For the first time Gd3+-doped (0.4–0.9 mass.%) ZnO:SiO2 composite films were obtained using the sol-gel method. Optical properties of the films and their structures were studied by absorption and fluorescence spectroscopy and scanning electron microscopy (SEM). The obtained SEM images suggest that the surface morphology of the films does not change qualitatively. However, it was found that doping with Gd3+ ions leads to a significant increase in the ultraviolet luminescence (UVL) of ZnO in ZnO:SiO2 composite by 2.9–3.4 times (λem  =  364 nm), which is accompanied by an increase in the band gap of Gd3+-doped films compared with non-doped films.

Second harmonic generation in zinc oxide films deposited by the hydrothermal method was investigated. A correlation between second-order optical susceptibility tensor components d311 and d333 was studied by using the model of noninteracting microcrystals, and the origin of different contributions to the film nonlinearities was discussed. The change of stacking sequences and the inhomogeneity in the distribution of the nonlinearities over the film thickness are the most probable effects hindering the investigations of the thickness dependence of ZnO film nonlinearities. A model of the inhomogeneous distribution of the nonlinearities over the film thickness was used for doing an analysis of the experimental data features, which were accounted for by a sublayer, adjacent to the seed layer, and possess high optical nonlinearity, d333 = −72.6 pm/V.

ZnO–SiO2 composite films doped with La3+ ions (0.1%–5.0% mass.) were obtained using the sol–gel method. The absorption and ultraviolet luminescence spectra of the films, as well as the change in spectral characteristics under the influence of DNA, were studied. Doping of ZnO:SiO2 films with La3+ ions leads to an increase in the transmittance in the UV range (λ = 357 nm) from 4.5% (for undoped films) to 32%–34%, and the transmittance is inversely proportional to the amount of dopant. In all doped films, the optical band gap increases in comparison with undoped films (3.35 eV) and amounts to 3.830–3.853 eV. The application of DNA to the surface weakly affects the value of optical band gap. The maximum of the ultraviolet luminescence (UVL) band in ZnO:SiO2:La3+ films is slightly shifted depending on the amount of dopant and is located at λem = 363–367 nm. An increase in UVL intensity was observed upon doping by a factor of 8.4–9.6 compared to ZnO:SiO2 films. A change in the amount of dopant does not lead to sharp changes in the magnitude of the intensity. Thus, the UVL intensity (λex = 260), compared with films with 0.1% La3+ content, varies by 5%–11%. The effect of small amounts of DNA was studied for films doped with La3+. In the case of ZnO:SiO2:La3+, both extinguishing (up to 12%) and ignition (up to 5%) of UVL were observed. Monotone dependencies (which are desirable for the biosensor sensing element) were obtained for samples with La3+ 0.1 and 1.0% content. SEM images show that the images for zinc oxide are white crystallites of different sizes: from 0.5 µm to conglomerates of crystallites −1 µm. In the presence of DNA, the surface structure changes due to the formation of rhomboid structures, whose sizes vary from 3 µm to 35 µm. It is known that lanthanum ions induce the compaction of DNA with the formation of nanoscale structures.

Thin films of zinc oxide and those doped with terbium (at concentrations of 0.1–5.0 mol%) were synthesized on glass substrates using the sol–gel method. The UV–Vis transmission spectra showed that transparency increases from 60% to 86% with an increase of Tb content. All terbium-doped samples exhibit a rise in Eg from 3.37 eV for zinc oxide to 3.827 eV for doped films. The photoluminescence (PL) of zinc oxide doped with terbium in the UV (260 nm) region and the fluorescence of terbium in the visible region (330 nm) were studied. The intensity of green luminescence with an increase in the amount of terbium increases by an average of 6%. The yield of green fluorescence relative to PL also goes up with an increase in the concentration of terbium concentration of terbium from 5% to 7.4%. DNA deposited on the surface of the plate extinguishes PL by an average of 5.5% and has a weak effect (<3%) on terbium fluorescence in the visible region. SEM images without DNA consist of spherical structures—0.5–2.0 μm in diameter, assembled in the form of pentagons. The presence of DNA on the surface is expressed as ‘stars’ of white color of regular and irregular shapes, located on the surface inside these pentagons.

This research presents a new perspective on optical biosensors based on zinc oxide nanoparticles. The widely known and successfully applied nanostructured material is modified by the dopant - the green phosphor Terbium, which embedded in the structure of zinc oxide and makes a significant contribution to the fluorescent response of the material in both the UV and visible spectral regions. The effect of various dopant concentrations on the fluorescence of nanostructures was studied; the nanostructures were examined by SEM.