Structure-dependent luminescence of Eu3+-doped strontium vanadates synthesized with different V : Sr ratios – application in WLEDs and ultra-sensitive optical thermometry

Abstract

This work mainly focused on luminescence color tuning, white light generation and ultra-sensitive temperature sensing based on complex strontium vanadates doped with Eu³⁺ ions. A series of materials whose crystal structure changes from orthorhombic SrCO₃, through hexagonal Sr₅V₃O₁₃ and trigonal Sr₃V₂O₈ to triclinic Sr₂V₂O₇ were obtained via a modified sol–gel method, using altered vanadate to strontium ion ratios (V : Sr). Changes in the charge transfer band (CTB), characteristics of the Eu³⁺ ion emission and luminescence intensity changes were observed with an increasing content of vanadate groups in the materials. Dual-mode, excitation-dependent luminescence, white (λ_ex = 345 nm) and red (λ_ex = 393 nm), is observed. The luminescence color, chromaticity coordinates, color purity, quantum efficiency and emission correlated color temperature (CCT) of materials were compared. The application of the optimized Sr₃V₂O₈:2%Eu³⁺ material as a multimodal temperature sensor is discussed. Temperature-dependent luminescence properties are investigated and an optical thermometer with high sensitivity is developed, revealing that the material has an extremely high spectral shift with a temperature of up to ∼0.862 nm K⁻¹, currently classifying it as the most sensitive shift-based optical thermometer. Additionally, thanks to the capability of the developed phosphors for efficient energy conversion, we demonstrated their applicability in white-light generation for LED devices.