Color-tunable and upconversion luminescence of Gd₂O₂S:Er,Tm phosphor. Experimental investigations and first-principles calculation

The Er³⁺, Tm³⁺ co-doped gadolinium oxysulfide phosphors were prepared using solid-state reaction in vacuum. The crystal structure, morphology, and photoluminescence characteristics were, respectively, investigated by X-ray diffraction, transmission electron microscope, upconversion luminescence spectra and Commission Internationale de L'Eclairage diagram. Under 980 nm excitation, the quenching concentration of Er³⁺ was revealed to be 7 mol% with highest luminescence intensity and fluorescence lifetime. The emitting color of Gd₂O₂S:Er,Tm phosphors can be tuned by adjusting the concentration of Er³⁺ and Tm³⁺. First-principles calculation was employed to clarify the luminescence mechanism of the impurities doped in gadolinium oxysulfide host lattice by calculated band structure, density of states and absorption spectrum. (orig.)