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In this study, Cr3+‐doped and Mn4+‐Cr3+ co‐doped double perovskite fluoride phosphors K2LiGaF6 are prepared using a simple hydrothermal method. High‐efficiency near‐infrared (NIR) emission near 762 nm is obtained under blue‐light excitation, and the co‐doping effect of Mn4+ on the NIR luminescence properties of Cr3+ is studied. Compared with the Cr3+ single‐doped phosphor, Mn4+, and Cr3+ co‐doped K2LiGaF6 exhibit a sharp increase of 129% in NIR emission, an enhancement in the internal quantum efficiency from 82.5% to 90.0%, and an enhancement in the thermal stability at 425 K from 85.0% to 90.7%. The encapsulated NIR phosphor‐converted light‐emitting diode device at 300 mA exhibits a photoelectric conversion efficiency of 15.3%. These values exceed most previously reported results. This study provides a new approach for enhancing the luminescence properties of Cr3+‐doped fluoride NIR phosphors. [ABSTRACT FROM AUTHOR]

A series of novel SrLu2O4: x Ho3+, y Yb3+ phosphors ( x=0.005-0.05, y=0.1-0.6) were synthesized by a simple solid-state reaction method. The phase purity, morphology, and upconversion luminescence were measured by X-ray diffraction ( XRD), scanning electron microscopy ( SEM), and photoluminescence ( PL) spectroscopy. The doping concentrations and sintering temperature were optimized to be x=0.01, y=0.5 and T=1400°C to obtain the strongest emission intensity. Under 980 nm laser diode excitation, the SrLu2O4:Ho3+, Yb3+ phosphors exhibit intense green upconversion ( UC) emission band centered at 541 nm (5F4,5S2→5I8) and weak red emission peaked at 673 nm (5F5→5I8). Under different pump-power excitation, the UC luminescence can be finely tuned from yellow-green to green light region to some extent. Based on energy level diagram, the energy-transfer mechanisms are investigated in detail according to the analysis of pump-power dependence and luminescence decay curves. The energy-transfer mechanisms for green and red UC emissions can be determined to be two-photon absorption processes. Compared with commercial NaYF4:Er3+, Yb3+ and common Y2O3:Ho3+, Yb3+ phosphors, the SrLu1.49Ho0.01Yb0.5O4 sample shows good color monochromaticity and relatively high UC luminescence intensity. The results imply that SrLu2O4:Ho3+, Yb3+ can be a good candidate for green UC material in display fields. [ABSTRACT FROM AUTHOR]