Effects of Eu2+ on the luminescence and afterglow that arise from defects in β-SiAlON:Eu2+

Abstract

Si6−z Al z O z N8−z (β-SiAlON):Eu2+ is known as a high brightness green phosphor. When β-SiAlON:Eu2+ is excited with UV light (approximately 265 nm), a curved decay afterglow is observed as a result of the trap levels created by the defects in the host crystal. However, the defect signals are hardly detected by electron spin resonance (ESR) and thermoluminescence (TL), which are common defect detection methods. Non-doped (Eu = 0) β-SiAlON emits blue light from a nitrogen defect, and the defect can be detected by time-resolved fluorescence (TR-F) measurement at 15 K. Similarly, upon measuring TR-F at 15 K for Eu-doped β-SiAlON, a blue emission (460 nm) is detected in addition to the green emission of Eu2+ (530 nm). The green emission has an afterglow of several milliseconds that decays with the same decay curve as the blue emission of the defect, and its time constant is 5–6 ms. This blue emission is quenched by the Eu concentration and temperature. The Si dangling bond signal intensity, observed by ESR, and the glow intensity, observed by TL, also decrease with the increment of the Eu concentration. It is difficult to detect the defect as an electron trap owing to the interaction between Eu2+ and the nitrogen defect. However, the afterglow arising from the electrons trapped at the defect level does not decrease with the Eu concentration. The blue emission was quenched at room temperature but the afterglow was not reduced, which also affected the light emission above room temperature. Therefore, it is possible to detect nitrogen defects optically by TR-F at low temperature, as well as the Eu2+ afterglow of several milliseconds.