Molten Salt Synthesized CaTa₄O₁₁:Er³⁺/Yb³⁺ with Superior Upconversion Luminescence

Abstract

Low phonon tantalate-based phosphors with a layer structure are considered to have excellent upconversion luminescence (UCL) intensity, which could be reduced due to the existence of impure phase defects and inappropriate doped rare earth ions. To improve their UCL performance, we have prepared single-phase CaTa4O11:Er3+/Yb3+ samples by a molten salt synthesis (MSS) using KCl as the reaction medium and compared its UCL properties with counterparts made by a conventional solid-state reaction (SSR) in this study. We have demonstrated that the MSS samples have a much higher UCL intensity under 980 nm laser excitation than the SSR ones due to accurate replacement of Ca2+ sites by Er3+/Yb3+ in high-purity single-phase MSS samples. We have further enhanced the green UCL intensity of the MSS samples by 1.57 times via acid picking (AP). Under 980 nm laser excitation at a high powder density of 61.3 W/cm2, the green UCL intensity of the MSS-AP samples can reach 3.72 times that of the SSR-AP samples. For potential luminescence thermometry applications, the maximum absolute sensitivity (S A) of the MSS-AP samples reaches 0.01316 K–1 at 501 K based on the luminescence intensity ratio. This study shows that CaTa4O11:Er3+/Yb3+ phosphors prepared by the MSS method are single-phase samples with excellent pure green UCL as a suitable temperature sensing material.

Engineering Visible to Near-Infrared Luminescence through a Selective Doping Strategy for High-Performance Temperature Sensing

“…Based on previous reports, two crucial parameters, absolute sensitivity ( S a ) and relative sensitivity ( S r ), are typically employed to precisely evaluate the thermal sensitivity characteristics across various thermometers, which can be determined using the following expression , S a = | d LIR italicdT | = a 0.25em exp ( − b T ) × b T 2 S r = | 1 LIR d LIR dT | = b T 2 The S r values calculated via eq are illustrated in Figure c. These models result in S r values of 1.30% K –1 ( I 655 / I 545 ) and 1.12% K –1 ( I 545 / I 525 ) at 313 K. It is noteworthy that the maximum S r values obtained exceed those recently reported for luminescent thermometers based on Er 3+ doping materials. − Furthermore, temperature resolution (δ T ) is a vital parameter for luminescent thermometers, which is defined as δ T = 1 S normalr δ LIR LIR where δLIR/LIR signifies the relative uncertainty of thermometric parameter readings. Based on the standard deviation, the δLIR/LIR values are determined to be 0.5% .…”