Synthesis and photoluminescence properties of a phase pure green-emitting Eu doped JEM sialon (LaSi6−zAl1+zN10−zOz, z ∼ 1) phosphor with a large red-shift of emission and unusual thermal quenching behavior
A green-emitting phosphor, Eu2+ doped LaAl(Si6−zAlz)(N10−zOz) (denoted as JEM, z ∼ 1), was synthesized via a solid-state reaction method. By the careful control of the sintering temperature and chemical composition of starting materials (z value, N/O ratio and Si/Al ratio), a single phase JEM phosphor was achieved for the first time. The JEM:Eu2+ phosphor displays a broad 4f–5d excitation band from the UV region up to 525 nm, with a maximum at 355 nm. Excitation at 355 nm results in a Eu2+ 5d–4f emission band, that shows a large red-shift (490 → 564 nm) and a change in shape with increasing Eu concentration. The thermal quenching behavior of JEM:Eu2+ has been investigated in the temperature range from 4 K to 573 K. An abnormal nearly linear relation is observed between temperature and luminescence intensity. These phenomena indicate that there are two types of Eu2+ sites, although only one crystallographic site can be found in the JEM structure. A non-linear decay behavior with a bi-exponential curve and time-resolved photoluminescence emission spectra with two distinctive Gaussian peaks further give strong evidence for two emission sites in the Eu2+ doped JEM phosphor.