Tunable photoluminescence of porous silicon by liquid crystal infiltration

The photoluminescence (PL) of porous silicon films has been investigated as a function of the amount of liquid crystal molecules that are infiltrated into the constricted geometry of the porous silicon films. A typical nematic liquid crystal 4-pentyl-4′-cyanobiphenyl was employed in our experiment as the filler to modify the PL of porous silicon. It is found that the originally red PL of porous silicon films can be tuned to blue by simply adjusting the amount of liquid crystal molecules in the microchannels of the porous films. The chromaticity coordinates are calculated for the recorded PL spectra. The mechanism of the tunable PL is discussed. Our results have demonstrated that the luminescent properties of porous silicon films can be efficiently tuned by liquid crystal infiltration.     

Comparative investigation of photoluminescence of silicon wire structures and silicon oxide films

Photoluminescence spectra and their dependence on temperature as well as Raman scattering spectra and Atomic Force Microscopy investigations have been used to study the peculiarities of the red photoluminescence band in low-dimensional Si structures, such as porous silicon and silicon oxide films. It has been shown that the red photoluminescence band of porous silicon is complex and can be decomposed into two elementary bands. It was discovered that elementary band intensities depend very much on surface morphology of porous silicon. The same positions of the photoluminescence bands are also observed in silicon oxide films for different oxide composition. Comparative investigation of the PL temperature dependences in porous silicon and silicon oxide films indicates that silicon-oxide defect related mechanisms of some elementary photoluminescence bands are involved.     

Radiation induced defects in SiO 2

The main luminescent centers in SiO 2 films are the red luminescence R (650 v nm; 1.85 v eV) of the non-bridging oxygen hole center (NBOHC) and the twofold-coordinated (divalent) silicon with a blue B (460 v nm; 2.7 v eV) and a UV band (285 v nm; 4.4 v eV). Especially the latter ones are produced under irradiation, but from existing precursors assumed as silicon related oxygen deficient centers (SiODC). Therefore, in order to prove these models we compare a direct oxygen implantation with a direct silicon implantation into SiO 2 layers. The main result is: implanting oxygen increases the red band R but does not affect the blue band B. Silicon surplus increases the amplitude of the blue (B) luminescence, but reduces the amplitude of the red (R) one. Studying the cathodoluminescence dose dependence of these blue and red bands we have established defect transformation kinetics in SiO 2 including six main defects and precursors as well as the mobile oxygen as the main transmitter between precursors and the radiation induced defects. The kinetics is described by eight rate equations which predict the dose dependence of the red (R) and blue (B) luminescence intensities and their temperature dependences very well.     

Photoluminescence excitation properties of porous silicon with and without Er-Yb-containing complex

Two bands in the photoluminescence excitation spectra have been studied for the red, blue, and IR emission of oxidized porous silicon (PS) and PS with Er³⁺- and Yb³⁺-containing gadolinium oxychloride complex (PS:Er,Yb), introduced by thermal diffusion. These two spectral bands were shown to reflect contributions of two different mechanisms of excitation-emission processes. The UV band for the IR emission of PS:Er,Yb rose sharply at about 290 nm and was explained by the direct photoemission of carriers from the valence band of Si crystallites into the conduction band of the oxide shell. The second band was found to be common for the red and blue emission and assosiated with the carriers photoexcitation inside the Si crystallites. Lifetimes for both bands were measured and the structure of the blue emission from PS:Er,Yb with peaks at 416, 440, 466, and 500 nm from PS:Er,Yb was observed.     

激光辅助阳极化制备多孔硅的蓝光发射与红外研究

发现由n型单晶硅光照辅助阳极化制备的多孔硅在经过较长时间室温空气中放置氧化后，部分样品出现了蓝色光致荧光.荧光及红外透射、反射测量表明，在较强的氩离子488nm激光照射下制备的样品，经放置氧化后形成氧化层的组织较好，即氧化层中的应力较小、非晶程度相对较低、Si-O-Si的网络结构比较完整.而这样的氧化层是有利于多孔硅光致荧光中的蓝光发射的. 关键词：     

二氧化硫监测的光纤传感方法研究

提出一种用于监测二氧化硫的光纤传感方法,该方法以光化学氧化的n型多孔硅作为传感材料和蓝光发光二激管作为激发光源,通过微型光纤光谱仪测量二氧化硫气氛中多孔硅的光致发光猝灭程度,从而获取二氧化硫含量信息;依据半导体电化学和固体光谱学理论分别讨论n型多孔硅形成和二氧化硫传感的基本原理,采用红外光谱仪研究光化学氧化的n型多孔硅化学组成,并进一步开展二氧化硫光纤传感实验,证明光化学氧化的n型多孔硅在传感过程中稳定性高、可逆性好,其光致发光峰强度随二氧化硫浓度增加而减小,多孔硅荧光峰强度对二氧化硫浓度的线性响应范围为10×10－6～10 000×10－6,检测限为10×10－6;可形成一种便携、全固态的二氧化硫光纤传感器.     

激光诱导多孔硅晶格畸变的Raman光谱和光致发光谱研究

研究了掺钛水热法制备多孔硅的Raman光谱和光致发光谱.实验发现,当激光功率较低时,多孔硅的Raman光谱在略低于520cm^-1附近表现为一锐的单峰,和晶体硅的Raman光谱类似.随激光功率增大,该单峰向低波数移动,Raman和光致发光峰的强度与激光强度的一次方成正比.当激光功率增大到一定值时,该单峰分裂成两个Raman峰,光致发光谱的强度突然增大,与激光强度之间不再满足一次方的关系,位于低波数一侧的Raman峰随激光功率增大进一步向低波数移动.多孔硅Raman光谱随激光功率的变化是 关键词： 多孔硅 Raman光谱 光致发光     

Excitons in silicon nanocrystallites

Recombination and binding energies of excitons in nanocrystalline silicon quantum dots are calculated within the effective mass approximation including the effects of the induced electrostatic polarization. The calculated exciton recombination energies compare well with other calculations and with the results from photoluminescence measurements in porous silicon. The calculated exciton binding energies are far larger than the bulk exciton binding energy and show substantial dependence on the matrix that surrounds the nanocrystallites. A model is proposed that explains the main orange-red, blue and infrared luminescence peaks of porous silicon within a simple unified framework.     

Nanocrystal and interface defects related photoluminescence in silicon-rich Al2O3 films

In this study, silicon nanocrystal-rich Al₂O₃ film has been prepared by co-sputtering a silicon and alumina composite target and subsequent annealing in N₂ atmosphere. The microstructure of the film has been characterized by infrared (IR) absorption, Raman spectra and UV-absorption spectra. Typical nanocrystal and interface defects related photoluminescence with the photon energy of 1.54 (IR band) and 1.69 eV (R band) has been observed by PL spectrum analysis. A post-annealing process in oxygen atmosphere has been carried out to clarify the emission mechanism. Despite the red shift of the spectra, enhanced emission of the 1.69 eV band together with the weak emission phenomenon of the 1.54 eV band has been found after the post-annealing. The R band is discussed to originate from silicon nanocrystal interface defects. The IR band is concluded to be a coupling effect between electronic and vibrational emissions.     

纳米硅粒子的表面氧化及其光致发光特性

采用射频等离子体增强化学气相沉积技术制备了纳米晶硅粒子,并对其溶液发光的稳态和瞬态特性进行了研究.稳态光致发光结果显示,新制备的纳米硅粉体表现为峰值位于440 nm附近的蓝色发光,经长时间氧化后,该波段发光强度显著增强,并且出现另一峰值位于750 nm附近的红色发光带.不同波长激发和时间分辨光致发光谱的分析表明,纳米硅...     

多孔硅中的蓝色发光谱带

采用YAG:Nd激光器的1.06μm谱线的三倍频355nm激光激发多孔硅样品时,观测到一个峰值位于465nm的发光谱带,通过样品的发光光谱、透射光谱、以及时间分辨光谱的测量,初步探讨了新谱带的起源.     

Characterization of nanostructured CuO–porous silicon matrix formed on copper-coated silicon substrate via electrochemical etching

A pulsed anodic etching method has been utilized for nanostructuring of a copper-coated p-type (100) silicon substrate, using HF-based solution as electrolyte. Scanning electron microscopy reveals the formation of a nanostructured matrix that consists of island-like textures with nanosize grains grown onto fiber-like columnar structures separated with etch pits of grooved porous structures. Spatial micro-Raman scattering analysis indicates that the island-like texture is composed of single-phase cupric oxide (CuO) nanocrystals, while the grooved porous structure is barely related to formation of porous silicon (PS). X-ray diffraction shows that both the grown CuO nanostructures and the etched silicon layer have the same preferred (220) orientation. Chemical composition obtained by means of X-ray photoelectron spectroscopic (XPS) analysis confirms the presence of the single-phase CuO on the surface of the patterned CuO–PS matrix. As compared to PS formed on the bare silicon substrate, the room-temperature photoluminescence (PL) from the CuO–PS matrix exhibits an additional weak ‘blue’ PL band as well as a blue shift in the PL band of PS (S-band). This has been revealed from XPS analysis to be associated with the enhancement in the SiO₂ content as well as formation of the carbonyl group on the surface in the case of the CuO–PS matrix.     

蓝光发射和红光发射多孔硅的XPS分析

绿色发光多孔硅在空气中经两种不同的氧化处理分别得到红色发光和蓝色发光.X射线光电子能谱分析显示红色发光多孔硅中含有一定比例的Si、SiOx(x=1～2)以及少量的氟化物;蓝色发光多孔硅的主要成份是SiO2及少量的氟化物.红处透射谱显示蓝光发射多孔硅几乎只存在Si-O-Si峰,而红光发射多孔硅除主要有Si-O-Si峰外,还有明显的SiHx峰.分析表明多孔硅中的蓝光发射来源于SiO2中的缺陷中心.     

退火对ZnS/PS复合体系光致发光特性的影响

用脉冲激光沉积(PLD)技术以多孔硅(PS)为衬底生长了ZnS薄膜,分别测量了ZnS、PS以及ZnS/PS复合体系在室温下的光致发光(PL)光谱。结果发现,ZnS/PS复合体系的PL光谱中PS的发光峰位相对于新制备的PS有所蓝移。把该ZnS/PS样品分成三块,在真空400℃分别退火10,20,30 min,研究不同退火时间对ZnS/PS复合体系光致发光特性的影响。发现退火后样品的PL光谱中都出现了一个新的绿色发光带,归结为ZnS的缺陷中心发光。随着退火时间的延长,PS的发光强度逐渐降低且峰位红移。把ZnS的蓝、绿光与PS的红光相叠加,整个ZnS/PS复合体系在可见光区450~700 nm形成一个较宽的光致发光谱带,呈现较强的白光发射。     

多孔硅的光致发光和红外吸收光谱研究

用电化学腐蚀法制备出多孔硅系列样品.室温下具有明亮可见的光致发光.增大电解电流或延长腐蚀时间,发光光谱明显地“蓝移”;提高样品测量温度,发光光谱也明显地“蓝移”。红外吸收光谱表明多孔硅中除了硅丝骨架以外,还含有H、F及O等元素,随着腐蚀时间的增加,F和O原子的相对含量增加.实验结果表明,多孔硅在可见光区的发光现象是一种量子尺寸效应.     

Multicolor photon emission from organic thin films on different substrates

Thin films of 1-pentyl-2^/,3^/-difluoro-3^///-methyl-4^////-octyl-p-quinquephenyl and 9,10-Bis (4-pentylphenylethynyl)antracene organic molecules were grown on optical glass, silicon and porous silicon substrates. First optical and luminescent properties of such hybrid composites are thoroughly studied using spectroscopic techniques. The strong decrease of aggregation in thin films of 1-pentyl-2^/,3^/-difluoro-3^///-methyl-4^////-octyl-p-quinquephenyl on porous silicon was observed. The possibility of simultaneous red, green and blue tunable photon emission from organic film/porous silicon hybrid structure is demonstrated.     

Study on the thermal isolation properties of porous silicon photonic crystal

The thermal isolation properties of porous silicon photonic crystal structures have been designed and discussed theoretically. Excellent thermal isolation properties can be obtained on such a porous silicon photonic crystal, even better than that of porous silicon with high porosity. Due to the excellent thermal isolation properties of the porous silicon photonic crystal structures, they can be used as the thermal isolation substrates in infrared detectors     

Properties of magnesium silicate doped with chromium in porous silicon

Forsterite doped with Cr⁴⁺ ions is prepared in silicon-based structures according to a simple technique. These structures are of interest due to the characteristic luminescence in the near-IR range. Forsterite is synthesized by impregnation of porous silicon layers on n⁺-Si and p⁺-Si substrates with subsequent annealing in air. A photoluminescence response at a wavelength of 1.15 μm is observed at room temperature in porous silicon layers doped with magnesium and chromium for which the optimum annealing temperature is close to 700°C. The photoluminescence spectrum of porous silicon on the p⁺-Si substrate contains a broad band at a wavelength of approximately 1.2 μm. This band does not depend on the annealing temperature and the magnesium and chromium content and is most likely associated with the presence of dislocations in silicon. The experimental EPR data and eletrical properties of the structures are discussed. It is found that layers of pure porous silicon and chromium-doped porous silicon on n⁺-Si subtructures exhibit indications of discrete electron tunneling.     

Photoluminescence quenching of porous silicon by noble metal adsorbates

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金－多孔硅光致发光和红外光谱研究

报道了金－多孔硅的稳态光致发光，瞬态光致发光和傅里叶变换红外光谱的研究，讨论了金在多孔硅表面吸附产生的表面电子态对多孔硅光致发光特性的影响。