Enhancement of luminescence and thermal stability in Sr2.92-xTmxSiO5:Eu2+ for white LEDs

Abstract

Sr2.92-xTmxSiO5:Eu2+ (x=0-0.09) orange emitting phosphors for white LED were prepared by solid-state method. The crystal structure and morphology of Sr2.92-xTmxSiO5 were determined by XRD and SEM. The phosphor showed strong absorption spectra and can be excited by near-ultraviolet (NUV) light in the range of 200−550 nm which matched well with the NUV light-emitting diode (LED) chips. The emission spectra showed asymmetric band around 585nm under NUV and assigned to the 4f65d-4f7 transition of Eu2+ occupied Sr2+ sites in the host lattice. It is observed that 5d electron state of Eu2+ which easily influenced by the crystal field was not changed after Tm3+ co-doping in the host. Enhanced emission intensity, improved thermostability and fluorencence decay time have been made via crystal chemical unequivalence substitution of Tm3+ in Sr2+ site. The energy transfer took place between the Tm3+ and Eu2+ activator, the underlying mechanisms of enhanced luminescence and decay fluorescence properties by energy transfer were analyzed.