Exploring Na0.1Sr9.8Eu0.1(PO4)6F2 both as a potential phosphor material and host for radioactive waste immobilization

Abstract

In this work, we have reported synthesis and characterization of Na0.1Sr9.8Eu0.1(PO4)6F2, which has potential application for immobilization of radioactive waste and also as red-emitting phosphor material. From PL spectra and lifetime study it was concluded that most of the Eu3+ ions (which are surrogate of radioactive Am3+ ions in the radioactive waste) are preferentially occupying M2A site which has a fluoride ion linkage compare to the M1A site without any such linkage. This was further supported by the XRD study. The compound is also found to be red emitting phosphor material for its application in LEDs with color purity of 86.13%. In order to investigate the radiation stability of the matrix considering its application in nuclear waste immobilization, the compound was exposed to different doses of gamma radiation and subsequent emission profiles are then recorded. We have observed that there was an initial increase in the intensity of the PL spectra due to the creation of the electron-hole pair. However, at very high doses such as 1000 kGy, the created defects provide non-radiative pathways to the excited state of Eu3+ ion which leads to decay in intensity. TL study showed the presence of different shallow and deep trap state for electron and hole generated due to irradiation. EPR study characterized various irradiation-induced defect states which play a prominent role in the emission characteristics.