Enhanced white light generation via Eu3+ co-doping and Dy3+→Eu3+ energy transfer in Ca3WO6 phosphors for WLEDs

Abstract

Dy³⁺/Eu³⁺ co-doped cold white-emitting Ca₃WO₆ double perovskites were synthesized via the conventional solid-state reaction at 1200 °C. The energy transfer (ET) mechanism and tunable white photoluminescence (PL) behavior of Ca₃WO₆:0.015Dy³⁺,yEu³⁺ phosphors were thoroughly examined. The monoclinic crystal structure of the phosphors was determined by X-ray diffraction (XRD), while morphological analysis was conducted via scanning electron microscopy (SEM). The Ca₃WO₆:0.015Dy³⁺ phosphor displays prominent blue emission at 485 nm (⁴F_9/2-⁶H_15/2) and yellow emission at 575 nm (⁴F_9/2-⁶H_13/2) when excited at 353 nm. Upon excitation at 353 nm, the emission spectrum of Ca₃WO₆:0.015Dy³⁺,yEu³⁺ (y = 0.01–0.05) reveals peaks at 485 nm, 575 nm, and 613 nm, attributed to the characteristic transitions of Dy³⁺ and Eu³⁺ ions. The Dy³⁺ → Eu³⁺ ET enabled tunable white emission within the white spectral region. The maximum ET efficiency, calculated to be 66.34%, was recorded at an optimal Eu³⁺ concentration of 0.05%. The mechanisms underlying the energy transfer and concentration quenching were explained using Dexter's theory. Additionally, the ET efficiency calculated using decay lifetime, i.e. 69.65%, validates the results of ET efficiency. A simplified energy level diagram of the Dy³⁺–Eu³⁺ co-doped system was created to illustrate ET pathways and clarify the fundamental mechanisms. The CIE color coordinates of Ca₃WO₆:0.015Dy³⁺,0.01Eu³⁺ are found very close to the standard white points, and hence, it is examined for temperature-dependent PL. The phosphor showed excellent thermal stability, retaining 81.09% of its intensity at LED operating temperature, making it a promising candidate for white LED applications.