Effect of chlorine concentration on the spectral characteristics of electroluminescence in ZnS: Cu: Cl phosphor

ZnS: Cu: Cl phosphor prepared under a vacuum firing process is found to give blue electroluminescence with emission peak at 460 nm which remains unaltered with the frequency of the excitation voltage. Addition of excess chlorine in the phosphor gives blue, green and red emission at 460, 520 and 640 nm. The intensity of the blue band decreases and it finally disappears as chlorine concentration is increased. A scheme involving three energy levels attributed to Cu²⁺, Cu⁺ and Cl^- centres in ZnS explains the experimental results completely.     

Orange emissive Sr3Al2O5Cl2:Eu2+ phosphor for warm-white light-emitting diodes

Orange-emitting Sr₃Al₂O₅Cl₂:Eu²⁺ phosphors were synthesized by a high-temperature solid-state reaction. The excitation spectrum shows a broad band from the UV region to the blue region. The emission spectrum shows strong orange emission peaking at 610 nm, attributed to the d–f transition of the Eu²⁺ ion. By combining the Sr₃Al₂O₅Cl₂:Eu²⁺ phosphor with 420 nm and 460 nm chips, three white light-emitting diodes (LEDs) were fabricated. The warm-white LEDs show color rendering indexes of 76, 66 and 90 with color temperatures of 2447, 3546 and 4300 K, respectively. This new phosphor exhibits the potential to act as a single host doped with Eu²⁺ phosphor for UV or blue chip excited white LEDs.     

Photoluminescence characteristics of ZnS nanocrystallites doped with Ti3+and Ti4+

Direct synthesis of ZnS nanocrystallites doped with Ti³⁺ or Ti⁴⁺ by precipitation has led to novel photoluminescence properties. Detailed X-ray diffraction (XRD), fluorescence spectrophotometry, UV–vis spectrophotometry and X-ray photoelectron spectroscopy (XPS) analysis reveal the crystal lattice structure, average size, emission spectra, absorption spectra and composition. The average crystallite size doped with different mole ratios, estimated from the Debye–Scherrer formula, is about 2.6±0.2 nm. The nanoparticles can be doped with Ti³⁺ and Ti⁴⁺ during the synthesis without the X-ray diffraction pattern being altered. The strong and stable visible-light emission has been observed from ZnS nanocrystallites doped with Ti³⁺ (its maximum fluorescence intensity is about twice that of undoped ZnS nanoparticles). However, the fluorescence intensity of the ZnS nanocrystallites doped with Ti⁴⁺ is almost the same as that of the undoped ZnS nanoparticles. The emission peak of the undoped sample is at 440–450 nm. The emission spectrum of the doped sample consists of two emission peaks, one at 420–430 nm and the other at 510 nm. Received: 27 April 2001 / Accepted: 16 August 2001 / Published online: 17 October 2001     

Dy3+掺杂硼硅酸盐玻璃的发光特性

采用高温熔融法制备了Dy3+掺杂硼硅酸盐玻璃,通过测试激发光谱和发射光谱,研究了其光谱性质.研究了玻璃组分及Dy3+掺杂浓度对发射光谱及发光强度的影响,并计算了色坐标,均位于白光区域.通过改变玻璃组分及掺杂浓度,调节黄、蓝发射峰的强度比,在387 nm长紫外光激发下实现了单一基质上有效的白光发射.     

Luminescence properties of novel NaBa4(BO3)3:Ce, Eu phosphors

Novel Eu³⁺, Ce³⁺ activated NaBa₄(BO₃)₃ phosphors were synthesized by solid-state reactions. The excitation spectrum of NaBa₄(BO₃)₃:Ce³⁺ consists of an intense band peaking at 350 nm and a weak band in the higher energy side, and the emission spectrum exhibits a blue band with a maximum at about 420 nm. The Eu³⁺ emission in NaBa₄(BO₃)₃ consists of the transitions from ⁵D₀ to ⁷F_J, and the excitation spectrum consists of broad excitation band peaking at 270 nm and some intense narrow lines. The optimum doped concentration, the critical distance of the concentration quenching, and the fluorescence lifetime have also been investigated.     

Blue up-conversion with excitation into Tm ions at 808 nm in YVO4 crystals co-doped with thulium and ytterbium

The up-conversion of infrared radiation at 808 nm, emitted by a diode laser, into blue emission centered at 480 nm in 1 at.% Tm, 5 at.% Yb: YVO₄; 1 at.% Tm, 8 at.% Yb: YVO₄ and 2 at.% Tm, 5 at.% Yb: YVO₄ has been studied. The highest intensity of blue emission is found for the 1 at.% Tm, 8 at.%Yb: YVO₄ system. The power dependence of up-converted emission upon continuous-wave excitation as well as the time evolution of its intensity upon short-pulse excitation were found to be consistent with a two-step excitation mechanism in which the forward Tm³⁺–Yb³⁺ energy transfer is followed by the back Yb³⁺–Tm³⁺ energy transfer. The effect of dopant concentrations on the up-conversion process is interpreted taking into account dynamics of the excited states involved.     

Relocalization of Ce 5d electrons from host conduction band

Single crystal fibers of Ce³⁺ doped SrAl₂O₄ and CaAl₄O₇ were prepared through the laser heated pedestal growth method. Sites dependent Ce³⁺ emissions were found at 385 nm (427 nm) and 420 nm (325 nm) in SrAl₂O₄ and CaAl₄O₇ hosts, respectively. The Ce³⁺ emissions at 385 nm and 420 nm in the two hosts exhibited strong afterglows. They could persist for more than 10 h. The long persistence and sites dependence of Ce³⁺ emissions were originated from charge compensation of doping Ce³⁺ into divalent cation sites. The lifetimes of Ce³⁺ emissions in both hosts were found to depend on the laser excitation wavelengths. With 266 nm laser excitation, Ce³⁺ 5d electrons were delocalized into the host's conduction band, resulting in a prolonged decay time. The 355 nm laser excitation did not delocalize the 5d electrons and hence the measured lifetimes were the intrinsic Ce³⁺ emission lifetimes that were 17 and 35.5 ns in SrAl₂O₄ and CaAl₄O₇ hosts, respectively. The prolonged Ce³⁺ emission lifetime on 266 nm laser excitation was because of the relocalization of the 5d electrons from the host conduction band. The lifetimes of Ce³⁺ 5d electrons within the conduction band were found to be 34 and 44 ns in SrAl₂O₄ and CaAl₄O₇ hosts, respectively.     

The UV,blue and green up-conversion luminescence of PbF2+GeO2:Er2O3 pumped with 650 nm

A detailed study of the spectroscopic properties of the PbF₂+GeO₂:Er₂O₃ vitroceramic sample upon 650 nm excitation was investigated. The absorption, emission, excitation spectra, and time-resolved spectra have been measured. The up-conversion of red radiation (650 nm) into UV (368 nm and 379 nm), blue (406.8 nm) and green (522 nm and 540 nm) emissions is observed for Er³⁺ ions in the sample. The up-conversion process involves a two-photon absorption for the violet, blue, and green emission bands. A three-photon process happens for another violet (379 nm) band.     

Photoluminescence excitation properties of porous silicon with and without Er-Yb-containing complex

Two bands in the photoluminescence excitation spectra have been studied for the red, blue, and IR emission of oxidized porous silicon (PS) and PS with Er³⁺- and Yb³⁺-containing gadolinium oxychloride complex (PS:Er,Yb), introduced by thermal diffusion. These two spectral bands were shown to reflect contributions of two different mechanisms of excitation-emission processes. The UV band for the IR emission of PS:Er,Yb rose sharply at about 290 nm and was explained by the direct photoemission of carriers from the valence band of Si crystallites into the conduction band of the oxide shell. The second band was found to be common for the red and blue emission and assosiated with the carriers photoexcitation inside the Si crystallites. Lifetimes for both bands were measured and the structure of the blue emission from PS:Er,Yb with peaks at 416, 440, 466, and 500 nm from PS:Er,Yb was observed.     

Upconverted VUV luminescence of Nd and Er doped into LiYF4 crystals under XeF-laser excitation

The upconverted VUV (185 nm) and UV (230 and 260 nm) luminescence due to 5d-4f radiative transitions in Nd³⁺ ions doped into a LiYF₄ crystal has been obtained under excitation by 351/353 nm radiation from a XeF excimer laser. The maximum upconversion efficiency, defined as the ratio of intensity for 5d-4f luminescence to overall intensity for 5d-4f and 4f-4f luminescence from the ⁴D_3/2 Nd³⁺ level, has been estimated to be about 70% under optimal focusing conditions for XeF laser radiation. A redistribution of intensity between three main components of 5d-4f Nd³⁺ luminescence is observed under changing the excitation power density, which favors the most long-wavelength band (260 nm) at higher excitation density level. The effect is interpreted as being due to excited state absorption of radiation emitted. The upconverted VUV and UV luminescence from the high-lying ²F(2)_7/2 4f level of Er³⁺ doped into a LiYF₄ crystal has also been obtained under XeF-laser excitation the most intense line being at 280 nm from the spin-allowed transition to the ²H(2)_11/2 4f level of Er³⁺, but the efficiency of upconversion for Er³⁺ emission is low, less than 5%.     

The luminescent properties of CaYBO4:Ln(Ln=Eu, Tb) under UV-VUV range

The luminescent properties of CaYBO₄:Ln(Ln=Eu³⁺, Tb³⁺) were investigated under ultraviolet (UV) and vacuum ultraviolet (VUV) region. The CT band of Eu³⁺ at about 245 nm blue-shifted to 230 nm in VUV excitation spectrum; the band with the maximum at 183 nm was considered as the host lattice absorption. For the sample of CaYBO₄:0.08Tb³⁺, the bands at about 235 and 263 nm were assigned to the f-d transitions of Tb³⁺ and the CT band of Tb³⁺ was calculated according to Jφrgensen's theory. Under UV and VUV excitation, the main emission of Eu³⁺ corresponding to the ⁵D₀-⁷F₂ transition located at about 610 nm and two intense emission of Tb³⁺ from the ⁵D₄-⁷F₅ transition had been observed at about 542 and 552 nm, respectively. With the incorporation of Gd³⁺ into the host lattice of CaYBO₄, the luminescence of Tb³⁺ was enhanced while that of Eu³⁺ was decreased because of their different excitation mechanism.     

Blue Cooperative Luminescence In Yb3+-Doped Barium Gallogermanate Glass Excited At 976 nm

The Yb³⁺-doped barium gallogermanate glass has been prepared via the conventional melt method. The absorption spectra, the near infrared emission spectra, the upconversion emission spectra and the differential scanning calorimetry have been measured. Bright blue upconversion emission centered at 476 nm has been observed under the 976 nm laser diode excitation at room temperature. The blue upconversion emission mechanism has been discussed on the blue emission intensity and the measured lifetime. The slope of the log-log plot of the blue emission intensity versus the pump power is equal to 1.98, and the blue luminescence decay time is half of the near infrared fluorescence decay time, confirming that the blue emission comes from Yb³⁺-Yb³⁺ pairs cooperative upconversion mechanism. The result of differential scanning calorimetry suggests that this type of glass is suitable as a potential candidate for fiber drawing.     

Ti：Al2O3晶体紫外及可见光谱的浓度效应研究

通过对不同浓度的Ｔｉ：Ａｌ２Ｏ３晶体紫外吸收光谱，可见偏振荧光光谱及其激发光谱的研究，发现峰值４２０ｎｍ的宽带可见荧光，室温下较强的σ偏振光在低温（７７Ｋ）下变得比π偏振光弱。在液氮温度下π偏振光谱分裂成３３０ｎｍ，４２０ｎｍ，４６０ｎｍ，５６０ｎｍ等离荧光带。研究认为，这些发光带分别与色心（Ｆ＾＋，Ｆ心）及Ｔｉ＾４＾＋离子的电荷转移跃适有关。并且室温下可见荧光具有的较强的浓度猝灭及现象来源于Ｔｉ     

Photoluminescence studies of red-emitting NaEu(WO4)2 as a near-UV or blue convertible phosphor

Sodium europium double tungstate [NaEu(WO₄)₂] phosphor was prepared by the solid-state reaction method. Its crystal structure, photoluminescence properties and thermal quenching characteristics were investigated aiming at the potential application in the field of white light-emitting diodes (LEDs). The influences of Sm doping on the photoluminescence properties of this phosphor were also studied. It is found that this phosphor can be effectively excited by 394 or 464 nm light, which nicely match the output wavelengths of near-ultraviolet (UV) or blue LED chips. Under 394 or 464 nm light excitation, this phosphor exhibits stronger emission intensity than the Y₂O₂S:Eu³⁺ or Eu²⁺-activated sulfide phosphor. The introduction of Sm³⁺ ions can broaden the excitation peaks at 394 and 464 nm of the NaEu(WO₄)₂ phosphor and significantly enhance its relative luminance under 400 and 460 nm LEDs excitation. Furthermore, the relative luminance of NaEu(WO₄)₂ phosphor shows a superior thermal stability compared with the commercially used sulfide or oxysulfide phosphor, and make it a promising red phosphor for solid-state lighting devices based on near-UV or blue LED chips.     

Ca2SiO4:Dy3+材料的制备及其发光特性

采用高温固相法制备了Ca₂SiO₄:Dy³⁺发光材料.在365nm紫外光激发下,测得Ca₂SiO₄:Dy³⁺材料的发射光谱为一多峰宽谱,主峰分别位于486nm,575nm和665nm处;监测575nm发射峰,测得材料的激发光谱为一多峰宽谱,主峰分别位于331nm,361nm,371nm,397nm,435nm,461nm和478nm处.研究了Dy³⁺掺杂浓度对Ca₂SiO₄:Dy³⁺材料发射光谱及发光强度的影响,结果显示,随Dy³⁺浓度的增大,黄、蓝发射峰强度比(Y/B)逐渐增大,利用Judd-Ofelt理论解释了其原因;随Dy³⁺浓度的增大,Ca₂SiO₄:Dy³⁺材料发光强度先增大,在Dy³⁺浓度为4 mol%时到达峰值,而后减小,根据Dexter理论其浓度猝灭机理为电偶极-电偶极相互作用.研究了电荷补偿剂Li⁺,Na⁺和K⁺对Ca₂SiO₄:Dy³⁺材料发射光谱的影响,结果显示,不同电荷补偿剂下,随电荷补偿剂掺杂浓度的增大,Ca₂SiO₄:Dy³⁺材料发射光谱强度的演化趋势相同,即Ca₂SiO₄:Dy³⁺材料发射峰强度先增大后减小,但不同电荷补偿剂下,材料发射峰强度最大处对应的补偿剂浓度不同,对应Li⁺,Na⁺和K⁺时,浓度分别为4mol%,4mol%和3mol%. 关键词： 白光LED 2SiO₄:Dy³⁺')" href="#">Ca₂SiO₄:Dy³⁺ 发光特性 电荷补偿     

白光LED用LiBaBO3:Eu2+材料发光特性研究

采用高温固相法制备了LiBaBO₃:Eu²⁺绿色发光材料.测量了Eu²⁺浓度为1mol%时样品的激发与发射光谱,其发射光谱为双峰宽谱,主峰分别为482和507nm,与理论计算值符合很好;监测482nm发射峰时,对应激发光谱的峰值为287和365nm,监测507nm发射峰时,对应的激发峰为365和405nm.研究了Eu²⁺浓度对材料发射光谱的影响,结果显示,随Eu²⁺浓度的增大,蓝、绿发射峰均发生了     

Luminescence spectroscopy of Ce3+-doped ABaPO4 (A=Li, Na, K) phosphors

Ce³⁺ doped ABaPO₄ (A=Li, Na, K) phosphors were prepared by conventional high temperature solid-state reaction. The phosphors were investigated by XRD, photoluminescence excitation and emission spectra, and luminescence decay curves. The five 5d levels corresponding to the 4f¹→4f⁰5d¹ transition of Ce³⁺ ions were identified. The spectroscopic parameters, e.g., the 5d barycenter, the crystal-field splitting, and the Stokes shift, were discussed. LiBaPO₄:Ce³⁺ phosphor could be efficiently excited by the near-UV lights (330–420 nm) and showed a broad emission band in the range of 430–620 nm with the maximum wavelength at 468 nm. In contrast, Ce³⁺-doped NaBaPO₄ and KBaPO₄ showed only excitation bands in a limited UV region (230–370 nm) and have blue emission at 385 nm and 416 nm, respectively. The temperature quenching of luminescence and the chromaticity coordinates were reported. The luminescence properties were discussed by analyzing the crystal structure and the local surroundings of Ce³⁺ ions on the Ba²⁺ sites.     

Eu$lt;sup$gt;2+$lt;/sup$gt;的掺杂浓度对BaAl$lt;sub$gt;2$lt;/sub$gt;Si$lt;sub$gt;2$lt;/sub$gt;O$lt;sub$gt;8$lt;/sub$gt;：Eu$lt;sup$gt;2+$lt;/sup$gt;荧光粉发光特性的影响

采用化学共沉淀法一次煅烧工艺合成了BaAl₂Si₂O₈：Eu²⁺蓝色荧光粉.用X射线衍射仪和荧光分光光度计等对BaAl₂Si₂O₈：Eu²⁺蓝色荧光粉的相结构、发光性能进行了测试.结果表明：化学共沉淀法一次煅烧工艺合成的BaAl₂Si₂O₈：Eu²⁺蓝色荧光粉为单相;其激发光谱分布在240—410 nm的波长范围,峰值位于320 nm处,可以被InGaN管芯产生的350—410 nm辐射有效激发;在365 nm近紫外光的激发下,测得其发射光谱是位于465 nm附近的宽带峰.BaAl₂Si₂O₈：Eu²⁺蓝色荧光粉的发光强度随Eu²⁺浓度的增大逐渐加强,当Eu²⁺掺杂的摩尔分数为3.5%时,发光强度达到最大值,而后随掺杂浓度的增加而减小,发生浓度猝灭;根据Dexter能量共振理论,该浓度猝灭是由于Eu²⁺的离子间交换相互作用引起的. 关键词： 2Si₂O₈：Eu²⁺')" href="#">BaAl₂Si₂O₈：Eu²⁺ 发光特性 蓝色荧光粉 化学共沉淀法     

β-Na(Y1.5Na0.5)F6:Tm—A blue upconversion phosphor

A luminescent material β-Na(Y_1.5Na_0.5)F₆ doped with Tm³⁺ was synthesized by a solid-state reaction method for a steady phosphor of blue upconversion. Under the 671 nm laser excitation, the green emission band of 511 nm due to the ¹D₂→³H₅ transition is obtained for the first time, while the ultraviolet emission band is also observed at 368 nm, associated with the ¹D₂→³H₆ transition. Especially, a wide band of blue emissions is obtained at the wavelength region of 440-490 nm, originated mainly from the ¹D₂→³F₄ (450 nm) and ¹G₄→³H₆ (471-487 nm) transitions, which have potential application in tunable solid-state blue laser of Tm³⁺. The upconversion mechanism is explored in terms of the energy-level structures of Tm³⁺ ion and the power dependence of upconverted emission intensity, which is believed to be performed by excited-state absorption.     

掺铒矾酸钇晶体上转换荧光研究

使用波长为808和658nm的半导体激光器和染料激光器作为激发源，测量了Er³⁺：YVO₄晶体的波长在553和410nm附近的上转换荧光.对激发过程的分析表明，贡献于上转换荧光的主要激发机制为激发态吸收.在不同浓度下对上转换荧光的寿命测量结果显示，随Er³⁺浓度的提高，553nm绿光的荧光寿命随浓度的增加而减小，但410nm的荧光寿命随Er³⁺浓度无明显变化.结合绿光强度随掺杂浓度增加而减小的结果，认为在所测浓度范围内 关键词：