Synthesis and Luminescence Properties of Nanostructured Gd3 –x – yYbxEryBWO9 Borate Tungstates

Abstract

Using the Pechini process in the presence of citric acid and mannitol, followed by annealing in the range 800–1000°C, we have synthesized nanostructured rare-earth borate tungstates crystallizing in hexagonal symmetry (sp. gr. P6₃): undoped Gd₃BWO₉ and Gd_{3 –x – y}Yb_xEr_yBWO₉, containing Yb³⁺ and Er³⁺ active ions. We have measured upconversion luminescence spectra of the Er³⁺ ions in Gd_{3 –x – y}Yb_xEr_yBWO₉ for the ²H_11/2, ⁴S_3/2 → ⁴I_15/2 and ⁴F_9/2 → ⁴I_15/2 transitions under excitation by an IR laser (λ = 974 nm). The spectra consist of two groups of broadened bands in the red and green spectral regions. Brighter luminescence is observed in the green spectral region, which contains two bands corresponding to the Er³⁺²H_11/2, ⁴S_3/2 → ⁴I_15/2 and ⁴F_9/2 → ⁴I_15/2 transitions. We have analyzed the effect of annealing temperature on the upconversion luminescence intensity of Gd_{3 –x – y}Yb_xEr_yBWO₉ and determined the energy yield of upconversion luminescence in the Gd_{3 – x – y}Yb_xEr_yBWO₉ borate tungstates. The highest value, B_en = 0.19%, has been obtained for the phosphor with Yb : Er = 7 : 1.