Structural Phase Transition and Cooperative Luminescence in K3Yb(PO4)2:Eu3+ for Multimodal Down-shifting and Up-converting Luminescence Thermometry

TL;DR

This study demonstrates that K3Yb(PO4)2:Eu3+ exhibits structural phase transitions and cooperative luminescence, enabling its use as a multimodal luminescent thermometer with high sensitivity across different spectral ranges.

Contribution

The paper introduces a new thermometric system based on K3Yb(PO4)2:Eu3+ that combines phase transition and luminescence properties for enhanced temperature sensing.

Findings

Phase transition occurs above 450 K, enabling ratiometric thermometry.

Eu3+ concentration shifts the phase transition temperature.

Dual luminescence signals allow for ratiometric temperature measurement.

Abstract

To develop a more universal luminescent thermometer that provides both high relative sensitivity and the ability to measure temperature across different spectral ranges and excitation wavelengths, the K3Yb(PO4)2:Eu3+ system was proposed in this work. It was demonstrated that this material undergoes a structural phase transition from the monoclinic to the hexagonal phase above 450 K. This transition enabled the construction of a ratiometric, phase-transition-based thermometer utilizing the luminescence intensity ratio of Stark lines of Eu3+ and Yb3+ ions, which exhibit SRmax values of 4.2% K^-1 and 1.15% K^-1, respectively. Moreover, increasing the Eu3+ ion concentration was shown to raise the phase transition temperature, thereby shifting the thermal operating range of both luminescent thermometers. Under 980 nm excitation, K3Yb(PO4)2:Eu3+ exhibits both cooperative luminescence from Yb3+ pairs and up-conversion emission from Eu3+ ions. Increasing the Eu3+ concentration enhances the Eu3+ luminescence intensity relative to the cooperative luminescence of Yb3+ pairs, resulting in a change in the emitted light color. The difference in the thermal quenching behavior of these two signals further enabled the development of a ratiometric thermometer with SRmax = 0.58% K^-1. These findings identify K3Yb(PO4)3:Eu3+ as a promising candidate for multimodal temperature sensing.