Broadband NIR emission in sol-gel Er(3+)-activated SiO2-Ta2O5 glass ceramic planar and channel waveguides for optical application

An Er(3+)-doped SiO2:Ta2O5 optical channel waveguide and nanocomposite were prepared by the sol-gel route at a Si:Ta 50:50 molar ratio. Channels with an excellent surface profile were easily and quickly fabricated by focusing a femtosecond laser onto the surface of multilayered films deposited on SiO2/Si substrates. In parallel, the same sol used to prepare the film was annealed at 900, 1000, and 1100 degrees C for 2 h, to get the nanocomposite materials. A broadband NIR emission around 1538 nm, assigned to the 4I13/2 --> 4I15/2 transition of the Er3+ ions was observed in the nanocomposites of amorphous SiO2 containing dispersed Ta2O5 nanocrystals. The 4I13/2 lifetime and emission bandwidth depend on the annealing temperature. In conclusion, Er(3+)-doped SiO2:Ta2O5 channel waveguides and nanocomposites are promising materials for photonic applications.     

Fabrication and photoluminescence of Er(3+)-doped Al2O3 thin films with sol-gel method

Erbium doped Al2O3 thin films were fabricated on quartz substrates in dip-coating process by sol-gel method, using the aluminum isopropoxide [Al(OC3H7)3]-derived AlOOH sols with the addition of erbium nitrate [Er(NO3)3 x 5H2O]. The as-deposited films, which erbium concentration was between 20 and 43 mol%, were annealed in air from 600 to 1200 degrees C. The phase structure was detected by X-ray diffraction (XRD) and the PL spectra in the wavelength range of 1400-1700 nm were investigated by spectrophotometer, which was exited by a 760 nm semiconductor LD. The PL spectrum shows a broadband extending from 1.430 to 1.670 microm and centered at 1.55 microm, corresponding to the intra-4f transition between the first excited (4I(13/2)) and the ground state (4I(15/2)) of Er3+. The full width at half maximum (FWHM) of PL peaks increase from 60 to 100 nm with temperature increased from 600 to 1200 degrees C.     

Improved infrared emissions of Er(3+)-Tm3+ co-doped Al2O3 thin films: the role of cross relaxation among rare earth ions

We report the infrared emissions of Er(3+)-Tm3+ co-doped amorphous Al2O3 thin films pumped at 791 nm by a Ti:sapphire laser. The as-deposited films were annealed to improve the photoluminescence performance. Three cross relaxation channels among Er(3+)-Tm3+ and Tm(3+)-Tm3+ ions incorporated in the films were investigated as annealing temperature increases especially from 800 to 850 degrees C. In order to understand the Stark effect and cross relaxations, the photoluminescence spectra were deconvoluted by Gaussian fittings. Our results indicate that the luminescence intensity of 1.62 microm in comparison to 1.5 microm can be enhanced by the cross relaxation process [Er3+ (4I13/2) + Tm3+ (3H6) --> Er3+ (4I15/2) + Tm3+ (3F4)], and the longer-wavelength side of Er3+ emission can be improved by the CR process [Er3+ (4I15/2) + Tm3+ (3H4) --> Er3+ (4I3/2) + Tm3+ (3F4) at expense of the Tm3+ 1.47 microm emission which is also maybe quenched by the CR effect between themselves. These results suggest one possible approach to achieve broadband infrared emissions at the wavelength region of 1.45-1.65 microm from the Er(3+)-Tm3+ co-doped systems.     

Enhanced surface-excitonic emission in ZnO/Al(2)O(3) core-shell nanowires

We report the influence of an Al(2)O(3) shell on the photoluminescence emission of ZnO nanowires. At room temperature, the spectrum of the core-shell nanowires shows a strong reduction of the relative intensity of the green defect emission with respect to the near-band-edge emission. At 5?K an increase of the relative intensity of the surface exciton band with respect to the donor-bound exciton emission is observed. Annealing the core-shell nanowires at 500?°C does not increase the green defect luminescence at 5?K. We propose a model explaining the spectral changes.     

Al(H2PO4)3/Al2O3复合硬质材料吸湿改性研究

磷酸二氢铝、磷酸铬铝等无机材料作为高温粘结剂具有固化收缩率低、高强度、耐高温等优点,被广泛应用于冶金、化工以及航天航空领域,但其可吸收空气中的水蒸汽,从而降低材料的强度和完整性.为减少无机高温粘结剂在大气环境下的吸湿量,以有机聚合物聚醚砜、无机添加剂氧化锆粉、热辐射屏蔽剂金粉制备出一种具有耐高温、低导热、热辐射屏蔽的复合密封材料,并将其应用在Al(H2PO4)3/Al2O3复合硬质材料的吸湿改性中.通过对比改性前后样品的扫描电镜图、吸湿率曲线,测试复合密封材料对基体材料吸湿性能的改性效果,并为研究喷涂密封材料对基体材料隔热、强度等性能的影响,进一步分析改性前后样品导热系数、弯曲强度的变化.结果表明,聚醚砜可在基体材料表面形成致密的密封膜,不仅可以隔绝空气中的水蒸汽,使吸湿率最高下降68.39％,还可以提升材料的弯曲强度.同时,金粉的添加可以形成辐射屏蔽层,从而降低材料的高温热导率.     

Giant white and blue light emission from Al(2)O(3) and ZnO nanocomposites

A new and general approach enabling us to amplify not only the bandgap emission of ZnO nanorods but also the defect emission of Al(2)O(3) is proposed. The light intensity of the band edge emission of ZnO nanorods can be improved by as much as 19 times after the decoration of Al(2)O(3) layers. Moreover, white light emission arising from Al(2)O(3) defects in ZnO/Al(2)O(3) nanostructures also shows a large enhancement factor of 12 times. Our new strategy offers an alternative possibility to create strong white and blue light-emitting devices.     

Diode-Pumped Violet Energy Upconversion in BaF(2):Er(3+)

Under 805-nm diode-laser excitation we detected intense upconversion signals at 410, 380, and 275 nm in BaF(2):Er(3+). Energy upconversion schemes and efficiencies are discussed in detail. Intensity parameters of Er(3+) in BaF(2) were derived as Omega(2) = 1.048 ? 0.117 x 10(-20) cm(2), Omega(4) = 1.478 ? 0.180 x 10(-20) cm(2), and Omega(6) = 1.009 ? 0.127 x 10(-20) cm(2).     

光悬浮区熔定向凝固Al2O3/Er3Al5O12和Al2O3/Yb3Al5O12共晶陶瓷的制备与性能研究

本研究探索了光悬浮区熔法制备Al₂O₃/Er₃Al₅O₁₂(ErAG)和Al₂O₃/Yb₃Al₅O₁₂(YbAG) 定向凝固共晶陶瓷。在10 mm/h的抽拉速率下成功获得了凝固组织均匀、内部无裂纹或孔洞的高质量共晶陶瓷。通过高分辨三维X射线衍射仪研究了Al₂O₃和RE₃Al₅O₁₂在三维空间的分布与组织结构; 利用电子背散射衍射技术分析了定向凝固末期Al₂O₃和RE₃Al₅O₁₂两相的晶体学择优取向和相界面关系。力学性能表征结果显示, Al₂O₃/ErAG和Al₂O₃/YbAG具有优异的力学性能, 二者的维氏硬度分别为(13.5±0.4)和(12.8±0.1) GPa;断裂韧性分别为(3.0±0.2)和(3.2±0.1) MPa·m^1/2。     

磁控溅射制备Er~(3+)掺杂Al_2O_3薄膜的上转换发光特性

Al_2O_3作为太阳能电池的钝化层,如果掺入稀土元素Er~(3+)通过吸收红外光并将其上转换为可见光被硅吸收,则可以提高太阳能的利用率。本文采用磁控溅射法制备得到厚度为500 nm左右的不同浓度Er~(3+)掺杂Al_2O_3薄膜。X射线衍射测试表明薄膜由θ-(Al,Er)_2O_3、Al_(10)Er_6O_(24)和ErAlO_3相构成。通过波长980nm的激光器激发产生光频上转换,获得了490 nm的绿光和670nm的红光发光,分别对应于Er~(3+)的~4F_(7/2)→~4I_(15/2)和~4F_(9/2)→~4I_(15/2)的能级跃迁。当Er~(3+)掺杂浓度为0.6%(摩尔比)时,上转换发光强度最强。上转换发光强度受到Al_(10)Er_6O_(24)和ErAlO_3晶体的生成以及Er~(3+)掺杂浓度的影响,并且对红光的影响要大于绿光。Er~(3+)掺杂Al_2O_3薄膜相比粉体材料具有较低的声子态密度,从而抑制了Er~(3+)无辐射跃迁,得到了不同于粉体材料的490nm绿光的发光。     

Synthesis and characterization of core–shell SiO2@(Er3+,Yb3+):Lu2O3

We synthesized crystalline Erbium Er³⁺ and Ytterbium Yb³⁺ codoped -Lu₂O₃ nanolayers on SiO₂ microspheres using the modified Pechini method. Two different kinds of precursors, nitrates and chlorides, have been used leading to a layer-to-layer morphology and necklaces structures, respectively. In both cases, the size of nanocrystallites constituting the optical active layer is around 5 nm. We performed X-ray powder diffraction to confirm the cubic crystalline structure of the sesquioxides layer. High resolution transmission electron microscopy analyses corroborate the crystalline nature of the layer. The optical emission of Er³⁺ in the visible range has been recorded.     

High oxygen ion conduction in some Bi2O3-Y2O3 (Er2O3) solid solutions

Highly densified bodies (~ 98 % theoretical density) of the Bi₂O₃-Y₂O₃(Er₂O₃) systems containing 30 moles % Y₂O₃ and 20 moles % Er₂O₃ respectively were prepared from both mixed oxides and coprecipitated oxalates. DC ionic conductivity and impedance complex plane analysis on sintered samples were performed. Under oxygen partial pressure ranging from 1 to 10 Pa was found that, samples containing 30 moles % yttria showed a pure ionic conductivity up to an oxygen partial pressure of 10⁻²⁰ Pa. Samples containing 20 moles % erbia, extended its ionic conductivity up to an oxygen partial pressure of 10⁻²² Pa. The impedance analysis shows the presence of only one semicircle at low tempertures and it is attributed to bulk conductivity contribution. The conductivity was higher for the Bi₂O₃-Er₂O₃ sintered solid electrolytes, in such a case, a conductivity as high as 1.38 ohm cm at 700ºC was obtained. The activation enthalpy for the conduction process was calculated in the temperature range from 200º to 700ºC in all the cases. Microstructural development in the sintered sample was also studied.     

掺Er3+:Al2O3平面光波导的溶胶-凝胶制备

掺铒光波导主要用来制作光波导放大器。采用溶胶-凝胶法制备了透明、稳定的掺铒的铝硅酸盐玻璃溶胶;使用浸渍提拉法或旋转涂敷法,并通过放在乙醇蒸汽中干燥,可在玻璃表面得到均匀的凝胶膜;最后样品在一定温度下烧结;通过多次重复涂敷-烧结这一工艺流程可以形成厚的硅酸盐玻璃膜层并得到波导结构。使用显微镜研究了凝胶膜表面性质,通过棱镜耦合法测量了波导的有效折射率Nm,也测定了所制备波导的吸收光谱。溶胶-凝胶法在制作均匀性好、高掺铒浓度的铝硅酸盐玻璃光波导上具有优势。     

Acoustic emission from Al2O3-Mo fibre composites

Acoustic emission has been used to investigate the fracture processs in Al₂O₃ and an Al₂O₃-Mo fibre composite. The acoustic emission data indicate extensive micro-fracturing at loads considerably less than that required to cause fracture in Al₂O₃. The acoustic emission emanating from the composite in the early stages of fracture is very similar to that observed in Al₂O₃. However, as final fracture is approached the acoustic emission profiles differ considerably. The acoustic emission profiles are discussed in terms of the fracture mechanisms.     

Luminescent properties and characterization of one dimensional Gd(2)O(3):Eu(3+) phosphor nano-wire for field emission application

Gd(2)O(3):Eu(3+) nano-wire phosphors embedded in SBA-15 silica templates were synthesized using a combination of the sol-gel method and hydrothermal reactions followed by a sintering process at 1000?°C. The crystal structure of Gd(2)O(3):Eu(3+) was confirmed using x-ray diffraction. Observation using transmission electron microscopy shows that the nano-wire diameters were very uniform in the 7-9?nm range. In comparison with bulk Gd(2)O(3):Eu(3+) materials, we found that the photo-luminescent property of the nano-wire was different. The analysis shows that the main nano-wire emission peaks were at 585, 597, 613 and 620?nm. The CIE value (x = 0.62, y = 0.38) indicates that the nano-wire emitted a pink colour and not red as for the bulk material. The field emission experimental results agreed well with the photo-luminescent analysis results.     

K(+)-Na+ ion-exchanged waveguides in Er(3+)-Yb3+ codoped phosphate glasses using field-assisted annealing

Buried channel waveguides were fabricated in Er(3+)-Yb3+ codoped phosphate glasses with use of the thermal two-step ion-exhange method. The K(+)-Na+ ion-exchange process was first carried out in pure KNO3 molten bath, and then field-assisted annealing (FAA) was used to make the buried waveguides. The fluorescence properties of bulk glasses and channel waveguides were characterized, and the waveguide properties were studied. The formation mechanism of buried waveguides was analyzed, and the improved gain characteristics of the waveguide amplifiers with use of different FAA temperatures were measured. The maximum net gain of the waveguide amplifiers at 1.534-microns wavelength was measured to be approximately 3.4 +/- 0.1 dB/cm with 120-mW pump power at 975-nm wavelength.     

Absorption and emission spectra of thallium activated Na2O-NaCl-B2O3 and K2O-KCl-B2O3 glasses

Absorption and emission spectra of two Na₂O-NaCl-B₂O₃ and two K₂O-KCl-B₂O₃ glasses, with large thallium concentrations (about 0.01 mol thallium per litre glass) have been studied. Absorption bands have been observed at 49 000, 44 500 and 40 000 cm^?1 for the Na₂O-NaCl-B₂O₃ glasses, and at 49 000, 43 500 and 38 500 cm^?1 for the K₂O-KCl-B₂O₃ glasses at 300 K. Emission spectra have been recorded at 83, 308, 445 and 485 K; generally two emission bands have been observed in the ultraviolet region, and the intensity of both bands increased with decreasing temperature. The absorption and emission bands have been assigned to electronic transitions in different centres formed by Tl⁺ ions in glass.     

Plasma spraying of Al2O3 and Al2O3Y2O3

A microstructural study has been carried out of plasma-sprayed Al₂O₃ and mixed and sintered Al₂O₃Y₂O₃. In order to ascertain the degree of metastability achieved by plasma spraying, these results are compared with a similar experiment utilizing a CO₂ laser for melting and the hammer-and-anvil technique for quenching of the same materials. X-ray diffraction methods were used to determine the obtained phases and crystal structures. In addition, transmission electron microscopy was used to confirm the phases present and to study their morpology. The porosity was studied with both mercury intrusion porosimetry and small angle neutron scattering. The addition of Y₂O₃ is shown to decrease the porosity from 15% to 7.5%. Adhesion is likewise related to the addition of Y₂O₃ and it is seen that adhesion of the mixture is measurably improved over that of pure Al₂O₃. The implication of these results is discussed.