The complex of Tb(III) with the biscoumarin derivative 3,3′-[(4-hydroxyphenyl)methyl)]bis-(4-hydroxy-2H-1-benzopyran-2-one), Tb(C₂₅H₁₅O₇)₃ · 5H₂O, was successfully immobilized by a simple technique in transparent SiO₂-based matrix. The films and monoliths obtained were studied by IR spectroscopy, fluorescent spectroscopy, and microscopy. The micromorphology of the films was studied by atomic force microscopy, proving their homogeneity. The 3-D surface of the films is very complex geometrically and appears relatively smooth, with very fine nano-asperities spread on the surface due to the preparation process. A detailed surface description of the surface morphology at nanometer scale using statistical parameters, according to ISO 25178-2: 2012, was made. The presence of the Tb(III) complex in the films and monoliths was proven by the characteristic emission bands of the Tb(III) ions. The lifetime of the immobilized Tb(III) complex was determined, showing better protection of the SiO₂ matrix in the monoliths than with the films.

The solvothermal synthesis of LnCl₃^.nH₂O with terephthalic acid (benzene-1,4-dicarboxylic acid, H₂BDC) produced metal–organic frameworks (LnBDC), [Ln₂(BDC)₃(H₂O)₄]_∞, where Ln = Sm, Eu, Tb, and Dy. The materials obtained were characterized by a number of physico-chemical techniques. The influence of the ionic radius of the lanthanides on the microstructural characteristics of the Ln-MOFs was evaluated by performing Rietveld refinement. The MOFs obtained were tested as fluorescent sensors for numerous cations and anions in water. The highly luminescent EuBDC and TbBDC demonstrated multi-responsive luminescence sensing functions to detect Ag(I), Fe(III), Cr(III), and Cr(VI), which are essential for their environmental applications. By applying the non-linear Stern–Volmer equation, the fluorescent quenching mechanism was determined. The stability of the obtained materials in water in a wide pH range (acidity pH = 4 and alkalinity pH = 9 solutions) was confirmed.

Light-emitting phosphors, doped with lanthanide ions of Tb(III) and Sm(III) of the type Gd_1.97−y Sm_yTb_0.03(MoO₄)₃ (y = 0.01–0.11, step 0.02) and Gd_1.95−xSm_0.05Tb_x(MoO₄)₃ (x = 0.01–0.09, step 0.02), were synthesized and characterized by X-ray diffraction, UV-Vis spectroscopy, scanning and transmitting electron microscopy (SEM, TEM) as well as photoluminescence spectroscopy. The effect of the doping content of Tb/Sm was followed. The unit cell parameters for Gd_1.97−ySm_yTb_0.03(MoO₄)₃ and Gd_1.95−xSm_0.05Tb_x(MoO₄)₃ changed with the increase in the Tb/Sm content. The microstrain values also increased, proposing an increased concentration of defects. The mean particle size was estimated to be approximately 0.6 µm. Based on a Williamson–Hall plot, the size of the crystallites was determined to be in the range of 42–60 nm for modified and pure Gd₂(MoO₄)₃ samples, respectively. The samples excited at 406 nm exhibited characteristic emission lines of Sm (485, 555, 646 nm). The host material Gd₂(MoO₄)₃ emission in visible light was explained by the crystal structure defects, namely, oxygen vacancies. The CIE x/y color coordinates of the phosphors were determined and the related points were located in the green-yellow/pale yellow region of the visible light. The excited state lifetimes were determined for both groups of the samples, showing values in the millisecond range and indicating the samples as promising phosphors.

Organic–inorganic hybrid materials produced from tetraethoxysilane, citric acid and ethylene glycol in different mole ratios and consisting of Si–O–Si and Si–O–C nets are prepared and their molecular structure (IR and NMR spectroscopy), morphology (fluorescent microscopy, SEM and AFM), thermochemical behavior and fluorescence properties (excitation and emission spectra) are studied. The optically active, oxygen sensitive complex of tris(4,7-diphenyl-1,10-phenanthroline) ruthenium(II) dichloride is immobilized in the so prepared matrix and the applicability of the composite as an optical oxygen sensor (response to O₂ in gaseous medium) is tested. The influence of the matrix composition on the linearity of the Stern–Volmer dependence and the films sensitivity to O₂ is studied.