Structural analysis and luminescent study of thin film zinc germanate doped with manganese

Thin films of zinc germanate doped with manganese (Zn2GeO4:Mn) were fabricated by radio frequency magnetron sputtering, and their structural characteristics and luminescent properties were studied. The Zn2GeO4:Mn films exhibited a pronounced absorption edge at around 271 nm and a high optical transparency in the visible wavelength region with a peak transmittance of 0.927 at 691 nm. While the as-deposited Zn2GeO4:Mn films had an amorphous structure, the annealed films possessed a rhombohedral polycrystalline structure with a random crystallographic orientation of grains. The broad-band photoluminescence (PL) emission was observed from the annealed Zn2GeO4:Mn films. The PL emission spectrum showed a peak maximum at around 537 nm in the green range, which was accounted for by the intrashell transition of 3d5 orbital electrons from the 4T1 lowest excitation state to the 6A1 ground state in the divalent manganese ions. Two discrete peaks were observed in the PL excitation spectrum at 256 and 296 nm, which are considered to be associated with the band-to-band absorption of the host and the sub-band absorption from defect states, respectively. The green cathodoluminescence (CL) emission was obtained from the annealed Zn2GeO4:Mn films with a peak centered at around 534 nm, analogous to the PL emission spectrum.