Temperature‐Dependent Luminescence Spectroscopy in Europium Complexes Based on Phthalic Acid: The Effect of Coordinated Water

ABSTRACT Thermal luminescence stability is a key challenge in developing luminescent materials for various applications. Photoluminescent properties of two red‐emitting complexes, [Eu (PHT) 3 ·H 2 O] and [Eu (PHT) 3 ], were studied. Infrared spectroscopy demonstrated characteristic ν as (COO − ) and ν s (COO − ) bands of coordinated carboxylates. Photoluminescence confirms an effective ligand to metal energy transfer in the [Eu (PHT) 3 ⸱H 2 O] and [Eu (PHT) 3 ] complexes, resulting in the characteristic Eu 3+ ion transitions corresponding to 5 D 0 → 7 F J ( J = 0–4). Luminescence lifetime (τ), Absolute Quantum Yield (Ф), and quantum efficiency (η) revealed an increase of nonradiative deactivation channels in the [Eu (PHT) 3 ⸱H 2 O] complex due to the presence of O–H oscillators when compared to the [Eu (PHT) 3 ] complex. Photometric analysis placed both complexes in close agreement with NTSC red coordinates ( x = 0.67, y = 0.33), and full color‐purity values above 93%. The temperature‐dependent luminescence of the [Eu (PHT) 3 ] complex exhibited thermal stability up to 423 K, maintaining a signal of 70%. In contrast, the initial intensity of the [Eu (PHT) 3 ·H 2 O] complex increases up to 50% in the 393–413 K range, causing intensity variations and reduced reproducibility suggested by the presence of the water molecule. These results indicate that the anhydrous [Eu (PHT) 3 ] complex is an efficient red‐emitting phosphor for optoelectronic devices.