大尺寸Co2+:ZnGa2O4单晶的生长与光学特性

The transition of cobalt ions located at tetrahedral sites will produce strong absorption in the visible and near-infrared regions,and is expected to work in a passively Q-switched solid-state laser at the eye-safe wavelength of 1.5 µm.In this study,Co2+ions were introduced into the wide bandgap semiconductor material ZnGa2O4,and large-sized and high-qual-ity Co2+-doped ZnGa2O4 crystals with a volume of about 20 cm3 were grown using the vertical gradient freeze(VGF)method.Crystal structure and optical properties were analyzed using X-ray powder diffraction(XRD),X-ray photoelectron spectroscopy(XPS),and absorption spectroscopy.XRD results show that the Co2+-doped ZnGa2O4 crystal has a pure spinel phase without impurity phases and the rocking curve full width at half maximum(FWHM)is only 58 arcsec.The concentration of Co2+in Co2+-doped ZnGa2O4 crystals was determined to be 0.2 at.%by the energy dispersive X-ray spectroscopy.The optical band gap of Co2+-doped ZnGa2O4 crystals is 4.44 eV.The optical absorption spectrum for Co2+-doped ZnGa2O4 reveals a prominent visible absorption band within 550-670 nm and a wide absorption band spanning from 1100 to 1700 nm.This suggests that the Co2+ions have substituted the Zn2+ions,which are typically tetrahedrally coordinated,within the lattice structure of ZnGa2O4.The vis-ible region's absorption peak and the near-infrared broad absorption band are ascribed to the 4A2(4F)→ 4T1(4P)and 4A2(4F)→4T1(4F)transitions,respectively.The optimal ground state absorption cross section was determined to be 3.07×10-19 cm2 in ZnGa2O4,a value that is comparatively large within the context of similar materials.This finding suggests that ZnGa2O4 is a promising candidate for use in near-infrared passive Q-switched solid-state lasers.