With the purpose of investigation on the visible emission properties of Tm3+ ions, a Tm3+-doped Y2O3 transparent ceramic was fabricated by sintering at 1800 °C for 20 hour with a vacuum degree of 1x10-3 Pa. 3 at% ZrO2 was introduced as the sintering aid and the average grain size was measured to be 22 μm. The optical transmittance of the ceramic achieved 76.3 % at 1 μm. The PL spectra at room temperature and low temperature were measured under 361 nm excitation. The ~453 nm emission bands were observed and the luminescence mechanisms were discussed. It was
found that the Tm: Y2O3 transparent ceramic have the potential to be used in white LED packaging structure.
La2O3, Y2O3, ZrO2, and MgO+TEOS were added as the sintering aid to prepare Yb3+:Y3Al5O12 transparent ceramics. Pre-calcination was adopted to improve the crystalline quality and morphology of the commercially available Y2O3 raw powders. The non-stoichiometricaly doped La2O3, Y2O3, and ZrO2 enhanced the grain boundary mobility so fast that
abnormal grain growth occurred and pores tended to be enclosed in these grains. It was found that MgO+TEOS had a
positive effect on full densification of the Yb:YAG ceramics. The grain boundaries moved moderately so that pores could
be eliminated well and meanwhile the grains would not get too large.
Laser output experiment was also carried out for the Yb:YAG transparent ceramics.
The non-polar m-plane GaN film and polarized InGaN/GaN light-emitting diode (LED) grown by metal-organic
chemical vapor deposition (MOCVD) on LiAlO2(100) substrates were investigated. Firstly, the simulation of excitonic
transition energies and polarization effects on band structure of non-polar plane GaN was studied using the k· p
Hamiltonian approach. Due to small lattice mismatch between GaN and LiAlO2 substrate, X-ray diffraction (XRD)
revealed that the obtained m-plane GaN film has only [11-00] orientation with single-crystalline quality. In addition,
anisotropic crystallographic properties and strain were found, which originates from the broken hexagonal symmetry.
The anisotropic strain further separates the energy levels of top valence band at Γ point. The energy splitting as 37meV
as well as in-plane polarization anisotropy for transitions are found by the polarized photoluminescence spectra at room
temperature, which is consistent with our simulation. The fabricated InGaN/GaN LED on LiAlO2(100) emits green
polarized light at room temperature. And the polarization degree of the emission reaches up to 60% at the wavelength of
Sapphire is widely used material for blue emitting diode, laser diode devices, visible-infrared window and radome applications. Although there is a large mismatch in the lattice constants and thermal expansion coefficient between nitride and sapphire, sapphire is still known as the most commonly used substrate in the GaN device for its physical robustness and high temperature stability. The ensuing component performance is highly dependent on the quality of the surface processing. In this work the effects of mechanical polishing, chemo-mechanical polishing (CMP) as well as CMP and subsequent chemical etching on the properties of sapphire substrate surfaces has been studied. The sapphire substrates have been investigated by means of polarizing microscopy, atomic force microscopy (AFM), X-ray diffraction rocking curves (XRCs) and micro-Raman spectroscopy. The results show that CMP with subsequent chemically etching yields the best quality sapphire substrate surfaces. The optimized conditions to realize good substrate and smoother surface morphology have been obtained.