Eu 3 + and Yb3+ codoped Gd2O3 single phase nanophosphor: An enhanced monochromatic red emission through cooperative upconversion and downconversion

Abstract

Single phase cubic ${\text{Gd}}_2{\text{O}}_3$ nanophosphor codoped with ${\text{Eu}}^{3+}$ and ${\text{Yb}}^{3+}$ ions has been synthesized through solution combustion route. Structural properties have been investigated using x-ray diffraction (XRD) and transmission electron microscopy (TEM). The as-synthesized ${\text{Gd}}_2{\text{O}}_3$ phosphor shows amorphous nature which changes to crystalline single cubic phase on annealing. Optical properties have been investigated through absorption, photoluminescence, and lifetime measurements. Intense red emission $\left({{}^5\text{D}}_0\to {{}^7\text{F}}_2\right)$ is observed both from cooperative upconversion (${\text{Yb}}^{3+}+{\text{Yb}}^{3+}\to {\text{Eu}}^{3+}$ on 976 nm excitation) as well as through downconversion process (on 355 nm excitation). The unusual and rarely reported emissions from the higher lying ${{}^5\text{D}}_{\text{J}}$ ($\text{J}=2$ , 3, and 4) to ${{}^7\text{F}}_{\text{J}}$ ($\text{J}=0$ , 1, 2, 3, and 4) levels are also observed with 976 nm excitation. Nearly twenty two times enhancement in the intensity of the hypersensitive transition $\left({{}^5\text{D}}_0\to {{}^7\text{F}}_2\right)$ along with an increase in the decay time $\left(770\mu \text{s}\right)$ is observed for the sample annealed at $1200°\text{C}$ on 355 nm excitation. These observations have been explained satisfactorily.