掺Ho~(3 )氟化物材料上转换发光的实验研究

本文制备了掺 Ho3 氟铝酸盐为基质的上转换发光材料 ,详细研究了蓝绿上转换发光强度及上转换发射峰的位置与强度随 Ho3 离子浓度的变化 ,确定了 Ho2 O3在该基质中合适的掺杂浓度 ,并简单讨论了其上转换机制     

掺Ho3+氟化物材料上转换发光的实验研究

本文制备了掺Ho3+氟铝酸盐为基质的上转换发光材料,详细研究了蓝绿上转换发光强度及上转换发射峰的位置与强度随Ho3+离子浓度的变化,确定了Ho2O3在该基质中合适的掺杂浓度,并简单讨论了其上转换机制.     

Synthesis and upconversion luminescence properties of NaYF4：yb^3＋/Er^3＋ microspheres

Cubic NaYF4:yb3+(20%)/Er3+(1%) microspheres were synthesized by EDTA-assisted hydrothermal method. Under 980 nm exci-tation, ultraviolet (4G11/2→4I15/2), violet (2H9/2→4I15/2), grogn (4F7/2→4I15/2, 2H11/2→4I15/2, and 4S3/2→4I15/2), and red (4F9/2→4I15/2) upconversion fluorescence were observed. The number of laser photons absorbed in one upconversion excitation process, n, was determined to be 3.89, 1.61, 2.55, and 1.09 for the ultraviolet, violet, green, and red emissions, respectively. Obviously, n=3.89 indicated that a four-photon process was involved in populating the 4G11/2 state, and n=2.55 indicated that a three-photon process was involved in populating the 4F7/2/2H<11/2>4S3/2 levels. For the violet and red emissions, the population of the states 2H9/2 and 4F9/2 separately came from three-photon and two-photon proc-esses. The decrease of n was well explained by the mechanism of competition between linear decay and upconversion processes for the de-pletion of the intermediate excited states.     

溶胶-凝胶法制备YAG:Ho~(3+),Yb~(3+)纳米晶

以稀土氧化物和硝酸铝为原料,采用溶胶-凝胶法合成了YAG:1%Ho~(3+),1%Yb~(3+)纳米晶,并通过正交试验法确定其干凝胶的合成条件.采用DTA-TG、XRD及TEM对干凝胶的合成过程、纳米晶的晶相组成及形貌进行了研究,表明干凝胶经1 200 ℃煅烧后形成了结晶完全的YAG相,无中间相产生.吸收光谱和上转换发射光谱分析表明,Yb~(3+)在材料的发光过程中具有传递能量的作用,Ho~(3+)在跃迁过程中发射出中心波长为650 nm的红色上转换荧光及540 nm的绿色上转换荧光.     

Yb3+，Er3+掺杂Y2Ti2O7荧光粉的制备与上转换发光机理研究

采用溶胶-凝胶法制备合成了(Y_0.98-xYb_xEr_0.02)₂Ti₂O₇(x=0, 0.02, 0.04...0.10)荧光粉, 分别采用XRD和荧光光谱仪对样品的结构和上转换发光性能进行了表征.研究了Yb3+掺杂浓度对样品上转换发光性能的影响, 并对样品的发光机理进行了研究.结果表明, 所得样品为面心立方结构的烧绿石相.在980nm激发下, 样品展现出很强的上转换荧光发射并且发光颜色可以通过Yb3+掺杂浓度来调节.样品上转换绿光和红光发射均为双光子过程并且交叉弛豫过程在上转换红光发射过程中占据主导作用.      

稀土掺杂钼酸盐发光材料的研究进展

近年来稀土掺杂钼酸盐发光材料已成为光学研究的热点之一.与其他基质材料相比,钼酸盐具有较高的量子产率、独特的物相结构以及多变的形貌;稀土离子掺杂的钼酸盐荧光粉表现出发光色纯度高、荧光寿命长、合成温度低等优势,在LED照明、温度传感、生物成像等领域展现出广阔的应用前景.综述了稀土掺杂钼酸盐常见的合成方法与研究现状,并归纳总...     

NaYF4∶Yb,Er材料的制备及其上转换发光性能

通过沉淀法制备Yb3+和Er3+共掺的NaYF4上转换发光材料,考察了主要制备工艺条件对材料上转换发光性能的影响,并探讨了其上转换发光的机理.利用x射线衍射(XRD)、透射电镜(TEM)、荧光光谱仪对样品进行了表征.结果表明,Yb3+和Er3+的掺杂浓度分别15％(摩尔分数,下同)、3％,焙烧温度为600℃时可得到发光性能较好的六方相NaYF4∶Yb,Er上转换材料,其主要上转换途径是Yb3+和Er3+之间的能量转移,且Er3+的红、绿光发射均为双光子过程.     

NaYF4:Yb,Er材料的制备及其上转换发光性能

通过沉淀法制备Yb3+和Er3+共掺的NaYF4上转换发光材料,考察了主要制备工艺条件对材料上转换发光性能的影响,并探讨了其上转换发光的机理。利用x射线衍射(XRD)、透射电镜(TEM)、荧光光谱仪对样品进行了表征。结果表明,Yb3+和Er3+的掺杂浓度分别15%(摩尔分数,下同)、3%,焙烧温度为600℃时可得到发光性能较好的六方相NaYF4:Yb,Er上转换材料,其主要上转换途径是Yb3+和Er3+之间的能量转移,且Er3+的红、绿光发射均为双光子过程。     

NaYF4: Yb,Er@SiO2的高温相变及上转换

通过固-液热分解法合成平均尺寸为27 nm的六方相NaYF₄: Yb, Er上转换纳米晶。制备了NaYF₄: Yb, Er@SiO₂核壳纳米粒子, 壳层厚度约为8 nm。将NaYF₄: Yb, Er@SiO₂分别在不同高温下焙烧3 h, 发现600 ℃下产物物相未发生变化, 但向非晶态过渡; 700、800 ℃下NaYF₄内核与SiO₂壳层发生化学反应, 产物物相均转变为NaYSiO₄。样品均用980 nm红外激光进行激发, 显示出强烈的可见光上转换发射。以初始NaYF₄: Yb, Er@SiO₂的上转换发光强度为对比样, 随着焙烧温度的升高, 样品的发光强度依次提高。这与理论上低声子能量的氟化物发光强度更高不符, 可能原因是高温处理后样品去除了部分晶格缺陷和有机杂质。      

多晶壳NaYF4纳米颗粒的能量传递机理研究

以乙二醇（EG）为溶剂，聚乙烯亚胺（PEI）为表面活性剂，采用溶剂热法合成了多晶壳结构的上转换纳米颗粒NaYF₄: 18 %Yb, 20 %Gd, 2 % Er@NaYF₄: 10 %Yb, 40 %Nd.通过HAADF元素分析和HRTEM确认多晶壳层的存在，壳层厚度用HRTEM直接观测和TEM粒径统计分布进行计算.通过调节壳层反应物的加入量，实现对外延生长的NaYF₄: Yb, Nd活性壳层厚度的精确调控.研究发现，当多晶壳层厚度为1.7 nm时，上转换发光强度达到最大，与上转换发光强度随单晶壳层厚度的单调递增的规律不同.可能原因是多晶活性壳层中的大量晶界，导致Yb-Yb长程能量传递过程中的能量损失率增高.      

Upconversion luminescence of Y2O3:Er3+, Yb3+ nanoparticles prepared by a homogeneous precipitation method

Y2O3: Er3 , Yb3 nanoparticles were synthesized by a homogeneous precipitation method without and with different concentrations of EDTA 2Na. Upconversion luminescence spectra of the samples were studied under 980 nm laser excitation. The results of XRD showed that the obtained Y2O3:Er3 ,Yb3 nanoparticles were of a cubic structure. The average crystallite sizes calculated were in the range of 28-40 nm. Green and red upconversion emission were observed, and attributed to 2H11/ 2,4S3/ 2→4I15/ 2 and 4F9/ 2→4I15/2 transitions of the Er3 ion, respectively. The ratio of the intensity of green emission to that of red emission drastically changed with a change in the EDTA 2Na concentration. In the sample synthesized without EDTA, the relative intensity of the green emission was weaker than that of the red emission. The relative intensities of green emission increased with the increased amount of EDTA 2Na used. The possible upconversion luminescence mechanisms were discussed.     

Energy transfer and frequency upconversion in Er~（3＋）-Yb~（3＋） codoped oxy-fluoro-tungstosilicate glasses

Er3+-Yb3+ codoped oxy-fluoro-tungstosilicate glasses with infrared-to-visible frequency upconversion luminescence were prepared by melting quenching in air.The effects of Er3+ doping on the optical properties of the samples were measured by means of techniques such as optical absorption spectra and photoluminescence spectra.The results showed that intense green and red signals centered at 546 and 665 nm,corresponding to the 4S3/2 → 4I15/2 and 4F9/2 → 4I15/2 transitions of Er3+ by a multiphoton stepwise phonon-assisted excited-state absorption process,respectively,were simultaneously observed by exciting the samples with a diode laser operating at 980 nm at room temperature.The upconversion process was found very sensitive to Er3+ content at a constant Yb2O3 content of 5 mol.%.With the increase of Er3+ content from 0.5% to 1.5%,the upconversion intensity increased gradually.Further increasing of Er3+ content to 3.0% resulted in a significant fluorescence quenching.Moreover,the possible upconversion mechanisms were discussed based on the energy-matching conditions and the quadratic dependence on excitation power.     

Influence of B2O3 on Spectroscopic Properties of Er^3＋/Yb^3＋ Co-Doped Tungsten-Tellurite Glasses

A series of novel Er^3＋/Yb^3＋ co-doped （85- x ） TeO2-15WO3-xB2O3 （TWB;x=2%,5%,8%（mole fraction） ） glasses were prepared. Influence of B203 on the spectroscopic properties of Er^3＋/Yb^3＋ co-doped tungsten-tellurite glasses were investigated. It is found that the intensity of 1.5μm fluorescence, lifetime of the ^4I13/2 level and upconversion fluorescence all decrease with the increase of B2O3 content. The product of full width at half maximum （FWHM） and stimulated emission cross-section （σe^peak） of Er^3＋ ：^4I13/2→^4I15/2 transition has an optimum when B203 is 5% （mole fraction）. The emission spectra of Er^3＋ ： ^4I13/2→^4I15/2 transition was analyzed using peak-fit routine, and an equivalent four-level system was proposed to estimate the stark splitting for the 411512 and ^4I13/2 levels of Er^3＋ ions in TWB glasses at room temperature.     

Upconversion Luminescent Properties of YVO4:Yb3+, Er3+ Nano-Powder by Sol-Gel Method

YVO4:Yb3 , Er3 nano-sized upconversion luminescent powder was prepared by sol-gel method in the presence of citric acid. It was characterized by XRD, TEM and emission spectrum. The results show that the grain size of YVO4:Yb3 , Er3 is under 100 nm, and its grain size and upconversion luminescent intensity all increase with roasting temperature raises. Under 980 nm laser diode(LD) excitation, two strong green emissions that centered around 523 and 551 nm were observed with naked eyes at room temperature, corresponding to the 2H11/2→4I15/2 and 4S3/2→4I15/2 transitions of Er3 , respectively. According to the dependence of green upconversion emission intensity on excitation power, it can be concluded that these two kinds of green emissions all belong to two-photon process.     

Polarized spectral analysis of Er3+ ions in Er3+/yb3+:LiLa(MoO4)2 crystal

Optical characteristics and upconversion dynamics of Er3+ in Er3+/Yb3+:LiLa(MoO4)2 crystals were investigated. The absorption spectra, fluorescence spectra and the fluorescence decay curves were analyzed at room temperature. The infrared emission at 1538 nm and visible emissions at 520–569 and 640–670 nm, corresponding to 2H11/2,4S3/2→4I15/2 and 4F9/2→4I15/2 transitions of Er3+ ions, were simultaneously observed in Er3+/Yb3+:LiLa(MoO4)2 crystals under 976 nm excitation at room temperature. The maximal emission cross-section near 1530 nm for π-polarization was 0.63×10–20 cm2 and the measured lifetime of 4I13/2 was 4.88 ms. The upconversion process was involved in sequential two-phonon processes, either the energy transfer from Yb3+ ions or by the excited state absorption.     

Structure Property and Visible Upconversion of Er^3＋ Doped Gd2O3 Nanocrystals

Gd2O3:Er nanoparticles were prepared by a simple sol-gel method, The structure properties ot Gd2O3:Er were studied by X-ray diffraction, transmission electron microscopy, Raman spectroscopy and Fourier transform infrared spectroscopy. The visible up-converted luminescence spectra of Er^3 were investigated under excitation to ^4I9/2 level by 785nm laser. Laser power, Er^3 ion concentration and temperature dependences of the upconverted emissions were investigated to understand the upconversion mechanisms. Excited state absorption and energy transfer process are discussed as the possible mechanisms for the upconversion.     

Green, orange, and red upconversion luminescence in Nd3+/Yb3+: Cs2NaGdCl6 powders under 785 nm laser excitation

Nd3+:Cs2NaGdCl6 and Nd3+, Yb3+:Cs2NaGdCl6 polycrystalline powder samples were prepared by Morss method E. Under 785 nm semiconductor laser pumping, the upconversion luminescence of Nd3+ ions in Cs2NaGdCl6 was investigated at room temperature, and three upconversion emissions near 538 nm (Green), 603 nm (Grange), and 675 nm (Red) were observed and assigned to 4G7/2→4I9/2, (4G7/2→4I11/2; 4G5/2→4I9/2), and (4G7/2→4I13/2; 4G5/2→4I11/2), respectively. The dependences of these upconverted emissions on laser power and Nd3+ ion con-eentration were investigated, to explore the upconversion mechanism. The effect of doping Yb3+ ions on the upconversion luminescence of Nd3+ in Cs2NaGdCl6 was also studied under 785 nm laser excitation. The energy transfer processes were discussed as the possible mecha-nism for the above upconversion emissions.     

Investigation on energy transfer from Er3+ to Nd3+ in teilurite glass

A study of energy transfer of Er3+/Nd3+ codoped tellurite glasses was presented. By Nd3+ co-doping, both the Er3+ green emission corresponding to the Er3+: (4S3/2,2H11/2)→4I15/2 transitions and the red emission corresponding to the Er3+: 4F9/2→4I15/2 transitions were quenched. The energy transfer mechanism between Er3+ and Nd3+ was discussed based on their energy level characteristics. The interaction parameters, CD-A, for the energy transfer processes from Er3+ to Nd3+ in tellurites glass were calculated. Finally, the resonant transfer Er3+: 4I9/2→Nd3+: (4F5/2, 2H9/2) was proposed to be the most probable microscopic process to occur in contrast with the other processes.     

Enhancement of 1.54 μm emission in Er：LiNbO_3 crystal by codoping with Zn~（2＋） ions

The enhanced intensity and lengthened lifetime of 1.54 μm emission were observed for Er:LiNbO3 crystal codoped with Zn2+ ions.The ZnO codoping led to the reduction of the green upconversion emission in Er:LiNbO3 crystals.The decay trace of the 4S3/2→4I15/2 was ob-viously nonexponential for Er:LiNbO3 codoped with 0 and 3 mol.% ZnO,but became exponential for one codoped with 6 mol.% ZnO.The OH-absorption spectra showed after codoping with Zn2+ ions,the OH-absorption peaking position shifted from ~3495 to 3484 cm-1,and the absorption cross section decreased.These spectroscopic characteristics suggested that the improvement of 1.54 μm emission was attributed to the reduction of Er3+ cluster sites.     

Mechanism of upconversion emission enhancement in Y_3Al_5O_（12）：Er~（3＋）/Li~＋ powders

Er3+ and Li+ codoped Y3Al5O12(YAG) powders were prepared for a systematic investigation of their upconversion emissions.X-ray diffraction(XRD),upconversion emission spectra,pump power dependence,FT-IR spectra and decay time were studied to characterize the samples.With Li+ doping,the upconversion emission intensity of Er3+ doped YAG powders was obviously enhanced,accompanied with an increase in the ratio of green to red intensity.The enhancement of emission intensity could be attributed to two mechanisms:on...