Spectroscopic properties of Eu-doped oxynitride glass–ceramics for white light LEDs

Abstract Novel oxynitride glass–ceramics with tremendously improved quantum yield and adjustable color coordinates were prepared with the conventional melt-and-quench method and subsequent annealing heat treatment. X-ray diffraction (XRD) and transmission electron microscopy (TEM) images revealed CaAl 2 Si 2 O 8 and Y 20 N 4 Si 12 O 48 crystalline phases were homogenously precipitated in the glass matrix. The optical absorption and photoluminescence (PL) spectrum measurements showed that a large portion of Eu 3 + ions were reduced into Eu 2 + which were crystallized into CaAl 2 Si 2 O 8 phase during the heat treatment by substituting Ca 2 + ions in them. Emission spectra evidently show that Eu 2 + and Eu 3 + ions were preferentially incorporated in CaAl 2 Si 2 O 8 and Y 20 N 4 Si 12 O 48 crystalline phases, respectively. This assignment was further supported by cation ionic radii and local charge balances, as well as defect chemistry considerations. The total emission intensity including both Eu 2 + and Eu 3 + ions was enhanced with increasing the annealing temperature, due to the conversion of Eu 3 + to Eu 2 + and the enhanced quantum efficiency of Eu 3 + in the crystalline phase as compared to the glass matrix. As a result, the quantum yields (QYs) of the glass–ceramics were also enhanced significantly from 2.07% (the precursor glass) up to 43.33% (the maximum of the glass–ceramics). The emission ratio of Eu 2 + /Eu 3 + changed from 4.0, which led this novel glass–ceramics with adjustable color coordinates ranging from red to blue controlled by varying the annealing temperature.