Photoluminescence properties of Tb3+-doped sodalite under VUV-UV light excitation

Natural sodalite (Na8Al6Si6O24Cl2) from Xinjiang, China, was activated with TbF3 by a high-temperature melting method and green luminescence phosphors were synthesized. The results of X-ray diffraction (XRD) test showed that the main crystal phase of the sample heat-treated at 1100 °C was sodalite, but the NaCl component in the sample was partially lost by the heat treatment and the minor content of nepheline (hexagonal) structure (syn. NaAlSiO4) was created. The vacuum ultra-violet (VUV) light excitation spectrum, obtained by monitoring the green luminescence at 541 nm, consisted of excitation bands with peaks at 174 and 222 nm. These excitation bands were assigned to the absorption band by the host crystal and the spin-allowed 4f8-4f75d transitions within Tb3+, respectively. The emission spectra under VUV-UV light excitation consisted of a series of narrow bands corresponding to the 5D3→7FJ (J=6, 5, 4, 3 and 2) and 5D4→7FJ (J=6, 5, 4 and 3) transitions within Tb3+. The predominant band at 541 nm corresponds to the 5D4→7F5 transition. The lifetime of luminescence corresponding to the 5D3→7FJ (J=6, 5 and 4) transitions was 1.2 ms, while the lifetimes of luminescence corresponding to the 5D4→7FJ (J=6 and 5) transitions were 2.5 and 2.8 ms, respectively. The CIE (Commission Internationale de l׳Éclairage) chromaticity coordinate of luminescence from the sample was (0.287, 0.301) and the correlated chromaticity temperature was 8796 K.