Tb3+→Eu3+ energy transfer and tunable photoluminescence in Ca3WO6:Tb3+, Eu3+ co-doped double perovskite

Abstract

The energy transfer mechanism and color-tunable photoluminescence (PL) properties of Ca₃WO₆:0.1 Tb³⁺, yEu³⁺ phosphors were systematically investigated and discussed. The PL spectra of the co-doped phosphor predominantly highlighted the green emission centred at 545 nm, originating from the Tb³⁺ (⁵D₄→⁷F₅) transitions, and red emission at 616 nm, attributed to the Eu³⁺ (⁵D₀→⁷F₂) transitions. Upon excitation at 278 nm, a notable enhancement in Eu³⁺ red emission was observed, facilitated by energy transfer (ET) from Tb³⁺ ions acting as sensitizers to Eu³⁺ activators. This energy transfer process from Tb³⁺ → Eu³⁺ enabled effective modulation of the emission color, shifting from green to orange-red, depending on the Eu³⁺ concentration. To understand the ET dynamics, several characterization techniques were employed, including the calculation of energy transfer efficiency, calculation of critical transfer distance, and analysis of PL decay lifetimes. The highest value of the energy transfer (77.43 %) was achieved for Eu³⁺ doping reaches to its maximum at 0.1 %. The specific reason of the energy transfer and concentration quenching phenomena was discussed by means of the Dexter's theory. Consistency across the various approaches (intensity variation and decay lifetime) confirmed the reliability of the ET efficiency evaluation. Furthermore, a simplified energy level diagram was constructed for the Tb³⁺-Eu³⁺ co-doped system to illustrate the energy transfer pathways and the associated emission transitions, offering a clearer understanding of the primary luminescence mechanisms.