Efficient Near-Infrared Quantum Cutting in Tm3＋/yb3＋ Codoped LiYF4 Single Crystals for Solar Photovoltaic

Downconversion （DC） with emission of two near-infrared photons about 1000 nm for each blue photon absorbed was obtained in thulium （Tm3＋） and ytterbium （Yb3＋） codoped yt- trium lithium fluoride （LiYF4） single crystals grown by an improved Bridgman method. The luminescent properties of the crystals were measured through photoluminescence excitation, emission spectra and decay curves. Luminescence between 960 and 1050 nm from yb3＋： 2Fs/2--＋2FT/2 transition, which was originated from the DC from Tm3＋ ions to Yb3＋ ions, was observed under the excitation of blue photon at 465 nm. Moreover, the energy transfer processes were studied based on the Inokuti-Hirayama model, and the results indicated that the energy transfer from Tm3＋ to Yb3＋ was an electric dipole-dipole interaction. The max- imum quantum cutting efficiency approached with 0.49mo1% Tm3＋ and 5.99mo1% Yb3＋. increasing the energy efficiency of crystalline energy part of the solar spectrum. up to 167.5% in LiYF4 single crystal codoped Application of this crystal has prospects for Si solar cells by photon doubling of the high

C-cut Tm:YAP晶体连续光特性实验研究

掺铥铝酸钇晶体(Tm:YAlO_(3),Tm:YAP)具有机械性能与热力学性能优良、发射截面大等优点,可用商用半导体激光器(laser diodes,LD)作为泵浦源,是2μm光源的理想增益介质。由于Tm:YAP晶体具有各向异性,不同切向轴向摆放下的激光输出特性有所不同。本文使用793 nm的LD作为泵浦源,研究了c向切割(c-cut)Tm:YAP晶体在激光偏振方向平行于a轴(E//a)和激光偏振方向平行于b轴(E//b)下的连续光运转输出特性以及波长调谐输出特性。研究表明:在28 W的泵浦功率下,当E//a时,Tm:YAP激光器连续光输出功率为8.66 W,斜率效率为32.1%;当E//b时,Tm:YAP激光器连续光输出功率为8.41 W,斜率效率为31.1%;在腔内以布儒斯特角插入双折射滤光片对输出激光波长进行调谐,在15 W的泵浦功率下,当E//a时,输出激光波长调谐范围为1 888.8~2 084.4 nm,调谐宽度为195.6 nm;当E//b时,输出激光波长调谐范围为1 889.6~2 043.1 nm,调谐宽度为153.5 nm。实验结果表明,c-cut Tm:YAP晶体沿a轴和b轴放置时都可以实现高功率高效率的连续光输出及宽范围的波长调谐,且E//a时和E//b时的波长调谐曲线形状近似互补,有潜力实现高功率窄脉宽的激光输出。

Optical high-resolution spectroscopic study of Tm^(3+) crystal-field levels in LiLuF_4

We report on the fast high-resohition study of LiLuF4：Tm3＋. The accurate energy level scheme of Tm3＋ in the LiLuF4 matrix was obtained for the 3H6.5.4, 3F4.3.2, and ^1G4 multiplets. It was shown that electric-dipole transitions dominate for all the studied multiplets except the 3H5 one.

Optical-transition Probability of Tm^(3+) Ions in Tm^(3+)/Er^(3+):YVO_4 Crystal

The polarized absorption spectra of Tm3+/Er3+:YVO4 crystal were measured at room temperature. Based on the Judd-Ofelt theory, the spectral parameters were obtained: the intensity parameters Wl of Tm3+ in Tm/Er:YVO4 crystal: W2 = 10.69×10-20, W4 = 0.604×10-20, W6 = 2.05×10-20 cm2 for the (100) face and W2 = 10.43×10-20, W4 = 0.13×10-20, W6 = 1.83×10-20 cm2 for the (001) face. Based on these values, the oscillator strength, radioactive lifetime and fluorescence branch ratio were calculated for Tm3+ in Tm/Er:YVO4 crystal.

Effect of Hf^(4+) doping on structure and enhancement of upconversion luminescence in Yb:Tm:LiNbO_3 crystals

A series of Yb：Tm：LiNbO_3 crystals doped with x mol% Hf^（4＋）ions（x = 2, 4, and 6） were grown by the Czochralski method. The dopant occupancy and defect structure of Hf：Yb：Tm：LiNbO_3 crystals were investigated by x-ray diffraction and infrared transmission spectra. The influence of Hf^（4＋）ions concentration on UV–VIS–NIR absorption spectra of Hf：Yb：Tm：LiNbO_3 crystals was discussed. The upconversion luminescence of Hf：Yb：Tm：LiNbO_3 crystals was obtained under 980 nm excitation. Strong emissions were observed at 475 nm in the blue wavelength range and 651 nm in the red wavelength range. Remarkably, enhancement of the red and blue upconversion luminescence was achieved by tridoping Hf^（4＋）ions.

Optimum fluorescence emission around 1.8μm for LiYF_4 single crystals of various Tm^(3+)-doping concentrations

In this paper, optical spectra of LiYF4 single crystals doped with Tm3＋ ions of various concentrations are reported. The emission intensity at 1.8 ktm first increases with increasing Tm3＋ concentration, and reaches a maximum value when the concentration of Tm3＋ is about 1.28 mol%, then it decreases rapidly as the concentration of Tm3＋ further increases to 3.49 mol%. The emission lifetime at 1.8 p.m also shows a similar tendency to the emission intensity. The maximum lifetime of 1.8 μm is measured to be 17.68 ms for the sample doped with Tm3＋ of 1.28 mol%. The emission cross section of 3F4 level is calculated. The maximum reaches 3.76 × 10 -21 cm2 at 1909 nm. The cross relaxation （3H6, 3H4 →3 F4, 3F4） between Tm3＋ ions and the concentration quenching effect are mainly attributed to the change of emission with Tm3＋ concentration. The largest quantum efficiency between Tm3＋ ions is estimated to be ,-147% from the measured lifetime and calculated radiative lifetime. All the results suggest that the Tm3＋/LiYF4 single crystal may have potential applications in 2 μm mid-infrared lasers.

Spectroscopy and Energy Transfer in Yb^(3+) and Tm^(3+) Co-doped Gd_3Ga_5O_(12) Crystal

Yb3＋/Tm3＋ co-doped Gd3Ga5O12 single crystal with a dimension of Φ30mm×20mm was grown successfully by Czochralski method.The absorption spectrum was recorded at room temperature and used to calculate the absorption cross-section.Based on the Judd-Ofelt（J-O） theory,we obtained the three intensity parameters and spectral parameters of this crystal,such as the line strengths,oscillator strengths,radiative probabilities and radiative lifetimes as well as the fluorescent branching ratios.Room temperature fluorescence spectra and luminescence decay curves were recorded.The energy transfer between Yb3＋-Tm3＋ was observed and the mechanism was discussed.The stimulated emission cross-section of the 3F4→3H6 transition was calculated by the Füchtbauer-Ladenburg（F-L） equation.The potential laser gains for this transition were also investigated.This crystal is promising as a tunable infrared laser crystal at 2.0 μm.

Tm^(3+)离子在钨酸锌单晶中的光谱特征

采用丘克拉斯基法生长出一系列ZnWO4:Tm3 + 单晶 ,Tm3 + 浓度x =0 1 ,0 3,0 5 ,0 7和 1 0mol%。用 80 7nmLD激发 ,观察到 4 86和 6 95nm的上转换发光 ,分别相应于 1 G4→ 3 H6和3 F3 → 3 H6的跃迁 ,发光强度与泵浦光功率成双对数关系 ,其指数分别为 0 8和 1 1次方关系。

2μm波段激光晶体Tm:YAP的生长缺陷

采用提拉法沿a、b、c轴方向生长了Tm:YAP晶体,研究了该晶体的几种常见缺陷。通过化学腐蚀,利用光学显微镜观察了Tm:YAP晶体主要晶面的位错腐蚀坑形貌,发现在沿b轴生长晶体的(010)面上存在位错蚀坑密度不同的区域,对其成因进行了分析。借助偏光显微镜研究了晶体中的孪晶及消光现象,分析了成因并提出了消除措施。用He-Ne激光对晶体内的散射颗粒分布进行了研究,在扫描电镜(SEM)下观察到形状不规则的散射颗粒夹杂。上述研究结果对获得优质Tm:YAP晶体具有重要意义。

Tm^(3+)掺杂CdWO_4单晶的发光特性

用坩埚下降法生长获得了尺寸为φ25 mm×90 mm、Tm2O3初始掺杂摩尔分数为0.5%的CdWO4单晶。晶体的颜色由上部血红色逐渐加深至下部的黑褐色。对不同部位的晶体薄片进行800℃的氧化处理,测定了处理前后不同部位的吸收光谱和FTIR红外光谱。经氧气退火处理后,由于氧空位缺陷减少,晶体的颜色明显变淡。在吸收光谱中观测到421,684,805 nm的吸收带。其中421 nm的吸收峰随退火温度的升高而逐步减弱,经800℃处理后基本消失。在808 nm激光二极管激发下,观察到中心波长为1.5μm和1.8μm的荧光发射,分别对应于Tm3+的3H4→3F4,3F4→3H6的能级跃迁。

RE∶YAP(RE=Nd,Tm)晶体缺陷与光谱分析

采用提拉法生长Nd∶YAP和Tm∶YAP晶体,利用吸收和荧光光谱表征样品。结果表明:经真空退火,提高了晶体质量。Nd∶YAP晶体在808 nm附近有较强的吸收,与商用激光二极管的发射波长匹配较好,获得了1064 nm荧光输出;Tm∶YAP晶体在790 nm附近有一定的吸收,在1.87μm处的荧光峰对应于3F4→3H6能级之间的跃迁,有利于激光的高能量调Q输出。

Tm∶YAP激光晶体的生长

采用提拉法生长了b轴Tm：YAP晶体，晶体尺寸为φ（20～25）mm×（60～70）mm．针对部分晶体中存在的开裂、散射颗粒等宏观缺陷，分析讨论了其成因并提出了改进措施．对晶体吸收光谱和荧光光谱的测定结果表明，晶体的吸收峰位于694和795nm，荧光谱峰值在2．01μm附近．

纳米晶ZrO_2:Tm^(3+)制备与发光性质研究

本文用共沉淀法制备了纳米晶ZrO2∶Tm3+荧光粉,并对它的晶体结构、颗粒大小和光致发光性质进行了表征。XRD测试结果表明:以此工艺制备的纳米晶ZrO2:Tm3+含有单斜相和四方相两种微观结构,四方相的含量与热处理的温度有关,Tm3+离子的掺入有稳定ZrO2四方晶相的作用。测量了各样品的荧光激发和发射光谱,当以264nm(3H6→3P2)和359nm(3H6→1D2)光激发分别得到Tm3+的355nm(1I6→3H4或3P0→3H4)和459nm(3P0、1I6→3F4或1D2→3H4)的较强荧光发射。通过对荧光强度与激活离子Tm3+浓度的关系研究发现:荧光强度先随浓度提高而增强,在浓度达1%摩尔数时达到最大,然后又随之降低。

Tm^（3＋）YAG晶体生长

本文研究Ｔｍ￣（３＋）：ＹＡＧ晶体生长、晶格常数、晶体形貌和有关生长的局域相图。晶体对高温辐射的吸收影响晶体中的温度分布。在低Ｔｍ￣（３＋）浓度区，晶格常数随Ｔｍ￣（３＋）浓度增大而减小。用晶体生长的方法，给出了Ｙ＿３Ａｌ＿５Ｏ＿（１２）－Ｔｍ＿３Ａｌ＿５Ｏ＿（１２）体系的局域相图。引上法晶体生长和熔化的相互作用起因于组分过冷，Ｔｍ￣（３＋）：ＹＡＧ生长时组分过冷不明显，仍能表现出固有的形貌。

浮区法生长Tm^(3+):CaYAlO_4晶体的研究

CaYAlO4是一种ABCO4型化合物 (A =Ba、Sr或Ca ,B =Y或稀土元素 ,C =Ga或Al) ,具有K2 NiF4型四方结构 ,可作为一种优良的激光基质材料。近年来 ,向该晶体中掺入不同的稀土离子 ,研究这些掺质晶体的性能已成为一个热点。特别值得注意的是 ,根据文献的报道 ,当掺Tm3 +浓度为lat.%时 ,CaYAlO4多晶样品在 36 0～ 46 0nm处有很强的发射 ,这一现象表明Tm3 +:CaYAlO4晶体有可能产生蓝光和紫光。因此 ,对该晶体的研究具有重要的意义。本文采用光加热浮区法生长了不同掺质浓度的Tm3 +:CaYAlO4晶体。实验表明 ,该晶体的生长受到生长气氛、转速、拉速、籽晶方向及功率控制程序等多种因素的影响 ,很难得到高质量的晶体。本文对这些影响因素分别进行了微观或宏观上的分析 ,找到了该晶体的最佳生长条件。由于该晶体极易沿 [0 0 1 ]方向开裂 ,因而掺Tm3 +量很难提高 ,而本文所生长晶体的最高掺质量达 7at.% ,远大于国外报道的数值 ( 2at.% )。所生长晶体的典型尺寸为 5mm× 5mm×30mm。观察发现 ,在所生长的Tm3 +:CaYAlO4晶体中 ,主要存在 2种缺陷 :包裹体和裂纹。其中 ,包裹体又分为气泡和第二相。本文分析了这些缺陷的产生原因 ,并提出了减少或消除这些缺陷的方法。此外 ,本文还对该晶体进行了化学分析 ,测定了其透过?

ZnWO_4:Tm^(3+)单晶的上转换研究

上转换发光的本质是一种反斯托克斯发光。由于可以用低能量的长波长光激发获得能量较高的短波长光 ,因此作为紧凑高效短波长的固体激光器的工作物质 ,上转换材料的前景十分看好。在实验室中用丘克拉斯基法成功地生长出了质量较好的单晶 ,名义掺杂浓度分别为 0 .2 %、0 .5 %和 1 .0 % (摩尔比 )。对样品进行了系统的光谱测试。从吸收谱可以看出 :样品的吸收峰位于 80 7nm( 3 H63 H4)左右 ,且谱线较宽。与吸收峰长位于 75 0nm ,谱线线宽Δλ =4nm的YAG :Tm3 +单晶相比 ,可以看出 :ZnWO4:Tm3 +更适合于激光二极管泵浦。值得注意的是基底在40 0nm左右的光吸收较强 ,退火可以在一定程度上消除基底的影响。对样品的荧光强度测试表明 :在 80 7nmLD泵浦下 ,样品主要有三个上转换荧光峰 ,分别位于 40 5、486和 6 95nm左右 ,其中以 6 95nm的峰为最强。荧光强度受出入射方向影响较大 ,在a轴方向接受时光的强度为最大 ,而且受激发方向影响较小。还测定了样品的荧光 ( 6 95nm)强度与激发功率之间的关系—线性关系。

掺Cr^(3+),Tm^(3+),Ho^(3+)离子的YAG晶体的光谱性能

作者测试了Ｃｒ３＋，Ｔｍ３＋和Ｈｏ３＋离子在ＹＡＧ晶体中的吸收谱、荧光谱及荧光衰减寿命。计算了Ｃｒ３＋向Ｔｍ３＋和Ｈｏ３＋及Ｔｍ３＋向Ｈｏ３＋的能量转移效率。表明在（Ｃｒ，Ｔｍ，Ｈｏ）：ＹＡＧ晶体中由于加入Ｃｒ３＋，Ｔｍ３＋离子，使Ｈｏ３＋离子被敏化，荧光强度增大。（Ｃｒ，Ｔｍ。

Tm^(3+)离子在YVO_4晶体中的光谱特征

本文应用Ｊｕｄｄ－Ｏｆｅｌｔ理论计算了Ｔｍ３＋离子在ＹＶＯ４晶体中的辐射跃迁几率ＡＪＪ′、无辐射跃迁几率ＷＪＪ′，振子强度ｆＪＪ′，荧光寿命τＪ，辐射跃迁截面σｅ和吸收截面σＡ等光谱特征参量．从速率方程得出在不同泵浦几率（１０２～１０５ｓ－１）下，荧光强度最大的掺杂浓度为４．５％～６．６ａｔ．％，并将这些结果与Ｔｍ３＋离子在ＹＡＧ晶体中的特征参量、最佳掺杂浓度进行了比较．

大尺寸Nd^(3+):YAP晶体中云层和孪晶的克服途径

本文报道用中频感应加热Czochralski法,在大的气-液温差场中生长大尺寸的Nd^(2+):YAP单晶,并在生长过程中采用“真空自然冷却法”退火工艺。即当大尺寸Nd^(3+):YAP单晶在高温下生成后,随即改变氮气氛成真空状态,由于真空状态下热辐射起主导作用,炉膛内温度梯度明显减少,使生成后的大单晶在这种由真空导致的低梯度的温场中自然冷却到室温。不仅可以克服云层的产生,而且可以克服孪晶的形成。

不同掺杂浓度Tm^(3+):LiLuF_4单晶的1800nm荧光发射(英文)

采用坩埚下降法生长了Tm3+掺杂浓度为0.45%,0.90%,1.63%与3.25%(摩尔分数,x)的LiLuF4单晶.测试了样品的电感耦合等离子体原子发射光谱(ICP-AES)、X射线衍射(XRD)谱、吸收光谱(1400-2000 nm),并且分析比较了808 nm半导体激光器(LD)激发下荧光光谱.结果表明:当Tm3+的浓度从0.45%变化到3.25%时,1800 nm处的荧光强度呈现了先增后减的趋势,当掺杂浓度约为0.90%时达到最大值,而位于1470 nm处的荧光强度则呈现了相反的趋势.Tm3+:3F4能级的荧光衰减寿命随着掺杂浓度的增加不断减小.1800 nm处的这种荧光强度变化归结于Tm3+离子间的交叉驰豫效应(3H6,3H4→3F4,3F4)和自身的浓度猝灭效应.同时计算得到了浓度为0.90%的样品在1890 nm处的最大发射截面为0.392×10-20cm2.并且根据Judd-Ofelt理论所得寿命和测定的荧光寿命计算得到了3F4→3H6的最大量子效率约为120%.