Annealing effect on structure and green emission of ZnO nanopowder by decomposing precursors

ZnO nanopowder is successfully synthesized by annealing the precursors in oxygen gas using the chemical precipitation method. Structural and optical properties of thus synthesized ZnO nanopowder are characterized by scanning electron microscopy (SEM) and photoluminescence (PL). The morphology of ZnO nanopowders evolves from nanorod to cobble as annealing temperature increases from 500 to 1000~\du, while spiral structures are observed in the samples annealed at 900 and 1000~\du. The PL spectra of ZnO nanopowder consist of largely green and yellow emission bands. The green emission from ZnO nanopowder depends strongly on the annealing temperature with a peak intensity at a temperature lower than 800~℃ while the yellow emission is associated with interstitial oxygen \rm O_\i.     

玻璃中CdSeS纳米晶体的室温光致发光谱

对掺有过饱和的镉、硒和少量硫的玻璃在500～800℃分别退火4h,生长了不同尺寸的CdSe_1-xS_x纳米晶体。测量了纳米晶体的室温吸收光谱和光致发光(PL)光谱,550℃生长的样品在300～800nm的范围没有观察到吸收和发光峰,表明温度低于550℃玻璃中不能形成纳米晶体。生长温度在600～650℃,纳米晶体的PL光谱主要为两个宽的发光带,即带边激子发光带和通过表面态复合的发光带。随着生长温度的升高,带边复合发光的蓝移减小,通过表面态的发光逐渐消失,并出现了叠加于宽发光带上的一系列明显的弱发射峰。不同温度生长的样品中,叠加峰的能量相同。同一样品中叠加峰的能量不随激发光波长的变化而变化。     

Electrical and deep levels characteristics of ZnO/Si heterostructure by MOCVD deposition

ZnO films have been prepared on p-type Si substrates by metal-organic chemical vapour deposition （MOCVD） at different total gas flow rates. The current versus voltage and temperature （I - V - T） characteristics, the deep-level transient spectroscopy （DLTS） and the photoluminescence （PL） spectra of the samples were measured. DLTS shows two deep-level centres of E1 （Ec-0.13±0.02eV） and E2 （Ec-0.43±0.05eV） in sample 1202a, which has a ZnO/p-Si heterostructure. A deep level at Ec-0.13±0.01 eV was also obtained from the I -T characteristics. It was considered to be the same as E1 obtained from DLTS measurement. The emission related to this deep level center was detected by PL spectra. In addition, the energy location and the relative trap density of E1 was varied when the total gas flow rate was changed.     

热退火对SiO2：Er薄膜发光特性的影响

利用离子注入法制备SiO₂:Er样品,并在不同温度下进行退火处理。通过微区拉曼光谱、吸收光谱、X射线光电子能谱等手段对其进行结构表征,并进行了室温和变温的光致发光特性研究,得到了可见区和红外区的光致发光。其中,⁴S_3/2→⁴I_15/2的发光强度随温度的升高,先增强后减弱,呈现出反常的温度淬灭效应,此现象是由Er³⁺与SiO₂的缺陷之间的能量传递造成的。     

Effect of post-thermal annealing on the structural and optical properties of ZnO thin films prepared from a polymer precursor

ZnO thin films were synthesised by a new method which uses polyvinyl alcohol (PVA) as the polymer precursor. The films are annealed at different temperatures and for different annealing times. The structural parameters, like grain size, lattice constants, optical band gap, and Urbach energy, depend on the annealing temperature and time. All the films possess tensile strain, which relaxes as the annealing temperature and time increase. The photoluminescence (PL) spectra contain only ultraviolet (UV) peaks at low temperature, but as the annealing temperature and time increase, we observe peaks at the blue and green regions with a variation in the intensities of these peaks with annealing temperature and time.     

Effect of post thermal annealing on the structural and optical properties of ZnO thin films prepared from polymer precursor

ZnO thin films were synthesised by a new method which uses polyvinyl alcohol (PVA) as polymer precursor. The films are annealed at different temperatures and for different annealing times. The structural parameters, like grain size, lattice constants, optical band gap, and Urbach energy, depend on the annealing temperature and annealing time. All the films possess tensile strain which relaxes as the annealing temperature and the annealing time increases. The photoluminescence (PL) spectra contain only ultraviolet (UV) peaks at low temperature, but as the annealing temperature and time increase we observe peaks at blue and green regions with variation of the intensities of these peaks with annealing temperature and annealing time.     

Influence of post-deposition annealing on the structural,optical and electrical properties of Li and Mg co-doped ZnO thin films deposited by sol–gel technique

Lithium (Li) and magnesium (Mg) co-doped zinc oxide (ZnO) thin films were deposited by sol–gel method using spin coating technique. The films were deposited on glass substrates and annealed at different temperatures. The effects of annealing temperature on the structural, optical and electrical properties of the deposited films were investigated using X-ray diffraction (XRD), Ultraviolet–Visible absorption spectra (UV–VIS), photoluminescence spectra (PL), X-ray photo electron spectroscopy (XPS) and Hall measurements. XRD patterns indicated that the deposited films had a polycrystalline hexagonal wurtzite structure with preferred (0 0 0 2) orientation. All films were found to exhibit a good transparency in the visible range. Analysis of the absorption edge revealed that the optical band gap energies of the films annealed at different temperatures varies between 3.49 eV and 3.69 eV. Room temperature PL spectra of the deposited films annealed at various temperatures consist of a near band edge emission and visible emission due to the electronic defects, which are related to deep level emissions, such as oxide antisite (O_Zn), interstitial zinc (Zn_i), interstitial oxygen (O_i) and zinc vacancy (V_Zn) which are generated during annealing process. The influence of annealing temperature on the chemical state of the dopants in the film was analysed by XPS spectra. Ion beam analysis (Rutherford back scattering) experiments were performed to evaluate the content of Li and Mg in the films. Hall measurements confirmed the p-type nature of the deposited films.     

Optical properties of ZnO thin films on SiO2 substrates deposited by radio frequency magnetron sputtering

The optical properties of both the annealed and as-deposited ZnO thin films by radio frequency (RF)magnetron sputtering on SiO2 substrates were studied. In the annealed films, two pronounced well defined exciton absorption peaks for the A and B excitons were obtained in the absorption spectra, a strong free exciton emission without deep-level emissions was observed in the photoluminescence (PL) spectra at room temperature. It was found that annealing the films in oxygen dramatically improved the optical properties and the quality of the films.     

Temperature dependence of the luminescence properties of LaCl3：Ce crystal

The optical properties of LaCl3：Ce crystal are reported in this paper. Optical transmission spectrum, photoluminescence and time resolved photoluminescence spectra at different temperatures are investigated. It is found that optical transmittance is as high as 80% between 320 nm and 600 nm, and no obvious absorption band is found in this region. Emission intensity and decay time of photoluminescence are quite stable with the change of the temperature between 80 K and 500 K. No thermal quenching is present up to 500 K, and decay time keeps at 17±2 ns. With the increase of the temperature, the whole emission bands and excitation bands present broadening and overlapping, leading to the strengthening of re-absorption of the Ce^3＋ emission, which makes the emission spectra have a red shift trend.     

Modified thermal evaporation process using GeO2 for growing ZnO structures

In the current work, zinc oxide (ZnO) nano/microstructures are synthesized using a modified thermal-evaporation process by introducing germanium oxide (GeO₂) powder mixed with metallic Zn powder as the raw material. Without the use of any catalyst and oxygen flow in the furnace system, GeO₂ is utilized to provide an oxygen source for the growth of ZnO structure. The samples are treated by different temperatures ranging from 500 to 900 °C. Morphology, phase structure, and photoluminescence properties are investigated by scanning electron microscopy (SEM), X-ray diffractometer (XRD) and photoluminescence (PL) spectrometer. The structures and morphologies of the samples were found to vary with growth temperature. The XRD diffraction peaks show that the films grown at temperature from 600 to 800 °C consist of hexagonal wurtzite ZnO structures. Room-temperature PL measurement revealed ZnO spectra representing two bands: near-band-edge emission in the ultraviolet (UV) region and broad deep-level emission centered at about 500 nm. The strong UV emission in the PL spectra indicates that the GeO₂ supplies sufficient oxygen for formation of ZnO structures with few oxygen vacancies. The growth mechanism and the roles of GeO₂ for formation of ZnO structures are discussed in detail.     

Optical and structural properties of Ge-ion-implanted fused silica after annealing in different ambient conditions

Ge+ ions are implanted into fused silica glass at room temperature and a fluence of 1×10 17 cm-2 . The as-implanted samples are annealed in O2, N2 and Ar atmospheres separately. Ge0 , GeO and GeO2 coexist in the as-implanted and annealed samples. Annealing in different atmospheres at 600℃ leads each composite to change its content. After annealing at 1000℃, there remains some amount of Ge 0 in the substrates. However, the content of Ge decreases due to out-diffusion. After annealing in N2 , Si–N composite is formed. The absorption peak of GeO appears at 240 nm after annealing in O2 atmosphere, and a new absorption peak occurs at 418 nm after annealing in N2 atmosphere, which is attributed to the Si–N composite. There is no absorption peak appearing after annealing in Ar atmosphere. Transmission electron microscopic images confirm the formation of Ge nanoparticles in the as-implanted sample and GeO 2 nanoparticles in the annealed sample. In the present study, the GeO content and the GeO2 content depend on annealing temperature and atmosphere. Three photoluminescence emission band peaks at 290, 385 and 415 nm appear after ion implantation and they become strong with the increase of annealing temperature below 700℃, and their photoluminescences recover to the values of as-grown samples after annealing at 700℃. Optical absorption and photoluminescence depend on the annealing temperature and atmosphere.     

原子层沉积制备氧化锌纳米薄膜的光学性质研究

采用原子层沉积技术(ALD),以二乙基锌和水为前驱体,在衬底温度分别为110和190 ℃的条件下制备了致密的氧化锌纳米薄膜。采用X射线光电子能谱,荧光光谱和椭偏仪等表征手段对薄膜的成分和光学性质进行了研究。结果表明,随着沉积温度的增加,氧化锌薄膜内—OH含量降低,说明氧化锌薄膜生长过程中的化学反应更加完全;另外,沉积温度增加后,薄膜在365 nm处的激子发射峰出现了明显的增强,同时可见光区的荧光发射峰消失,表明薄膜内的缺陷态减少。随着成膜质量的提高,氧化锌薄膜的电子迁移率从25提高至32 cm2·(V·S)-1。椭偏测量的拟合结果表明,在375～800 nm的波长范围内,氧化锌薄膜的折射率逐渐从2.33降至1.9,呈现出明显的色散现象;另外,不同温度下制备的氧化锌薄膜光学带隙均为3.27 eV左右,这说明沉积温度对薄膜的带隙没有明显影响。     

Temperature dependent surface and spectral modifications of nano V<Subscript>2</Subscript>O<Subscript>5</Subscript> films

Nanocrystalline V₂O₅ films have been deposited on glass substrates at 300°C substrate temperature using thermal evaporation technique and were subjected to thermal annealing at different temperatures 350, 400, and 550°C. X-ray diffraction (XRD) spectra exhibit sharper and broader characteristic peaks respectively indicating the rearrangement of nanocrystallite phases with annealing temperatures. Other phases of vanadium oxides started emerging with the rise in annealing temperature and the sample converted completely to VO₂ (B) phase at 550°C annealing. FESEM images showed an increase in crystallite size with 350 and 400°C annealing temperatures followed by a decrease in crystallite size for the sample annealed at 550°C. Transmission spectra showed an initial redshift of the fundamental band edge with 350 and 400°C while a blue shift for the sample annealed at 550°C, which was in agreement with XRD and SEM results. The films exhibited smart window properties as well as nanorod growth at specific annealing temperatures. Apart from showing the PL and defect related peaks, PL studies also supported the observations made in the transmission spectra.     

不同退火条件对纳米多孔氧化铝薄膜光致发光的影响

以草酸为电解液,采用二次阳极氧化法制备出了纳米多孔氧化铝薄膜,经不同退火温度和退火气氛处理氧化铝薄膜后,通过分析其光致发光光谱得出：相同的退火气氛中, 退火温度T≤600 ℃ 时,T=500 ℃具有最大的光致发光强度;退火温度T≥700 ℃时,随着退火温度的升高,样品的发光强度增大。在不同的退火气氛中,多孔氧化铝薄膜随着退火温度的升高,发光峰位改变不同,即在空气中退火处理后,随着退火温度的升高,发光峰位蓝移,而在真空中退火处理后,发光峰位并不随退火温度的升高而变化;通过对1 100 ℃高温退火处理后的氧化铝薄膜的光致发光曲线的高斯拟合,可以看出,经退火处理后的多孔氧化铝,主要存在三个发光中心,发光曲线在350～600 nm范围内对应三个发射峰, 发射波长分别为387,410,439 nm。相同的退火温度下,空气中退火得到的氧化铝薄膜的光致发光强度大于真空中退火处理后的氧化铝薄膜。基于实验结果,结合X射线色散能谱(EDS)、红外反射光谱等表征手段,探讨了多孔氧化铝薄膜的发光机制,并对经过不同退火条件得到的多孔氧化铝薄膜的光致发光特性的改变做出了合理的解释。     

Exciton localization behaviour in different well width undoped GaN/Al0.07Ga0.93N nanostructures

We report results from optical spectroscopy such as photoluminescence (PL) and time resolved photo-luminescence (TRPL) techniques from different well width MOCVD grown GaN/Al_0.07Ga_0.93N MQW samples. There is evidence of localization at low temperature in all samples. The decay time of all samples becomes non-exponential when the detection energy is increased with respect to the peak of the emission. Localization of carriers (excitons) is demonstrated by the “S-shape” dependences of the PL peak energies on the temperature. The time-resolved PL spectra of the 3-nm well multi quantum wells reveal that the spectral peak position shifts toward lower energies as the decay time increases and becomes red-shifted at longer decay times. There is a gradient in the PL decay time across the emission peak profile, so that the PL process at low temperatures is a free electron-localized hole transition.     

Structural and optical properties of nanocrystalline ZnO thin films synthesized by the citrate precursor route

Nanocrystalline zinc oxide (ZnO) thin films have been deposited by spin-coating polymeric precursors synthesized by the citrate precursor route using ethylene glycol and citric acid as chelating agents. The ZnO thin films were annealed in air at different temperatures for 10 min. The films were characterized by different structural and optical techniques, including X-ray diffraction (XRD), atomic force microscopy (AFM), optical transmission spectroscopy, and photoluminescence (PL). The thermal decomposition of polymeric precursor was studied by thermogravimetric analysis (TGA). XRD analysis with grazing incidence and rocking curves indicate that the ZnO films are polycrystalline with preferential orientation along the c-axis direction with a full-width at half-maximum (FWHM) of 0.31° for 600 °C-annealed samples. On annealing, the texturing in films increased along with a decrease in FWHM. AFM micrographs illustrate that the ZnO films are crack-free with well-dispersed homogeneous and uniformly distributed spherical morphology. The synthesized ZnO thin films have transparency >85% in the visible region exhibiting band edge at 375 nm, which becomes sharper with anneal. Room temperature PL spectra of these films show strong ultraviolet (UV) emission around 392 nm with an increase in intensity with annealing temperature, attributed to grain growth. Deconvolution of the PL spectra reveals that there is coupling of free excitons with higher orders of longitudinal optical (LO) phonon replicas leading to a broad asymmetric near-band-edge peak.     

退火对Pb辐照Al2O3单晶发光特性的影响

研究了230MeV的²⁰⁸Pb²⁷⁺辐照Al₂O₃样品及随后在600,900,1100K高温条件下退火后的光致发光特性。从辐照样品的测试结果可以清楚地看到在波长为390,450nm处出现了强的发光峰。辐照量为1×10¹³ions/cm²时,样品的发光峰最强。经过600K退火2h后测试结果显示,380nm发光峰剧烈增强,而其他发光峰显示不明显。在900K退火条件下,380nm的发光峰开始减弱,而在360,510nm出现了明显的发光峰,至到1100K退火完毕后380nm的发光峰完全消失,而360,510nm的发光峰相对增强。从被辐照样品的FTIR谱中看到,波数在460~510cm^-1间的吸收是振动模式,经过离子辐照后,吸收带展宽,随着辐照量的增大,Al₂O₃振动吸收峰消失,说明Al₂O₃振动模式被完全破坏。1000~1300cm^-1之间为Al—O—Al桥氧的伸缩振动模式,辐照后吸收带向高波数方向移动,说明其振动模式受到影响。辐照剂量较小的样品,损伤程度相对较低,经退火晶化后,振动模式基本恢复到单晶状态;辐照剂量较高的样品,损伤程度大,退火处理后表面变得较粗糙,振动模式并未出现,说明结构破坏严重。     

生长温度对6H-SiC上SiCGe薄膜发光特性的影响

利用低压化学气相淀积工艺在6H-SiC衬底成功制备了SiCGe薄膜。通过光致发光(PL)谱研究了生长温度对SiCGe薄膜发光特性的影响。结果表明:生长温度为980,1030,1060℃的SiCGe薄膜的室温光致发光峰分别位于2.13,2.18,2.31eV处;通过组分分析和带隙计算,认定该发光峰来自于带间辐射复合,证实了改变生长温度对SiCGe薄膜带隙的调节作用。同时,对SiCGe薄膜进行了变温PL测试,发现当测试温度高于200K时,发光峰呈现出蓝移现象。认为这是不同机制参与发光所造成的。     

Effects of annealing in nitrogen atmosphere and HCl-etching on the photoluminescence spectra of spray-deposited CdS:In thin films

The aim of this work is to find the effect of processing on the photoluminescence (PL) of spray-deposited CdS:In thin films. So the PL spectra of the as-deposited, annealed and HCl-etched CdS:In thin films prepared by the spray pyrolysis (SP) technique were recorded at T = 23 K. The yellow and red bands were observed in the spectrum of the as-deposited film beside bands with weaker intensity in the infrared region. The PL signal was weakened by annealing in nitrogen atmosphere at T = 400 °C and HCl-etching. A deconvolution peak fit was established to find the effects of these treatments on the different bands. The spectrum of the as-deposited film was deconvoluted to 12 peaks, which were reduced to 6 peaks after both treatments. It was found that both treatments have approximately the same effects on the PL spectra; that is they removed most of the peaks and shoulders in the red and infrared regions and attenuated most of the peaks in the yellow region. Some peaks were blue-shifted after annealing which was explained by the growth of nanocrystallites due to the thermal stress that results from the different expansion coefficients of the film and the substrate. These changes were accompanied by a phase change from the mixed (cubic and hexagonal) phase to the hexagonal phase as shown in the X-ray diffractograms.     

退火对电子束热蒸发Al2O3薄膜性能影响的实验研究

 用电子束热蒸发方法镀制了Al₂O₃材料的单层膜,对它们在空气中进行了250~400 ℃的高温退火。对样品的透射率光谱曲线进行了测量,计算了样品的消光系数、折射率和截止波长。通过X射线衍射仪（XRD）测量分析了薄膜的微观结构,采用表面轮廓仪测量了样品的表面均方根粗糙度。结果发现随着退火温度的提高光学损耗下降,薄膜结构在退火温度为400 ℃时仍然为无定形态,样品的表面粗糙度随退火温度的升高而增加。引起光学损耗下降起主导作用的是吸收而不是散射,吸收损耗的下降主要是由于退火使材料吸收空气中的氧而进一步氧化,从而使薄膜材料的非化学计量比趋于正常。