Boltzmann relation reliability in optical temperature sensing based on upconversion studies of Er3+ /Yb3+ codoped PZT ceramics

The fluorescence intensity ratio (FIR) of two thermally coupled levels with temperature follows the Boltzmann equation and shows an exponential nature to the temperature which is purely dependent on the energy difference between the levels. Despite the identical energy difference between the thermally coupled levels, researchers have observed varying sensitivities for various samples. In this article, the FIR and sensitivities were calculated using the Boltzmann equation by changing various parameters such as energy difference (ΔE) and the value of the constant C. The results were compared with various reports for Er³⁺ /Yb³⁺ ions. After analysis, a new polynomial fit equation was used to determine the temperature sensitivities for the Er³⁺ /Yb³⁺ codoped PbZrTiO₃ phosphor in lieu of the conventional Boltzmann equation. The polynomial fit equation eliminated the dependency of the sensitivity on the inverse of the FIR factor and a flat sensitivity curve was obtained with temperature.

Luminescent properties of Eu3+-activated Gd2ZnTiO6 double perovskite red-emitting phosphors for white light-emitting diodes and field emission displays

We synthesized a series of double perovskite Eu3+-activated Gd2ZnTiO6 red-emitting phosphors by a solid-state reaction route and analyzed their morphology, crystallinity, luminescent properties, and thermal stability. Under 270 nm of excitation, the prominent emission peak of the phosphors was found to be located in the red region with the central wavelength of 613 nm corresponding to the intra-4f transition of Eu3+ ions from the 5D0 to 7F2 level. The optimum concentration of the activator was determined to be 7 mol%. The studied phosphors also exhibited good thermal stability with the activation energy of 0.233 eV. The white color emitted from the ultraviolet (UV) light-emitting diode device which was coated by commercial blue-/green-emitting phosphors and Gd1.86ZnTiO6:0.14Eu3+ phosphors exhibited a high color rendering index of 82.9. Furthermore, the cathodoluminescence performance of the resultant phosphors was also investigated in detail. These characteristics of Gd2-2x ZnTiO6:2xEu3+ phosphors make them potential candidates for UV-based white light-emitting diodes and field emission displays.

Investigation on Two Forms of Temperature-Sensing Parameters for Fluorescence Intensity Ratio Thermometry Based on Thermal Coupled Theory

Absolute temperature sensitivity (S_a) reflects the precision of sensors that belong to the same mechanism, whereas relative temperature sensitivity (S_r) is used to compare sensors from different mechanisms. For the fluorescence intensity ratio (FIR) thermometry based on two thermally coupled energy levels of one rare earth (RE) ion, we define a new ratio as the temperature-sensing parameter that can vary greatly with temperature in some circumstances, which can obtain higher S_a without changing S_r. Further discussion is made on the conditions under which these two forms of temperature-sensing parameters can be used to achieve higher S_a for biomedical temperature sensing. Based on the new ratio as the temperature-sensing parameter, the S_a and S_r of the BaTiO₃: 0.01%Pr³⁺, 8%Yb³⁺ nanoparticles at 313 K reach as high as 0.1380 K^-1 and 1.23% K^-1, respectively. Similarly, the S_a and S_r of the BaTiO₃: 1%Er³⁺, 3%Yb³⁺ nanoparticles at 313 K are as high as 0.0413 K^-1 and 1.05% K^-1, respectively. By flexibly choosing the two ratios as the temperature-sensing parameter, higher S_a can be obtained at the target temperature, which means higher precision for the FIR thermometers.

Simultaneous phase and size manipulation in NaYF4:Er3+/Yb3+ upconverting nanoparticles for a non-invasion optical thermometer

A series of Er³⁺/Yb³⁺-codoped NaYF₄ upconverting nanoparticles were synthesized via a hydrothermal method.

Yb3+-Concentration dependent upconversion luminescence and temperature sensing behavior in Yb3+/Er3+ codoped Gd2MoO6 nanocrystals prepared by a facile citric-assisted sol–gel method

Er³⁺/Yb³⁺-Codoped Gd₂MoO₆ upconversion nanocrystals with high sensor sensitivity and wide operation range were demonstrated for non-contact optical thermometry.