Redesign and manually control the commercial plasma green Zn2SiO4:Mn2+ phosphor with high quantum efficiency for white light emitting diodes

Abstract

By reduce the stoichiometry ratio of ZnO raw materials, we successfully redesign and tailor the luminescence properties of commercial plasma green Zn2SiO4:Mn2+ phosphors for using as white light emitting diodes phosphors due to the strong absorption intensity at 420 nm. When excited at 420 nm, the quantum efficiency of the best redesigned Zn2SiO4:Mn2+ green phosphor can reach 76.2% which is much higher than 1.26% of the original Zn2SiO4:Mn2+ phosphor. To make clear the mechanism of the strong absorption at 420 nm as well as the increasing quantum efficiency, several classical methods of investigation including Rietveld refinement, X-ray diffraction patterns, Raman spectra and PL/PLE spectra are measured in this study. When reducing ZnO raw materials, the increased randomly distributed oxygen vacancies will induce the deviation from the inversion center of symmetry lattice site and then increase the quantum efficiency. Moreover, the FWHM of the best redesigned Zn2SiO4:Mn2+ is narrower that of β-SiAlON:Eu2+ and commercial green phosphor LMS-520B which indicates the redesigned Zn2SiO4:Mn2+ is more suitable for using as backlights for LCD. The redesigned Zn2SiO4:Mn2+ phosphor can also exhibit 81.2% color purity and excellent thermal stability with only 30% emission intensity loss at 140 °C. In addition, with reduced ZnO, the long decay times of Zn2SiO4:Mn2+ phosphor caused by the restriction of parity-forbidden and spin-forbidden 4T1-6A1 transition of Mn2+ can decrease from 4.168 ms to 3.268 ms. All the results suggest its great potential applications as backlights for LCD.