlights for cellular phones and 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. In general, there are three methods of creating white light in LEDs: (i) using three individual monochromatic LEDs with blue, green, and red colors; (ii) combining an ultraviolet (UV) LED with blue, green, and red phosphors; and (iii) using a blue LED to pump yellow or green and red phosphors [2]. In the latter two cases, appropriate phosphors are used as downconversion luminescent materials. The excitation sources used for phosphors in LEDs differ greatly from those of phosphors in conventional lighting. The excitation sources for phosphors in LEDs are UV (360–410 nm) or blue light (420–480 nm), whereas those for conventional inorganic phosphors in cathode-ray tubes (CRTs) or fluorescent lamps are electron beams or mercury gas (lem ¼ 254 nm). Therefore, the phosphors in LEDs should have high absorption of UV or blue light. In addition, they should also have the following characteristics: (i) high conversion efficiency; (ii) high stability against chemical, oxygen, carbon dioxide, and moisture; (iii) low thermal quenching; (iv) small and uniform particle size (5–20 mm); and (v) appropriate emission colors. The phosphor most commonly utilized in bichromatic white LEDs is the yellow-emitting (Y1aGda)3(Al1bGab) O12:Ce3+ (YAG:Ce)[1]. Other types of phosphor such as orthosilicates [3,4], aluminates [5], and sulfides [5,6] have also been used in white LEDs. However, most oxide-based phosphors have low absorption in the visible-light spectrum, making it impossible for them to be coupled with blue LEDs. On the other hand, sulfide-based phosphors are thermally unstable and very sensitive to moisture, and their luminescence degrades significantly under ambient atmosphere without a protective coating layer. Consequently, to solve these problems and develop high-performance phosphors for LEDs, it is essential to modify existing phosphors or to explore new host crystals for phosphors such as nitrides. Luminescence in rare-earth-doped III–V group nitrides such as AlN, GaN, InGaN, and AlInGaN has been intensively investigated because of their potential applications in blue-UV optoelectronic and microelectronic devices [7–10]. However, less attention has been paid to the luminescence of silicon-based oxynitride and nitride compounds, perhaps due to (i) their critical preparation conditions (high temperature, high N2 pressure, and airsensitive starting powders); (ii) the lack of general synthetic routes; (iii) the strong impression that they are used as high-temperature structural materials; and (iv) the limited understanding of their crystal structures as a result of the difficulties in crystal growth. Silicon-based oxynitride and nitride phosphors have received significant attention in recent years because of their encouraging luminescent properties (excitability by blue light, high conversion efficiency, and the possibility of full color emission), as well as their low thermal quenching, high chemical stability, and high potential for use in white LEDs [11–14]. In this review, we discuss recent developments in rare-earth-activated oxynitride and nitride phosphors, including their crystal structure, preparation, luminescent properties, and applications in white LEDs. 2. Classification and crystal chemistry of nitride compounds Nitride compounds are a large family of nitrogencontaining compounds that are formed by combining nitrogen with less electronegative elements. Generally, nitrides can be grouped into three types: (i) metallic, (ii) ionic, and (iii) covalent compounds, based on the chemical characteristics of the bonds between nitrogen and other elements [15]. Metallic nitrides, such as TiN, ZrN, VN, CrN, and FeN, are usually produced by combining nitrogen with transition metals. Ionic nitrides are usually of the form of M–N, with M being an alkali-, alkaline-earth metal, and/or rare-earth metal; examples include Li3N, Ca3N2, CeN, and LiMnN2. Covalent nitrides, such as BN, AlN, GaN, silicon nitride (Si3N4), and P3N5, are formed by combining nitrogen with IIIB–VB group metals. From the viewpoint of luminescent materials, covalent nitrides can be considered as host lattices for phosphors because they have the characteristics of an insulator or semiconductor and wide band gaps, whereas metallic and ionic nitrides are either electrical or ionic conductors and both have narrow band gaps. Furthermore, the covalent chemical bonding in nitrides gives rise to a strong nephelauxetic effect (i.e., electron cloud expansion), reducing the energy of the excited state of the 5d electrons of the activators (e.g., Eu2+, Ce3+) [16–20]. This results in long excitation/ emission wavelengths and low thermal quenching, which cannot be achieved in conventional phosphors used in lamps and CRTs. ARTICLE IN PRESS 2 R.-J. Xie, N. Hirosaki / Science and Technology of Advanced Materials ] (]]]]) ]]]–]]] Please cite this article as: R.-J. Xie, N. Hirosaki, Sci. Technol. Adv. Mater. (2007), doi:10.1016/j.stam.2007.08.005

ARTICLE IN PRESS R-J.Xle,N.Hirosaki/Sclence and Technology of Adeanced Materials() Alternatively.nitride com ounds can also be divided engineers.For rare-earth ions (ie..Eu2 and Ce)with the 5d electrons unshielded from the crystal field by the 5 ents i binary,(ii)ter (quaternary and 5p electrons wher in the excite te,the spe BN. and AIN not bary ent m asily d as hen a for phosphors in white LEDs because they do not have bond length,site size,crystal-field strength,etc.).Becaus of the higher formal charge of N compared with 7-10 The he nepe covalent nitride iicon-based nitride of gravity of the sd states is shifted to lower are interesting because of their unique and rigid crystal ab ty of s able environmen oxynitride earth ions to provide u ping c and emission wavelengths than their oxide Furthermore,the Stokes shift becomes smaller in a rigid the preparation and crysta silicon-base etwork of SIN tetrahedr tena sialons is formed by the integ tion of nit gen in silicates A variety of oxynitride and nitride materials with aluminosilicat Com with the romising umine nt prope erties have been discovered dly [1-1 9 3].In t of thes addition to these nitride compounds oxynitrides (i.e. oxon 3.1.Blue-emitting phosphors mbind with aluminum resp vely.Therefore.m to oxosilicate and red phosphors to create white light when UV or near structure: oxyni and t(NUV)LED is used.Although a large numbe omp hedra.The degree of condensation in the netw ork of Six nal degradation is a serious problem if they are used in tetrahedra is simply evaluated by the ratio 「44D. Ce s to b ging atom the ate oxynitr pho S ratio n a h indicates that nitrides have a high degree of condensatior white LEDs.In the following.three types of blue-emitting due to the fact the and he phospho atoms O: xyger 1 ides are generall connected with two(N thre Al)N.O was re atoms such as in BaSiN Sr Ba)[24,25 eque (spac rdin ted h (N.O) elements result in the extraordinary chemical and ther vielding an Al(Si.Al)(N,O)network (see Fig.1).The La stability of silicon-based oxynitride and nitride materials caCanmodhedntunncheiendhng re along the and lumings ence of silicon-based oxynitride and nitride phosphors et al.1]reported the luminescence of Ce+-doped JEM As shown in Fig 2,the emission spectrum ,sulfide of JEM:C tending nm nhors is at oxy The road excitatic m extending from 200 to 450m realizing white LEDs has greatly catalyzed the research and due to the 4f. .5d electronic transition of Ce Both ment of oxynitride and nitride pho spectra redshifted whe value Please cite this article as:R.Xie.N.Hirosaki,Sci.Technol.Adv.Mater .(2007.doi10.1016 j.stam2007.08.00

Alternatively, nitride compounds can also be divided into the following groups depending on the number of elements included: (i) binary, (ii) ternary, (iii) quaternary, and (iv) multinary. Binary covalent nitrides, such as GaN, BN, and AlN, cannot be easily considered as host lattices for phosphors in white LEDs because they do not have suitable crystal sites for activators [13], although some of them show interesting luminescence properties in thin-film form [7–10]. The ternary, quaternary, and multinary covalent nitride compounds, typically silicon-based nitrides, are interesting because of their unique and rigid crystal structures, availability of suitable crystal sites for activators, and their structural versatility, which enable the doping of rare-earth ions to provide useful photoluminescence. Schnick and coworkers [21–28] extensively investigated the preparation and crystal structures of silicon-based oxynitride and nitride compounds. A new class of materials consisting of nitridosilicates, nitridoaluminosilicates, and sialons is formed by the integration of nitrogen in silicates or aluminosilicates. Compared with the well-known oxosilicates, the newly developed nitrides exhibit a much wider range of structural complexity and flexibility, forming a large family of multiternary compounds. In addition to these nitride compounds, oxynitrides (i.e., oxonitridosilicates and oxonitridoaluminosilicates) are derived from oxosilicates and oxoaluminosilicates by exchanges of oxygen with nitrogen and of silicon with aluminum, respectively. Therefore, similar to oxosilicates, the structures of silicon-based oxynitride and nitride compounds are generally built up of highly condensed networks constructed from linked SiX4 (X=O, N) tetrahedra. The degree of condensation in the network of SiX4 tetrahedra is simply evaluated by the ratio of tetrahedral Si centers to bridging atoms X. In oxosilicates the Si:X ratio reaches a maximum of 0.5 in SiO2, while in nitrides the Si:X ratio may vary in a broad range of 0.25–0.75. This indicates that nitrides have a high degree of condensation due to the fact that the structural possibilities in oxosilicates are limited to terminal oxygen atoms and simple bridging O[2] atoms, whereas the nitrogen atoms in nitrides are generally connected with two (N[2]), three (N[3]), even four (N[4]) silicon atoms such as in BaSi7N10 [23] and MYbSi4N7 (M ¼ Sr, Ba) [24,25]. Consequently, the highly condensed SiN4-based networks and the high stability of the chemical bonding between the constituent elements result in the extraordinary chemical and thermal stability of silicon-based oxynitride and nitride materials. 3. Structure and luminescence of silicon-based oxynitride and nitride phosphors Compared with oxide-, boride-, sulfide-, or phosphatebased phosphors, the study of oxynitride and nitride phosphors is at a very early stage. The possibility of realizing white LEDs has greatly catalyzed the research and development of oxynitride and nitride phosphors, and they are receiving significant attention from both scientists and engineers. For rare-earth ions (i.e., Eu2+ and Ce3+) with the 5d electrons unshielded from the crystal field by the 5s and 5p electrons when in the excited state, the spectral properties are strongly affected by the surrounding environment (e.g., symmetry, covalence, coordination, bond length, site size, crystal-field strength, etc.). Because of the higher formal charge of N3 compared with O2 and the nephelauxetic effect (covalence), the crystal-field splitting of the 5d levels of rare earths is larger and the center of gravity of the 5d states is shifted to lower energies (i.e., longer wavelength) than in an analogous oxygen environment. Consequently, silicon-based oxynitride and nitride phosphors are anticipated to show longer excitation and emission wavelengths than their oxide counterparts. Furthermore, the Stokes shift becomes smaller in a rigid lattice with a more extended network of SiN4 tetrahedra. A small Stokes shift leads to high conversion efficiency and small thermal quenching of phosphors. A variety of oxynitride and nitride materials with promising luminescent properties have been discovered recently [11–14,16–19,29–43]. In this section, we will review the structure and luminescence of these rare-earth-doped oxynitride and nitride phosphors. 3.1. Blue-emitting phosphors A blue-emitting phosphor must be combined with green and red phosphors to create white light when UV or near ultraviolet (NUV) LED is used. Although a large number of oxide-based phosphors emit an intense blue color under UV or NUV light excitation, the high thermal quenching or thermal degradation is a serious problem if they are used in white LEDs (e.g., BaMgAl10O17:Eu2+ [44]). Ce3+- or Eu2+-activated oxynitride blue phosphors undergo little thermal degradation and have strong absorption of UV or NUV light, enabling them to be alternative candidates for white LEDs. In the following, three types of blue-emitting oxynitride phosphor (i.e., LaAl(Si6zAlz)N10zOz:Ce3+, a-sialon:Ce3+, and (Y,La)-Si–O–N:Ce3+) will be described. The preparation and crystal structure of a JEM phase with chemical formula LaAl(Si6zAlz)N10zOz was reported by Grins et al. [45]. JEM has an orthorhombic structure (space group Pbcn) with a ¼ 9.4303 A˚ , b ¼ 9.7689 A˚ , and c ¼ 8.9386 A˚ . The Al atoms and (Si, Al) atoms are tetrahedrally coordinated by (N, O) atoms, yielding an Al(Si,Al)6(N,O)10 3 network (see Fig. 1). The La atoms are accommodated in tunnels extending along the [0 0 1] direction and are irregularly coordinated by seven (N, O) atoms at an average distance of 2.70 A˚ . Hirosaki et al. [11] reported the luminescence of Ce3+-doped JEM. As shown in Fig. 2, the emission spectrum of JEM:Ce3+ displays a broad band extending from 400 to 700 nm under 368 nm excitation, with a peak located at 475 nm. The broad excitation spectrum extending from 200 to 450 nm is due to the 4f-5d electronic transition of Ce3+. Both spectra are redshifted when the concentration of Ce3+ or the z value increases, enabling this blue phosphor to be ARTICLE IN PRESS R.-J. Xie, N. Hirosaki / Science and Technology of Advanced Materials ] (]]]]) ]]]–]]] 3 Please cite this article as: R.-J. Xie, N. Hirosaki, Sci. Technol. Adv. Mater. (2007), doi:10.1016/j.stam.2007.08.005

excited efficiently by UV (370–400 nm) or NUV (400–410 nm) LEDs. a-Sialon is a solid solution of a-Si3N4 and is formed by the partial replacement of Si–N bonds with Al–N and Al–O bonds. The general formula of a-sialon, consisting of four ‘‘Si3N4’’ units, can be given as MxSi12mn Alm+nOnN16n (x is the solubility of the M metal) [46–48], where m and n are the numbers of Al–N and Al–O bonds substituting for Si–N bonds, respectively. The charge discrepancy caused by the substitution is compensated for by the introduction of the M cations including Li+, Mg2+, Ca2+, Y3+, and some lanthanides. It has a hexagonal crystal structure and the P31c space group. In the structure of a-sialon, the M cations occupy the interstitial sites and are coordinated by seven (N, O) anions [49]. The crystal structure is shown in Fig. 3. The Ce3+-activated a-sialon (Ca0.898Ce0.068Si9Al3ON15) shows blue emission, as shown in Fig. 4. The emission spectrum, centered at 495 nm, extends from 400 to 650 nm upon 389 nm excitation. The peak emission wavelength is redshifted from 485 to 503 nm when the Ce concentration increases from 5 to 25 mol% [29,30]. Moreover, the emission of a-sialon:Ce3+ can also be tuned by varying the values of m and n. The excitation spectrum shows a broad band with a peak located at 389 nm, which closely matches the emission wavelengths of UV or NUV LEDs. There are several compounds in Y–Si–O–N and La– Si–O–N systems, and their luminescence spectra have been reported recently [17,31]. Van Krevel et al. [17] investigated the luminescent properties of Ce3+-doped Y–Si–O–N oxynitride compounds. Generally, these compounds emit a blue color with a peak emission wavelength of 400–500 nm and show maximum excitation bands at ARTICLE IN PRESS Fig. 2. Excitation and emission spectra of JEM:Ce3+. Fig. 4. Excitation and emission spectra of Ca-a-sialon:Ce3+. Fig. 1. Crystal structure of JEM viewed along the [0 0 1] direction. The blue, pale blue, red, and green spheres represented are La, Al, Si/Al, and O/N atoms, respectively. Fig. 3. Crystal structure of Ca-a-sialon viewed along the [0 0 1] direction. The blue, red, and green spheres represent Ca, Si/Al, and O/N atoms, respectively. 4 R.-J. Xie, N. Hirosaki / Science and Technology of Advanced Materials ] (]]]]) ]]]–]]] Please cite this article as: R.-J. Xie, N. Hirosaki, Sci. Technol. Adv. Mater. (2007), doi:10.1016/j.stam.2007.08.005

325–400 nm. They demonstrated that the N/O ratio and the crystal structure had a strong effect on the emission, Stokes shift, and crystal-field splitting. Larger N/O ratios and stiffer structures led to longer-wavelength emissions, smaller Stokes shifts, and larger crystal-field splitting [17]. A similar tendency was observed in Ce3+-doped La– Si–O–N materials [31]. We have studied the emission of Ce3+ in La–Si–O–N compounds with different structures: La5Si3O12N (hexagonal), LaSiO2N (hexagonal), and La3Si8O4N11 (orthorhombic), and have shown that La3Si8O4N11 has encouraging luminescent properties for white LEDs. Fig. 5 shows the structure of La3Si8O4N11, which contains ribbons as structural units with a composition of Si6(O,N)14. The ribbons extend along the [0 1 0] direction and are formed by corner-sharing Si(O,N)4 tetrahedra. The La1 atom is octahedrally coordinated by 4 O/N and 2 O atoms, and the La2 atom is coordinated by 5 O/N, 2 O atoms, and 1 N atom, which approximately form a cubic antiprism [50]. Fig. 6 shows the excitation and emission spectra of Ce3+-doped La–Si–O–N materials. It reveals that the peak excitation band of La–Si–O–N:Ce3+ is around 360 nm, and those of La4.9Ce0.1Si3O12N, La0.96 Ce0.04SiO2N, and La2.82Ce0.18Si8O4N11 are 472, 416, and 425 nm, respectively. We have also investigated the temperature dependence of the luminescence of Ce3+-doped La–Si–O–N materials and observed that La3Si8O4N11:Ce has the lowest thermal quenching because it has the densest structure and highest N/O ratio [31]. 3.2. Green-emitting phosphors A green-emitting phosphor is used in the case when white LEDs utilize a UV-, NUV-, or blue LED as the primary lighting source. Rare-earth-doped oxynitride and nitride green phosphors highly suitable for use in white LEDs have been reported in the literature [25,32–36], and they are reviewed below. Hirosaki et al. [32] reported a green oxynitride phosphor based on Eu2+-doped b-sialon. b-Sialon is structurally derived from b-Si3N4 by the equivalent substitution of ARTICLE IN PRESS Fig. 5. Crystal structure of La3Si8O4N11 viewed along the [0 0 1] direction. The blue, green, pale blue, red, and gray spheres represent La, N, O, Si, and O/N atoms, respectively. Fig. 6. Excitation (a) and emission (b) spectra of La4.9Ce0.1Si3O12N, La0.96Ce0.04SiO2N, and La2.82Ce0.18Si8O4N11. R.-J. Xie, N. Hirosaki / Science and Technology of Advanced Materials ] (]]]]) ]]]–]]] 5 Please cite this article as: R.-J. Xie, N. Hirosaki, Sci. Technol. Adv. Mater. (2007), doi:10.1016/j.stam.2007.08.005

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北京化工大学：《材料导论》课程阅读材料（无极非金属）Silicon-based_oxynitride_and_nitride_phosphors_for_white_LEDs_review