The decay curves of luminescence from Eu2+ in β-SiAlON are effectively analyzed using the general-order kinetics formula

Abstract

Defects in phosphors affect not only luminescence intensity but also emission peak width, decay time, and afterglow. The green phosphor β-SiAlON:Eu2+ exhibits the green emission of Eu2+ at 520 nm and the blue emission of nitrogen vacancies at 460 nm in time-resolved fluorescence measurements. The decay time of the intrinsic Eu2+ transition is 0.7 μs, but afterglow is detected from 50 μs to 0.01 s. This afterglow decay curve is the same for the green emission of Eu2+ and the blue emission of nitrogen vacancies, suggesting that the defect levels of the nitrogen vacancies affect the Eu2+ transition. The afterglow decay curves were analyzed using the formula of the general-order kinetics, 1+t/τB−n , where n is the decay power and τB is the decay time. This equation is generally used when analyzing afterglow on the order of seconds to hours but has not been examined systematically applied in samples with different concentrations of Eu2+ and temperatures on the order of nanoseconds to milliseconds. The decay power n is approximately 1 for all Eu2+ concentrations (x = 0.001–0.3) and undoped β-SiAlON. The decay time τB is correlated with the density of the nitrogen vacancies determined by electron spin resonance. Furthermore, the value of n is approximately 1 for 50 μs to 0.01 s and 0.3 for 1–1000 s. Thus, the luminescence mechanism of Eu2+ can be discussed by comparing n and τB obtained from the decay curves. In addition, several different Eu2+-doped phosphors, namely SrAl2O4:Eu2+, Dy3+, CaAlSiN3:Eu2+, and CaS:Eu2+, Tm3+, are studied.