Synthesis and photoluminescence properties of high-quality reddish-orange emitting Ca₄Nb₂O₉:Eu³⁺ phosphors for WLEDs and anti-counterfeiting

In this report, we successfully synthesized a novel trivalent europium (Eu³⁺)-activated Ca₄Nb₂O₉ phosphor emitting reddish-orange light via its ⁵D₀ → ⁷F₁ and ⁵D₀ → ⁷F₂ transitions. In the Ca₄Nb₂O₉ host, Eu³⁺ ions exhibited optimal doping at a concentration of 15 mol%, with the concentration-quenching mechanism predominantly driven by electric dipole-dipole interactions. In addition, the Ca₄Nb₂O₉:Eu³⁺ phosphor exhibited excellent thermal stability with a photoluminescence (PL) intensity of 71.6% at a working temperature of 423 K. Interestingly, the internal PL quantum yield (PLQY) of the optimal sample was obtained to be 87.43%, and the external PLQY was determined to be 47.81%. The fabricated white light-emitting diode that employed this optimized phosphor alongside commercial phosphors, via a novel silica epoxy gel (parts A and B)-based method, exhibited good color rendering index (color rendering index = 80.65), excellent warm-correlated color temperature (correlated color temperature = 3753 K), and Commission International de l'Eclairage chromaticity coordinate (0.3922, 0.3845). Moreover, the optimal phosphor was introduced into the polyvinyl alcohol (PVA) polymer film, creating a translucent film. These films were then fabricated on glass, plastic, and card, which showed a satisfying emission under ultraviolet radiation. Consequently, the proposed Eu³⁺-activated Ca₄Nb₂O₉ phosphors can be used as light sources and the Ca₄Nb₂O₉:Eu³⁺-PVA film is proposed for anti-counterfeiting applications.