Synthesis and emission properties of Tm, Yb doped BaGd 2 ZnO 5 up-conversion phosphors

Up-conversion phosphors emit light by excitation of light of which wavelength is longer than that of emission. This phenomena is caused by multi-photon excitation and energy transfer in f orbital of rare earth elements. In this study, BaGd 2 ZnO 5 doped with different amount of Tm and Yb were prepared, and their up-conversion emissions were measured. Main phase of the prepared samples were identified as BaGd 2 ZnO 5 by X-ray diffraction. Up-conversion emissions were measured using multi-channel photo detector and 980 nm diode laser, and the optimum amount of Tm and Yb were 0.3% and 7% respectively for the up-conversion emission. The optimized sample showed blue, red, and near infrared emissions. Excitation power intensity dependence of each emission was investigated by changing the excitation laser power. Blue emission intensity was proportional to the 2.5th power of the excitation, and near infrared emission was proportional to the 1.8th power of the excitation. These results indicate blue up-conversion emission is 3 photon excitation process and near infrared emission is 2 photon excitation process. Quantum efficiency was measured using fluorescence spectrometer equipped with integral sphere. Absorption rate of 980 nm was 22.68%. Internal quantum efficiency of blue emission was 0.02%, and of near infrared was 2.38%.