The features of nonlinear absorption during resonance one- and two-photon excitation of the basic exciton transition in colloidal CdSe/ZnS quantum dots

The features of the nonlinear absorption of CdSe/ZnS quantum dots (colloidal solution) in the case of resonant one- and two-photon excitation of the basic exciton transition by powerful ultra-short laser pulses were determined. In one-photon excitation, with an increasing intensity of impulses, a decrease in absorption (bleaching) is relayed by an increase in absorption, which is associated with the process of the filling of the states (saturation) of a two-level system with the lifetime of the excited state depending on the light intensity. The arising Fresnel or Fraunhofer diffraction of the laser ray that pass through a colloidal solution with a high concentration of quantum dots is associated with the formation of the transparency channel and self-diffraction of laser ray on an induced diaphragm. In two-photon excitation, the features of the nonlinear absorption and luminescence tracks (the dependence of luminescence intensity on distance) were explained by the influence, in addition to the two-photon absorption, of the processes that are responsible for the slower growth of nonlinear absorption and luminescence quenching at high intensities of laser pulses.     

电致发光衰减测量系统的搭建及应用

发光衰减是发光的重要过程,测量发光寿命对研究发光机理十分重要,但传统研究在概念和方法上存在两个差错：(1)概念上认为衰减等同于激发态数目的减少,而忽视了衰减是发光强度的下降,两者是不同的概念;(2)方法上基于激发态规律推导,假设的边界条件不符合实际,没有实验的支持。同时,传统方法对设备的要求很高,且只限于光致发光。为了纠正差错,降低成本,搭建了一套全新的电致发光衰减测量系统,可用于所有可以周期激发的发光类型。从能量转换原理出发,采用周期激发,用脉冲间隔时间作为时间尺度来度量发光衰减持续的时间,通过脉冲间隔时间与发光寿命的对比,相应地发光强度有不同的变化,根据该现象简便地测量出发光寿命。基于该原理搭建的发光衰减测量系统,实验结果表明了发光强度随着激发频率,先保持不变然后逐渐下降,通过测量下折点即能够推算出发光衰减寿命,而且还发现发光衰减寿命与初始发光强度呈正相关的关系。认为发光寿命是发光强度的变化,是区别于传统研究以激发态数目为研究对象的一大创新,同时通过实验证明了发光寿命与初始亮度相关,也拓展了对发光寿命的新认识。     

发光寿命在发光特性表征中的重要影响

吸收是发光的前提条件,吸收变了,发光的其他特性也就随之而变.但是发光寿命的长短又会反过来影响吸收的多少,这不仅存在于光致发光中,而且是一个普遍规律.从电场引起的场致发光中发现,在同一种材料中掺入两种发光寿命长短相差悬殊的发光中心Cu和Mn,利用激发电源频率的变化,明确地显示出发光寿命短的Cu的发光与发光寿命长的Mn的发光强度之比随频率的增加而增大,而且也显示了Cu的两种发光也有这种规律.实验结果说明,这种规律只取决于发光中心的寿命长短,而与激发方式及猝灭原因无关.     

Decay of electronic excitations in colloidal thioglycolic acid (TGA)-capped CdS/ZnS quantum dots

Investigations of dynamics of exciton relaxation in colloidal thioglycolic acid (TGA)-capped CdS/ZnS core/shell systems with diameter of 3.6 nm by means of femtosecond transient absorption spectroscopy, thermostimulated luminescence (TSL), and decay of luminescence are presented in this paper. It was found that the intensity of trap-state luminescence increases when one and two ZnS monolayers are formed. Also, the lifetime of trap-state luminescence increases. Two types of trap states with different depths were found, using thermostimulated luminescence technique. Localized states of the first type with depth of 0.085 eV do not change their concentration during sell formation. In contrast, trap state of the second type with depth of 0.125 eV are almost completely removed. It was found that the electron lifetime, investigated femtosecond transient absorption is not changed during formation of ZnS shell. It was concluded that localized states are channels of non-radiative recombination, direct quenching the center of trap-state luminescence. The absence of exciton luminescence is caused by rapid localization of holes at luminescence center.     

水杨酸酯-铽络合物的发光及其向铕离子的能量传递

本文应用稳态和瞬态光谱技术探讨了稀土离子铽与水杨酸甲酯,苯酯所形成络合物的发光特性,它们向铕离子的能量传递过程;以及pH值对络合物的发光和能量传递的影响。络合物的发光比络合前铽离子的发光增强了几至十几倍;介质的pH变化影响到络合物的发光强度和能量传递效率,中性介质(pH:6～8)下的量传递效率最高。     

熔制温度对铋离子掺杂钡铝硅酸盐玻璃发光性能的影响

研究了熔制温度对铋离子掺杂钡铝硅酸盐玻璃发光性能的影响.当用紫外光和808nm的激光二极管激发时,分别在425nm和1330nm附近观察到可见和宽带红外发光.可见荧光的发射强度随着熔制温度的升高逐渐下降,而红外发光强度随着熔制温度的升高先是增强然后减弱.对光致发光的机理进行了探讨.     

双脉冲注入式LD模块的红外能级寿命可见区测试系统

Er3+的4I_13/2能级寿命的长短对评估Er3+掺杂材料在光通讯波段的应用十分重要。基于980 nm双脉冲注入式LD激发下的Er3+激发态吸收上转换发光,测量在不同双脉冲时间间隔下的上转换红光发光强度,再根据上转换红光的发光强度随双脉冲时间间隔的变化关系,推导出了Er3+红外4I_13/2能级寿命的拟合公式,实现了红外能级寿命的可见区测量。因此,结合兼具时间间隔可调和同步脉冲取样的双脉冲注入式LD模块和光电倍增管(R2658),就可以实现所有Er3+红外能级寿命的测量,这是一种十分经济的微秒量级荧光寿命测试系统。     

Photo-stimulated emission of X-irradiated BaFBr:Eu

Abstract

The photo-stimulated luminescence (PSL) of Eu²⁺-doped BaFBr is excited in the two F centre absorption bands produced by X-irradiation at room temperature. The PSL intensity decreases with decreasing temperature by about a factor of 10. After bleaching at low temperatures the PSL is nearly zero, it can be regenerated by warming the crystal to room temperature. The results are discussed with a new model of the PSL process.     

微波吸收法研究Mn,Cu掺杂对ZnS:Mn,Cu光生载流子复合过程的影响

采用微波吸收法，测量了ZnS:Mn,Cu粉末材料受到超短脉冲激光激发后，其光生电子和浅束缚态电子的衰减过程.发现Mn,Cu的浓度对导带电子的寿命有明显的影响，提高掺杂浓度会使光生电子的寿命大大缩短，还研究了掺杂浓度对光致发光强度的影响. 关键词： 发光材料 硫化锌 光电子 微波吸收技术     

Yb3+离子掺杂浓度对Yb∶YAG晶体发光及荧光寿命的影响

研究了不同掺杂浓度Yb∶YAG晶体的发光特性和荧光寿命.Yb3+在YAG晶体中的掺杂浓度分别为5at%、10at%、20at%、30at%.Yb3+离子掺杂浓度越高，Yb∶YAG晶体的吸收系数越大.采用940 nm波长的LD泵浦源和TRIA X550荧光谱仪，对这一系列掺有不同浓度Yb3+的Yb∶YAG晶体进行了荧光光谱的测定.结果表明:在1030 nm主发光波段的荧光强度以10at%Yb∶YAG的为最强.同时发现它在450 nm-680 nm波段有明显的可见发光，其强度随Yb3+掺杂浓度的增加而迅速地增强.Yb∶YAG晶体的荧光寿命存在浓度猝灭现象，对猝灭机制进行了分析研究，指出浓度猝灭的主要原因是合作发光和痕量稀土离子的上转换发光.     

GaN深中心Zn的低温瞬态研究

本文研究了GaN:Zn的低温瞬态过程,同时测量了衰减中的时间分辨光谱,从两者测量的结果得出:2.89eV的光致发光寿命为300ns(2K).实验证实,Zn作为发光中心的同时也引起一些非辐射陷阱.2.89eV的瞬态曲线可分为两部分,在短时范围(1μs)内基本上是指数形式,可归结为导带中光激发的电子和束缚在ZnGa受主上空穴的复合.在长时范围(t>>1μs)内瞬态曲线则偏离了指数规律,相当好地符合Becqureal经验公式.     

钕敏化多层壳纳米结构的增强型染料敏化上转换发光

对于稀土离子掺杂的上转换发光,由于稀土离子吸收截面小、吸收范围窄,导致其发光强度受限.最近,在稀土上转换纳米粒子的表面连接近红外染料分子敏化发光,被证实是提高上转换发光强度的有效策略.然而,将染料分子连接经典的稀土Yb掺杂纳米粒子,并不能有效利用染料分子的敏化能力.针对这一问题,本文通过高温热分解法成功制备了Nd3+敏...     

TIME-RESOLVED PHOTOLUMINESCENCE OF SINTERED ZnO CERAMICS

The time-resolved photoluminescence (TRPL) of sintered ZnO ceramics was measured at low temperatures. A broad luminescence band was observed in the visible region. The TRPL experiment shows that photoluminescence decay behaviour can be depicted as t^-n(r). The decay rate n(r) and lifetime are wavelength dependent, and the former varies exponentially with wavelength. The power-lowering behaviour of the luminescence intensity indicates that the luminescence band originates from the recombination of donor-acceptor pairs.     

Luminescence bands in natural brown diamonds

We report on new luminescence bands exhibited by natural brown/mauve diamonds. We describe detailed absorption and luminescence measurements in the visible spectral region. The structured bands with ZPL at 2.424 eV, 2.114 eV, 1.819 eV and 1.707 eV, and a broad band with a maximum at 1.8 eV are shown to be the main components of the visible luminescence. Bands with ZPL at 2.114 eV, 1.819 eV and 1.707 eV are shown to correspond to forbidden transitions with lifetimes of the order of msec. Energy absorbed by the 2.424 eV centre is transferred into the 1.819 eV centre.     

Luminescence lifetimes in quartz: dependence on annealing temperature prior to beta irradiation

It is well known that the thermal history of a quartz sample influences the optically stimulated luminescence sensitivity of the quartz. It is found that the optically stimulated luminescence lifetime, determined from time resolved spectra obtained with pulsed stimulation, also depends on past thermal treatment. For samples at 20°C during stimulation, the lifetime depends on beta dose and on duration of preheating at 220°C prior to stimulation for quartz annealed at 600°C and above, but is independent of these factors for quartz annealed at 500°C and below. For stimulation at higher temperatures, the lifetime becomes shorter if the sample is held at temperatures above 125°C during stimulation, in a manner consistent with thermal quenching. A single exponential decay is all that is required to fit the time resolved spectra for un-annealed quartz regardless of the temperature during stimulation (20–175°C), or to fit the time resolved spectra from all samples held at 20°C during stimulation, regardless of annealing temperature (20–1000°C). An additional shorter lifetime is found for some combinations of annealing temperature and temperature during stimulation. The results are discussed in terms of a model previously used to explain thermal sensitisation. The luminescence lifetime data are best explained by the presence of two principal luminescence centres, their relative importance depending on the annealing temperature, with a third centre involved for limited combinations of annealing temperature and temperature during stimulation.     

Up-conversion luminescence saturation under pulsed excitation of erbium-doped, SiO2–TiO2 sol–gel powders

The intensity of erbium up-conversion luminescence could be limited by a saturation effect due to increased pump power. We studied the luminescence saturation of the 550 nm emission on erbium-doped, SiO₂–TiO₂ sol–gel powders under pulsed excitation at 979 and 1532 nm. From the latter, the up-converted luminescence intensity decreased with increasing excitation power, whereas no saturation was observed at 979 nm excitation. We proposed that the saturation effect is determined by the pump power, the erbium content and the lifetime of the corresponding first excited states at different pumping schemes.     

Tm:YVO4晶体的光谱参数计算

由测量的Tm :YVO4晶体的吸收光谱 ,考虑到单轴晶体在各个方向上的吸收不同和折射率随波长的变化 ,根据Judd Ofelt理论计算了Tm3 +在YVO4中的强度参数、各个能级的振子强度、自发辐射几率、荧光分支比、积分发射截面等参数。强度参数为Ω2 =1 9416× 10 - 2 0 (cm2 ) ,Ω4=0 15 6 8× 10 - 2 0 (cm2 ) ,Ω6=0 396 3× 10 - 2 0 (cm2 )。计算结果表明 ,1 D2 → 3 F4的跃迁几率远大于1 D2 向其他各个能级的跃迁几率     

Luminescence properties of BeO optically stimulated luminescence (OSL) detectors

The objective of this work is to investigate basic luminescence properties of BeO optically stimulated luminescence (OSL) detectors, including the OSL emission and stimulation spectrum, the lifetime of the luminescence centers contributing to the OSL signal, and the temperature dependence of the luminescence lifetime and of the luminescence efficiency. The OSL stimulation spectrum shows a continuous increase in OSL intensity with decreasing stimulation wavelength. The emission spectrum indicates two OSL emission bands at ～310 nm and ～370 nm, the latter being the dominant OSL emission band. We also observed that the luminescence centers associated with the OSL signal are strongly quenched above room temperature, resulting in a reduction in luminescence lifetime from ～27 μs at room temperature down to ～800 ns at 140 °C. The activation energy for non-radiative decay of the luminescence center was determined to be E = (0.568 ± 0.023) eV. The ～27 μs luminescence lifetime observed for BeO indicate that POSL technique may be used to improve the signal-to-noise ratio using stimulation pulses of the order of microseconds. The information obtained in this study may help further optimize the BeO dosimetry systems and provide guidance on the timing parameters to be used for POSL measurements of this material.     

Effect of Nanorod Diameters on Optical Properties of GaN-Based Dual-Color Nanorod Arrays

Dual-color(blue and green) InGaN/GaN nanorod light-emitting diodes(LEDs) with three different nanorod diameters are fabricated. Enhancement of luminescence intensity per area is observed in blue and green wells,to varying degrees. When the diameter is 40 nm, it sharply decreases, which could be explained by the sidewall nonradiative recombination. Time-resolved photoluminescence is conducted to study the carrier lifetime. High recombination rate is observed in nanorod arrays, and is an order of magnitude less than that of the planar LED.When the diameter is 40 nm, the nonradiative lifetime decreases, and this explains the decrease of intensity. The3 D-FDTD simulations show the enhancement of light extraction out of geometry structure by calculating the transmittance of the nanorod arrays.     

磷酸盐、锗酸盐和碲酸盐玻璃中Ce3+、Tb3+、Er3+和Tm3+离子的发光和敏化作用的研究——Ⅱ.辐射跃迁、无辐射跃迁和能量转移

对不同玻璃基质中的Tb3+、Er3+和Tm3+离子的辐射跃迁和无辐射跃迁速率进行了计算和测量,并讨论了基质玻璃对跃迁特性的影响。研究了Ce3+对Er3+、Tm3+,Tb3+的敏化作用,得出Ce3+对Er3+离子的敏化作用是弱的,而Ce3+对Tm3+和Tb3+是较强的,并对敏化机理进行了讨论。