A systematic study of the optical properties of mononuclear hybrid organo–inorganic lanthanoid complexes

Abstract

A series of hybrid organo–inorganic mononuclear lanthanoid complexes, [n-NBu₄]₃[LnH(PW₁₁O₃₉)(phen)₂]·H₂O, denoted as LM⁴-1-Ln (Ln = Dy^III, Tb^III, Eu^III, Nd^III, Er^III, Ho^III and Gd^III), were synthesized via hydrothermal synthesis and were structurally characterized by X-ray diffraction. The optical properties of all complexes have been investigated in the solid state. The temperature-dependent emission spectra of LM⁴-1-Dy, LM⁴-1-Tb and LM⁴-1-Eu complexes show intense lanthanoid emissions in the visible region, while LM4-1-Nd shows near-infrared (NIR) luminescence. The Eu^III complex shows typical strong red emissions from the ⁵D₀ → ⁷F_0,1,2,3,4 transitions, with the CIE colour coordinates (0.631,0.364), the colour purity value of 83.9% and a quantum yield of up to 4.3%, suggesting that the organic fragment has an effect on the optical properties compared to fully inorganic systems, making this complex very attractive as a red component of light-emitting diodes. The luminescence decays of LM⁴-1-Dy, LM⁴-1-Tb and LM⁴-1-Eu exhibit a biexponential behaviour, with τ_AV = 4.1(7) μs, 0.35(2) ms and 0.94(3) ms, respectively. The values obtained for Judd–Ofelt intensity parameters Ω₂ and Ω₄ support the interaction between the Eu^III and the ligands. Furthermore, those with Er^III and Ho^III present weak emissions in the visible region. The T-dependent photoluminescence results show that the LM⁴-1-Dy, LM⁴-1-Tb and LM⁴-1-Nd complexes have good temperature sensitivity, demonstrating that the materials have the potential to be used as a sensing element for luminescent thermometers in different temperature ranges.