Bright and persistent green emitting MgGa2O4:Mn2+ for phosphor converted white light emitting diodes

Abstract

Narrow band green emitting phosphors have gained widespread attention due to their application in white light emitting diode (wLED) backlight displays. Commercial backlight displays have a broad band green phosphor which limits their performance. In this work, bright, narrow and thermally stable green emitting MgGa₂O₄:Mn²⁺ (MGO-Mn) has been synthesized. Time-resolved emission spectroscopy suggested that Mn²⁺ ions are distributed at both Mg²⁺ and Ga³⁺ sites of the MGO spinel, which resulted in a high internal quantum efficiency of 63%. The colour purity of MGO-Mn (76.4%) superseded that of the commercial green phosphor β-SiAlON:Eu²⁺ (59.12%). Doping-induced creation of oxygen vacancies endows MGO-Mn with excellent persistent luminescence with a time duration of more than 900 s upon 4 min charging with 270 nm UV light and persistent radioluminescence of more than 6000 s when charged with X-rays for 1 min. Finally, tunable white LEDs (cool and neutral white LEDs) are fabricated by combining the RGB mixture of the green phosphor with commercial red and blue phosphors along with a 280 nm UV LED chip. This work also showcases the importance of different annealing atmospheres in the photoluminescence and persistent luminescence of the MGO-Mn phosphor.