Hydrothermal synthesis and upconversion luminescent properties of Sr2LaF7 doped with Yb3+ and Er3+ nanophosphors

Abstract

Upconversion phosphors Sr2LaF7 co-doped with Yb3+ and Er3+ are synthesized via hydrothermal method. The phase compositions of Sr2LaF7 phosphors with different amounts of Yb3+ and Er3+ dopants, pH values, and complexing agents are characterized by X-ray diffraction (XRD). The crystal structure and morphology of Sr2LaF7 phosphor doped with 15% Yb3+/ 1% Er3+ is refined by the Rietveld method and transmission electron microscopy (TEM). Under 980 nm laser excitation, Yb3+ and Er3+ co-doped Sr2LaF7 phosphors exhibit red emission around 670 nm generated by the 4F9/2 → 4I15/2 transition and green emissions centering around 550 nm and 523 nm generated by the 4S3/2 → 4I15/2 and 2H11/2 → 4I15/2 transitions of Er3+, respectively. The optimum synthetic conditions for upconversion luminescence for Sr2LaF7 co-doped with Yb3+ and Er3+ are discussed and determined to be 15% Yb3+/ 1% Er3+ with EDTA-2Na as the complexing agent under pH value = 8, and the corresponding Commission International de L′Eclairage (CIE) coordinates are calculated to be x = 0.4293 and y = 0.5589 with reddish yellow color visible to naked eyes under the 980 nm laser excitation. The related upconversion mechanisms of Yb3+ and Er3+ co-doped Sr2LaF7 depending on the pump power are also studied in detail.