Optical absorption of AlN thin films shows a ’’knee’’ structure at 6.2 eV and an intense band at 7.8 eV. The structure at 6.2 eV is interpreted as excitonic absorptions due to transitions across the direct energy gap of about 6.2 eV. Dichroism observed at the absorption edge indicates that the transition Γ1v–Γ1c (E∥c) is of lower energy than the transition Γ6v–Γ1c (E⊥c). Strong dichroism in the 7–8-eV region is thought to cause the birefringence of AlN.

Thin films of CaWO4 were synthesized by pulsed laser deposition (PLD) using targets composed of CaO and WO3 oxide mixtures. The crystallinity of CaWO4 thin films strongly depended on PLD conditions, that is, substrate temperature, ambient oxygen pressure, and laser fluence. Congruent thin films with stoichiometry were obtained at 873 K. They showed photoluminescence (PL) at room temperature. PL spectra were characteristic with excitation wavelength, peaked at 440 and 520 nm, which were excited with 340–360 and 300–330 nm, respectively. Cathodeluminescence (CL) spectra could be recorded at room temperature on the PLD thin films and were composed of the same species as observed in PL spectra. Intensity of CL spectra increased drastically after postannealing the PLD thin films at 873 K. PLD experiments were also carried out using CaWO4 targets at the same conditions. Crystalline CaWO4 thin films were obtained much easier than PLD using targets composed of CaO and WO3 oxide mixtures.

Visible and ultraviolet photoluminescence and photoluminescence excitation spectra of quaternary InAlGaN alloys were measured. The excitation photon energy covers from band edge to 180 eV, near both nitrogen K (~400eV) and aluminium K (~1.5 keV) inner shell energy region. From photoluminescence excitation spectra photoluminescence intensity per incident photon number varies in proportion to incident photon energy. This result implies that many conduction band electron -valence band hole pairs which are responsible for photoluminescence are produced by high energy excitation. Time resolved decay curves were also measured in the same energy region. No effect of high energy excitation on time resolved decay measurements suggests a role of indium on the photoluminescence mechanism in InAlGaN system.