Temperature-, power-, and concentration-dependent two and three photon upconversion in Er3+/Yb3+ co-doped lanthanum ortho-niobate phosphors

Abstract

Lanthanum ortho-niobate matrices, LaNbO₄ (LNO), doped with rare-earth ions (Er³⁺ and Yb³⁺), were prepared by a high-temperature solid-state reaction method. The LNO matrices thus prepared were confirmed by X-ray diffraction followed by Rietveld refinement. Raman spectroscopy was used to analyze the vibrational energy of the undoped and rare-earth doped LNO ceramics. The upconversion fluorescence was studied in the co-doped samples using an NIR laser (980 nm) at low and high pump power as well as the effect of sample temperature. The effect of the laser power and concentration of Yb³⁺ ions on the fluorescence properties were elucidated. The upconversion obtained was found to be due to two as well as three photon processes. Temperature-dependent upconversion measurements were performed to elucidate the nature of the emission processes, and it was concluded that two and three photon upconversion processes have different behaviors.