Crystal structure and color point tuning of β-Sr1.98-yMgySiO4-1.5xNx: 0.02Eu2+: A single-phase white light-emitting phosphor

Abstract

A series of β-Sr1.98-yMgySiO4-1.5xNx: 0.02Eu2+ (x = 0, 0.3, 0.6, 0.9, 1.2 and 4/3, 0 ≤ y ≤ 0.5, β-S(M)SON: Eu2+) phosphors were synthesized by a conventional solid state reaction method. The coordination environments of Eu2+ are modified effectively via the introduction of N3- and Mg2+ using different concentration, which is confirmed by XRD refinement results and PL spectra. Both fourier transform infrared (FT-IR) spectra and energy dispersive spectroscopy (EDS) analysis qualitatively confirm that the existence of N3-. The crystal structures of β-Sr2SiO4-1.5xNx (β-SSON): Eu2+ and β-Sr2-yMgySi(O,N)4: Eu2+ (β-SMSON, x = 4/3, y = 0.1) have been determined effectively. Rietveld refinement indicates that N3- dopants most likely partly substitute O22− site. With the increase of N content, the unit cell volume and partial SiO and SrN bond lengths gradually decrease, which are coincided each other. With the introduction of N3-, the emission of Eu(I) (∼465 nm) hardly change but that of Eu(II) (∼540 nm) splits into two emission bands as Eu(II) (∼540 nm) and Eu(II)′ (∼616 nm). According to the analysis of XRD data, unit cell volume, FT-IR spectra, photoluminescence (PL) and reflectance spectra of β-SMSON: Eu2+, it can be concluded that the incorporation of Mg2+ into the host leads to interstitial sites rather than substitutional ones. Mg2+ doping couldn't change the dominant peak wavelengths (DPWs) of Eu(I), Eu(II) and Eu(II)′ sites but only affects the PL intensity of title phosphors and could offset the nitridation effects. The concentration quenching mechanism and thermal activation energy of β-SSON: Eu2+ phosphors are determined effectively. The β-S(M)SON: 0.02Eu2+ phosphor have the feature that it can achieve color-tunable white light-emitting combined with blue light emitting diodes (LEDs) with single activator doped and single-phase host, which enables these materials to be enormous possibilities used in white light emitting diodes.