High-Quantum-Yield [Eu(Phen) ₂ (NO ₃ ) ₃ ] Phosphor Exhibiting Zero Thermal Quenching under Real Operating Conditions (30–150 °C)

In this study, we present the first investigation of the temperature-dependent luminescence properties of the [Eu-(Phen)₂(NO₃)₃] complex across the 30-150 °C range. The coordination environment, thermal stability, and structural analysis of the complex were studied by Fourier-transform infrared spectroscopy, thermogravimetric analysis, and powder X-ray diffraction techniques. Photoluminescence studies under excitation at 350 and 396 nm revealed the characteristic Eu³⁺ emission arising from the ⁵D₀ → ⁷F _<i>J</i> (<i>J</i> = 1-4) transitions. Additionally, the complex exhibits a long luminescence lifetime (τ = 1.096 ± 0.001 ms) and a high photoluminescence quantum yield (Φ = 96%) with λ_exc = 350 nm. The photometric analysis confirms deep-red emission with 99% color purity and CIE 1931 chromaticity coordinates (<i>x</i>, <i>y</i>) = (0.66, 0.33). Notably, the [Eu-(Phen)₂(NO₃)₃] complex exhibits zero thermal quenching over the temperature range, which could be attributed to the effective suppression of thermally activated back-energy transfer. These results demonstrate exceptional thermal robustness, highlighting its potential for thermally stable red-emitting optical applications.