Regulating photoluminescence behavior by neighboring-cation-size in Sr8CaX(PO4)7: Eu2+ (X = Al and Ga) phosphors for high color rendering solid-state lighting source

Abstract

The photoluminescence behavior in a multiple cation lattice host for obtaining desired spectral emission is an important scientific question to develop next-generation high quality lighting sources. However, how to manipulate the distribution of rare-earth activators over various cation sites is still a technical challenge. Herein, for the first time, trivalent ions Al3+ and Ga3+ were introduced to β-Ca3(PO4)2-kind host for preparing the new isostructural Sr8CaAl(PO4)7 (SCAP) and Sr8CaGa(PO4)7 (SCGP) hosts and controlling the incorporation of activators Eu2+ in the M(4) sites. Their structural evolution, morphology, diffuse reflection spectrum, electron structure and luminescent properties were systemically investigated. The emission of Eu2+ ions distributed over the nine-coordinated Sr(1, 3, 5)O9, eight-coordinated Sr(2)O8 and special coordinated Sr(4)O6 sites was located in the green (507 nm), yellow (555 nm) and red (610 nm) regions, respectively. Further, a smaller cation radius (Al3+) allowed higher number of activators (Eu2+) to be accessed to the neighboring M(4) lattice site for obtaining more intense red emission, which would enable these kinds of phosphors-converted white light emitting diodes to show quite high color-rendering indexes (Ra = 94.4). This neighboring-cation-size strategy mentioned here can become a novel approach to PL spectral modulation through controlling the distribution of Eu2+ activators over various lattice sites for excellent solid state lighting.