Synthesis and photoluminescence properties of high-quality reddish-orange emitting Ca 4 Nb 2 O 9 :Eu 3+ phosphors for WLEDs and anti-counterfeiting.

In this report, we successfully synthesized a novel trivalent europium (Eu ³⁺ )-activated Ca ₄ Nb ₂ O ₉ phosphor emitting reddish-orange light via its ⁵ D ₀ → ⁷ F ₁ and ⁵ D ₀ → ⁷ F ₂ transitions. In the Ca ₄ Nb ₂ O ₉ host, Eu ³⁺ 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 Ca ₄ Nb ₂ O ₉ :Eu ³⁺ 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 Eu ³⁺ -activated Ca ₄ Nb ₂ O ₉ phosphors can be used as light sources and the Ca ₄ Nb ₂ O ₉ :Eu ³⁺ -PVA film is proposed for anti-counterfeiting applications.