A super broad emission band in tri-doped orthosilicate phosphors for full-spectrum white light illumination

Abstract

A series of solid solution Sr_mCa_2−mSiO₄ (SCS) tri-doped with Ce³⁺, Tb³⁺, Eu³⁺ (SCS: Ce, Tb, Eu) phosphors were synthesized by the traditional high-temperature solid-state reaction. In the orthosilicate crystal system Sr_1.5Ca_0.5SiO₄, tri-doped rare earth ions Ce³⁺, Tb³⁺, and Eu³⁺ are independent luminescent centers. Under the excitation of UV light, they exhibited three emission bands: the first broadband peaked at 420 nm, the second band with sharp lines peaked in green (about 554 nm), and the third band in the orange-red region (588–720 nm), which are originated from 5d → 4f of Ce³⁺,⁵D₄ →⁷F_J of Tb³⁺, and ⁵D₀ →⁷F_J of Eu³⁺, respectively. On the other hand, as aggregated luminescent centers which emission is with comparable intensities at suitable concentration resulted in separate luminescent peaks connected, form a super broad emission band and lead to color-tunable emission. To fine control white emission, a series of solid solution phosphors Sr_mCa_1.969−mSiO₄:0.6% Ce³⁺, 0.15% Tb³⁺, 0.8% Eu³⁺, 1.55%Li⁺ (SCS: Ce,Tb,Eu) had been prepared. This phosphor reveals that a full-spectra emission in the visible light region can be obtained when the mole percent of Sr²⁺ in the solid solution matrix is 65%–90% (m = 1.3–1.8), and the nominal composition Sr_1.7Ca_0.3SiO₄: 0.6% Ce³⁺, 0.15% Tb³⁺, 0.8% Eu³⁺, 1.55% Li⁺ phosphor can realize a super broad emission band with a full width at half maximum (FWHM) of 147 nm that match well with the solar spectrum in the visible light region. The result reveals that it is a potential single-phase full-spectrum white light (SFWL) phosphor for UV-chip-based white LED, which can be applied in full spectrum illumination and plant growth light sources. The luminescent mechanism was also discussed in detail.