Spectroscopic in-depths of upconverting NaZr2(PO4)3 phosphors for LIR-based thermometry

This study employed solid-state synthesis to develop the green emitting Er³⁺-Yb³⁺:NaZr₂(PO₄)₃, NASICON material. Using Rietveld refinement, the crystallographic variables of the synthesized phosphors were precisely calculated. The upconverting phenomenon was seen with naked eye when exposed to 980 nm laser radiation. The intermediate excited state dependency on the unusual photon number dependence on the green and red emission has been understood using the steady-state rate law equations. Further, the temperature sensing performances with good repeatability were compared with different laser densities, and it was found that the prepared phosphors could be an ideal material for upconverting and temperature sensing applications.

Excellent upconversion luminescence and temperature sensing performance of CdMoO4:Er3+,Yb3+ phosphors

In this paper, Er³⁺/Yb³⁺ co-doped CdMoO₄ phosphors were prepared by a traditional high temperature solid state reaction method. Based on the 3D network structure of the CdMoO₄ host and the efficient Er³⁺/Yb³⁺ upconversion luminescence combinations, excellent green emission properties were observed when the prepared sample is irradiated with a laser at about 980 nm. For optical temperature sensors based on the fluorescence intensity ratio (FIR), the prepared phosphors have excellent sensitivity to temperature in the range of 293 to 473 K. With increasing environmental temperatures, the absolute sensitivity of the CdMoO₄:0.02Er³⁺,0.08Yb³⁺ sample reached a maximum at about 473 K (S_a = 1.388% K^-1). The calculated relative sensitivity of the optical temperature sensor was S_r = 1.631% K^-1 at 293 K. This is due to the sensitive thermally coupled energy levels (TCLs) of the Er³⁺ ions (²H_11/2 and ⁴S_3/2) in the CdMoO₄ structure. Therefore, it is shown that the prepared CdMoO₄:0.02Er³⁺,0.08Yb³⁺ phosphor has excellent applications in non-contact optical temperature measurement.

Linear red/green ratiometric thermometry of Ho3+/Cr3+ co-doped red up-conversion tungstate materials

Existing optical thermometers are faced with the challenges of high sensitivity limited to a very narrow high temperature range, while also lacking low temperature sensing performance. A new linear up-conversion (UC) optical thermometer with high sensitivity over a wide temperature range was reported here. The introduction of Cr³⁺ optimized the red-green (R/G) ratio and improved the temperature sensing characteristics of Ho³⁺-doped tungstate materials. Notably, as a temperature-related parameter, the R/G emission intensity ratio of Ho³⁺/Cr³⁺ co-doped tungstate material fitted well linearly with temperature. The slope of the fitted line corresponded to the absolute sensitivity value; that is, the sensitivity was constantly 0.0217 K^-1 over the wide range of 163-663 K. This new UC temperature sensor with high sensitivity extended a new field of optical temperature measurement and demonstrated the possibility of applying this linear sensitivity effect in sensing applications. Most importantly, from an optical temperature sensing point of view, this study provided a novel and effective strategy for linear optical temperature measurement.

Bifunctional application of La3BWO9:Bi3+,Sm3+ phosphors with strong orange-red emission and sensitive temperature sensing properties

Through a solid-phase reaction technique, Sm³⁺ and Bi³⁺ co-doped La₃BWO₉ phosphors with high emission intensity and sensitive temperature sensing properties have been successfully synthesized. Based on XRD Rietveld refinement, the optimized crystal structure was used as the original model to calculate the band structure and partial density of states (PDOS) by density functional theory (DFT) calculations. The luminescence characteristics of Sm³⁺ and Bi³⁺ co-doped La₃BWO₉ phosphors were measured and analyzed. In addition, the optimal doping concentrations of Sm³⁺ and Bi³⁺ were investigated. The luminescence properties of Sm³⁺ doped phosphors were optimized by introducing Bi³⁺ ions. Efficient energy transfer from Bi³⁺ to Sm³⁺ ions was observed in La₃BWO₉:Sm³⁺, Bi³⁺ phosphors. An optical temperature sensor with high sensitivity was designed based on the different thermal quenching properties of Sm³⁺ and Bi³⁺ ions. In the temperature range of 293-498 K, the optimum absolute sensitivity (S_a) and maximum relative sensitivity (S_r) were 2.88 %K^-1 and 1.32 %K^-1, respectively. These results indicated that the prepared La₃BWO₉:Bi³⁺, Sm³⁺ phosphors have wide application prospects as solid state lighting materials and optical temperature sensors.