A white light phosphor suitable for near ultraviolet excitation

Luminescent properties of Eu²⁺-doped phosphors with nominal composition of 2SrO·MgO·xSiO₂ (0.8≤x≤1.2) are studied. The emission spectra consist of a blue band (460 nm) and a yellow band (550 nm), the relative intensities of which change with the SiO₂ composition x. It is found that a combination of the blue and yellow bands can generate white light at x around 1 under near- ultraviolet excitation. X-ray diffraction patterns of the phosphors demonstrate both Sr₃MgSi₂O₈ and Sr₂SiO₄ phases, in which Eu²⁺ contributes to the blue and yellow emissions, respectively. The relative intensity variation of the two bands is attributed to the relative proportion of the two phases dependent on SiO₂ composition. A white light emitting diode fabricated using a GaN chip (λ_em=400 nm) and this phosphor is obtained, exhibiting color coordinates of x=0.33, y=0.34, color rendering index of 85 and luminous efficiency of 6 lm/W.