Effect of surface modification by thermally oxidization and HF etching on UV photoluminescence emission of porous silicon

Photoluminescence of porous silicon (PS) is instable due perhaps to the nanostructure modification in air. The controllable structure modification processes on the as-prepared PS were conducted by thermal oxidization and/or HF etching. The PL spectra taken from thermally oxidized PS showed a stable photoluminescence emission of 355 nm. The photoluminescence emission taken from both of PS and oxidized porous silicon (OPS) samples etched with HF were instable, which can be reversibly recovered by the HF etching procedure. The mechanism of UV photoluminescence is discussed and attributed to the transformation of luminescence centers from oxygen deficient defects to the oxygen excess defects in the thermal oxidized PS sample and surface absorbed silanol groups on PS samples during the chemical etched procedure.     

InP中和C带有关深能级的近红外光致发光

本文用红外光致发光方法研究了InP中与C带有关的深能级的性质和起源。峰值位于价带上0.34eV(77K)附近的宽谱带普遍存在于不同方式生长的InP外延层和掺Sn与不掺杂的衬底中,且与P空位引起的复合缺陷有关。 通过红外光致发光强度对温度的依赖关系得到C带的热激活能为0.17eV。这刚好与采用σ函数来描述深能级的Locovsky模型相吻合,光谱线型与温度猝灭的量子力学位形坐标模型拟合,得到与C带有关的深能级hv=0.02eV,S=8。     

Photophysical processes stimulated in nanoporous silicon by high-power laser radiation

Photoprocesses initiated on the surface of porous silicon irradiated with laser radiation with wavelengths (λ = 266, 337, and 532 nm) in a wide range of intensities (up to 2 × 10⁷W/cm²) were investigated. Laser-induced luminescence and laser mass-spectrometry were used as experimental procedures. X-ray reflection was used to determine the parameters of the porous silicon films. The photoluminescence spectra obtained at different wavelengths and low intensities were analyzed. This analysis showed that for an optically thin layer of porous silicon the luminescence spectrum does not depend on the wavelength of the exciting radiation. This indicates the existence of a separate system of levels in porous silicon that are responsible for the luminescence. The behavior of the photoluminescence spectra as a function of the intensity q of the exciting radiation was investigated. It was shown that the luminescence intensity is a nonlinear function of q. At high intensities of the exciting radiation, the luminescence intensity saturates and a short-wavelength shift of the spectra is observed; this is due to the high concentrations of photoexcited carriers. This increases the probability of the experimentally observed nonequilibrium photodesorption of H₂ and Si from the surface of porous silicon.     

Stable blue-green and ul traviolet photoluminescence from silicon carbide on porous silicon

β-Silicon carbide layers have been prepared by high temperature pyrolysis of polyimide Langmuir-Blodgett films on porous silicon substrate in vacuum. The formation of silicon carbide is confirmed by the IR and XRD spectra. It is found that photoluminescence still exists and appears in the blue-green and ultraviolet regions after thermal treatment at 900°C. These results indicate that the silicon carbide layers, which are formed, are responsible for the blue-green luminescence.     

Optical properties of zinc telluride with cadmium telluride submonolayers

Reflection, luminescence, and Raman spectra of epitaxial ZnTe layers nominally incorporating double CdTe submonolayers were studied. The band of an exciton localized at the potential produced by narrow-gap planar inclusions dominated the luminescence of these heterostructures. The emission parameters of localized excitons (specifically, the ratio of integral emission intensity to localization energy) were determined, and it was found that excitons interact with longitudinal optical phonons of the layer enriched with cadmium. Giant amplification of the Stokes component resonant with the localized exciton level was observed in Raman scattering.     

Pulsed electroluminescence in silicon nanocrystals-based devices fabricated by PECVD

Fully compatible CMOS capacitive devices have been developed in order to obtain electrically stimulated luminescence. By high-temperature annealing in N₂ atmosphere PECVD non-stoichiometric silica layers, silicon nanocrystals were formed. Photoluminescence, as well as structural studies, were carried out on these layers to decide the best material composition, which lies next to 17% of silicon excess. Under pulsed electrical stimulation, devices show sharp, narrow, less than 5 μs and pulse-frequency-independent, luminescence peaks at the end of the stimulation pulse. Current analysis on those capacities show hole injection at the beginning and electron injection at the end of the stimulation pulses. It is seen that no positive pulses are needed for attaining bipolar charge injection. Electroluminescence is detected when biasing with negative pulses at about 15 V and increasing up to 50 V. The electroluminescence spectrum matches photoluminescence one, allowing assigning both luminescent radiation to the same emission mechanism, that is, electron–hole recombination within the silicon nanocrystals.     

Experimental study and interpretation of the emission band situated at 1.65 eV in cinnabar

In this paper we analyse the cathodoluminescence of cinnabar powder which emission appears as a broad band peaked at 1.65 eV at liquid helium temperature.In a previous paper we showed by kinetics measurements that this luminescence was due to a donor-acceptor pair emission mechanism.However the donor-acceptor model was not sufficient to explain the Gaussian shape of the emission band as well as its important width.We show here the influence of a strong phonon coupling by measurements in terms of temperature. Application of both donor-acceptor and vibronic models allows us to interpret this luminescence satisfactorily. We calculate the fundamental parameters of the emission (Bohr half-radius R_B, maximum radiative probability W_MAX, emission energy of the pairs at infinite separation hv_∞).At the end a deconvolution method which takes into account the vibronic influence permits us to calculate the time-resolved spectra and to compare them with the experimental ones.     

Photoluminescence from gold centre in silicon

A sharp line structure attributable to ?honon assisted radiative emission has been observed in the low temperature photoluminescence spectra from deep centres in bulk samples of gold-doped silicon. The entire luminescence band which peaks near 0.78 eV is attributed to transitions of conduction electrons towards the gold-related donor level.     

自受激拉曼晶体Nd3+:SrMoO4的光谱性质研究

通过拉曼散射光谱，吸收光谱，荧光发射寿命和808 nm LD激发下的红外荧光光谱的实验测量，系统研究了Nd³⁺:SrMoO₄晶体的自受激拉曼光谱性质.分析指认了拉曼散射光谱中各拉曼峰所对应的晶格振动模式，得出了其SRS活性最强的声子频率约为898 cm^-1，对应于(MoO^2-₄)离子团的完全对称光学伸缩振动A_g模；通过J-O理论对晶体的吸收谱进行了全面的光谱参数计算，得出⁴F_3/2→⁴I_11/2跃迁的积分发射截面达0.57×10^-18 cm²，自发辐射概率为141.06 s^-1；同时，实验测得该跃迁的荧光发射寿命约为0.2 ms.最后，结合808 nm LD激发下的红外波段荧光光谱，论证了SrMoO₄晶体中Nd³⁺离子1068 nm发射通过拉曼频移获得1180 nm一级斯托克斯激光发射的可能性，为Nd³⁺:SrMoO₄晶体的自受激拉曼激光器研究提供了理论依据. 关键词： 3+离子')" href="#">d³⁺离子 4 晶体')" href="#">SrMoO₄ 晶体 自受激拉曼散射     

Carrier localization effect on luminescence spectra of III-V heterostructures

A steady-state rate-equation model for temperature-dependent luminescence spectra from localized-state material system is presented. The effects of thermal emission, recapturing, radiative and nonradiative recombination are taken into account in the model. Two localized-state material systems, including InAs/GaAs quantum-dot and InGaN/GaN-multi-quantum-well samples were prepared. It is found that the temperature-dependent behaviors of luminescence emission energy obtained from the two samples are quite different. In the mid-temperature range, the emission peaks exhibit a redshift for quantum-dot sample, but a blueshift for multi-quantum-well sample. The peak energies of the luminescence spectra are simulated in this model and show a good agreement with experiment. The corresponding luminescence mechanisms of carriers in localized-state material systems, which lead to the diversity are quantitatively discussed in detail by the model.     

Localization of exciton excitation in planar structures Cd0.9Mn0.1Te/Cd0.7Mg0.3Te

The spectra of exciton emission in a series of periodic structures with ultrathin Cd_0.9Mn_0.1Te inclusions in the Cd_0.7Mg_0.3Te matrix have been studied. The complex structure of the luminescence spectra and their relation to the luminescence excitation spectra indicate large-scale fluctuations in thickness of narrow-band-gap layers. Two types of temperature dependences of the luminescence intensity of localized excitons are found: (1) the complete suppression of emission above 80 K and (2) the relative enhancement of temperature-insensitive low-energy band that corresponds to local bulges in planar Cd_0.9Mn_0.1Te layers.     

Effect of photonic bandgap on luminescence from silicon nanocrystals

The modification of the luminescence of silicon nanocrystals experiencing the effect of a photonic bandgap in a 2D photonic crystal was investigated. The time-integrated photoluminescence spectra detected in the plane of the photonic crystal revealed a dip in the light emission corresponding to the wavelength of the bandgap, whose position changes according to the geometry of the prepatterned pillar array. The calculated emission pattern for a pointlike dipole placed in such a structure suggests an inhibition of the spontaneous emission rate at certain directions as a physical reason for the observed modification of luminescence.     

Full-profile fitting of emission spectrum to determine transition intensity parameters of Yb~(3+):GdTaO_4

The Judd-Ofelt theoretic transition intensity parameters A_(tp)~k of luminescence of rare-earth ions in solids are important for the quantitative analysis of luminescence.It is very difficult to determine them with emission or absorption spectra for a long time.A "full profile fitting" method to obtain A_(tp)~k in solids with its emission spectrum is proposed,in which the contribution of a radiative transition to the emission spectrum is expressed as the product of transition probability,line profile function,instrument measurement constant and transition center frequency or wavelength,and the whole experimental emission spectrum is the sum of all transitions.In this way,the emission spectrum is expressed as a function with the independent variables intensity parameters A_(tp)~k,full width at half maximum(FWHM) of profile functions,instrument measurement constant,wavelength,and the Huang-Rhys factor S if the lattice vibronic peaks in the emission spectrum should be considered.The ratios of the experimental to the calculated energy lifetimes are incorporated into the fitting function to remove the arbitrariness during fitting A_(tp)~k and other parameters.Employing this method obviates measurement of the absolute emission spectrum intensity.It also eliminates dependence upon the number of emission transition peaks.Every experiment point in emission spectra,which usually have at least hundreds of data points,is the function with variables A_(tp)~k and other parameters,so it is usually viable to determine A_(tp)~k and other parameters using a large number of experimental values.We applied this method to determine twenty-five A_(tp)~k of Yb~(3+) in GdTaO_4.The calculated and experiment energy lifetimes,experimental and calculated emission spectrum are very consistent,indicating that it is viable to obtain the transition intensity parameters of rare-earth ions in solids by a full profile fitting to the ions' emission spectrum.The calculated emission cross sections of Yb~(3+):GdTaO_4 also indicate that the F-L formula gives larger values in the wavelength range with reabsorption.     

On the mechanism of luminescence of silicon nanostructures

A new model of porous-silicon (PS) luminescence based on hot-electron generation in silicon nanoparticles is proposed. This mechanism was used earlier for interpretation of light emission in island metal films (IMF). This paper offers a theoretical analysis of possible mechanisms capable of producing light emission in hot-electron collisions with a surface. Experimental data are presented in support of the applicability of this model to PS and silicon nanoparticles (the existence of electron emission in semiconductor structures and the correlation between the electron emission current and the luminescence intensity).     

Electron-excited luminescence of SiO2 layers on silicon

An analysis of cathodoluminescence and electroluminescence spectra of Si-SiO₂ structures suggests a conclusion concerning the processes involved in excitation of the luminescence centers generated in the UV spectral region and their localization. The electroluminescence observed in this region of the spectrum is generated in excitation of luminescence centers localized in the immediate vicinity of the Si-SiO₂ phase boundary. In the case of cathodoluminescence, the observed emission bands at ??4.3 and ??2.7 eV appear in excitation of the luminescence of silylene centers at the Si-SiO₂ phase boundary.     

纳米ZnO镶嵌SiO2薄膜的磁控溅射制备和发光性质的研究

采用射频磁控反应溅射方法在SiO衬底上制备了纳米ZnO镶嵌SiO2薄膜.在室温下利用吸收光谱和光致发光光谱研究了样品的光学性质.发现吸收光谱随纳米ZnO尺寸的减小发生了明显的蓝移,表明随着ZnO尺寸的减小,量子尺寸效应增强,导致带隙展宽,吸收峰蓝移.光致发光光谱在387和441 nm附近出现了两个发光带,分析认为紫外发光来源于自由激子的辐射复合,而蓝色发光带来自于氧空位的电子到价带的跃迁,并用时间分辨光谱和发光衰减证实了上述观点.     

多孔硅发光与量子尺寸效应的实验研究

利用电化学阳极腐蚀的方法制备了多孔硅膜,实验发现多孔硅膜为多层结构,表面层为纳米结构,其余为微米结构,多孔硅的物理及化学结构的研究表明多孔硅是一种表面上含硅、氧、氢、氟元素组成的化合物包覆着的纳米晶硅粒和微米硅丝.多孔硅的发光主要来自表面纳米结构层,亚微米结构层并未见发光,从实验上证实了多孔硅的发光与量子尺寸效应紧密关联.     

Effect of pore structure parameters of porous glass on luminescence properties of Eu/Dy co-doped high silica luminescence glass

The Eu²⁺/Dy³⁺ co-doped high silica luminescence glasses were prepared through sintering porous glasses which have adsorbed rare earth ions previously and the effect of pore structure parameters including average pore size, specific surface area, and pore volume on luminescence properties of high silica glass were analyzed by utilizing BET method and emission spectra. The results show that the pore parameters of porous glasses do not affect the shapes of emission spectra but affect the luminescence intensities of high silica glasses. The luminescence intensities of high silica glass increase when the specific surface area of porous glasses increases, which can be interpreted by mechanism of adsorption of rare earth ions onto porous glass. The average pore size and pore volume indirectly affect the luminescence intensities through influencing specific surface area of porous glass.     

Blue electroluminescence nanodevice prototype based on vertical ZnO nanowire/polymer film on silicon substrate

We present a polymer-complexing soft template technique to construct the ZnO-nanowire/polymer light emitting device prototype that exhibits blue electrically driven emission with a relatively low-threshold voltage at room temperature in ambient atmosphere, and the ZnO-nanowire-based LED’s emission wavelength is easily tuned by controlling the applied-excitation voltage. The nearly vertically aligned ZnO-nanowires with polymer film were used as emissive layers in the devices. The method uses polymer as binder in the LED device and dispersion medium in the luminescence layer, which stabilizes the quasi-arrays of ZnO nanowires embedding in a thin polymer film on silicon substrate and passivates the surface of ZnO nanocrystals, to prevent the quenching of luminescence. Additionally, the measurements of electrical properties showed that ZnO-nanowire/polymer film could significantly improve the conductivity of the film, which could be attributed to an increase in both Hall mobility and carrier concentration. The results indicated that the novel technique is a low-cost process for ZnO-based UV or blue light emission and reduces the requirement for achieving robust p-doping of ZnO film. It suggests that such ZnO-nanowire/polymer-based LEDs will be suitable for the electro-optical application.     

Electroluminescence from Si quantum dots/SiO2 multilayers with ultrathin oxide layers due to bipolar injection

Si quantum dots/SiO₂ multilayers with ultrathin oxide layers (2.4 nm) were fabricated on a p-type Si substrate in order to enhance the hole injection. Besides the luminescence band at 900 nm which was also shown in photoluminescence spectra, another strong luminescence band near the infrared region (1200 nm) can be observed in electroluminescence spectra. It can be assigned to the band-edge emission from the quasi 2-dimensional potential well in the Si substrate. Moreover, it is interesting to find the reduction of photoluminescence intensity under biased conditions which can be attributed to the occurrence of non-radiative Auger recombination process in charged Si quantum dots.