Single White-Emitting Phosphor (Ba,Sr,Ce)4-mLi(Si,Al)19+2m(O,N)29+m for White LEDs

A new sialon compound, with the composition (Ba,Ce,Sr)4-mLi(Si,Al)19+2m(O,N)29+m (m = 0.3, n = 1), has been discovered. It crystallizes in the P3m1 space group, with two types of Ba/Sr sites: a ninefold coordinated site located in the cavities of the SiN4 tetrahedral framework and a sixfold coordinated site that is in substitutional disorder with a (Si/Al)2(O,N) group. This interesting structural feature gives rise to a rare occurrence of (Si,Al) atoms in a fivefold trigonal bipyramidal configuration with (O,N) anions, as confirmed by high-resolution solid-state 29Si MAS NMR and 27Al 2D 3QMAS NMR spectroscopy. At high Ce concentrations, the Ce ions substitute on both Ba/Sr sites, resulting in white light emission upon UV light excitation due to a double broad-band emission with peaks around 465 and 625 nm. This is a rare occasion of a single activator white-light-emitting phosphor, and the first Ce-doped sialon-based one to be reported. The new phosphor is promising for UV-excitable white LED applications because a single white-light-emitting phosphor with a single dopant does not rely on energy transfer between different activators or a complicated color balance for RGB phosphors, resulting in a cheaper and easier process to fabricate white LEDs.