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

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 degrees is beneficial to achieving efficient Mn4+: E-2(g) -> (4)A(2) 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 R-9 value to 43, which validates that GZT:Mn4+ is a promising red color converter for UV-based w-LEDs.