Synthesis, photoluminescence, and up-conversion luminescence of niobates co-doped with Er³⁺ and Yb³⁺

Abstract

Niobates, CaNb₂O₆ with columbite-type structure doped with Er³⁺ (CaNb₂O₆:Er³⁺) and co-doped with Er³⁺ and Yb³⁺ (CaNb₂O₆:Er³⁺/Yb³⁺) were synthesized from precursor solutions using inorganic salts under mild hydrothermal conditions at 240 °C. The as-prepared niobates appeared to be a sheaf of aligned acicular particles. At 3 mol % Er³⁺, the as-prepared CaNb₂O₆:Er³⁺ showed the strongest photoluminescence (PL) in the characteristic green spectral region corresponding to the ²H_11/2 → ⁴I_15/2 and ⁴S_3/2 → ⁴I_15/2 transitions of Er³⁺. The green PL intensity of the sample doped with 5 mol % Er³⁺ after heating at 1300 °C in air was more than 10 times stronger than that before heating when exciting directly at 377 nm. The effect of the concentration of the sensitizer Yb³⁺ on the up-conversion emission of CaNb₂O₆:Er³⁺/Yb³⁺ was investigated using samples after heating in air. The up-conversion emission intensity of CaNb₂O₆:Er³⁺/Yb³⁺ became the maximum at 5 mol % Er³⁺ and 20 mol % Yb³⁺ under excitation at 980 nm.