Sol–gel synthesis, structural and optical characteristics of Sr_1−x Zn₂Si_2yO_7+δ: xEu²⁺ as a potential nanocrystalline phosphor for near-ultraviolet white light-emitting diodes

In this research, a new blue-emitting phosphor Eu²⁺-doped SrZn₂Si₂O₇ was developed for white light-emitting diodes via the sol–gel process. Thermogravimetric-differential thermal analysis, X-ray diffraction, scanning and transmission electron microscopy (SEM and TEM), and photoluminescence (PL) spectra were used to characterize the resulting phosphors. The obtained phosphor is efficiently excited in the wavelength range of 340–400 nm which matches to a near-UV-emitting InGaN chip and emits strong band blue light peaking at 481 nm because of 4f ⁶5d ¹(² D) → 4f ⁷(⁸ S _7/2) transition of Eu²⁺ ions. The effects of the activator concentration and excess Si (y > 1) on the luminescence properties were evaluated. It was found that, when the Eu²⁺ content (x) and the Si concentration (2y) were 0.04 and 2.4, respectively, the optimum phosphor can be achieved. Also, the mechanism of concentration quenching was determined to be the dipole–dipole interaction using Dexter’s theory. Finally, the mean crystallite size of the products was estimated to be approximately 30 nm using Scherrer’s equation, which was confirmed by the TEM observations.