Temperature sensitivity of Nd³⁺, Yb³⁺:YF<inf>3</inf> ratiometric luminescent thermometers at different Yb³⁺ concentration

Abstract

Nd3+ (0.5 mol.%), Yb3+ (1.0, 2.0, 3.0, 4.0, and 8.0 mol.%):YF3 phosphors were synthesized using a co-precipitation method with subsequent hydrothermal treatment and annealing in vacuum. The Nd3+, Yb3+:YF3 phosphors are orthorhombic phase nano-crystals. Luminescence intensity ratio (LIR) of Nd3+ (4F3/2 – 4I9/2, ~866 nm) and Yb3+ (2F5/2 – 2F7/2, ~980 nm) emissions was chosen as temperature-dependent parameter. The energy exchange between 4F3/2 (Nd3+) and 2F5/2 (Yb3+) is phonon-assisted which explains the temperature dependence of LIR. There are Nd3+ to Yb3+ energy transfer (ET), Yb3+ to Nd3+ back energy transfer (BET) and energy diffusion (ED) between Yb3+ ions. The probability of BET decreases with the increase of Yb3+ concentration which leads to LIR dependence on Yb3+ concentration. The maximum absolute temperature sensitivity (Sa) was achieved for Nd3+ (0.5%), Yb3+ (1.0%):YF3 (Sa = 0.0018 K−1 at 148 K). The studied samples demonstrate high stability after 8 cooling-heating cycles. The Nd3+ (0.5%), Yb3+ (1.0%):YF3 phosphors are very promising for temperature sensing.