采用低温PL谱研究探测器级CdZnTe晶体

采用低温光致发光谱技术研究了核辐射探测器用高阻CdZnTe晶体。发现PL谱中的三个特征峰均与晶体质量有关,其中(D0,X)峰FWHM值和I DAP/I(D0,X)与晶格完整性和浅能级缺陷密度有关联,D2峰则与位错密度密切相关。采用双晶X射线摇摆曲线和位错腐蚀坑密度对此表征进行了验证。低温PL谱测试结果显示晶体质量较高的CdZnTe晶片,其探测器的能谱分辨率也相对较高。     

CdZnTe晶片的Raman光谱研究

利用Raman光谱技术研究了CdZnTe晶片表面处理方法、激光功率及波长变化对CdZnTe晶片的Raman谱线影响.研究表明:CdZnTe晶片分别经过机械抛光、Br-MeOH溶液处理以及Br-MeOH溶液+ KOH/甲醇溶液处理后,由于表面晶格完整性的改变, Raman光谱出现了明显变化.采用514.5 nm、632.8 nm及785 nm激光激发CdZnTe晶片时,晶片的Raman波谱也有所不同,其中用785 nm激光激发样品,荧光发光峰位于100～200 cm~(-1)范围,掩盖了晶片Raman特征峰.在对CdZnTe晶片做Raman测试时,尽可能选择较低功率.     

ACRT-Te溶剂法生长的ZnTe∶Cr晶体的光谱性能

采用改进的ACRT-Te溶剂法制备了ZnTe∶ Cr晶体,并对晶体的光谱特性进行了表征.紫外-可见-近红外透过光谱分析表明,晶体在800 nm和1790 nm处出现了与Cr2+有关的强吸收,并在570 ～ 750 nm范围内存在与Zn空位有关的吸收.低温光致发光(PL)谱分析表明,晶体在530 nm附近和595 ～ 630 nm之间出现近带边(NBE)发射和自激活(SA)发射.进一步分析表明,NBE发射由受主束缚激子(A1,X)峰、电子-受主对(e,A)峰和施主-受主对(DAP)发光峰组成.利用Arrhenius公式对变温PL谱上的NBE峰进行拟合,得出样品在低温(＜50 K)和高温(＞50 K)时的热猝灭激活能分别为3.87 meV和59.53 meV.红外荧光谱分析表明,ZnTe∶ Cr晶体的室温荧光发射带为2～2.6 μm,荧光寿命为1.0 ×10-6s.     

MOCVD法在(220)CaF2衬底上生长ZnO薄膜及其性能研究

采用金属有机化学汽相沉积(MOCVD)法在(220)CaF2衬底上外延生长ZnO薄膜.利用X射线衍射(XRD)、紫外-可见光谱和光致发光谱(PL)对ZnO薄膜的结构和光学性能进行了分析.XRD结果表明,所制备的ZnO薄膜结晶性能良好,具有高度的(002)的择优取向,002衍射峰的半高宽(FMHM)为0.115°.所制备的ZnO薄膜透明,透过率超过85;.在常温的(He-Cd激光器)PL谱中,只有378.5 nm的带边发射.用同步辐射光源测试的真空紫外光谱中,在低温20K时,出现218 nm、368 nm、418 nm、554 nm发光峰,其中368 nm峰强度随着温度的升高强度逐渐下降,到常温时几乎消失.     

Er:BaY_2F_8晶体中绿光发射的温度特性

利用温度梯度法生长了BaY2F8晶体和Er3+:BaY2F8晶体。测试了Er3+:BaY2F8晶体的室温吸收光谱以及从室温(299 K)到12 K的荧光光谱,分析了温度对Er3+:BaY2F8晶体发光强度的影响。结果表明,在375 nm泵浦光源的激发下,观察到峰值为520 nm和552 nm两种较强的绿光发射,随着温度的升高,520 nm发光峰逐渐增强而552 nm发光峰逐渐减弱;在温度为12 K时,对应于Er3+4I13/2→4I15/2的跃迁处(1.5μm附近)出现多个分立的发射峰,随着温度的升高,这些发光峰逐渐出现展宽并且峰位发生蓝移。最后利用多声子辅助跃迁以及多声子弛豫对于温度的依赖关系来解释上述现象。     

掺镨钒酸钆晶体的研究

生长了新型激光晶体Pr:GdVO4,经XRD分析可知生长的晶体与纯GdVO4晶体结构一致,晶体质量良好.室温下测试了晶体400～3000 nm范围内的吸收光谱.通过对吸收光谱研究,发现σ谱图中各吸收峰吸收强度更大,宜选择入射光传播方向和电矢量均垂直于光轴的方向进行激光实验.采用404 nm的激发源抽运Pr:GdVO4晶体,测试其荧光光谱,发现其在可见波段有宽且强荧光发射(604 nm、616 nm),对应于1D2→3H4.比较不同浓度晶体的荧光谱,荧光强度呈现如下趋势:0.5;>0.7;>0.32;.     

不同X射线管电压下CsI和CsI(Tl)晶体的X射线辐照致发光

在室温(290 K)和低温(25 K)下,测量了从11～40 kV的一系列管电压下X射线激发纯CsI和CsI (Tl)晶体的辐照致发光(RL)谱.结果表明:在固定温度下,管电压变化后, 305 nm和340 nm的本征发光带和580 nm的非本征发光带的形状结构均不发生变化,只是其强度发生变化.对所测得的各发光带强度随管电压的变化关系用抛物线模型进行了拟合分析,得到了较好的结果.同时还发现纯CsI和CsI (Tl)晶体中所有本征RL发光带强度与X射线强度基本上成正比关系,而当管电压增加时,CsI (Tl)晶体中非本征发光带强度的增加速度慢于本征发光带.分析认为,290 K时这可能与样品中另一个位于400 nm左右的发光带有关;而在25 K时则可能和H心与VK心的竞争有关.     

高温闪烁晶体Ce∶LSO的生长研究

Ce∶LSO晶体具有优良的闪烁性能,其主要特点是光产额大、发光衰减时间快、密度大、有效原子序数大、辐射长度短、发射峰与光电倍增管的接收范围相匹配,在γ射线探测方面有着广泛的应用.我们用提拉法生长了不同掺杂浓度的Ce∶LSO晶体,成功地解决了在生长过程中出现的晶体开裂及籽晶熔断问题,并对晶体生长过程中的表面重熔、晶体着色及Ce的偏析等现象作了讨论.荧光光谱分析表明晶体最大激发波长为353nm,发射峰由391nm和425nm处两个峰组成,吸收谱则显示晶体在209～370nm之间具有多个吸收峰.     

溶胶-凝胶法制备MgxZn1-xO及其特性

采用溶胶-凝胶法制备了不同组分(x=0.1～0.3)的MgxZn1-xO前驱体,并对它进行不同温度的热处理(550℃～1000℃).X射线衍射(XRD)结果表明,Mg0.1Zn0.9O具有和ZnO一样的衍射谱,为六方纤锌矿结构,而且随着热处理温度的升高,ZnO衍射峰的强度逐渐增强,半高宽不断减小;Mg元素掺杂浓度增大后,出现了MgO的峰位.扫描电子显微镜(SEM)显示Mg0.1Zn0.9O晶粒粒径分布较均匀;热处理温度升高,晶粒的尺寸不断变大.用室温荧光光谱(PL)分析了经过550～1000℃热处理获得的Mg0.1Zn0.9O粉末,结果发现除了550℃下处理的样品,其它都有紫外发射峰(350nm左右),而且随着热处理温度的升高紫外峰有明显的蓝移现象.     

高温闪烁晶体Ce∶YAP的生长研究

Ce∶YAP晶体具有优良的闪烁性能,其主要特点是光产额大,衰减时间短,发射峰与光电倍增管的接收范围相匹配,在γ射线探测、核医学等方面有着广阔的应用前景.我们用提拉法生长了不同掺杂浓度的Ce∶YAP晶体,成功地解决了在生长过程中出现的晶体开裂及孪晶问题,并对晶体生长过程中的爬料、纯YAP晶体着色等现象作了讨论.X射线激发发射谱表明晶体的发射峰在388nm,吸收测试则显示晶体在254nm、366nm处有两个吸收峰.     

Characterization of polycrystalline GaN grown on silica glass substrates

The structural, optical, and electrical properties of GaN films grown on silica glass substrate by metalorganic chemical vapor deposition were studied. X-ray diffraction showed that the films were grown in hexagonal structure with a predominant (0 0 0 2) peak. A broad and strong band-edge emission and very weak yellow luminescence in photoluminescence (PL) spectra were observed. And the temperature dependence of the PL spectra was extensively studied. The thermal quenching activation energy was found to be very close to the donor activation energy determined from the temperature dependence of the carrier concentration. Longitudinal optical phonons were found to be responsible for the PL broadening above 100 K.     

Thermal quenching of defect photoluminescence and recombination rates of electron–hole pairs in a-Si:H

Temperature variation of non-radiative recombination rate, competing with defect photoluminescence (PL), has been obtained from characteristic lifetimes estimated from experiments by means of frequency resolved spectroscopy (FRS) for a-Si:H films after illumination of pulsed light. Conventional interpretation of thermal quenching of the PL in a-Si:H, where the non-radiative recombination rate has an activation-type temperature dependence and the radiative recombination rate is independent of the temperature, is not suitable to explain the experimental results of the defect PL. The temperature variation of the non-radiative recombination rate obtained for the defect PL is well described by a theory of Englman and Jortner for the case of strong electron–phonon coupling.     

Temperature dependence of photoluminescence from ordered GaInP2 epitaxial layers

The temperature behavior of the integrated intensity of photoluminescence (PL) emission from ordered GaInP₂ epitaxial layer was measured at temperatures of 10 ‐ 300 K. Within this temperature range the PL emission is dominated by band‐to‐band radiative recombination. The PL intensity temperature dependence has two regions: at low temperatures it quenches rapidly as the temperature increases, and above 100 K it reduces slowly. This temperature behavior is compared with that of disordered GaInP₂ layer. The specter of the PL emission of the disordered layer has two peaks, which are identified as due to donor‐accepter (D‐A) and band‐to‐band recombination. The PL intensity quenching of these spectral bands is very different: With increasing temperature, the D‐A peak intensity remains almost unchanged at low temperatures and then decreases at a higher rate. The intensity of the band‐to‐band recombination peak decays gradually, having a higher rate at low temperatures than at higher temperatures. Comparing these temperature dependencies of these PL peaks of ordered and disordered alloys and the temperature behavior of their full width at half maximum (FWHM), we conclude that the different morphology of these alloys causes their different temperature behavior. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Infrared photoluminescence from TlGaS2 layered single crystals

Photolimuniscence (PL) spectra of TlGaS₂ layered crystals were studied in the wavelength region 500‐1400 nm and in the temperature range 15‐115 K. We observed three broad bands centered at 568 nm (A‐band), 718 nm (B‐band) and 1102 nm (C‐band) in the PL spectrum. The observed bands have half‐widths of 0.221, 0.258 and 0.067 eV for A‐, B‐, and C‐bands, respectively. The increase of the emission band half‐width, the blue shift of the emission band peak energy and the quenching of the PL with increasing temperature are explained using the configuration coordinate model. We have also studied the variations of emission band intensity versus excitation laser intensity in the range from 0.4 to 19.5 W cm^‐2. The proposed energy‐level diagram allows us to interpret the recombination processes in TlGaS₂ crystals. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Temperature quenching of photoluminescence of ordered GaInP2 alloy under different excitation densities

The photoluminescence (PL) emission from an epi‐structure containing an atomically ordered GaInP₂ layer and a GaAs layer was studied under excitation power densities of 0.03 – 3 W/cm²at temperatures of 10 to 300 K. The quenching of the integrated PL intensity from both: the GaInP₂and the GaAs layers is stronger under low excitation, than under high excitation density. The temperature dependence, however, have different shapes being the PL decay observed for the GaInP₂ layer stronger than that for the GaAs layer. Comparing the temperature dependence of the PL intensity from the ordered GaInP₂ and the GaAs layers under different excitation densities and analyzing them together, we conclude that the inhomogeneity of the ordered layer is responsible for the different temperature behavior of the GaInP₂ alloy PL emission. To explain the experimentally observed PL intensity temperature dependence an additional nonradiative recombination mechanism due to a thermally activated escape of the carriers from its confinement within regions of lower bandgap has to be taken into account. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

CdZnTe晶体位错处的Raman光谱及PL谱研究

利用显微Raman光谱技术,对比研究了CdZnTe晶体无位错区和位锘密集区的Raman光谱.研究发现,CdZnTe晶体无位错区的Raman光谱出现了与Te有关的A1模(119 cm-1)、类CdTe的TO1模(138 cm-1)和类ZnTe 的TO2模(179 cm-1);CdZnTe晶体位错密集区的Raman光谱中仅出现了与Te有关的A1模和类CdTe的TO1模,CdZnTe晶体类ZnTe的TO2模消失.对CdZnTe试样位错密集区进行变温光致发光谱测试,结果表明,束缚在中性施主上的激子的离解为电子空穴对,电子空穴的非辐射复合过程吸收了类ZnTe的TO2模声子能量,造成Raman 光谱中类ZnTe的TO2模缺失.     

Anomalous temperature-dependent photoluminescence characteristic of as-grown GaInNAs/GaAs quantum well grown by solid source molecular beam epitaxy

The photoluminescence (PL) mechanisms of as-grown GaInNAs/GaAs quantum well were investigated by temperature-dependent PL measurements. An anomalous two-segmented trend in the PL peak energy vs. temperature curve was observed, which has higher and lower temperature-dependent characteristics at low temperature (5–80 K) and high temperature (above 80 K), respectively. The low and high-temperature segments were fitted with two separate Varshni fitting curves, namely Fit_low and Fit_high, respectively, as the low-temperature PL mechanism is dominated by localized PL transitions while the high-temperature PL mechanism is dominated by the e1–hh1 PL transition. Further investigation of the PL efficiency vs. 1/kT relationship suggests that the main localized state is located at 34 meV below the e1 state. It is also found that the temperature (80 K) at which the PL full-width at half-maximum changes from linear trend to almost constant trend correlates well with the temperature at which the PL peak energy vs. temperature curve changes from Fit_low to Fit_high.     

Observation of a new photoluminescence band at 320 nm under 270 nm excitation in Ge-doped silica glass

We investigate the influence of temperature on photoluminescence (PL) in Ge-doped silica glass. Under 270 nm excitation, we observe only one PL band at 424 nm at room temperature (RT). This band shifts to 436 nm with cooling (4 K), and a new PL band is recorded at 320 nm. We assign these PL bands to triplet-to-singlet and singlet-to-singlet transitions of a same Ge-related defect, whose structure is still unknown. The shift of the PL band (from 424 nm at RT to 436 nm at 4 K) is explained by the decrease of the overlap between PLs from different centers.     

Low-temperature Er3+ emission in Ge–S–Ga glasses excited by host absorption

The photoluminescence (PL) of a series of (GeS₂)₈₀(Ga₂S₃)₂₀ glasses doped with different amounts of Er (0.17, 0.35, 0.52, 1.05 and 1.39 at.%) at 77 and 4.2 K has been studied. The influence of the temperature on the emission cross-section of the PL bands at ∼1540, 980 and 820 nm under host excitation has been defined. A quenching effect of the host photoluminescence has been established from the compositional dependence of the PL intensity. It has been found that the present Er³⁺-doped Ge–S–Ga glasses posses PL lifetime values about 3.25 ms.     

碱金属掺杂ZnO薄膜发光性能研究

采用固相反应法制备了不同比例的碱金属掺杂ZnO靶材,并利用磁控溅射法在Si(111)基片上制备不同温度下生长的c轴择优取向ZnO薄膜.通过XRD、AFM和荧光光谱(PL谱)研究了掺杂元素和掺杂比例对薄膜结构和发光特性的影响.结果表明,掺杂未改变ZnO的结构,薄膜具有很好的c轴择优取向.室温下用325 nm的氙灯作为激发光源得到不同样品的 PL 谱,分析表明,紫外发光峰来源于自由激子的复合辐射与带间跃迁,蓝绿发光峰与锌缺陷和氧缺陷有关.此外还探讨了紫外发光峰红移的可能机理.