Molten salt-synthesized Er3+/Yb3+/Sr2+-doped L-Ta2O5 with an intercalated intergrowth structure to boost the pure green upconversion luminescence

Abstract

Er³⁺/Yb³⁺/Sr²⁺-doped L-Ta₂O₅ upconversion phosphors were synthesized using the molten salt method with B₂O₃ as the solvent. High-resolution transmission electron microscopy (HRTEM) results showed that Er³⁺/Yb³⁺/Sr²⁺ underwent intercalated intergrowth in L-Ta₂O₅. This structure facilitates energy transfer from Yb³⁺ to Er³⁺, resulting in outstanding pure green upconversion luminescence (UCL) intensity. The green UCL integrated intensity of L-Ta₂O₅:Er³⁺/Yb³⁺/Sr²⁺ was 1.53 and 3.14 times greater than that of β-NaYF₄:Er³⁺/Yb³⁺ and the optimal NaY(WO₄)₂:Er³⁺/Yb³⁺ samples, respectively. The absolute and relative temperature sensitivity reached 1.383% and 0.992% K⁻¹, respectively. The shift rate of the peak centroids reached 0.273 nm GPa⁻¹ under high pressure. With its excellent performance, L-Ta₂O₅:Er³⁺/Yb³⁺/Sr²⁺ can be used in the fields of UCL display, temperature and pressure sensing.