Evidence of the primary-color photoluminescence in ion (H,H,C) irradiated and thermal annealed SrTiO3

We have measured photoluminescence (PL) spectrum of (1) thermal-annealed SrTiO₃/Si thin film and undoped SrTiO₃ single crystal; (2) SrTiO₃ single crystal irradiated by high energy (3 MeV) proton, deuterium, and He ion beams and (3) SrTiO₃ single crystal irradiated by low energy (60 keV) H⁺ and C⁻ ions. Two PL emissions are induced in (1) and (2) at visible frequencies 3 and 2.45 eV, while another PL peak is induced at 2 eV in (3). When compared with our previous PL experiments on high-temperature annealed SrTiO₃/SiO₂/Si thin film and 3 MeV proton (H⁺) irradiated STO single crystal, these results confirm that the three PL emissions with blue (3 eV), green (2.45 eV), and red-orange (2 eV) frequencies originate indeed from SrTiO₃. These primary-color PL effect induced at room-temperature makes STO a strong candidate material for future oxide-based optoelectronic application.     

Cathodoluminescent and nonlinear optical properties of undoped and erbium doped nanostructured ZnO films deposited by spray pyrolysis

We have deposited zinc oxide (ZnO) and erbium doped zinc oxide (ZnO:Er) thin films on heated glass substrates using spray pyrolysis technique. The effect of erbium dopant on structural, morphological, luminescent and nonlinear optical properties was studied. The deposited films have been analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), ex situ compositional analysis (ESCA), profilometry, cathodoluminescence (CL) and third harmonic generation (THG) measurements. All films were polycrystalline, having a preferential growth orientation along the ZnO (0 0 2) plane, with a corresponding average crystallite size of less than 41 nm. Addition of erbium can effectively control the film surface morphology and its cathodoluminescent properties. The films containing low erbium concentration show a uniform surface covered with hexagonal shaped grains and a strong UV light emission intensity as well as TH response. In contrast, when the erbium doping ratio exceeds 3%, a porous surface with columnar textural growth becomes more pronounced, and a substantial reduction of the cathodoluminescent and TH response. A strong TH signal was obtained for the film with good crystalline quality at the concentration of 2%. Third order nonlinear optical susceptibility (χ^〈3〉) values of the studied materials were in the remarkable range of 10⁻¹² esu.     

Sensitisation of erbium emission by silicon nanocrystals-doped SnO2

SnO₂ thin films undoped and doped with antimony (Sb), erbium (Er) and Si nanocrystals (Si-nc) have been grown on silicon (Si) substrate using sol-gel method. Room-temperature photoluminescence (PL) measurement of undoped SnO₂, under excitation at 280 nm, shows only one broad emission at 395 nm, which is related to oxygen vacancies. The PL of Er³⁺ ions was found to be enhanced after doping SnO₂ with Sb and Si-nc. The excitation process of Er is studied and discussed. The calculation of cross-section suggests a sensitisation of Er PL by Si-nc.     

Photoluminescence study of ZnO nano-islands

ZnO nano-islands, with much more uniform size, have been grown through two-step method by metal organic chemical vapor deposition (MOCVD). The room temperature band-edge UV emission intensity of nano-islands was usually undetectable or much smaller than that of thin film. Photoluminescence (PL) emission of those nano-islands shows the high intensity nearly as that of ZnO thin film, which is great different from previous reports. By meaningfully analyzing both PL and growth condition of those three samples (bulk ZnO wafer, nano-islands and film), neutral-donor-bound-exciton (D⁰X) emission observed on ZnO nano-islands sample is eventually attributed to hydrogen and aluminum, respectively. The abnormal phenomenon of nano-islands PL intensity has been explained by the point of zinc vacancies (V_Zn) complex defects. It is considered to govern the nonradiative combination and lead enhanced intensity of UV emission in ZnO nano-islands.     

Excitation mechanisms and localization sites of erbium-doped porous silicon

Porous silicon (PS) is doped with erbium by electrochemical anodisation. The penetration of erbium into the PS layer is confirmed by Rutherford backscattering spectroscopy (RBS) and energy dispersive X-ray (EDX) measurements. Efficient green and infrared emissions were observed at room temperature. The investigations are focused on the evolutions versus temperature and pump intensity of the green photoluminescence (PL) corresponding to the ⁴S_3/2 → ⁴I_15/2 transition. It was found that an erbium related level defect can be involved on the excitation and emission processes of erbium. Pump intensity dependent PL studies revealed that for the electrochemical incorporation, most of the Er³⁺ ions are localized inside the Si nanocrystallites and not in stoichiometric SiO₂. The optical cross-section is close to that of erbium in Si nanocrystallites.     

YZr2OZr3:Er3+纳米晶anti-Stokes发光性质的研究

采用均相沉积法制备了不同Er³⁺离子浓度掺杂的Y₂O₃纳米晶, 应用XRD，SEM和PL光谱对该体系材料进行了表征.在Y₂O₃:Er³⁺纳米材料体系中, 观察和研究了Stokes及anti-Stokes PL谱强度与Er³⁺离子摩尔浓度变化的关系, 当Er³⁺离子浓度为2.0mol%时, anti-Stokes PL强度最强.粉末X 关键词： 氧化钇纳米晶 anti-Stokes PL 双光子吸收     

Rate equation modelling of erbium luminescence dynamics in erbium-doped silicon-rich-silicon-oxide

Erbium doped silicon-rich silica offers broad band and very efficient excitation of erbium photoluminescence (PL) due to a sensitization effect attributed to silicon nanocrystals (Si-nc), which grow during thermal treatment. PL decay lifetime measurements of sensitised Er³⁺ ions are usually reported to be stretched or multi exponential, very different to those that are directly excited, which usually show a single exponential decay component.In this paper, we report on SiO₂ thin films doped with Si-nc's and erbium. Time resolved PL measurements reveal two distinct 1.54 μm Er decay components; a fast microsecond component, and a relatively long lifetime component (10 ms). We also study the structural properties of these samples through TEM measurements, and reveal the formation of Er clusters. We propose that these Er clusters are responsible for the fast μs decay component, and we develop rate equation models that reproduce the experimental transient observations, and can explain some of the reported transient behaviour in previously published literature.     

掺饵氢化非晶氧化硅1.54μm发光性质的研究

采用等离子体增强化学汽相沉积技术生长不同氧含量的氢化非晶氧化硅薄膜(a-SiO_{x∶H),离子注入铒及退火后在室温观察到很强的光致发光.当材料中氧硅含量比约为1和 1.76时,分别对应77Ｋ和室温测量时最强的1.54μm光致发光.从15到250Ｋ的变温实验显示 出三个不同的强度与温度变化关系,表明氢化非晶氧化硅中铒离子的能量激发和发光是一个 复杂的过程.提出氢化非晶氧化硅薄膜中发光铒离子来自于富氧区,并对实验现象进行了解 释.氢化非晶氧化硅中铒发光的温度淬灭效应很弱.从15到250Ｋ,光致发光强度减弱约1/2. 关键词： 铒 光致发光 氧含量}     

Photoluminescence Properties of Conjugated Phenylacetylene Monodendrons in Thin Films

We report the absorption, photoluminescence (PL), and time-dependent PL of thin films of conjugated phenylacetylene monodendrons at both room temperature and at cryogenic temperature. We find that the PL properties of the monodendron thin films are significantly different from their fluorescence in dilute solution due to the presence of interactions between monodendrons in the thin film. These interactions lead to aggregate species in the thin films, which result in broader PL spectra and lower PL quantum yields than for monodendrons in dilute solution. Evidence for excimer-like aggregates in the monodendron thin films is found from time-resolved PL spectra.     

Effect of ion irradiation on the structure and luminescence characteristics of porous silicon impregnated with tungsten-telluride glass doped by Er and Yb impurities

Using transmission electron microscopy and elemental analysis, it has been shown that tungsten telluride glass (TTG) containing erbium and ytterbium as impurities penetrates into pores of porous silicon (PS) when melted in vacuum at 500°C. It has been found that the intensity of photoluminescence (PL) of erbium at the wavelength of 1.54 μm in PS: TTG layers increases by a factor of up to 5 in the layers irradiated by P⁺ and Ar⁺ ions. This is assigned to ion mixing which favors interaction among the Er ions and PS-embedded Si nanocrystals initiating sensitization of the PL, as well as to broadening of the glass-impregnated PS region. Implantation of the lighter Ne⁺ ions affects only weakly the PL of erbium ions.     

Photoluminescence spectra of doped GaAs films

We have studied the dependence of the photoluminescence (PL) spectrum on the doping level and the film thickness of n-GaAs thin films, both experimentally and theoretically. It has been shown theoretically that modification of the PL spectrum of p-type material by p-type doping is very small due to the large valence-band hole effective mass. The PL spectrum of n-type material is affected by two factors: (1) the electron concentration which determines the Fermi level in the material; (2) the thickness of the film due to re-absorption of the PL signal. For the n-type GaAs thin films under current investigation, the doping level as well as the film thickness can be very well calibrated by the PL spectrum when the doping level is less than 2×10¹⁸ cm^-3 and the film thickness is in the range of the penetration length of the PL excitation laser. PACS 78.20.-e; 78.55.Cr; 78.66.Fd     

Effects of γ rays irradiation on structure and property of TiO2 thin films

TiO₂ thin films were deposited on a glass substrate by the radio frequency magnetron sputtering method, and annealed for 2 h at temperatures of 550°C. Then, ⁶⁰Co γ rays with different doses were used to irradiate the resulting TiO₂ thin films. The surface features of films before and after irradiation were observed by scanning electron microscope (SEM). Simultaneously, the crystal structure and optical properties of films before and after irradiation were studied by X-ray diffraction (XRD), UV–VIS transmission spectrum and Photoluminescence (PL) spectrum, respectively. The SEM analysis shows that the film is smooth with tiny particles on the film surface, and non-crystallization trend was clear after irradiated with γ rays. The XRD results indicated that the structure of the film at the room temperature mainly exists in the form of amorphous and mixed crystal at a sputtering power of 200 W, and non-crystallinity was more obvious after irradiation. Obvious difference can be found for the transmissibility of the irradiated and pre irradiation TiO₂ films by the UV-VIS spectra. The color becomes light yellow, and the new absorption edge also appeared at about 430 nm. PL spectra and photocatalysis experiments indicate that the photocatalysis degradation rate of the TiO₂ films on methylthionine chloride solution irradiated with the maximum dose can be increased to 90%.     

The comparison between CdS thin films grown on Si(111) substrate and quartz substrate by femtosecond pulsed laser deposition

Two kinds of cadmium sulfate (CdS) thin films have been grown at 600 °C onto Si(111) and quartz substrates using femtosecond pulsed laser deposition (PLD). The influence of substrates on the structural and optical properties of the CdS thin films grown by femtosecond pulsed laser deposition have been studied. The CdS thin films were characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), photoluminescence (PL) and Raman spectroscopy. Although CdS thin films deposited both on Si(111) and quartz substrates were polycrystalline and hexagonal as shown by the XRD , SEM and AFM results, the crystalline quality and optical properties were found to be different. The size of the grains for the CdS thin film grown on Si(111) substrate were observed to be larger than that of the CdS thin film grown on quartz substrate, and there is more microcrystalline perpendicularity of c-axis for the film deposited on the quartz substrate than that for the films deposited on the Si substrate. In addition, in the PL spectra, the excitonic peak is more intense and resolved for CdS film deposited on quartz than that for the CdS film deposited on Si(111) substrate. The LO and TO Raman peaks in the CdS films grown on Si(111) substrate and quartz substrate are different, which is due to higher stress and bigger grain size in the CdS film grown on Si(111) substrate, than that of the CdS film grown on the amorphous quartz substrate. All this suggests that the substrates have a significant effect on the structural and optical properties of thin CdS films. PACS 81.15.Fg; 81.05.Ea; 78.20.-e; 78.67.-n; 42.62.-b     

Novel chemical synthetic route and characterization of zinc selenide thin films

Zinc selenide (ZnSe) thin film have been deposited using chemical bath method on non-conducting glass substrate in a tartarate bath containing zinc sulfate, ammonia, hydrazine hydrate, sodium selenosulfate in an aqueous alkaline medium at 333 K. The deposition parameter of the ZnSe thin film is interpreted in the present investigation. The films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), optical absorption, electrical measurements, atomic absorption spectroscopy (AAS). The ZnSe thin layers grown with polycrystalline zinc blende system along with some amorphous phase present in ZnSe film. The direct optical band gap ‘E_g’ for the film was found to be 2.81 eV and electrical conductivity in the order of 10⁻⁸(Ω cm)⁻¹ with n-type conduction mechanism.     

Oxygen deficiency effects on recombination lifetime and photoluminescence characteristics of ZnO thin films; correlation with crystal structure

The photoluminescence (PL), recombination lifetime (RL), and X-ray diffraction (XRD) spectra of the samples grown at various O₂ fractions of 0.290 (Zn-rich), 0.585 (moderate), and 0.836 (O-rich) over the total pressures in the growth chamber were investigated. XRD measurements revealed that all the films show highly preferred (0002) orientation. The PL measurements exhibit different dominant emissions in the ultraviolet (UV), violet and blue regions for Zn-rich, moderate and O-rich samples, respectively. Well-known green emission and high intensity of free exciton (FX) transition has been observed in Zn-rich sample after the sample is annealed at vacuum probably due to the oxygen deficiencies. Annealing the moderate sample gives rise to the UV emission at energy of 3.263 eV similar to the observed PL emission spectrum for the Zn-rich thin film. O-rich thin film exhibits a 338 meV acceptor level above the valance band maximum, most probably related to zinc vacancy (V_Zn). Free exciton RL measurements result in 568.23, 397.65, and 797.46 ps for Zn-rich, moderate, and O-rich thin films, respectively. A good correlation was found between crystallite size and the lifetime values.     

The effects of substrate temperature on the structure, morphology and photoluminescence properties of pulsed laser deposited SrAl2O4:Eu,Dy thin films

In this study, SrAl₂O₄:Eu²⁺,Dy³⁺ thin film phosphors were deposited on Si (1 0 0) substrates using the pulsed laser deposition (PLD) technique. The films were deposited at different substrate temperatures in the range of 40-700 °C. The structure, morphology and topography of the films were determined by using X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM). Photoluminescence (PL) data was collected in air at room temperature using a 325 nm He-Cd laser as an excitation source. The PL spectra of all the films were characterized by green phosphorescent photoluminescence at ∼530 nm. This emission was attributed to 4f⁶5d¹→4f⁷ transition of Eu²⁺. The highest PL intensity was observed from the films deposited at a substrate temperature of 400 °C. The effects of varying substrate temperature on the PL intensity were discussed.     

Effects of the substrate and oxygen partial pressure on the microstructures and optical properties of Ti-doped ZnO thin films

Ti-doped ZnO (ZnO:Ti) thin films were deposited on the glass and Si substrates using radio frequency reactive magnetron sputtering. The effects of substrate on the microstructures and optical properties of ZnO:Ti thin films were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and a fluorescence spectrophotometer. The structural analyses of the films indicated that they were polycrystalline and had a hexagonal wurtzite structure on different substrates. When ZnO:Ti thin film was deposited on Si substrate, the film had a c-axis preferred orientation, while preferred orientation of ZnO:Ti thin film deposited on glass substrate changed towards (1 0 0). Finally, we discussed the influence of the oxygen partial pressures on the structural and optical properties of glass-substrate ZnO:Ti thin films. At a high ratio of O₂:Ar of 18:10 sccm, the intensity of (0 0 2) diffraction peak was stronger than that of (1 0 0) diffraction peak, which indicated that preferred orientation changed with the increase of O₂:Ar ratios. The average optical transmittance with over 93% in the visible range was obtained independent of the O₂:Ar ratio. The photoluminescence (PL) spectra measured at room temperature revealed four main emission peaks located at 428, 444, 476 and 527 nm. Intense blue-green luminescence was obtained from the sample deposited at a ratio of O₂:Ar of 14:10 sccm. The results showed that the oxygen partial pressures had an important influence for PL spectra and the origin of these emissions was discussed.     

Influence of crystallisation on the photoluminescence properties of Y2-xErxTi2O7 sol-gel thin films

Optically active Er₂Ti₂O₇ (ETO) and Y_2-xEr_xTi₂O₇ (YETO) films have been successfully deposited using the aerosol-gel process. Several heat-treatment procedures are investigated in the 600–850 °C range. ETO and YETO films start to crystallise in the pyrochlore phase at about 750 °C, depending on the heat-treatment time. Crystalline YETO films form a solid solution where the erbium ions are well diluted. Up-conversion emission (UPE) in the visible wavelength range and infrared photoluminescence (PL) at 1.53 m are investigated. PL spectra are composed of several sharp peaks. Stark splitting of the ⁴I_13/2 and ⁴I_15/2 erbium levels is analysed. A clear correlation between spectroscopic properties and film microstructure is evidenced. YETO films exhibit strong PL compared to ETO films. PL lifetimes of up to 8.6 ms were measured on YETO films at an erbium concentration of 2×10²⁰ ions/cm³. The YETO compound is found to be a suitable material, improving the erbium active properties. PACS 81.20.Fw; 78.55; 78.66     

Investigation of Cu Doping,Morphology and Annealing Effects on Structural and Optical Properties of ZnO:Dy Nanostructures

Dysprosium (Dy) doped ZnO nanosheets and nanorods were synthesized by hydrothermal method. Effects of Cu doping, morphology and annealing in Oxygen ambient on structural and optical properties of ZnO nanostructures were investigated using X–ray diffraction (XRD), scanning electron microscopy (SEM), diffuse reflectance spectra (DRS) and photoluminescence (PL) spectroscopy. This study recommends that both of intrinsic and extrinsic defects facilitate energy transfer (ET) from the ZnO host to Dy³⁺ ions and consequently have an effective role on producing intense Dy emissions at indirect excitation. The results also revealed that annealing process improved the crystal structure of ZnO nanorods due to decrease of surface; however decreased ET and Dy emissions because of diminishing in oxygen vacancy. In addition, as a result of increasing of surface area in nanorods compared to nanosheets, the oxygen vacancies and ET were enhanced. Moreover the results exhibited that electrical and optical properties of ZnO:Dy can be tuned by various amount of Dy concentrations and also Cu doping.     

Enhanced visible light emission from Co doped ZnS nanoparticles

ZnS nanoparticles with Co²⁺ doping have been prepared at room temperature through a soft chemical route, namely the chemical co-precipitation method. The nanostructures of the prepared nanoparticles have been analyzed using X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), selected-area electron diffraction (SAED), and UV-vis spectrophotometer. The sizes of as prepared nanoparticles are found to be in 1–4 nm range. Room-temperature photoluminescence (PL) spectrum of the undoped sample exhibits emission in the blue region with multiple peaks under UV excitation. On the other hand, in the Co²⁺ doped ZnS samples enhanced visible light emissions with emission intensities of ~35 times larger than that of the undoped sample are observed under the same UV excitation wavelength of 280 nm.