Tb2(DPA)2(HDPA)2 Green Emitter Coordination Compound: Photometric Analysis and Temperature-Dependence Luminescence

Lanthanide-based coordination compounds are attractive materials for developing light-emitting systems and optical sensors due to their sharp emissions and long-lived excited states. In this work, we report the synthesis, characterization, and luminescent performance of a novel terbium-based coordination compound, Tb₂(DPA)₂(HDPA)₂, obtained through a low-temperature reaction between terbium (III) nitrate and dipicolinic acid (H₂DPA) in methanol. FTIR, TGA, and PXRD analyses confirmed the coordination of H₂DPA to Tb³⁺ through both singly (HDPA⁻) and fully deprotonated (DPA²⁻) forms, resulting in a 2:2:2 stoichiometry. The compound exhibits strong green photoluminescence dominated by the ⁵D₄ → ⁷F₅ transition, with a lifetime of 1.5 ms and an absolute quantum yield of 50% under λ_exc = 330 nm. Photometric characterization revealed CIE 1931 chromaticity coordinates of x = 0.33, y = 0.56 very close to the green standard phosphor European Broadcasting Union illuminant green (x = 0.29, y = 0.60) and a color purity of 70%. For the ⁵D₄ → ⁷F₅ transition, a purity of 99.9% was calculated, confirming its potential for solid-state lighting applications. Temperature-dependent luminescence studies (30°C–150°C) presented a 90% loss in emission intensity at 100°C, rendering the material visually inactive beyond this point. This behavior supports its application as a thermal on/off indicator in areas such as electronics, industrial processing, and safety labeling.