Pure and Intense Green Upconversion Emission and Temperature Sensing Properties of Ba5Gd8Zn4O21:Ho3+/Yb3+ Nanophosphors

Ho 3+ /Yb 3+ co-doped zincate Ba 5 Gd 8 Zn 4 O 21 nanophosphors were successfully synthesized by solid-state reaction. The crystal structure and phase purity were measured by X-ray diffraction (XRD) and the luminescence spectra and CIE chromaticity were investigated. The results show that the upconversion (UC) luminescence intensities are heavily dependent on the rare-earth dopant concentration but the emission colors are almost the same. Both the green and red UC emissions under 980 nm excitation are shown to be two-photon processes independent of doping concentrations. Furthermore, the optical temperature sensing performance shows that Ho 3+ /Yb 3+ co-doped Ba 5 Gd 8 Zn 4 O 21 nanophosphors are promising candidates for room-temperature applications. The temperature quenching process of green UC emission was modeled using a simplified 4-level diagram and well explained by crossover process and thermal excitation.