Effect of annealing on the optical properties of Nd:YAG transparent ceramics

The Nd:YAG transparent ceramics were fabricated by vacuum sintering at 1750 °C for 20 h, where the raw nanopowders were synthesized by a modified co-precipitation method. Subsequently the Nd:YAG ceramic specimens were annealed or even re-annealed in air or vacuum at 1250-1500 °C for 20 h. The Nd:YAG ceramic specimens were investigated by X-ray diffraction, ultraviolet spectroscopy, inductively coupled plasma atomic emission spectroscopy, electron paramagnetic resonance spectroscopy and scanning electron microscopy. The results showed that post-annealing could improve the optical properties and microstructure of Nd:YAG transparent ceramics. By air annealing, the in-line transmittances of the specimens increased, mainly due to the decrease of oxygen vacancies concentration in specimens. The air annealing at 1450 °C for 20 h was optimum for preparation of Nd:YAG transparent ceramics. Furthermore, the red shift of UV absorption edge after air annealing could be attributed to the absorption by Fe³⁺ charge transfer bands.     

Low temperature annealing effects on the structure and optical properties of ZnO films grown by pulsed laser deposition

ZnO thin films were deposited on glass substrates at room temperature (RT) ∼500 °C by pulsed laser deposition (PLD) technique and then were annealed at 150-450 °C in air. The effects of annealing temperature on the microstructure and optical properties of the thin films deposited at each substrate temperature were investigated by XRD, SEM, transmittance spectra, and photoluminescence (PL). The results showed that the c-axis orientation of ZnO thin films was not destroyed by annealing treatments; the grain size increased and stress relaxed for the films deposited at 200-500 °C, and thin films densified for the films deposited at RT with increasing annealing temperature. The transmittance spectra indicated that E_g of thin films showed a decreased trend with annealing temperature. From the PL measurements, there was a general trend, that is UV emission enhanced with lower annealing temperature and disappeared at higher annealing temperature for the films deposited at 200-500 °C; no UV emission was observed for the films deposited at RT regardless of annealing treatment. Improvement of grain size and stoichiometric ratio with annealing temperature can be attributed to the enhancement of UV emission, but the adsorbed oxygen species on the surface and grain boundary of films are thought to contribute the annihilation of UV emission. It seems that annealing at lower temperature in air is an effective method to improve the UV emission for thin films deposited on glass substrate at substrate temperature above RT.     

Improvement of optical properties of Nd:YAG transparent ceramics by post-annealing and post hot isostatic pressing

The Nd:YAG transparent ceramics were fabricated by vacuum sintering. The Nd:YAG samples were annealed at 1450 °C for 20 h in air and followed by hot isostatic pressing (HIP) at 1700 °C for 2 h in 200 MPa Ar and then re-annealed at 1250–1450 °C for 10 h in air. The experimental results showed that the optical properties of Nd:YAG samples varied markedly with different post treatments. After air annealing at 1450 °C for 20 h and HIP at 1700 °C for 2 h under 200 MPa of Ar and then air re-annealing at 1250 °C for 10 h, the transmittances of the samples increased from 51.2% to 77.2% (at 400 nm) and 78.4% to 83.6% (at 1064 nm), respectively. The annealing and HIP are effective post treatments to reduce oxygen vacancies and intergranular pores respectively in Nd:YAG transparent ceramics.     

Effects of thermal annealing on the optical,spectroscopic, and structural properties of tris (8-hydroxyquinolinate) gallium films grown on quartz substrates

In this study we report the optical, spectroscopic, and structural properties of vacuum deposited tris (8-hydroxyquinolinate) gallium film upon thermal annealing in the temperature range from 85 °C to 255 °C under a flowing nitrogen gas for 10 min. The optical UV–vis–NIR and luminescence spectroscopy measurements were performed to estimate the absorption bands, optical energy gap (E_g), and photoluminescence (PL) of the films. Fourier transform infrared (FTIR) spectroscopy and X-ray diffraction (XRD) techniques were used to probe the spectroscopic and structural nature of the films. We show that, by annealing the films from 85 °C to 235 °C, it is possible to achieve an enhanced absorption and increased photoluminescence to five times stronger than that of the pristine film. The PL quenching at 255 °C was attributed to the presence of plainer chains allow easy going for excitons to a long distance due to the crystalline region formation of α-Gaq3 polymorph. The reduction in E_g and infrared absorption bands upon annealing were referred to the enhancement in π–π interchain interaction and conformational changes by re-arrangement of the Gaq3 quinolinate ligands, respectively. Stokes shift for the films were observed and calculated. From the differential scanning calorimetry, DSC measurements, higher glass transition temperature was observed for Gaq3 (T_g = 182 °C) compared to that of Alq3 (T_g = 173 °C), which suggests the existence of stronger dipolar interaction in Gaq3 due to the Ga³⁺ cation effect, in comparison to that of Alq3.     

Influence of rapid thermal annealing effect on electrical and structural properties of Pd/Ru Schottky contacts to n-type GaN

Pd/Ru metallization scheme is fabricated on n-GaN as a Schottky contact, and the electrical and structural properties have been investigated as a function of annealing temperature by current–voltage (I–V), capacitance–voltage (C–V), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) measurements. As-deposited Ru/Pd/n-GaN contact yielded Schottky barrier height (SBH) of 0.67 eV (I–V) and 0.79 eV (C–V), respectively. Further, it is observed that the Schottky barrier height increases to 0.80 eV (I–V) and 0.96 eV (C–V) for the contact annealed at 300 °C. However, both I–V and C–V measurements indicate that the barrier height slightly decreased when the contacts are annealed at 400 °C and 500 °C. From the above observations, the optimum annealing temperature for Pd/Ru Schottky contact is 300 °C. Norde method is also employed to extract the barrier height of Pd/Ru Schottky contacts which are in good agreement with those obtained by the I–V technique. X-ray photoelectron spectroscopy results shows that the Ga 2p core-level shift towards the low-energy side for the contact annealed at 300 °C compared to the as-deposited contact. Based on the XPS and XRD results, the reason for the increase in SBH upon annealing at 300 °C could be attributed to the formation of gallide phases at the Ru/Pd/n-GaN interface vicinity. The AFM results showed that the overall surface morphology of the Pd/Ru Schottky contacts on n-GaN is fairly smooth. The above observations reveal that the Pd/Ru Schottky contact is attractive for high-temperature device applications.     

Effect of growth temperature on the structural and transport properties of magnetite thin films prepared by pulse laser deposition on single crystal Si substrate

Magnetite (Fe₃O₄) thin films are prepared by pulsed laser deposition using an α-Fe₂O₃ target on silicon (111) substrate in the substrate temperature range of 350 °C to 550 °C. X-ray diffraction (XRD) measurement shows that the film deposited at 450 °C is a single phase Fe₃O₄ film oriented along [111] direction. However, the film grown at 350 °C reveals mixed oxide phases (FeO and Fe₃O₄), while the film deposited at 550 °C is a polycrystalline Fe₃O₄. X-ray photoelectron spectroscopy study confirms the XRD findings. Raman measurements reveal identical spectra for all the films deposited at different substrate temperatures. We observe abrupt increase in the resistivity behavior of all the films around Verwey transition temperature (T_V) (125 K-120 K) though the transition is broader in the film deposited at 350 °C. We observe that the optimized temperature for the growth of Fe₃O₄ film on Si is 450 °C. The electrical transport behavior follows Shklovskii and Efros variable range hopping type conduction mechanism below T_V for the film deposited at 450 °C possibly due to the granular growth of the film.     

Room temperature deposition of Al-doped ZnO films on quartz substrates by radio-frequency magnetron sputtering and effects of thermal annealing

High-quality Al-doped zinc oxide (AZO) thin films have been deposited on quartz substrates by radio-frequency magnetron sputtering at room temperature for thin film solar cell applications as transparent conductive oxide (TCO) electrode layers. Effects of post-deposition annealing treatment in pure nitrogen and nitrogen/hydrogen atmosphere have been investigated. Annealing treatments were carried out from 300 °C to 600 °C for compatibility with typical optoelectronic device fabrication processes. A series of characterization techniques, including X-ray diffraction, scanning electron microscopy, Hall, optical transmission, and X-ray photoelectron spectroscopy has been employed to study these AZO materials. It was found that there were significant changes in crystallinity of the films, resistivity increased from 4.60 × 10^− 4 to 4.66 × 10^− 3 Ω cm and carrier concentration decreased from 8.68 × 10²⁰ to 2.77 × 10²⁰ cm^− 3 when annealing in 400 °C pure nitrogen. Whereas there were no significant changes in electrical and optical properties of the AZO films when annealing in 300-500 °C nitrogen/hydrogen atmosphere, the electrical stability of the AZO films during the hydrogen treatment is attributed to both desorption of adsorbed oxygen from the grain boundaries and production of additional oxygen vacancies that act as donor centers in the films by removal of oxygen from the ZnO matrix. These results demonstrated that the AZO films are stably suited for TCO electrodes in display devices and solar cells.     

Specific features of the electronic structure and optical properties of KPb2Br5: DFT calculations and X-ray spectroscopy measurements

Density functional theory (DFT) calculations are made in order to explore the total and partial densities of states of potassium dilead pentabromide, KPb₂Br₅, by using the augmented plane wave + local orbitals (APW + lo) method as incorporated in the WIEN2k package. The present calculations reveal that the principle contributors to the valence band of KPb₂Br₅ are the Pb 6s and Br 4p states contributing predominantly at the bottom and at the top of the band, respectively, while the bottom of the conduction band is formed mainly from contributions of the unoccupied Pb 6p states. The curves of total density of states derived by the present DFT calculations of KPb₂Br₅ are found to be in agreement with the experimental X-ray photoelectron valence-band spectrum of the compound studied. Comparison on a common energy scale of the X-ray emission bands representing the energy distribution of the valence Br p and K s states and the X-ray photoelectron valence-band spectrum of the KPb₂Br₅ single crystal indicate that the Br 4p and K 4s states contribute mainly at the top and in the upper portion of the valence band, respectively, being in agreement with data of the present DFT band-structure calculations of this compound. Principal optical characteristics of KPb₂Br₅, namely dispersion of the absorption coefficient, real and imaginary parts of dielectric function, electron energy-loss spectrum, refractive index, extinction coefficient and optical reflectivity are also studied by the DFT calculations.     

Structural and optical properties of hydrothermally grown zinc oxide nanorods on polyethersulfone substrates as a function of the growth temperature and duration

Zinc oxide (ZnO) nanorods were grown on polyethersulfone substrates with a seed layer by hydrothermal synthesis. The effects of the growth temperature and duration on the structural and optical properties of the ZnO nanorods were investigated by X-ray diffraction, field emission scanning electron microscope and photoluminescence measurements. Improvement of the structural properties was confirmed when the ZnO nanorods were grown at a moderate thermal energy. Thermal energies that were too high or too low resulted in structural degradation: low thermal energies did not provide enough energy for the ZnO growth, and high thermal energies contributed to improper growth by creating an uncommon flake-like structure. Photoluminescence measurements showed that the near-band-edge emission to deep-level emission peak ratio increases with increasing growth temperature at growth duration of 5 h.     

不同籽晶DKDP晶体生长和光学性能研究

籽晶是影响DKDP晶体生长和光学性能的一个重要因素.通过传统降温法,分别利用Z片和[101]晶片作为籽晶,从氘化程度为85%的溶液中生长DKDP晶体并对加工样品进行了相关测试.研究了不同籽晶对DKDP晶体的生长和光学性能的影响.实验表明,[101]晶片籽晶所得DKDP晶体能有效缩短生长周期,晶体损伤阈值提高明显,但光学均匀性和透过性能有所下降.     

Influence of Nb dopant on the structural and optical properties of nanocrystalline TiO2 thin films

In this study, preparation of Nb-doped (0-20 mol% Nb) TiO₂ dip-coated thin films on glazed porcelain substrates via sol-gel process has been investigated. The effects of Nb on the structural, optical, and photo-catalytic properties of applied thin films have been studied by X-ray diffraction, Raman spectroscopy, and scanning electron microscopy. Surface topography and surface chemical state of thin films was examined by atomic force microscope and X-ray photoelectron spectroscopy. XRD and Raman study showed that the Nb doping inhibited the grain growth. The photo-catalytic activity of the film was tested on degradation of methylene blue. Best photo-catalytic activity of Nb-doped TiO₂ thin films were measured in the TiO₂-1 mol% Nb sample. The average optical transmittance of about 47% in the visible range and the band gap of films became wider with increasing Nb doping concentration. The Nb⁵⁺ dopant presented substitutional Ti⁴⁺ into TiO₂ lattice.     

高分子网络凝胶法制备YAG:Er~(3+)纳米晶粉体及其光谱性质

采用高分子网络凝胶法,在较低温度下制备了YAG:Er~(3+)纳米晶粉体.分别用热重-差热分析(TG-DSC)、X射线衍射(XRD)、扫描电子显微镜(SEM)以及激发和发射光谱对样品进行了表征.结果表明:石榴石晶相的形成温度为880℃,与YAG纳米晶粉体相比,用Er~(3+)代替Y~(3+)后,YAG:Er~(3+)纳米晶粉体还是以石榴石晶相为主,未发生明显变化;YAG:Er3~(3+)纳米晶粉体有丰富的吸收谱线,并且在260nm激发光激发下YAG:Er~(3+)纳米晶粉体可以发射出377nm紫光,可以作为紫光光源的考虑对象.     

Influence of oxygen in the deposition and annealing atmosphere on the characteristics of ITO thin films prepared by sputtering at room temperature

Indium tin oxide (ITO) thin films have been grown onto glass substrates by sputtering at room temperature with various controlled oxygen and argon ratios used as reactive and sputter gases, respectively. After deposition, the samples have been annealed at 350 °C in the same sputtering chamber in vacuum or in air. The structure, morphology and electro-optical characteristics of the ITO coatings have been analyzed as a function of the oxygen added during deposition and of the annealing atmosphere by X-ray diffraction, atomic force microscopy, four points electrical measurements and spectrophotometry. It has been found that the as-deposited amorphous samples crystallize in the cubic structure by annealing. The optical transmittance and the electrical resistance decrease when the oxygen content in the deposition and the annealing atmosphere is reduced.     

Influence of CTAB surfactant on structural and optical properties of CuS and CdS nanoparticles by hydrothermal route

Metal sulphide CuS and CdS nanoparticles capped with Cetyltrimethylammonium bromide (CTAB) were synthesized by hydrothermal method. Structural, morphological, chemical composition, optical and luminescent properties were evaluated by different analytical techniques. X-ray diffraction (XRD) analysis of the CTAB capped metal sulfide nanoparticles reveals the formation of hexagonal structure. High-resolution transmission electron microscopy (HRTEM) images show that the morphology of the capped copper sulphide samples consists of hexagonal structure and capped cadmium has spherical shape and also confirms the crystalline nature of the particles with distinct lattice fringes. In FTIR spectroscopy, the composition of the CTAB capped CuS and CdS nanoparticles have been confirmed. The analysis of photoluminescence (PL) and optical transition show a red shift due to the reduction of band gap energy and it is attributed to the low defects and high crystallinity. The optical studies indicate that CuS and CdS nanoparticles with CTAB can be suitable for optoelectronic devices and photovoltaic applications.     

Influence of annealing temperature on the properties of ZnO:Zr films deposited by direct current magnetron sputtering

Transparent conducting zirconium-doped zinc oxide (ZnO:Zr) films were deposited on quartz substrates by direct current (DC) magnetron sputtering at room temperature. The influence of post-annealing temperature on the structural, morphological, electrical and optical properties of ZnO:Zr films were investigated. When annealing temperature increases from room temperature to 573 K, the resistivity decreases obviously due to an improvement of the crystallinity. However, with further increase in annealing temperature, the crystallinity deteriorates leading to an increase in resistivity. The films annealed at the optimum annealing temperature of 573 K in vacuum have the lowest resistivity of 9.8 × 10⁻⁴ Ω cm and a high transmittance of above 92% in the visible range.     

Effect of annealing on the structural and optical properties of non-coated and silica-coated ZnS:Mn nanoparticles

The Mn²⁺-doped ZnS nanoparticles stabilized by sodium citrate were synthesized through a simple chemical route. Using the ZnS:Mn nanoparticles as seeds, the silica-coated ZnS:Mn nanocomposites were formed in isopropanol by the controlled hydrolysis of tetraethyl orthosilicate. The photoluminescence spectra confirmed that the Mn²⁺ ions were incorporated into the ZnS nanoparticles. The annealing effect on the structural and optical properties of these particles was studied over a range of 100–400 °C. The results of X-ray diffraction and photoluminescence showed that the silica shell not only improved the thermal stability but also resisted the lattice-deformation and oxidation of the particles. The thermal analysis further confirmed that the non-coated ZnS:Mn nanoparticles were unstable beyond 200 °C.     

Influence of 250 keV Ge ions fluence on electrical and optical properties of SiC

Commercially graded SiC samples were implanted with 250 keV germanium ions (Ge⁺) at room temperature. For Ge⁺ ions source, laser-induced plasma (LIP) technique was used. Ge⁺ implantation was confirmed by energy dispersive X-ray (EDX) analysis. Change in FWHM and lattice constant of SiC samples has been observed after the Ge implantation, calculated by Bragg's law from XRD analysis. A comparison of the electrical and optical properties of SiC before and after Ge⁺ implantation (SiC:Ge) has also been made. Electrical diagnostic comprises of a four-probe method for the measurement of resistivity whereas Raman spectroscopy is employed for the optical investigation. Resistivity measurements of SiC and SiC:Ge samples showed that resistivity decreases as Ge⁺ implantation increases. Raman spectroscopy of the SiC and SiC:Ge showed that Raman band became broadened and is shifted towards the lower wave number with the increase in Ge ion fluence. The increase in Ge ions fluence enhances the lattice defects which are responsible for broadening in XRD and Raman peaks as well as increase in conductivity of the samples.     

Substrate and annealing temperature effects on the crystallographic and optical properties of MoO3 thin films prepared by laser assisted evaporation

MoO₃ thin Films were prepared using the assisted laser evaporation technique. Samples were grown on glass and silicon substrates at different substrates temperatures. The effect on structural and optical properties of the substrate and on annealing temperatures was evaluated. A phase transition was found around 200 °C in all samples from the amorphous to the β phase with a small percentage of α phase, and another one was found around 500 °C from the α + β to the α phase. The percentage errors between the lattice parameter a₀ of the crystallographic index card for the MoO₃ alpha phase and the indexed lattice parameters were 1.4% and 0.3% for the samples deposited on glass and silicon respectively, indicating the crystalline structure of the silicon substrate favors the formation of the MoO₃ alpha orthorhombic phase. The spectral variation of the refractive index and the absorption coefficient were theoretically determined. The amorphous samples presented a constant gap of 3.2 eV while the optical properties critically depended on the substrate and annealing temperatures.     

Growth, characterization and optical quality of CaF2 single crystals grown by the temperature gradient technique

The CaF₂ single crystals with diameters up to 200 mm were successfully grown by modified temperature gradient technique (TGT), which are suitable for application as optical elements in the ultraviolet range. The optimizations of various growth parameters were systematically studied. Properties of as-grown CaF₂ crystals were characterized by the nature of inclusions, dislocations, crystallinity, and impurities contents. The results showed that the dislocations and multinucleation were mostly constrained in the conical part of the crystals with the cylindrical parts having the best crystalline quality and lowest impurity contents. The high optical quality of TGT-grown CaF₂ single crystals was also confirmed to have excellent optical transmission in 190-2500 nm and refractive index homogeneity.     

The influence of annealing temperature on the structural, electrical and optical properties of ion beam sputtered CuInSe2 thin films

CuInSe₂ (CIS) thin films were prepared by ion beam sputtering deposition of copper layer, indium layer and selenium layer on BK7 glass substrates followed by annealing at different temperatures for 1 h in the same vacuum chamber. The influence of annealing temperature (100-400 °C) on the structural, optical and electrical properties of CIS thin films was investigated. X-ray diffraction (XRD) analysis revealed that CIS thin films exhibit chalcopyrite phase and preferential (112) orientation when the annealing temperature is over 300 °C. Both XRD and Raman show that the crystalline quality of CIS thin film and the grain size increase with increasing annealing temperature. The reduction of the stoichiometry deviation during the deposition of CIS thin films is achieved and the elemental composition of Cu, In and Se in the sample annealed at 400 °C is very near to the stoichiometric ratio of 1:1:2. This sample also has an optical energy band gap of about 1.05 eV, a high absorption coefficient of 10⁵ cm⁻¹ and a resistivity of about 0.01 Ω cm.