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 180deg is beneficial to achieving efficient Mn4+ 2Eg 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.