Double perovskite Sr2GdTaO6: Tm3+ blue phosphors: Luminescence properties, optical transition and white LED application

Abstract

To explore blue phosphors excited by near ultraviolet light for applications in white light-emitting diodes, a series of double perovskite Sr₂GdTaO₆ (SGT) powders doped with Tm³⁺ were synthesized by a high-temperature solid-state method. The samples’ crystal structure, luminescent properties, fluorescence dynamic, luminescent thermal stability, and optical transition properties were all thoroughly investigated. Under 360 nm excitation, both the narrowband emission from Tm³⁺ ions and the broadband emission from host were simultaneously observed. The strongest emission of narrowband was observed at 2 mol% Tm³⁺ doping concentration. An electric dipole-dipole interaction mechanism among Tm³⁺ ions was identified to be responsible for the concentration quenching process of the narrowband emission. The chromaticity coordinates and color purity for the SGT: 2 mol% Tm³⁺ sample were determined to be (0.19, 0.15) and 74.3 %, respectively, which fell into the blue region. Moreover, the luminescence intensity for blue emission retained 92.5 % of its room temperature intensity even at 423 K, thus indicating good luminescent thermal stability. Optical transition properties of Tm³⁺ ions in SGT were evaluated with the aid of Judd-Ofelt theory, based on the diffuse reflectance spectra and the decay of ¹D₂ level. In addition, the blue-emitting SGT: Tm³⁺ phosphor was used to demonstrate a light-emitting diode prototype that emits a full spectrum warm white light, characterized by a chromaticity coordinate of (0.33, 0.33), a low correlated color temperature of 5750 K, and an impressive color rendering index of 96.8. These findings suggest that this efficient blue-emitting phosphor holds promise for application in white light-emitting diodes.