Second-order nonlinear green light emission in sol–gel derived opaque ZnO–GeO₂ oxides by near-infrared laser irradiation

抄録

Oxides of xZnO–(100 − x)GeO₂ (x = 0, 25, 50, 66.7, 75 and 100 mol %) were produced mainly by sol–gel method. Their XRD patterns show that there exist hexagonal ZnO (wurtzite), rhombohedral Zn₂GeO₄, and hexagonal GeO₂ (α-quartz type). All the oxides showed second harmonic generation (SHG) green emission peaking around 532 nm with luminance of about 0.05–1.20 cd·m⁻² when irradiated with an Nd:YAG pulsed laser of 1064 nm. The more the amount of hexagonal ZnO or hexagonal GeO₂ increased, the more the SHG emission intensity increased. Both of hexagonal ZnO and hexagonal GeO₂ do not have centrosymmetry and cause SHG, while rhombohedral Zn₂GeO₄ has centrosymmetry and does not. Therefore, the SHG emission intensity was changed with the amounts of these ZnO and GeO₂ crystals.