ZnO:Er3+纳米晶的制备及发光性质研究

为了探讨稀土Er3 与纳米ZnO基质之间的能量传递,利用化学方法制备了ZnO:Er3 纳米晶,测量了样品的X射线衍射谱(XRD)、光致发光谱(PL)和激发谱(PLE).X射线衍射结果表明,ZnO:Er3 具有六角纤锌矿晶体结构.室温下,在365 nm激发下,在ZnO宽的可见发射背景上,观测到了Er3 的激发态4S3/2(550 nm),2H11/2(521 nm)和4F5/2(456 nn)的特征发射.分析了ZnO:Er3 纳米晶的带边发射和稀土Er3 的特征发射的峰值强度随掺Er3 浓度的变化关系,比较了ZnO:Er3 与未掺杂的ZnO的光致发射峰值强度的变化,给出了稀土Er3 的激发态4S3/2→4I15/2,2H11/2→4I15/2和4F5/2→4I15/2的发射机制,证实了纳米ZnO基质与稀土Er3 离子之间存在能量传递.     

ZnO∶Tb3+纳米晶的制备及发光性质研究

利用溶胶-凝胶法（Sol-Gel）制备了不同浓度的ZnO∶Tb3+纳米晶，测量了样品的光致发光谱(PL)和激发谱(PLE).在ZnO宽的可见发射背景上，观察到样品在485 nm、544 nm、584 nm和620 nm附近出现了稀土Tb3+的特征发射.给出了ZnO∶Tb3+纳米晶光致发光的峰值强度随掺Tb3+浓度的变化关系，分析了稀土Tb3+的激发态5D4→7F6、5D4→7F5和5D4→7F4的发射机制，证实了稀土Tb3+的特征发射来源于稀土离子内部4f电子的f-f跃迁和ZnO基质与稀土Tb3+离子之间能量传递.     

Influence of the magnetic field and measurement temperature on the shape of microphotoluminescence spectra of Eu-Doped InGaN/GaN quantum-well structures

Based on the results of complex investigations of the influence of the magnetic field strength and measurement temperature on the shape of microphotoluminescence (micro-PL) spectra of Eu-doped InGaN/GaN quantum-well structures, the determination of the charge state of Eu impurity ions, and the change in the concentration of dopant ions, it has been shown that an increase in the magnetic field strength (0–5 T) leads to a more significant decrease in the luminescence intensity as compared to the undoped structures. An increase in the measurement temperature from 4.2 to 78 K results in an enhancement of the effect of the magnetic field on the shape of the micro-PL spectra of Eu-doped InGaN/GaN structures. It has been demonstrated that the doping of InGaN/GaN quantum-well structures with europium at a high excitation level leads to a shift in the maximum of the luminescence intensity toward the long-wavelength range of the spectrum.     

较高掺杂浓度下CdSe/ZnS量子点光纤光致荧光光谱

制备了一种较高浓度掺杂的CdSe/ZnS量子点掺杂光纤.测量了不同掺杂浓度和不同光纤长度下的量子点光纤光致荧光光谱,得剑了荧光峰值增益最大时的量子点掺杂浓度和光纤长度.与低浓度掺杂光纤相比,较高掺杂浓度光纤中的荧光峰值光强明显提高.荧光峰值光强随光纤长度的变化在短距离内(L<1 cm)急剧上升,之后缓慢均匀下降.波长473 nm激励光强随光纤}乏度的变化呈指数形式衰减,消光系数为0.26～1.02 cm-1.在给定激励光强和激励波长的条件下,光纤中可达到最大荧光辐射的晕子点总数为一恒量.光纤中的荧光峰值波长存在红移,红移大小约8～15 nm,红移量与掺杂浓度以及光纤长度有关.这些实验结果可为今后量子点光纤放大器的研制提供参考.     

Synthesis and photoluminescence of CeO2:Eu phosphor powders

The crystalline structure and photoluminescence (PL) properties of europium-doped cerium dioxide synthesized by the solid-state reaction method were analyzed. CeO₂:Eu³⁺ phosphor powders exhibit the pure cubic fluorite phase up to 10 mol% doping concentration of Eu³⁺. With indirect excitation of CeO₂ host at 373 nm, the PL intensity quickly increases with increasing Eu³⁺ concentration, up to about 1 mol%, and then decreases indicating the concentration quenching. While with direct excitation (467 nm), much more stronger PL emissions, especially the electric dipole emission ⁵D₀-⁷F₂ at 612 nm, are observed and no concentration quenching occurs up to 10 mol% doping concentration of Eu³⁺. The nature of this behavior and the cause of the concentration quenching were discussed.     

稀土Tb3+掺杂纳米ZnO的发光性质

ZnO是一种优良的直接宽带隙半导体发光材料(Eg=3.4 eV),具有优异的晶格、光学和电学性质,稀土离子掺杂浓度和热处理温度对ZnO∶Re3 纳米晶发光强度、峰位变化等光学性质具有重要影响.利用溶胶-凝胶法(Sol-Gel),在不同退火温度下,制备了不同浓度的ZnO∶Tb3 纳米晶.室温下,测量了样品的X射线衍射谱(XRD)、光致发光谱(PL)和激发谱(PLE).观察到纳米ZnO基质在520 nm附近宽的绿光可见发射和稀土Tb3 在485,544,584和620 nm附近的特征发射.通过ZnO基质可见发射强度和稀土Tb3 特征发射强度随Tb3 掺杂浓度、退火温度的变化关系,获得了5D4→7F5跃迁的绿色主发射峰最强的样品制备工艺参数,其退火温度为600℃、掺杂浓度为4 at%;给出了稀土Tb3 的激发态5D4→7F6(485 nm),5D4→7F5(544 nm)和5D4→7F4(584 nm)的发射机制;证实了稀土Tb3 与纳米ZnO基质之间存在双向能量传递.     

Green Emitting Cerium Doped CaS Whiskers Grown by Solid State Diffusion Method

Undoped and cerium doped Calcium sulfide (CaS) phosphors were synthesized using solid state diffusion method. The X-ray diffraction pattern revealed that both undoped and doped CaS crystallites have cubic structure with average crystallite size varying from 20 to 30 nm. Scanning electron micrographs indicated that Ce doped CaS phosphors were composed of whiskers with different dimensions and orientations. The optical properties of undoped and Ce doped particles were characterized using Photoluminescence (PL) and UV-Vis absorption spectroscopy. The PL emission spectrum of cerium doped CaS phosphors for an excitation wavelength 465 nm showed a main peak at 500 nm and a shoulder peak at 556 nm due to 5d?→?4f transition in Ce³⁺ ions. The variation of PL intensity with cerium concentration was investigated and the maximum PL intensity was obtained for a doping concentration of 3 wt.%. The optical band gap of the samples was estimated from the diffuse reflectance spectrum and was found to increase with increase in cerium concentration. The enhanced optical properties of these phosphors can be exploited in various optoelectronic devices including displays and bioimaging techniques.     

Violet-to-red photoluminescence of spiro-TAD organic films doped with different organic dyes

Photoluminescence (PL) and photoluminescence excitation (PLE) spectra of undoped spiro-TAD films and spiro-TAD films doped either by the organic dyes coumarin 7 or DCM as well as by both of these dyes simultaneously were investigated at different dye concentrations. A widened PL spectrum caused by doping was encountered and violet-to-red emission was obtained. It was established that excitation of the dyes is realized most efficiently through spiro-TAD. The overall integral PL intensity of the coumarin 7 doped films increased with dye concentration due to the suppression of nonradiative recombination in the film caused by a transfer of spiro-TAD excitation energy to the dye molecules. Mainly radiative energy transfer from semiconductor to dye molecules occurs in the case of DCM doping. No mutual influence on the luminescence of both dyes in the spiro-TAD film was observed and as a consequence, the PL band intensity of each dye can be adjusted separately.     

基于分子束外延生长的1.05 eV InGaAsP的超快光学特性研究

利用分子束外延方法制备了应用于四结光伏电池的1.05 eV InGaAsP薄膜, 并对其超快光学特性进行了研究. 温度和激发功率有关的发光特性表明: InGaAsP材料以自由激子发光为主. 室温下InGaAsP材料的载流子发光弛豫时间达到10.4 ns, 且随激发功率增大而增大. 发光弛豫时间随温度升高呈现S形变化, 在低于50 K时随温度升高而增大, 在50–150 K之间时减小, 而温度高于150 K时再次增大. 基于载流子弛豫动力学, 分析并解释了温度及非辐射复合中心浓度对样品材料载流子发光弛豫时间S形变化的影响.     

Hydrothermal-assisted ion exchange synthesis and photoluminescence of Li+ and Eu3+ co-doped NaLa(WO4)2 as near-UV type red phosphors

A series of Li⁺ and Eu³⁺ co-doped double tungstate NaLa(WO₄)₂ (NLW) red phosphors have been successfully synthesized by an ion exchange method under a hydrothermal condition. The effects of Li⁺ doping concentration on the crystal structure, morphology and photoluminescence properties were investigated using the XRD, TEM and photoluminescence (PL) measurements. The results reveal that the samples have phase-pure scheelite structure and adopt spherical particle morphology. Furthermore, room temperature PL spectrum shows that the optical brightness is highly dependent on the concentration of doping Li⁺, which is determined by ion exchange duration and the precursor concentration of LiNO₃. As 5% Li⁺ ions was introduced into the crystal lattice, the emission intensity was enhanced by more than 10-fold as compared with the pristine one. Moreover, the co-doping of Li⁺ can substantially improve the effective excitation of the NaLa(WO₄)₂:Eu³⁺ phosphors under near-UV region.     

Photoluminescence and optical characterization of CdS nanoparticles prepared by solid-state method at low temperature

The photoluminescence (PL) and optical properties of CdS nanoparticles prepared by the solid-state method at low temperature have been discussed. The effects of NaCl and anionic surfactant SDBS (sodium dodecylbenzene sulfonate) on the luminescent properties of CdS nanophosphors prepared using this method, without the inert gas or the H₂S environment, were studied separately. The synthesized products were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), field emission scanning electron microscope (FESEM), and energy dispersive X-ray spectroscopy (EDAX). UV–VIS absorption and PL spectra were also studied. XRD studies confirmed the single-phase formation of CdS nanoparticles. TEM micrograph revealed the formation of nearly spherical nanoparticles with a diameter of 2.5 nm. The PL emission for the CdS shows the main peak at 560 nm with a shoulder at 624 nm, with an increase in the PL intensity after the addition of SDBS. The effect of Mn doping on PL intensity has also been investigated. The PL spectra show that the emission intensity decreases as the dopant concentration increases.     

Sr2CeO4∶Dy3+荧光粉的合成以及发光特性的研究

以亚甲基双丙烯酰胺为网络剂,采用高分子网络凝胶法合成了Sr₂CeO₄∶Dy3+荧光粉,并表征其结构、颗粒形貌及发光性能。研究结果表明：Sr₂CeO₄∶Dy3+无其他杂相存在且粉末颗粒大小均匀。其紫外-可见吸收带集中在480 nm附近;在370 nm紫外光激发下,其发射图谱为一多峰发射;监测470 nm的发射峰,所得样品的激发谱为一双峰宽谱,峰位为292和338 nm。同时研究了Dy3+掺杂浓度对样品发射光谱的影响,结果显示,随着Dy3+浓度的增大,其黄、蓝发射峰强度比值逐渐增大,但发光强度呈现先增大后减小的趋势,在Dy3+掺杂浓度为0.4 mol%时达到最大值。     

Excitation process and photoluminescence properties of Tb and Eu ions in SnO2 and in SnO2: Porous silicon hosts

Tin oxide (SnO₂)-layers-doped terbium and europium ions are elaborated by the sol-gel method on silicon substrates. After annealing at 500 °C, the transmission electron microscopy revealed a crystallization of tin oxide.The emission properties of rare-earth in SnO₂ are studied systematically against temperature annealing and Tb³⁺ concentration. The PL spectrum is optimal after annealing at 900 °C and the corresponding photoluminescence (PL) decay is nearly exponential, showing that the sample is homogenous and the PL process can be described by two levels system.The concentration effect shows a quenching of the PL intensity for Tb³⁺ concentration above 4%. From the investigation of the decay rate from the ⁷F₅ state within terbium concentration, we show that self-quenching is insured by dipole - dipole interaction. The evolutions of both PL intensity and PL lifetime versus temperature are studied. The PL intensity and PL lifetime are enhanced by deposing SnO₂:Tb³⁺ and SnO₂:Eu³⁺ in porous silicon. We show that an efficient excitation transfer from Si nanocrystallites to RE ions can occur.     

Yb掺杂对Er/Yb共掺Al2O3薄膜光致荧光性能的影响

采用反应射频磁控溅射技术,通过调整溅射靶面上金属Er和Yb的面积比例制备出了不同Yb含量的Er／Yb共掺Al2O3薄膜,重点探讨了薄膜制备过程中Er、Yb成分比例控制的可靠性及Yb的掺杂浓度对Er／Yb共掺Al2O3薄膜室温光致荧光谱强度及峰型的影响。利用卢瑟福背散射谱(RBS)和电子能谱(EDX)对薄膜成分进行的分析表明：薄膜中Er、Yb成分的比例与实际的Er、Yb靶面积比基本一致。薄膜经过1000℃退火2h的室温光致发光谱表明：Yb掺杂显著提高了薄膜的光致荧光强度,当Yb／Er靶面积比为4：1时,光致荧光强度和半峰全宽最大。研究结果表明：对于Al2O3薄膜,合适的Yb／Er浓度,不仅可以显著改善薄膜的发光效率,而且可以增加频带带宽。     

Infrared radiation of zinc selenide single crystals

Long-wave photoluminescence (PL) spectra of both as-grown and Au-doped n-ZnSe single crystals are studied in the temperature range from 81 to 300 K. A narrow band of infrared (IR) radiation centered at 878 nm (1.411 eV) manifests itself in the low-temperature PL spectrum. It is established that this band intensity first increases and then decreases with increasing concentration of doping impurity. With increasing excitation radiation intensity, spectral position of the IR PL band is unchanged and its intensity increases under the linear law. With increasing excitation radiation wavelength, the IR PL band intensity increases, it becomes narrower and shifts towards long wavelengths. It is shown that the observed IR radiation is caused by recombination of free electrons with holes localized on associative acceptors in the ZnSe:Zn:Au crystals or in the undoped crystals.     

Er~(3+)及Er~(3+)/Yb~(3+)掺杂纳米晶CaWO_4的发光性质

利用共沉淀法制备了Er3+掺杂及Er3+/Yb3+共掺杂纳米晶CaWO4发光粉体,室温下观察到Er3+的下转换和上转换特征发射。研究了不同煅烧温度、不同掺杂浓度对Er3+离子特征发射的影响。结果表明:随着煅烧温度的升高,发射强度增强;掺杂浓度的改变,导致了Er3+的浓度猝灭现象,其适宜的掺杂原子数分数为0.6%。同时观测到O-W的电荷迁移态与稀土离子之间的能量传递现象,并给出了能量传递的模型。对Er3+的上转换研究观察到:在976nm激光激发下Yb3+对Er3+的上转换发射起到了很好的敏化作用,两个Yb3+同时将能量以共振方式传递给一个Er3+离子,Er3+、Yb3+共掺杂样品的绿光上转换过程展示了双光子过程。     

紫外光激发下氧化锌纳米线的发光特性研究

室温条件下,用355 nm的激光激发氧化锌纳米线,测量了其发光光谱.观察到半宽度较小、峰值波长约382 nm的紫光峰和半宽度较宽、峰值波长约507 nm的绿光峰;两峰的发光强度随激发光功率密度的变化而变化,且均存在饱和效应,但各自的变化规律及饱和值的大小不同;紫光峰的中心波长随激发光功率密度的增加而发生了明显的红移.对两峰产生的机理、强度饱和值存在的原由、强度随激发光功率密度变化及紫光峰红移的起因进行了分析.     

近紫外LED用黄色荧光粉Sr3SiO5：Ce3+, Li+的发光特性

采用高温固相法快速降温合成Sr_3-2xSiO₅：xCe³⁺,xLi⁺荧光粉。用X射线衍射仪和荧光分光光度计测试荧光粉的样品结构和发光性能。在1 420 ℃下煅烧得到四方相结构的Sr₃SiO₅：Ce³⁺,Li⁺。样品的激发光谱分布于270~500 nm的波长范围,有两个激发带,峰位分别位于328 nm和410 nm,表明样品可以被近紫外光有效激发。样品的发射光谱分布于420~650 nm,发射峰位于528 nm处。在410 nm左右的近紫外光激发下,宽带发射的峰位于528 nm。Ce³⁺的最佳掺杂量x（Ce³⁺）为0.8%,并且发光强度随掺杂浓度的增加先升高后降低,出现浓度猝灭。根据Dexter能量共振理论,该浓度猝灭的原因是Ce³⁺的电偶极-电偶极相互作用。     

Temperature and concentration dependences of the photoluminescence of MEH-PPV polymer composite films with ZnO nanoparticles

The absorption and photoluminescence (PL) spectra of MEH-PPV: ZnO composite films have been investigated at different concentrations of ZnO nanoparticles and at different temperatures (in the case of PL). It has been shown that, at 297 K, with increasing concentration of ZnO nanoparticles in the composite, the intensity of the PL lines of MEH-PPV decreases, whereas the intensity of the PL lines of ZnO increases. At a relatively low concentration of ZnO nanoparticles, a decrease in the temperature leads to an increase in the intensity of PL lines associated with MEH-PPV and ZnO, whereas at higher concentrations of ZnO nanoparticles, the intensity of these lines decreases. This is accompanied by a slight shift in the maximum of the PL toward the infrared (IR) region and a narrowing of the PL line of MEH-PPV with a decrease in the temperature and with an increase in the ZnO concentration. The mechanism of energy transfer in composite systems consisting of a polymer and inorganic nanoparticles that can be responsible for the observed effects has been discussed.     

ZnO薄膜表面和边缘的发光特性

研究了分子束外延方法生长的ZnO薄膜的光学特性,首先测量样品反射光谱,然后重点研究其光致发光光谱。实验中通过改变激发光的强度,以及采用波导配置和不同的实验几何配置等手段,观察到了ZnO薄膜中起源于激子-激子散射和电子-空穴等离子体复合发光的受激辐射,同时观察到两种配置下自发辐射谱中存在巨大的差异。通过对实验数据和理论计算结果的分析,初步认为造成了从ZnO薄膜表面和侧面得到的PL谱之间的显著区别原因有两种:一是非对称薄膜波导的吸收损耗造成的波长选择效应,二是薄膜波导对掠出射光的类似薄膜微腔的微腔效应。