Design and Discovery of Nitride Phosphors with Unique Properties

Abstract

Inorganic luminescent materials, acting as color converters, play key roles in solid state lighting. Among a large quantity of phosphors, nitride phosphors have attracted great attentions as they show promising photoluminescence properties (i.e., high conversion efficiency of blue light, thermally robust, and abundant emission color). With advances in solid state lighting techologies, phosphors with desired properties are reuiqred, which is thus necessary to search for appriporate phosphors. In this presentation, we will introduce two nitride phosphors, Sr2AlSi2O6N:Eu2+ and La2.9Si6-x Al x N11-x/3:Ce3+. Sr2AlSi2O6N:Eu2+ was predicted by using high-throughput calculations, and synthesized in a gas-pressure sintering furnace at 1400oC. The crystal structure of Sr2AlSi2O6N (space group: P4̅21m) was derived from Ba2ZnGe2S6O (ICSD no. 14174) via a multispecies substitution of Ba2+ with Sr2+, Zn2+ with Al3+, Ge4+ with Si4+,S2− with O2−, and O2− with N3−. This phosphor showed a super-broad emissin band spaning from 400 to 850 nm and a full-width at half maximum (fwhm) of 230 nm, under 330 nm excitation. The super-broad emission was ascribed to the structural disorder of Si/Al and O/N. Combined with a UV LED, Sr2AlSi2O6N:Eu2+ enabled to produce a white LED with superior color quality (Ra = 97, R9 = 91). La2.9Si6-x Al x N11-x/3:Ce3+ (LSN:Ce,Al) was designed by applying the interstitial site engineering strategy, i.e., partially substituting Si by Al. The introduction of Al in the lattice created a new site for Ce3+, leading to an additional red emission (λ em = 600-665 nm). The origin of this red emission was assigned from the first-principles calculation to the Ce3+ ion occupying the [Si8N8] void in the c~1/2 layer, of which the calculated transition energies matching with experiment within 0.1 eV. Such an interstitial Ce3+ site was created as a charge compensator for the aliovalent substitution of Si4+ by Al3+ ions. The red-enhanced LSN:Ce,Al phosphor showed great potentials for improving the optical quality (i.e., color temperature and color rendition) of laser-driven white light.