Color-tunable luminescence by energy transfer mechanism in RE (RE = Eu²⁺, Tb³⁺)–doped Na₂SrPO₄F phosphors

Abstract

In the current research work, Eu²⁺, Tb³⁺ singly doped and co-doped Na₂SrPO₄F phosphors have been synthesized by solid-state reaction method relatively low temperature. Eu²⁺-doped Na₂SrPO₄F phosphor shows broad excitation spectra in the range of 270–425 nm, which matches well with near ultraviolet (NUV) LED chips. Under 334 nm excitation, blue emission observed due to 4f⁶5d¹ → 4f⁷ transition of Eu²⁺ ions. The maximum emission intensity was observed for 1 mol% concentration of Eu²⁺ ions, thereafter concentration quenching was observed. In the present work, energy transfer from Eu²⁺ to Tb³⁺ is observed in Na₂SrPO₄F: Eu²⁺, Tb³⁺ phosphor. Under 350 nm excitation, it was observed that with the variation in the concentration of Tb³⁺ ions, the Commission Internationale de l'Elcairage (CIE) chromaticity coordinates shift toward the white region which confirms that the synthesized sample shows tunable emission. In addition, current–voltage (I–V) characteristic curves of proposed phosphor coated and without coated solar cells were measured under direct sunlight and solar simulator. The obtained results indicate that proposed samples have potential for White light-emitting diodes (WLEDs) and photovoltaic applications.