THE GREEN PHOSPHOR SrAl2O4:Eu2+, R3+ (R=Y, Dy) AND ITS APPLICATION IN ALTERNATING CURRENT LIGHT-EMITTING DIODES

Abstract

The aim of the present investigation was to develop a phosphor to solve the flickering luminescence of alternating current (AC) light-emitting diodes (LED) by compensating the dark duration with appropriately persistent luminescence. The phosphor SrAl 2 O 4: Eu 2+ co-doped with Y 3+ or Dy 3+ was synthesized via solid-state reaction with H 3 BO 3 as flux. The crystal structure and morphology were characterized by using X-ray diffraction (XRD) and Scanning Electron Microscope (SEM), respectively. The photoluminescence spectra were collected with a fluorescence spectrometer. The results demonstrated that appropriate amount of Y 3+ or DY 3+ doped was beneficial to suppress the by-product of Sr 4 Al 14 O 25 which easily co-existed with the SrAl 2 O 4 phase brought by the flux of H 3 BO 3. However, too much Y 3+ or DY 3+ doped resulted in the formation of another impurity phase, i.e., the yttrium aluminum garnet of Y 3 Al 5 O 12 and Dy 3 Al 5 O 12. Comparatively, the doped DY 3+ was more helpful in prolonging the persistent luminescence, while Y 3+ was more efficient in enhancing luminescence intensity. To demonstrate the feasibility of the phosphor applied in AC LEDs, a nearly white AC LED was fabricated by coating the phosphor on a blue AC LED chip. The persistent luminescence was radiated from the AC LED device after turning power off. Moreover, the effect of the phosphor on compensating the AC LED dark duration through persistent luminescence was revealed by using the Keyence VW-9000 High-speed Microscope for the first time.