A Single Phase LaAl(Si_6-zAl_z)(N_10-zO_z):Eu²⁺ Phosphor with Large Red-Shift of the Emission and Anomalous Decay Behavior

Phosphor-converted light-emitting diodes (pc-LEDs) have penetrated to solid-state lighting over the last decades because of high energy conversion efficiency, long lifetime and environmental benefits. White pc-LEDs with high luminous efficacy and color rendition are urgently required, especially for illumination-grade light sources. Ce doped LaAl(Si6-zAlz)(N10-zOz) (termed JEM) phosphor has been reported as a promising phosphor for white LEDs using near UV excitation, particularly for home illumination.1 However, the unavailability of a phase pure JEM:Ce phosphor prevents widespread application and detailed crystal structure analysis. In addition, Eu2+ and Ce3+ are the most effective activators for white LED phosphors, but there is no report on the photoluminescence properties of an Eu2+doped JEM phosphor. In the present study, a phase pure Eu2+ doped JEM phosphor and non-doped JEM were successfully obtained with a solid-state reaction method by carefully controlling the synthesis temperature and chemical composition of starting materials. The Eu2+ doped JEM phosphors show a very interesting red-shift of the emission band; the emission color after excitation with 355 nm light can be tuned from blue-green to yellow by increasing the Eu concentration. Furthermore, an anomalous decay behavior with bi-exponential decay was observed, although there is only one crystallographic site in the JEM structure. 2With the single phase JEM sample achieved, we investigated the details of the crystal structure by XRD and magic-angle spinning (MAS) solid state nuclear magnetic resonance (NMR). Reference 1. K. Takahashi, N. Hirosaki, R.-J. Xie, M. Harada, K. Yoshimura and Y. Tomomura, Appl. Phys. Lett. 91, 091923 (2007). 2. J. Grins, Z. Shen, M. Nygren and T. Ekström, J. Mater. Chem. 5, 2001 (1995). Fig1. A scheme of the large red-shift emission (a) and anomalous decay behavior (b) for JEM:Eu2+ phosphor and JEM crystal structure (c). Figure 1