掺Co钨酸镉单晶体的坩埚下降生长及光谱特性

应用坩埚下降法,采用70℃.cm-1的固液界面温度梯度与0.50 mm.h-1生长速度,生长出了初始Co掺杂摩尔百分浓度为0.5 mol%、尺寸为Ф25 mm×120 mm的钨酸镉单晶体。晶体呈透明深蓝色。用XRD表征了获得的晶体。观测到518,564和655 nm三个可见波段吸收带以及发光中心1 863 nm(1 323～2 220 nm)的超宽吸收带。可见波段的吸收归属于Co2+在八面晶格场中4T1(4F)→4A2(4F),4T1(4F)→4T1(4P)跃迁叠加,而红外波段的宽带吸收则为八面体场Co2+的4T1(4F)→4T2(4F)能级跃起所致。从吸收特性表明,Co离子掺杂于畸变的氧八面体中,呈现+2价态。根据吸收光谱计算出晶格场参数Dq=990 cm-1,Racah参数BC=726.3 cm-1。在520 nm波长光的激发下,观察到778 nm波段的荧光发射,归属于八面体晶格场中Co2+的4T1(4P)→4T1(4F)能级的跃迁。从吸收与荧光强度的变化推断:沿着晶体生长方向,Co2+浓度逐渐增加,有效分凝系数小于1。     

Ni2+掺杂近化学计量比铌酸锂晶体的生长及光谱特性

以K2O为助熔剂,在较大的固液界面温度梯度条件下,应用坩埚下降法技术生长了初始Ni2 掺杂摩尔分数为0.5%的近化学计量比铌酸锂晶体。测定了晶体的吸收光谱,观测到由Ni2 离子在八面体中3A2g(F)→3T1g(P)、3A2g(F)→3T1g(F)、3A2g(F)→3T2g(F)能级的正常自旋允许跃迁所产生的381 nm,733 nm,1280 nm吸收峰和3A2g(F)→1T2g(D)和3A2g(F)→1E(D)能级的自旋禁戒跃迁产生的430 nm与840 nm吸收峰。从晶体紫外吸收边的位置初步估算其摩尔分数比x(Li )/x(Nb5 )为0.981。根据晶体分裂场理论和吸收光谱,计算了Ni2 在该铌酸锂晶体中的晶格场分裂参量Dq=781 cm-1、Racah参量B=1096 cm-1与C=4353 cm-1。研究了在不同激发波长下晶体在可见光波段的荧光特征,观察到500~630 nm的绿色与800~850 nm的红色荧光发射带,它们归结为1T2g(D)→3A2g(F)与1T2g(D)→3T2g(F)的能级跃迁所致。     

LiNbO3:Cr:ZnO晶体生长和光谱特性的研究

采用提拉法从近化学计量比的熔体中生长出尺寸为φ20 mm×50 mm的优质LiNbO3:Cr:ZnO(CZLN)晶体,其光学均匀度为7.59(10-5).进行了吸收和荧光光谱的测定研究.吸收谱测试表明:Cr3 离子在晶体中有2个宽且强的吸收带及1个微弱的吸收线,两宽带中心波长分别为480和660 nm,对应于4A2→4T1和4A2→4T2两个具有相同的总自旋能级之间的跃迁,在4A2→4T2吸收宽带的长波边缘处有个很小的吸收峰,其波长为727nm,对应于4A2→2E(R线)的跃迁.荧光测试表明:当激发波长为660 nm时,CZLN晶体荧光宽带和1个较弱的荧光线峰并存,宽带范围为802～988 nm,峰值波长为871 nm,对应于4T2→2E,4A2的联合能级跃迁,荧光线峰波长约为754 nm,其强度较弱,相应于2E→4A2(零声子线)能级跃迁.计算了晶场强度和Racah参数,其Dq/B=2.72,晶体属于强场介质.研究表明,CZLN晶体具备可调谐激光晶体的基本光谱要求,且有良好的物化性能,可以实现宽频带可调谐激光输出.它又具有较大的倍频系数,有望实现420 nm附近紫外的自倍频激光输出.     

KMgF3:Eu2+晶体中Eu2+的受激发射研究

二价铕离子(Eu2 )在KMgF3晶体中产生窄带线状发射,峰值位于360 nm.依据自身建立的激发态能量损耗模型,预测了4f7(6P7/2)→4f7(8S7/2)跃迁实现受激发射的可能性.采用ASE技术测得了KMgF3:Eu2 晶体360 nm发射的光学增益,得到净光学增益系数g=(11.4±3.2)cm-1,实验证实了理论预测.晶体退火或掺杂敏化离子Gd3 或Ce3 可以改善Eu2 的增益效果.     

白光荧光粉Ca9.95-xNa0.75K0.25(PO4)7:Eu2+0.05,Mn2x+的制备及其发光特性

高温固相法合成了Ca9.95-xNa0.75 K0.25 (PO4)7∶Eu0.052+,Mn2+x(x=0,0.1,0.2,0.3,0.4,0.5,0.6和0.7)荧光粉,研究了其相组成和荧光发射性能.结果表明,由于样品中存在着晶体结构相似的双相,使得Eu2+的5d-4f跃迁辐射出峰值分别位于491和540 nm宽谱...     

Dy3+掺杂Sr1-xCaxMoO4的制备及发光性能研究

采用高温固栩法制备了Dy<'3+>掺杂的Sr1-xCaxMoO<,4>荧光粉.利用XRD、SEM、激发发射光谱以及色参数等研究了所制备荧光粉的结构和发光性能以及x值埘荧光粉性能的影响.XRD图像农明当x=1和x=0时样品为CaMoO<,4>和SrMoO<,4>单一相.SEM 图像表明在750℃下煅烧3 h制备的样品粒径为0.2～1.0μm,适合同态发光器件的要求.监测576 nm得到的样品的激发光谱由250～340 nm之间的一个宽带和340～460 nm之间的一系列尖峰组成.改变Sr/Ca的值,电荷迁移带激发峰位置发生变化,而窄带跃迁的激发峰强度发生变化.用350 nm波长激发样品得到的发射谱由峰值位于480和576 nm的两个窄带组成,它们是由和跃迁引起的.黄色发射峰和监色发射峰的强度比Y/B随着Sr/Ca比值的变化而变化.     

Optical spectroscopy of Mn2+ ions in CaCl2 single crystals

Abstract

In the present investigation the excitation and fluorescence spectra and lifetimes of Mn²⁺ ions in calcium chloride, for various manganese concentrations and sample temperatures have been studied for the first time. The fluorescence spectrum consists of an asymmetric broad band, which upon lowering the sample temperature, shifts its maximum from 580 nm at 300 K to 596 nm at 11 K. This luminescence band was associated with the ⁴T_lg(⁴G)→⁶A_lg(⁶S) spin-forbidden transition in the manganese ions occupying Ca-sites in the lattice of CaCl₂. The excitation spectrum of the Mn²⁺ fluorescence revealed the features of manganese ions in octahedral coordination and consisted of nine excitation peaks which were associated with Mn²⁺-crystal-field-sensitive transitions. A crystal field analysis of the wavelength positions of these transitions by means of the model developed by Curie et al. allowed us to determine the magnitude of the cubic field splitting 10Dq, the reduced Racah parameter B', the Koide-Pryce covalency parameter ε and the spin transfer coefficients f _[sgrave] and f _σ. From the measurement of the temperature dependence of the Mn²⁺ fluorescence lifetime, we have also obtained information about the different mechanisms which are involved in the relaxation of excited Mn²⁺ ions in this host crystal in the temperature range (11–300 K).     

Growth and optical properties of Cr~（3＋）-doped CdWO_4 single crystals

A high-quality Cr 3+:CdWO4 single crystal at a size of approximatelyΦ25×80 mm is grown using the Bridgman method with CdO,WO3,and Cr2O3 as raw materials and their molar ratio of 100:100:0.5.The temperature gradient of solid-liquid interface at growth is approximately 50?C/cm and the growth rate is 0.05 mm/h.The X-ray diffraction(XRD),absorption,excitation,and emission spectra of different parts of the as-grown and O2-annealed crystals are investigated.Two strong broad optical absorption bands of about 472 and 708 nm are observed,and they are associated with the transitions 4 A2→ 4 T1 and 4 A2→ 4 T2.The weak 4 T2→ 2 E transition(the R-line)at 632 nm is also observed.The crystal-field parameter Dq and the Racah parameters B and C are estimated to be 1 412.4,776.8,and 3 427.6 cm? 1,respectively,according to the absorption spectra and crystal-splitting theory.A broadband fluorescence at about 1 000 nm due to 4 T2→ 4 A2 transition is produced by exciting the samples at 675 nm.After being annealed in an O2 atmosphere,the crystals become more transparent,while the effective light absorption of Cr 3+ ions is evidently enhanced and the emission intensity is also strengthened due to the reduction of oxygen vacancies in the CdWO4 crystal after annealing.     

Charge ordering and magnetopolarons in Na0.82CoO2

Using spectral ellipsometry, we measured the dielectric function of a Na(0.82(2))CoO2 crystal that exhibits bulk antiferromagnetism with T(N)=19.8 K. We identify two prominent transitions as a function of temperature. The first one at 280 K involves marked changes of the electronic and lattice responses that are indicative of charge ordering in the CoO2 layers. The second transition occurs around T(N)=19.8 K and reveals sizable spin-charge coupling. The data are discussed in terms of charge ordering and formation of magnetopolarons due to a charge-induced spin-state transition of adjacent Co3+ ions.     

Thermoelectric power of HoBaCo2O5.5: possible evidence of the spin blockade in cobaltites

Thermoelectric power measurements have been performed for an ordered oxygen-deficient perovskite, HoBaCo2O5.5, in which the alternative layers of CoO6 octahedra and of [CoO(5)](2) bipyramids are occupied by Co3+ species. The T-dependent Seebeck coefficient S shows a clear change of the conduction regime at the metal-insulator (MI) transition (T(MI) approximately 285 K). The sign change of S from S<0 to S>0 can be explained assuming that a spin state transition occurs at T(MI). In the metallic state, Co2+ e(g) electrons are moving in a broad band on the background of high or intermediate spin Co3+ species. In contrast, the insulating behavior may result from the Co3+ spin state transition to a low-spin Co3+ occurring in the octahedra. In this phase the transport would occur by hopping of the low-spin Co(4+)t(2g) holes, whereas the high-spin Co2+ electrons become immobilized due to a spin blockade.     

Ab initio and crystal field studies of the Mn4+-doped Ba2LaNbO6 double-perovskite

A detailed study using the ab initio DFT-based calculations of the electronic and optical properties of pure and Mn⁴⁺ doped Ba₂LaNbO₆ is presented in this paper. Comparison of the calculated electronic bands structure, density of states diagrams, and dielectric functions for the pure and doped crystal reveals the changes induced by the Mn⁴⁺ impurity ions. In addition, the energy levels of the Mn⁴⁺ ion in the ordered perovskite Ba₂LaNbO₆ are calculated by the exchange charge model (ECM) of crystal field theory and compared with the experimental data that has been presented in the literature. The calculated Mn⁴⁺ energy levels are in good agreement with the experimental spectra. Additionally, the excitation band shapes of the ⁴A_2g(⁴F)–⁴T_2g(⁴F) and ⁴A_2g(⁴F)–⁴T_1g(⁴F) transitions are modeled to estimate the zero-phonon lines (ZPL) positions and the effective number of phonons, which are involved in the corresponding excitation transition. The results of our calculations yield the crystal field parameter of Dq=1780 cm^?1 and Racah parameters B=670 and C=3290 cm^?1, with C/B=4.9 for the Mn⁴⁺ ion in the double-perovskite Ba₂LaNbO₆.     

白光LED用单基质荧光粉BaSrMg( PO4)2∶Eu2+的制备及发光性能研究

采用高温固相反应法在1 200℃下制备了 Eu2+激活的BaSrMg( PO4)2高亮度白光荧光粉,并对其晶体结构和发光性能进行了研究.荧光光谱研究表明该荧光粉的发射光谱由两个谱带组成,其中心分别位于424和585 nm处,归结为Eu2+分别占据了基质中Sr2+,Ba2+格位而导致的4f 65d1→4f7电子跃迁.两个...     

CaMgSi2O6:Eu的真空紫外光谱特性

采用高温固相反应利用原料CaCO3,MgO,SiO2和Eu2O3合成CaMgSi2O6:Eu3 样品,并研究了其结构特性、光谱特性.CaMgSi2O6:Eu3 属于单科晶系,基质掺入Eu离子后结构没有明显变化.CaMgSi2O6:Eu3 在147 nm真空紫外光激发下呈红色发射,发射主峰位于611 nm,是Eu3 的5D0→7F2跃迁的典型发射.当Eu3 的相对摩尔浓度在0.02到0.10 mol之间变化时,由相关数据可以发现有浓度猝灭现象发生.CaMgsi2O6:Eu2 在172 nm真空紫外光激发下呈蓝色发射,发射主峰位于452 nm,是Eu2 的5d→4f跃迁的典型发射.添加不同浓度的H3BO3后可大大提高样品的发光强度.     

Bi2Sr2Co2O8体系中Pb替代及I插层对其结构和物性的影响

自今年3月在NaxCo2O4 Yh2o中发现超导电性以来,具有层状结构的Co系氧化物又受到人们广泛的关注.本文在成功合成具有misfit层状结构Bi2Sr2Co2Oy单相样品的基础上,通过Pb对Bi的部分替代、以及I的插层,成功地使其c轴由1.49nm增至1.87nm,并对其输运性质和磁性质进行了系统研究.结果发现:Pb的部分替代并没有使该体系的电阻-温度关系行为发生显著变化,但在低温下使样品呈现自旋玻璃态行为;I的插入不仅使其c轴长度增加,而且样品变为半导体,并不呈现超导电性,在低温下同样呈现自旋玻璃态行为.同时对Pb替代及I插层效应进行了讨论.     

大尺寸掺钛铝酸铍(Ti~(3+):BeAl_2O_4)激光晶体的提拉法生长

应用提拉法技术,采用BeO:Al2O3:Ti2O3摩尔比=100:99.85:0.15的化学组分配比,以及选用合适的固液界面温度梯度与生长速度等优化工艺条件,成功地生长出了T3+离子掺杂、无气泡、无云层和核心、尺寸≈Ф60mm×85mm的粉红色Ti3+:BeAl2O4大尺寸晶体。测定了Ti3+:BeAl2O4晶体的激发与荧光光谱。沿着晶体生长方向,晶体的颜色变深。在激发光谱中观测到了502 nm与567nm的激发峰,在发射光谱中观察到了发光中心为710nm的宽带荧光。两激发峰与Ti3+离子的2T2→2E能级跃迁有关,710nm的荧光峰是由振动能级2E→2T2产生的。从不同部位晶体的吸收强度和颜色变化可得到Ti3+离子在BeAl2O4晶体中的有效分凝系数小于1。     

A3M2GeO12石榴石体系中Cr^3＋离子的宽带发射光谱

首次报道在Ａ３Ｍ２Ｇｅ３Ｏ１２：Ｃｒ（Ａ＝Ｃｄ＾２＋,Ｍ＝Ａｌ＾３＋,Ｇａ＾３＋,Ｓｃ＾３＋）锗酸盐石榴石体系中,Ｃｒ＾３＋离子室温下的红－近红外宽发射带光谱性质。随位于八面体格位上的Ａｌ＾３＋→Ｇａ＾３＋→Ｓｃ＾３＋和十二面体格位上的Ｃｄ＾２＋→Ｃａ＾２＋组成顺序变化,室温下,Ｃｒ＾３＋离子的＾４Ｔ２→＾４Ａ２能级跃迁的Ｒ－ＮＩＲ宽发射带,发射峰及光谱的长波和短波边逐渐向低能长波边移动。     

Sr3Gd(PO4)3:Tm3+的真空紫外光谱特性

研究了Sr3Gd(PO4)3 : Tm3 和GdPO4 : Tm3 样品的结构特性、光谱特性.GdPO4 : Tm3 为单斜晶系,基质掺入铥离子后结构没有明显变化.GdPO4:Tm3 在164和210 nm附近有强烈的吸收峰.位于164 nm附近的强烈的吸收峰是归因于基质的吸收引起,210 nm附近的吸收峰则归因于Gd 的8S7/2-6GJ的能级跃迁.在164 nm真空紫外光激发下,样品于453及363 nm处有较强的发射峰,发射主峰位于453nm,属于Tm3 的1D2→3H4(22,123 cm-1)跃迁的典型发射.由于阳离子质量的不同,Sr3Gd(PO4)3:Tm3 在166 nm附近的激发峰高于GdPO4: Tm3 的同位置的激发峰,其在363 nm处的发射有明显减弱,而在453 nm处的蓝色发射有显著的增强.     

White-light generation through Ce3+/Mn2+-codoped and Eu2+-doped Ba1.2Ca0.8SiO4 T-phase phosphors

Hexagonal Ba_1.20Ca_0.8?2x?ySiO₄:xCe³⁺,xLi⁺,yMn²⁺ phosphors exhibit two emission bands peaking near 400 and 600 nm from the allowed f–d transition of Ce³⁺ ions and the forbidden ⁴T₁–⁶A₁ transition of Mn²⁺ ions, respectively. The strong interaction between Ce³⁺/Mn²⁺ ions is investigated in terms of energy transfer, crystal field effect, and microstructure by varying their concentrations. They show a higher quenching temperature of 250 °C than that of a commercially used (Ba,Sr)₂SiO₄:Eu²⁺ phosphor (150 °C). Finally, mixtures of these phosphors with green-emissive Ba_1.20Ca_0.70SiO₄:0.10Eu²⁺ are tested and yielded correlated color temperatures from 3500 to 7000 K, and color rendering indices up to 95%.     

水热法与固相法制备Ca2B5O9Cl:Eu光谱特性的研究

对比研究了制备方法(水热法与高温固相法)、激发条件、Eu离子浓度对Ca2B5O9Cl:Eu发光体光谱特性及制备条件对晶体形貌的影响.结果表明,水热法制备的Ca2B5O9Cl:Eu发光体在254 nm激发下主要以Eu3 的5D0→7FJ(J=1,2,3,4)跃迁发射为主,365 nm激发下则以Eu2 的4f65d1→8S7/2跃迁发射为主.高温固相法制备的发光体在365 nm激发下主要是Eu2 的4f65d1→8S7/2跃迁发射,而254 nm激发下Eu2 和Eu3 的发射均较弱.Eu浓度对Ca2B5O9Cl : Eu的光谱特性影响较小,而制备方法和激发条件却对其影响较大.SEM揭示了空气条件与还原气氛制备的产品结晶完美、表面光滑、颗粒度在0.82～1.06 μm之间.     

Tunable continuous-wave operation of a Cr3+,Li+:Mg2SiO4 laser

Room-temperature tunable cw laser oscillation of Cr3+ ions in forsterite crystals (Mg2SiO4) codoped with chromium and lithium has been demonstrated, for the first time to the authors' knowledge, in pumping a crystal with a Ti:sapphire laser into the first excited level of Cr3+ ions (4A2-4T2 transition). The laser is smoothly tunable in the region of 1095-1170 nm. A slope efficiency as great as 4.4% has been achieved.