Mn2+- doped Zn2SnO4 green phosphor for WLED applications

Abstract

Eco-friendly phosphors based on non-rare-earth elements have received increasing interest in the field of fabricating white light-emitting diodes (WLEDs). In this work, Mn2+- activated Zn2SnO4 green phosphors were synthesized by high energy planetary ball milling followed by annealing at 1000 °C in a reducing gas environment. The effects of the annealing temperature and the Mn2+ doping concentration on the structural and optical properties were studied. Photoluminescence spectrum displays a green emission band peaking at 523 nm with full width at half maximum of about 32 nm, which is assigned to the spin forbidden d-d transition (4T1(4G) → 6A1(6S)) of the Mn2+ ions. The photoluminescence excitation spectrum of Zn2SnO4:5%Mn2+, monitored at 523 nm, presents five distinct peaks at 359, 380, 424, 435, and 444 nm, which are in good agreement with Mn2+ absorption transitions. The absorption peak at 444 nm well coincides with the peak wavelength of a blue LED emission. By coating the prepared phosphor on a blue LED chip, a green-emitting LED was successfully fabricated. Moreover, a series of white LEDs were made based on 450 nm chip coated with a blend of the Zn2SnO4:5%Mn2+ phosphor with a red phosphor (Zn2SnO4:3%Cr3+,0.6%Al). Warm white light with the correlated color temperature of 3858 K and a high color rendering index of 91 was achieved. These results indicate that the Zn2SnO4:5%Mn2+ phosphor is a promising material for applications in phosphor-converted WLEDs.