Synthesis of Eu3+- and Er3+/Yb3+-doped GdVO4 nanoparticles in reverse micelles and their multifunctional luminescence properties are presented. Using cyclohexane, Triton X-100, and n-pentanol as the oil, surfactant, and co-surfactant, respectively, crystalline nanoparticles with ~4 nm diameter are prepared at low temperatures. The particle size assessed using transmission electron microscopy is similar to the crystallite size obtained from X-ray diffraction measurements, suggesting that each particle comprises a single crystallite. Eu3+-doped GdVO4 nanoparticles emit red light through downconversion upon UV excitation. Er3+/Yb3+-doped GdVO4 nanoparticles exhibit several functions; apart from the downconversion of UV radiation into visible green light, they act as upconvertors, transforming near-infrared excitation (980 nm) into visible green light. The ratio of green emissions from 2H11/2 → 2I15/2 and 4S3/2 → 4I15/2 transitions is temperature dependent and can be used for nanoscale temperature sensing with near-infrared excitation. The relative sensor sensitivity is 1.11%K−1, which is among the highest sensitivities recorded for upconversion-luminescence-based thermometers.

This study explores potential of Er³⁺-Yb³⁺ doped phosphors for up-conversion luminescence thermometry in the temperature range from 10 K to 300 K. Yttrium oxide nanopowder doped with trivalent ytterbium and erbium ions (Y_1.97Yb_0.02Er_0.01O₃) was prepared by hydrothermal synthesis as an example. The intensity ratios of up-conversion emissions from thermally coupled ²H_11/2 and ⁴S_3/2 levels of Er³⁺ show strong temperature dependence (in the range 150 K–300 K) with much higher relative sensitivity than those reported for thermometry above room temperature with Er³⁺-Yb³⁺ based up-conversion materials. The maximal value of relative sensitivity is 5.28%K⁻¹ at 150 K, with temperature resolution ranging from 0.81 K to 0.06 K. In addition, the intensity ratios of emission from thermally non-coupled Er³⁺ levels (²H_9/2 and ⁴F_9/2) and from ⁴S_3/2 also show temperature dependence that can be approximated with an exponential function. With these up-conversion emission ratios, it is possible measure temperature in the range of 10 K to 300 K with excellent sensitivity and resolution.

Herein, temperature dependencies of emission and emission decay of Zn₂SiO₄:Mn²⁺ powder in the range from room temperature to 300 °C is reported. These dependencies allow temperature sensing from luminescence measurements, since Mn²⁺ emission intensity, emission band spectral position, and emission decay are rapidly changing over the entire temperature range. For fluorescence intensity ratio method, measurement that relays on emission intensity changes with temperature, sensitivity of 12.2% is found. In the case of lifetime thermometry, method that relays on emission decay changes with temperature, sensitivity of 0.48% is determined. Both sensitivity values are among the highest ever recorded for inorganic materials.