Utilization of Judd-Ofelt theory to assess the photophysical properties of β-keto carboxylate Tb(III) complexes with heterocyclic secondary sensitizer

One binary and five ternary green glowing Tb(III) complexes with β-keto acid as primary sensitizer and heterocyclic aromatic system as secondary sensitizer, were synthesised by an eco-friendly method and characterized via various spectroscopic techniques. The assessment of photoluminescent properties in solid complexes and in solution phase with DMSO as solvent, revealed the bright green emission of complexes on irradiation of UV light due to 5D4 → 7F5 transition, whose intensity persistently increased on insertion of secondary sensitizer. Higher relative quantum yield in ternary complexes communicated the contribution of secondary sensitizers in enhancement of luminescence. Judd-Ofelt parameters (Ω2, Ω4, Ω6) were evaluated from NIR absorption spectra of complexes. Higher Ω2 value in complexes demonstrated the higher covalence character and asymmetry around Tb(III) ion. Radiative, nonradiative transition probabilities, radiative life time, branching ratios and luminescence efficiency were also estimated. Complex T6 reported to have 72.5% efficiency which signalizes superb luminescence performance of this complex. Colorimetric parameters were obtained in solid as well as solution form. Exquisite color purity and CCT value > 4000 K established these complexes as cold green light source. Band gap energy and Urbach band tail, obtained via nonlinear fitting of absorption coefficient, turned out to be in semiconductor range thus can have materiality in various photonic devices. The large value of stimulated emission cross section and narrow full width at half maxima (FWHM) of 5D4 → 7F5 emission peak suggested the prospective use of synthesised complexes as laser media for green color lasers.