Development of new Eu3+/Sm3+ co-doped CaWO4 and CaMoO4 phosphors for optical thermometry based on ratiometric approach

Abstract

The Eu3+/Sm3+-co-doped CaWO4 and CaMoO4 scheelite-type phosphors were successfully synthesized by high-temperature solid-phase method and were investigated in detail for their promising applications in luminescence thermometry. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) analyses were used to study the structure and morphology of the phosphors synthesized. The co-doped CaMO4 (M = W, Mo): Eu3+/Sm3+ phosphors showed characteristic emission peaks at 534, 594, 657 and 705 nm corresponding to the intra-configurational transitions of 5D1→7F1, 5D0→7F2, 5D0→7F3 and 5D0→7F4 of Eu3+ ions, as well as other emissions at 564, 603 and 648 nm, which were ascribed to 4G5/2 → 6H5/2, 4G5/2 → 6H7/2, and 4G5/2 → 6G9/2 transitions of Sm3+, respectively. The temperature sensing properties of both phosphors were investigated based on different temperature evolution of several emission bands of Eu3+ and Sm3+. Specifically, using the luminescence intensity ratio (LIR) technique, we found that monitoring evolution of the LIR parameter 652/617 nm for the CaMoO4:1%Eu3+/1%Sm3+ the maximum relative sensitivity of 1.28% K−1 can be achieved in the cryogenic T-range (93 K). Whereas, utilizing the same LIR for the CaWO4:1%Eu3+/1%Sm3+ results in slightly smaller sensitivity of 1.18% K−1. The obtained results, indicate that the developed phosphors may work as effective, remote temperature sensors, having great application potential in optical thermometry.