SiC衬底上异质外延GaN薄膜XPS谱和PL谱研究

利用X射线光电子能谱,对在SiC衬底上采用MOCVD异质外延的未故意掺杂的GaN进行N、Ga组份测试,同时用光致发光技术对样品进行发光特性的研究.结果表明,随着GaN薄膜中Ga百分含量逐渐减小,室温下黄光输出峰值强度却逐渐增加.因此,在Ga含量相对低的GaN薄膜中容易形成Ga空位(即Ga空位浓度较高),而此时,黄光辐射强度单调递增证明,黄光辐射与VGa密切相关.     

激光二极管抽运共轴双晶体黄光激光器

提出一种全新的单抽运源、共轴双晶体实现黄光激光的方法,并对其进行了理论分析和实验研究.利用该方法在抽运功率为1.5 W时,获得了54 mW的黄光激光输出,激光不稳定度为5%,光-光转换率为3.6%,而利用对1064 nm损耗的方法在相同条件下只获得15 mW的黄光输出. 该方法结构简单、灵活多样,可以应用到很多弱增益谱线与强增益谱线和频的结构当中,实现诸如491,488,593.5,555和500.8 nm的激光输出. 关键词： 黄光激光器 单抽运源 双晶体 和频     

高功率准连续波腔内和频全固态黄光激光器

报道了高功率准连续波腔内和频全固态黄光激光器的研究结果.为获得高功率的黄光输出,首先,激光器采用准连续方式运转,在保持抽运水平的条件下降低热效应,从而提高光束质量和光光转换效率;第二,采用热近非稳腔腔型设计,双棒串接补偿热致双折射技术,获得大基模体积高光束质量的基频光;第三,通过优化腔型,采用L型共折叠臂平-凹对称腔,使两束基频光达到空间重合且满足功率配比.通过这些方法,得到了输出功率7.6W,重复频率1.1kHz的准连续波黄光输出.据我们所知,这是目前腔内和频方案所获得的最高功率全固态黄光输出. 关键词： 黄光激光 腔内和频 Nd：YAG激光 全固态激光器     

LD抽运Nd:YVO4/KTP复合腔和频黄光激光器

在LD抽运的三镜复合腔Nd:YVO4激光器中,采用Ⅱ类临界相位匹配的KTP晶体对1064 nm和1342 nm两种波长激光进行和频,获得593 nm黄光连续输出.理论上从速率方程出发,导出1064 nm激光谐振腔和1342 nm激光谐振腔腔长之间的关系以及两个腔的腔镜透过率之间的关系.实验中,当808 nm抽运光的功率为12 W时,和频输出的黄光功率为340 Mw.光-光转换效率为2.8%.结果表明,采用三镜复合腔结构进行腔内和频是实现593 nm黄光输出的一种有效方法.     

V型腔腔内和频产生3 W连续波589 nm黄光激光器

报道了双Nd：YAG棒串接V型折叠腔腔内KTP和频全固态黄光激光器，得到了3 W连续波589 nm黄光输出.为了提高黄光输出功率，采用了两种手段：一是通过优化腔型设计使得两束基频在腔内达到了最佳的空间重合，二是通过选择合适大小的二极管激光器的抽运功率使得两束基频在腔内达到了最佳的功率配比. 关键词： 全固态激光器 Nd：YAG激光器 黄光 腔内和频     

基于扭转模腔的全固态单纵模拉曼黄光激光器设计

输出波长在560~590nm的全固态拉曼黄光激光器是近几年兴起的激光器之一。目前,此类激光器内部多模振荡引起的黄光输出谱线单色性较差的问题还没有得到解决。针对这一情况,提出将扭转模腔与拉曼复合腔相结合的新型解决方案,从根本上消除增益介质中空间烧孔效应引起的基频光多模振荡,实现单纵模黄光输出。拉曼复合腔由L型基频光谐振腔与直线型拉曼谐振腔耦合而成,既保证各个非线性变换过程可充分利用腔内的高功率密度,又可相对独立地对不同波长的光路进行优化调节,从而使整个系统实现最佳输出。该设计有助于在全固态拉曼激光器中实现毫瓦量级的单纵模黄光输出,为基于黄激光的生物医疗、钠导星、空间目标识别等系统提供理想的固体黄光光源。     

氮化蓝宝石衬底上GaN薄膜的微结构与光学性质

用透射电子显微镜(TEM),X射线衍射(XRD)和光荧光谱(PL)等测量手段研究了GaN薄膜的微结构和光学性质。样品是用光辐射加热MOCVD在蓝宝石衬底上制备的。随着衬底氮化时间的增加,扩展缺陷的密度显著增加。在位错密度增加一个数量级时,XRD摇摆曲线半宽度(FWHM)由11″增加到15″,PL谱的黄光发射从几乎可忽略增加到带边发射强度的100倍。结合生长条件,我们对黄光与微结构的关系作了讨论。     

激光二极管抽运Nd∶YVO_4和频黄光激光器的理论及实验研究

为了达到最佳和频593nm黄色激光输出,采用激光二极管(LD)端面抽运Nd∶YVO4晶体,根据四能级系统的速率方程理论,建立了空间相关的两波长激光运转速率方程模型,由此导出两波光子数表达式。对LD端面抽运Nd∶YVO4/KTP三镜复合腔结构的腔内和频黄光激光器,在满足参与和频的两基频光光子数密度相等的条件下,理论上得到了谐振腔的各个参数。实验比较了在满足两波光子数密度相等和两波振荡阈值相等两种情况下激光器输出的593nm黄色激光功率。在抽运功率为12W时,二种情况下分别得到了410mW和340mW的黄光输出,光-光转换效率分别为3.4%和2.8%。由此可见,在满足两波光子数密度相等的条件下可以得到更高转换效率的和频黄光输出。     

激光二极管抽运Nd:YV04和频黄光激光器的理论及实验研究

为了达到最佳和频593 nm黄色激光输出,采用激光二极管(LD)端面抽运Nd:YVO4晶体,根据四能级系统的速率方程理论,建立了空间相关的两波长激光运转速率方程模型,由此导出两波光子数表达式.对LD端面抽运Nd:YVO4/KTP三镜复合腔结构的腔内和频黄光激光器,在满足参与和频的两基频光光子数密度相等的条件下,理论上得到了谐振腔的各个参数.实验比较了在满足两波光子数密度相等和两波振荡阈值相等两种情况下激光器输出的593 nm黄色激光功率.在抽运功率为12 W时,二种情况下分别得到了410 mW和340 mW的黄光输出,光一光转换效率分别为3.4%和2.8%.由此可见,在满足两波光子数密度相等的条件下可以得到更高转换效率的和频黄光输出.     

对撞脉冲锁模环形染料激光器的运转特性(英文)

研究了用DODCI和DQOCI染料作为可饱和吸收体的对撞脉冲锁模环形染料激光器的运转特性。提供锁模脉冲宽度、激光器以稳定单脉冲工作的稳定性范围和阈值泵浦功率等,对吸收体染料浓度依赖关系的测试结果。表明了用此激光器,在低的泵浦功率(约2W)下,日常能产生脉宽为0.12ps、峰值功率为1kW的稳定脉冲。给出用光谱分辨的二次谐波自相关法测量输出脉冲的结果,证实在锁模脉冲中已发生频率调制。实验中发现用DQOCI染料作为可饱和吸收体时,激光输出光谱由黄光和红光两个分立部分构成。当黄光的振荡被抑制时,锁模稳定性改善且输出脉冲形状整齐、前后沿包含很小的能量。     

Hydrogen passivation effect on the yellow-green emission band and bound exciton in n - ZnO

Photoluminescence (PL) measurements performed on as-grown, hydrogenated, and annealed n-type ZnO bulk samples investigated the origins of their yellow (2.10 eV) and green (2.43 eV) emission bands. After hydrogenation, the defect-related peak at 2.10 eV was no longer present in the room temperature PL spectrum, the peak intensity at 2.43 eV was unchanged, and the intensity of the emission peak at 3.27 eV increased significantly. These results indicate that yellow band emission is due to oxygen vacancies, as the emission peak at 2.10 eV disappears when hydrogen atoms passivate these vacancies. The emission peak at 2.43 eV originates from complexes between oxygen vacancies and other crystal defects. We discuss the shallow donor impurities arising due to these hydrogen atoms in the ZnO bulk sample.     

The I.R. photoluminescence emission band in ZnO

Measurements of emission spectra, excitation spectra, intensity dependence of the luminescence, decay of the luminescence, and temperature dependence of the luminescence in ZnO are reported. The results for the emission at 1·70 eV, with the exception of the decay of the luminescence, were found to be similar to those of the yellow (2·02 eV) emission band in ZnO. Both bands could be excited at the band edge and directly, the intensity of both bands was found to be linear with excitation strength and the asymptotic regions of the temperature dependence of both bands could be approximated by exponential functions. It is proposed that the luminescent transition is an electron transition from the edge of the conduction band to a hole trapped in the bulk at 1·60 eV above the edge of the valence band, and that the luminescence center is an unassociated acceptor-like center.     

Investigation of crystal/electronic structure effects on the photoluminescence properties in the BaO–SiO2:Eu2+ systems

BaO–SiO₂:Eu²⁺ phosphors with different Ba/Si mole ratio were prepared using a solid-state reaction method, and their crystal structure dependent-photoluminescence properties were investigated. The prepared phosphor powders were characterized using X-ray diffraction (XRD), field-emission electron microscopy (FE-SEM) and fluorescence spectroscopy. The emission band of the Eu²⁺ activator varied from orange to blue with varying crystal structure of the host materials, which was related to the crystal field splitting of the Eu 5d orbitals. These emission color changes were examined by calculating the electronic band structure properties such as the density of the state. Moreover, the host material with Ba/Si=1 (BaSiO₃) for Eu²⁺, which exhibited a yellow emission when excited with near UV light, was further characterized for enhancing its emission intensity.     

Electroluminescence of an n-ZnO/p-GaN Heterojunction under Forward and Reverse Biases

Electroluminescent characteristics of n-ZnO/p-GaN heterojunctions under forward and reverse biases are studied. Emissions at 389nm and 57Ohm are observed under forward bias. An unusual emission at 390ram appears under reverse bias, and is attributed to the recombination in the p-GaN side of the heterojunction. The yellow emission peaked at 57Ohm is suppressed under reverse bias. The light intensity exponentially depends on the reverse current. The emission under reverse bias is correlated to tunnelling carrier transport in the heterostructure. Our results also support that the well-known yellow band of GaN comes from the transitions between some near-conduction-band-edge states and deep localized acceptor states.     

Transient gain in photonic crystals

Using the optical response formula for photonic crystals and the Bloch equations, we analyze coherent emission in arbitrary two-dimensional photonic crystals. The transient emission depends not only on the photon density of the states, but also on the intensity and duration of the pump laser pulses. A transient gain exists if the pump pulse area is a certain value and the transition frequency is tuned to the band edge. The sharp structure of the density of states near the band edge leads to a dramatic enhancement of the transient emission intensity and an abrupt change in the oscillation of the emission field. PACS 42.70.Qs; 32.80.-t; 42.25.Bs     

Cd3Al2Ge3O12:Mn2+锗酸盐石榴石光谱性质

本文报道室温下Cd₃Al₂Ge₃O₁₂:Mn²⁺(简称CAGG:Mn²⁺)锗酸盐石榴石的漫反射光谱、激发和发射光谱.在UV光激发下,在CAGG中Mn²⁺离子发射强黄光,这是基质到Mn²⁺离子无辐射能量传递的结果.Mn²⁺的黄发射带是由一个弱的红带和一个强的绿带所组成.讨论了这两个Mn²⁺发射带的起因.     

Bound-to-bound and bound-to-free yellow emission of ion-implanted zinc telluride

Broad structureless emission bands centred near 580 nm have been observed in the low temperature cathodoluminescence emission spectra of zinc telluride single crystals implanted with zinc, argon or aluminum ions. Time-resolved spectroscopy measurements and measurements of the emission intensities as a function of sample temperature and of temperature of post-implantation isochronal annealing show that one yellow band occurs in both ZnTe : Zn and ZnTe : Ar and results from bound-to-free recombination involving an intrinsic donor level, probably due to a V_Te defect. In addition, there is a second yellow band present in ZnTe : A1 which is due to donor-acceptor pair recombination with the donors and acceptors identified with Al_Zn and V_ZnAl_Zn respectively.     

LiAl_5O_8∶Fe~(3+)发光粉的发光性能(英文)

Fe3+激活的铝酸锂是深红色发射的红色荧光粉,其发射的峰值波长为675nm,呈现出少有的纯正的深红色发光。本文对LiAl5O8:Fe3+荧光粉的基质组成和激活剂浓度进行了研究。结果表明:Fe3+掺杂LiAl5O8的激发光谱,在λem=673nm的波长监测下,有序相的激发光谱在284nm处有强吸收带,为Fe3+-O2-电荷迁移带;激发波长λex=254nm的有序相样品的发射波长峰值为673nm,并伴随一个在长波方向轻微不对称得,发射是属于4T1(4G)-6A1(6S)的跃迁。当原料Li2CO3与Al2O3的量的比为0.21时,样品的发光强度最好;样品的发光强度随激活剂Fe3+的浓度的增加而提高,当浓度达到0.5%时,发光强度达到最大值,超过0.5%时呈现出浓度猝灭效应。     

CL study of yellow emission in ZnO nanostructures annealed in Ar and O2 atmospheres

The yellow emission of thermally treated undoped and In doped ZnO nanostructures was studied by the cathodoluminescence (CL) technique. CL spectra acquired at room temperature of the as-grown samples revealed two emissions at about 3.2 eV and 2.13 eV, corresponding to the near band edge and defect related emissions, respectively. On annealing the samples at 600  ^°C in Ar and O₂ atmospheres, the defect emission suffers a red shift, irrespective of the annealing atmosphere. This red shift is explained in terms of variations in the relative intensities of the two component bands centered at about 2.24 eV and 1.77 eV, which were clearly resolved in the CL spectra acquired at low temperature of the annealed samples. A decrease of the relative intensity of the yellow emission (2.24 eV) was observed for all thermally annealed samples. The annealing of zinc interstitial point defects is proposed as a possible mechanism to explain this intensity decrease.     

Temperature dependence of photoluminescence property in BaIn2O4

The temperature-dependent photoluminescence(PL) spectra of BaIn2O4,prepared by coprecipitation,are measured and discussed.Aside from the reported 3.02-eV violet emission,the 1.81-eV yellow emission involved with oxygen vacancy is also observed at room temperature wherein the deep donor level is at 1.2 eV.With the temperature increasing,the peak energies for both emissions show a red shift.Moreover,the yellow emission intensity decreases while the violet emission intensity increases.The temperature dependence of the yellow emission intensity fits very well into the one-step quenching process equation,indicating a fitted activation energy at 19.2 meV.