Tunable dual-mode photoluminescence from nanocrystalline Eu-doped Li2ZnSiO4 glass ceramic phosphors

Abstract

We report on tunable photoluminescence from mixed-valence Eu-doped nanocrystalline Li₂ZnSiO₄ glass ceramics. After preparation of the precursor glass in air, gradual reduction of Eu³⁺ to Eu²⁺ occurs intrinsically during thermal annealing and precipitation of crystalline Li₂ZnSiO₄. Dual-mode photoemission can be generated for exciting at a wavelength of about 360 nm. The resulting colour of luminescence, ranging from orange/red to blue, can be controlled by adjusting the annealing temperature and, hence, the degree of crystallization: with increasing annealing temperature, the ratio of luminescence intensities related to Eu³⁺ and Eu²⁺ species, respectively, varies as a result of increasing degree of Eu³⁺-reduction as well as distinct changes in the optical scattering behaviour of the obtained glass ceramic. At the same time, the bandwidth of Eu²⁺-related photoemission increases from 87 to 154 nm. The underlying mechanisms of photoemission and energy transfer from Eu²⁺ to Eu³⁺ are discussed on the basis of dynamic emission spectroscopy and structural considerations, and a description of the internal reduction process is given.