Lanthanum Silicate and Lanthanum Zirconate Nanoparticles Co-Doped with Ho3+and Yb3+: Matrix-Dependent Red and Green Upconversion Emissions

Excitation of Ho 3+ and Yb 3+ co-doped lanthanum silicate and lanthanum zirconate nanoparticles with 980 nm diode laser light gave a red and green glow, respectively, observable by naked eye. Spectroscopic investigations on these materials revealed green (540 nm), red (660 nm), and near-infrared (750 nm) upconversion emissions with the green to red ratio varying with the matrix type and the dopant ion (Yb 3+ ) concentration. The emission was predominantly red for Ho 3+:Yb 3+ (1:3) in lanthanum silicate nanoparticles, while it was predominantly green for Ho 3+:Yb 3+ (1:7) in lanthanum zirconate nanoparticles. A mechanism involving cross-relaxations and energy back transfer has been proposed to explain the observed behavior. The predominance of red emission has been attributed to a strong quenching of Ho 3+ green emitting level mainly by energy back transfer from Ho 3+ to Yb 3+ on the basis of the near-infrared (NIR) emission spectral analysis.