Blue–green color-tunable emissions in novel transparent Sr2LuF7:Eu/Tb glass-ceramics for WLEDs

Abstract

To introduce ordered nano-structures inside a transparent amorphous matrix with superior optical and mechanical properties bears scientific and technological importance, yet limited success has been achieved. Here, via simple melting-quenching and subsequent thermal activation, we report the successful preparation of transparent nano-structured glass-ceramics embedded in Sr2LuF7 nano-crystals (∼26 nm), as evidenced by X-ray diffraction, transmission electron microscopy (TEM), and high resolution TEM. The successful incorporation of dopants into formed Sr2LuF7 nano-crystals with low phonon energy results in highly tunable blue–green photoemission, which depends on excitation wavelength, dopant type, and temperature. We found that Eu3+ and Eu2+ ions co-exist in this hybrid optical material, accompanied by the broadband blue emission of Eu2+ and sharp red emissions of Eu3+. A series of optical characterizations are summoned, including emission/excitation spectrum and decay curve measurement, to reveal the reduction mechanism of Eu3+ to Eu2+. Furthermore, near green–white photoemission is achieved via the enrichment of Tb3+/Eu3+ into crystallized Sr2LuF7 nano-crystals. The temperature-dependent visible photoemission reveals thermal activation energy increases with the precipitation of Sr2LuF7 nano-crystals in a glass matrix, suggesting better thermal stability of glass-ceramics than precursor glasses. These results could not only deepen the understanding of glass-ceramics but also indicate the promising potential of Eu3+/Tb3+-ions-doped Sr2LuF7 glass-ceramics for UV pumped white light emitting diodes (WLEDs) with good thermal stability.