Preparation of the ultrafine SrAl2O4:Eu,Dy needle-like phosphor and its optical properties

Sr(NO3)2, NH4HCO3, Al(NO3)3, Eu(NO3)3 and Dy(NO3)3 are used as the raw materials for the preparation of SrCO3-Al2O3-RE(OH)3 (RE: Eu, Dy) precursor by the ‘soft’ chemical synthesis method, which is convenient to make the components uniformly. The ultrafine needle-like phosphors with high brightness and long afterglow were obtained by sintering the precursor at high temperature and at weak reductive atmosphere (1.5% H2 and 98.5% N2) for the first time. The average particle size of the SrAl2O4:Eu,Dy needle-like phosphors was less than 100 nm as observed by the transmission electron microscopy (TEM) and its optical properties have been studied systematically. The results indicated that the main peaks in the emission spectrum and the excitation spectrum shifted to the short wavelength compared with the phosphor prepared by the traditional ‘ramic’ method. The decay speed of the afterglow prepared by this method was faster than that of the ceramic method. As for the mechanism of long afterglow of the SrAl2O4:Eu,Dy phosphor, Dy3+ played an important role and acted as the trap levels in the system, which lied in between the excited state and the ground state of Eu2+. It is the holes thermally released from the trap levels that resulted in the long afterglow phenomenon of phosphors.