NaLaCaWO6 double perovskite: Structure analysis, efficient Bi3+ to Eu3+ energy transfer and favourable visual optical thermometry

Abstract

Herein, we report a series of NaLaCaWO₆: Bi³⁺, Eu³⁺ double perovskite phosphors with a monoclinic crystal structure, achieving high-precision optical thermometry. Comprehensive characterisations, including X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy and thermoluminescence, revealed detailed material properties. The electronic structure and formation energies of NaLaCaWO₆: Bi³⁺, Eu³⁺ were calculated using density functional theory (DFT), and the influence of luminescent centers (Bi³⁺ and Eu³⁺) on the optical properties was analyzed. The emission colour was tuned from green to red with increasing Eu³⁺, and efficient Bi³⁺ → Eu³⁺ energy transfer was achieved through dipole–dipole interaction, with an energy transfer efficiency of 59.4 %. In addition, the distinct temperature response characteristics of Bi³⁺ and Eu³⁺ fulfilled the prerequisites for efficient temperature signal resolution, demonstrating a high relative sensor sensitivity of 0.74 % K⁻¹ (at 298 K) and minimal temperature resolution (δ_T = 0.14 K) for the NaLaCaWO₆: 0.05Bi³⁺, 0.01Eu³⁺. The moisture resistance of the phosphor was confirmed through a water immersion test, demonstrating excellent moisture resistance. These findings not only elucidate the photoluminescence behaviour of Bi³⁺ and Eu³⁺ in NaLaCaWO₆ but also highlights its promising application prospects in optical thermometry.