A novel double-perovskite Gd2ZnTiO6:Mn4+ red phosphor for UV-based w-LEDs: structure and luminescence properties

Abstract

Red-emitting Mn⁴⁺ activated oxide phosphors with a cheap price and excellent physical/chemical stability have become a hot research topic for their potential applications in white LEDs (w-LEDs). Herein, we report a novel double-perovskite Gd₂ZnTiO₆:Mn⁴⁺ (GZT:Mn⁴⁺) red phosphor. The material microstructures were characterized with the aid of XRD Rietveld refinement and HRTEM observations. The luminescence properties and dynamics of Mn⁴⁺ in GZT were studied in detail using low/room temperature steady/transient spectroscopic techniques. The crystal field strength and nephelauxetic effect influencing the Mn⁴⁺ emission energy were also analyzed. It is revealed that the special crystal structure of GZT featuring alternately slant-wise arranged [TiO₆]/[ZnO₆] octahedrons with the [–Mn⁴⁺–O²⁻–Zn²⁺–] bond angle deviating from 180° is beneficial to achieving efficient Mn⁴⁺: ²E_g → ⁴A₂ transition in the deep-red region. After mixing the red-emitting GZT:Mn⁴⁺ with the commercial blue and green phosphors in various ratios, and then coupling the mixture with a 365 nm UV chip to build a w-LED, the white light was found to evolve from cool to warm with a tunable correlated color temperature (CCT) from 6977 K to 4742 K, a color rendering index (CRI) up to 82.9, and an improved R₉ value to 43, which validates that GZT:Mn⁴⁺ is a promising red color converter for UV-based w-LEDs.