Effects of Isomorphous Substitution on Photophysical and Magnetic Properties of Complexes [Ln _1‐ <i> _x </i> Dy <i> _x </i> (MeDPQ) ₂ Cl ₃ ] (Ln = Y ³⁺ , Ho ³⁺ , and Er <sup>3

This work encompasses the study of magnetic, optical, and structural properties of the coordination compounds [Ln(MeDPQ)₂Cl₃] (Ln ─ Ho³⁺, Er³⁺, Dy³⁺, and Y³⁺; MeDPQ - 2-methyldipyrido-[3,2-f:2',3'-h]-quinoxaline) and substituted complexes [Ln_1- _xDy_x(MeDPQ)₂Cl₃] (Ln = Ho³⁺, Er³⁺, and Y³⁺) based on them. Magnetic measurements within the range 5-300 K revealed single ion anisotropy in [Dy(MeDPQ)₂Cl₃], with the Curie-Weiss temperature θ being -3.69 ± 0.03 K. Complexes of Ho³⁺ and Er³⁺ exhibited f-f emission in the visible range, while the latter was also emissive in the NIR. Dilution of the Dy³⁺ complex with diamagnetic Y³⁺ ions resulted in alterations of magnetic and photophysical properties. The substituted complexes Y_0.5Dy_0.5 and Y_0.9Dy_0.1 demonstrated paramagnetic behavior, with θ being 3.06 ± 0.12 K and 9.64 ± 0.23 K, respectively. In both cases, the emission decay times of Dy³⁺ changed insignificantly, 21.02 ± 0.41 µs and 14.56 ± 0.22 µs, respectively, compared to the value (18.92 ± 0.03 µs) of the individual Dy³⁺ complex. Additional ligand-based emission bands were observed in the Ho³⁺ and Er³⁺ complexes at room temperature and 77 K and in the substituted complexes Ho_0.5Dy_0.5 and Er_0.5Dy_0.5 at room temperature, which were assigned to the exciplex states. The thermal stability of [Er_0.5Dy_0.5(MeDPQ)₂Cl₃] was determined to be the same as for the individual complexes, starting to oxidize at 410°C.