Near infrared to ultraviolet (UV) and visible upconversion luminescence was observed in ZnO single crystalline under femtosecond laser irradiation. The optical properties of the crystal reveal that the UV and visible emission band are due to the exciton transition (D0X) bound to neutral donors and the deep luminescent centers in ZnO, respectively. The relationship between the upconversion luminescence intensity and the pump power of the femtosecond laser reveals that the UV emission belongs to three-photon simultaneous band-to-band excitation and the visible emission belongs to two-photon simultaneous defect-absorption-induced luminescence. The saturation effects are also found in the upconversion process of ZnO.
© 2007 Chinese Optics LettersPDF Article