Effect of Y3+ codoping on luminescence decays of the 4I13/2 level in Er3+-doped Al2O3 powders prepared by a sol-gel method

The luminescence lifetime of the 0.01 mol.%-0.1 mol.% Er³⁺- and 0–20 mol.% Y³⁺-codoped Al₂O₃ powders prepared at a sintering temperature of 900°C in a non-aqueous sol-gel method has been investigated to explore the enhanced mechanism of photoluminescence properties of the Er³⁺-doped Al₂O₃ by Y³⁺ codoping. For the 0.1 mol.% Er³⁺-Y³⁺-codoped Al₂O₃ powders, the measured lifetime of Er³⁺ gradually increases with increasing Y³⁺ concentration. Consequently, codoping with 20 mol.% Y³⁺ leads to an increase in the measured lifetime from 3.5 to 5.8 ms. By comparing the measured lifetime for different Er³⁺ concentrations in the Al₂O₃ powders, the radiative lifetime of both the Er³⁺-doped and the Er³⁺-Y³⁺-codoped Al₂O₃ powders is estimated to be about 7.5 ms. Infrared absorption spectra indicate that Y³⁺ codoping does not change the-OH content in the Er³⁺-Y³⁺-codoped Al₂O₃ powders. The prolonged luminescence lifetime of the ⁴I_13/2 level of Er³⁺ in Er³⁺-doped Al₂O₃ powders by Y³⁺ codoping is ascribed to the decrease in the energy transfer rate between the Er³⁺ ions and the Er³⁺ and -OH, respectively, due to the suppressed interaction between Er³⁺ ions.     

Spontaneous formation of Ge nanocrystals with the capping layer of Si3N4 by N2 implantation and rapid thermal annealing

We studied Ge nanocrystals (nc-Ge) formed by bombarding Ge(100) surface with N₂⁺ gas followed by rapid thermal annealing (RTA). After initial N₂⁺ implantation, near-edge x-ray absorption fine structure and x-ray photoelectron spectroscopy (XPS) data showed formation of molecule-like N₂ species and chemically metastable Ge nitrides (GeN_x). The RTA transformed these into hemispherical nc-Ge of 10-25 nm in the diameter as clearly seen in transmission electron microscope images. XPS confirmed that the surface of the nc-Ge was covered with Ge₃N₄ layer and underlying layer is also mostly likely Ge₃N₄. This simple process of forming isolated nc-Ge with Ge₃N₄ surrounding layer can be useful in non-volatile memory applications.     

The influence of the molar ratio of Al2O3 to Y2O3 on sintering behavior and the mechanical properties of a SiC–Al2O3–Y2O3 ceramic composite

The influence of the molar ratio of Al₂O₃ to Y₂O₃ (i.e. M_Al2O3/M_Y2O3) on sintering densification, microstructure and the mechanical properties of a SiC–Al₂O₃–Y₂O₃ ceramic composite were studied. It was shown that the optimal value of M_Al2O3/M_Y2O3 was 3/2, not 5/3, which is customarily considered the optimal molar ratio for the formation of YAG (Y₃Al₅O₁₂) phase. When M_Al2O3/M_Y2O3 is 5/3, materials existed in two phases of YAG and very little YAM phases. The sintering mechanism of the solid phase occurred at 1850 °C. When M_Al2O3/M_Y2O3 was 3/2, materials existed in the two phases YAG (Y₃Al₅O₁₂) and YAM (Y₄Al₂O₉). The formation of the low melting point eutectic liquid phase (YAG + YAM) increased sintering densification. Flexure strength, hardness and relative density were all higher.     

Greatly improved photoluminescence properties of the electrodeposited Y2O3:Eu thin film phosphors by the addition of Na and K ions

In this work, Y₂O₃:Eu³⁺ thin film phosphors were prepared by electro-deposition method. The effect of Na⁺ and K⁺ ions on the photoluminescence properties of Y₂O₃:Eu³⁺ thin film phosphor was studied in details. It was found that the addition of Na⁺ and K⁺ ions could improve the photoluminescence intensity by 3 to 4 times. The highly improved photoluminescence intensity may be caused by different factors. The improved crystallinity and the increased optical volume caused by the flux effect of Na⁺ and K⁺ ions could be the major reasons for the enhanced photoluminescence intensity. It was also found that the average lifetime of Y₂O₃:Eu³⁺ thin film phosphors could be adjusted by the molar amount of Na⁺ and K⁺ ions.     

Influence of modulation periods and modulation ratios on the structure and mechanical properties of nanoscale TiAlN/TiB2 multilayers prepared by IBAD

Alternate hard TiAlN/TiB₂ multilayers with different modulation periods (Λ) ranging from 0.6 to 27 nm and modulation ratios (t_TiAlN:t_TiB2) ranging from 8:1 to 25:1 were prepared using an ion beam assisted deposition (IBAD) system. The effect of Λ and t_TiAlN:t_TiB2 on the hardness, elastic modulus, residual stress, and fracture resistance were investigated using various characterization techniques. All multilayers with clear interfaces displayed higher hardness than individual TiAlN and TiB₂ layers. The maximum hardness of 35 GPa and critical load of 84 mN were obtained for the multilayer with a Λ of 2.2-8.8 nm and t_TiAlN:t_TiB2 of 8:1. Strong TiAlN (111) crystallographic texture as well as multilayer structure is thought to be be responsible for the increasing hardness of the TiAlN/TiB₂ multilayers.