Upconversion Luminescence of Fluoride Phosphors SrF2:Er,Yb under Laser Excitation at 1.5 μm

Abstract

Upconversion luminescence of fluoride phosphors SrF₂:Er,Yb co-precipitated from aqueous solutions is studied. Under excitation of Er³⁺ ions to the ⁴I_13/2 level, upconversion luminescence spectra are recorded in the visible and near-IR spectral regions, which correspond to the ⁴G_11/2 → ⁴I_15/2, ²H_9/2 → ⁴I_15/2, ⁴F_5/2 → ⁴I_15/2, ⁴F_7/2 → ⁴I_15/2, ²H_11/2 → ⁴I_15/2, ⁴S_3/2 → ⁴I_15/2, ⁴F_9/2 → ⁴I_15/2, ⁴I_9/2 → ⁴I_15/2, and ⁴I_11/2 → ⁴I_15/2, electronic transitions of Er³⁺ ions and to the ²F_5/2 → ²F_7/2 transition of Yb³⁺. The absolute quantum yields of visible upconversion luminescence under excitation in the region of 1.5 μm are determined for SrF₂:Er,Yb phosphors with different concentrations of Er³⁺ and Yb³⁺ ions and analyzed comparatively with the corresponding values for SrF₂:Er phosphor. A study of chromaticity coordinates showed that the yellow-green upconversion luminescence of SrF₂:Er,Yb phosphors is characterized by color temperatures of 3037–3526 K at an incident power density of 850 W/cm².