Highly-sensitive lifetime optical thermometers based on Nd3+, Yb3+:YF3 phosphors

Optical thermometers based on Nd 3+ (0.5 mol.%), Yb 3+ (1.0, 2,0, 4.0, and 8.0 mol.%):YF 3 nano-phosphors were studied in the 80–320 K temperature range. The Nd 3+ , Yb 3+ :YF 3 phosphors were nanoparticles having 48 ± 1 nm average diameter with the orthorhombic crystal structure. The effective luminescence lifetime (τ eff ) of 4 F 3/2 of Nd 3+ ( 4 F 3/2 – 4 I 9/2 transition, λ em = 866 nm) was taken as a temperature-dependent parameter. The excitation wavelength λ ex = 355 nm corresponds to 4 I 9/2 – 4 D 3/2 absorption band of Nd 3+ (non-resonant excitation). It was revealed that the τ eff decreases with the temperature decrease in the 80–260 K range. In turn, τ eff temperature dependence in the 260–320 K range is less pronounced. The temperature-dependent X-ray diffraction (XRD) experiments revealed that the XRD patterns shift toward fewer angles as temperature increases. This phenomenon was explained by the temperature expansion of the crystal lattice. At lower temperatures the distance between Nd 3+ and Yb 3+ is less in comparison to the distance at higher temperatures. At shorter distances the quenching of τ eff Nd 3+ is more efficient hence the τ eff is less. It was suggested that the contribution of phonon-assisted energy transfer between Nd 3+ and Yb 3+ has less impact on the τ eff temperature dependence. Finally, the Nd 3+ , Yb 3+ :YF 3 phosphors demonstrated the highest performances in the 100–250 K range. Particularly, Nd 3+ (0.5%), Yb 3+ (8.0%):YF 3 and Nd 3+ (0.5%), Yb 3+ (1.0%):YF 3 samples showed the highest S r values (0.80 μ%/K (at 80 K) and 0.58%/K (at 148 K), respectively. • The effective lifetime (τ eff ) of Nd 3+ , Yb 3+ :YF 3 decreases with the temperature decrease in the 80–260 K range. • The temperature-dependence of τ eff is explained by the lattice parameters change with the temperature (thermal expansion). • Nd 3+ (0.5%), Yb 3+ (8.0%):YF 3 sample showed the highest S r values (0.80 μ%/K (at 80 K).