Synthesis and spectroscopic properties of Er3+/Yb3+-codoped GdNbO4 phosphor for thermometry and marine safety protection

Micron-sized GdNbO4:Er3+/Yb3+ phosphors were prepared by employing a high-temperature solid-state reaction. The crystalline phase, morphology, composition, spectroscopic properties, and impact of rare-earth ion concentration, temperature and high salinity environment were systematically characterized. The extracted results show that phosphor is dominated by the existence of the GdNbO4 crystalline phase. Their morphology and agglomeration phenomenon are strongly dependent on the rare-earth concentration. The phosphor exhibits also excellent up-conversion luminescence (UCL) properties under 980 nm excitation, while a two-photon process accounts for UCL. The following optimal concentrations were selected for enhanced UCL intensity: 10 mol% for Yb3+ and 3 mol% for Er3+. The phosphor shows excellent thermometric performances including strong UCL, good thermal stability, appropriate sensitivity and a wide sensitivity response range. To evaluate the accuracy of the present optical thermometer, the temperature of a heated bench has been comparatively measured by using the proposed optical thermometer and a commercial thermocouple with an accuracy of 1 K. By comparing the temperature values measured by the two methods, it can be concluded that the present optical thermometer has an accuracy better than 1.6 K. In addition, the phosphor exhibits good chemical stability in high salinity environment. Interestingly, its crystalline phase, structure, and UCL spectral structure, intensity and color are all preserved after one-month immersion into a high salinity solution.

Automated summary

Micron-sized GdNbO4:Er3+/Yb3+ phosphors were synthesized and characterized in terms of crystalline phase, morphology, composition, spectroscopic properties, and the effects of rare-earth ion concentration, temperature, and high salinity environment. The phosphor was dominated by GdNbO4 crystalline phase and its morphology and agglomeration were dependent on the rare-earth concentration. It exhibited excellent up-conversion luminescence properties under 980 nm excitation, attributed to a two-photon process. Optimal concentrations of 10 mol% Yb3+ and 3 mol% Er3+ were selected for enhanced up-conversion luminescence intensity. The phosphor showed strong up-conversion luminescence, good thermal stability, appropriate sensitivity, and a wide sensitivity response range. The accuracy of the optical thermometer based on the phosphor was found to be better than 1.6 K compared to a commercial thermocouple. Additionally, the phosphor demonstrated good chemical stability in a high salinity environment, preserving its crystalline phase, structure, and up-conversion luminescence properties.