Highly Luminous and Thermally Stable Mg-Substituted CaMgSiO:Ce (0 ≤ x ≤ 1) Phosphor for NUV-LEDs.

Blue-emitting CaMgSiO:Ce (0.0 ≤ x ≤ 1.0) phosphors were successfully synthesized and characterized. Rietveld refinement revealed that four main phases exist within the solid-solution range of CaO-MgO-SiO, namely, β-CaSiO (Mg (x) = 0.0), CaMg(SiO) (Mg (x) = 0.25), CaMg(SiO) (Mg (x) = 0.5), and CaMgSiO (Mg (x) = 1.0). The variation of the IR modes was more prominent with increasing Mg content in the CaMgSiO materials. The sharing of O atoms of the SiO-tetrahedra by the MgO-octahedra induced weakening of the Si-O bonds, which resulted in the red shift of the [SiO] internal modes and appearance of a Mg-O stretching vibration at ∼418 cm. Raman measurement revealed that the change of the Ca-O bond lengths because of the Mg-substitution directly reflected the frequency shift of the Si-O stretching-Raman modes. Notably, the thermal stability of CaMgSiO:Ce (Mg (x) > 0.0) phosphors was superior to that of β-CaSiO:Ce (Mg (x) = 0.0) as confirmed by temperature-dependent photoluminescence (PL) measurements. This indicated that Mg ions play an important role in enhancement of the thermal stability. In combination with the results from PL and electroluminescence (EL), it was elucidated that the luminous efficiency of CaMgSiO:Ce (Mg (x) = 0.1) was approximately twice as much as β-CaSiO:Ce (Mg (x) = 0.00), directly indicating a "Mg-substitution effect". The large enhancements of PL, EL, and thermal stability because of Mg-substitution may provide a platform in the discovery of more efficient phosphors for NUV-LEDs.