Tailoring the Luminescent Properties of SrS:Ce³⁺ by Sr-Deficiency and Na⁺ Doping

Ce³⁺-doped SrS phosphors with a charge-compensating Na⁺ addition were successfully synthesized via a solid-state reaction method, and the related X-ray diffraction patterns can be indexed to the rock-salt-like crystal structure of the Fm3̅m space group. SrS:(Ce³⁺) (0.005 ≤ x ≤ 0.05) and SrS:(Ce³⁺)_0.01,(Na⁺) (0.005 ≤ y ≤ 0.030) phosphors were excited by 430 nm UV-Vis light, targeted to the 5d¹ → 4f¹ transition of Ce³⁺. The composition-optimized SrS:(Ce³⁺)_0.01, (Na⁺)_0.015 phosphors showed an intense broad emission band at λ = 430-700 nm. The doping of Na⁺ was probed by solid-state nuclear magnetic resonance. The 430 nm pumped white light-emitting diode structure fabricated with a combination of SrS:(Ce³⁺)_0.01,(Na⁺)_0.015 and Sr₂Si₅N₈:Eu²⁺ phosphors shows a color-rendering index (R_a) of 89.7. The proposed strategy provides new avenues for the design and realization of novel high color quality solid-state LEDs.