The current research project is focused on developing high quantum yield glasses with improved optical properties for a wide range of spectral and scintillating applications. To ascertain their effective suitability for high quantum yield, optical applications; Eu3+-ion-doped germanate glasses with and without gadolinium were synthesised and analysed spectroscopically. Raman analyses were performed and found that addition of lanthanide into the glass will disrupt the bonds to create more non-bridging oxygens in the network. The synthesised glasses exhibit lower phonon energy similar to 798 cm(-1) with electron-phonon coupling strength (g) similar to 0.009. Thermal corrections were applied to study how they are populated at lower levels of J = 1 for Eu3+ ions. Addition of Gd2O3 content to the glass matrix show higher value of Omega(4) suggesting their role in long-range effects in their glass network. Stimulated emission cross-section sigma(lambda(p)) show 28.47 x 10(-22) cm(2) and 22.19 x 10(-22) cm(2) for without gadolinium content and with gadolinium content glasses after thermal correction. The absolute photoluminescence quantum yield showed 39.9 +/- 1.6 % and 89.2 +/- 4.0 % without Gd2O3 and with Gd2O3 ions in the glass. The donor-acceptor energy transfer parameters such as efficiency and probability show 69.15 % and 576 s(-1) respectively. Radioluminescence studies reveal that these glasses show bright reddish-orange light emission when X-rays are used as source of excitation and studied their luminescence ability. The obtained results suggest that the present glass system show promising candidates for scintillating materials due to their bright reddish-orange light emitting devices under UV light and X-ray as a source.

The present study highlights the influence of Dy3+ ions on the luminescent properties of glass matrices, specifically focusing on the effects of oxide, oxyfluoride, and sensitizer content. The emission behaviour and characteristics of dysprosium in these different environments have been extensively investigated. Absorption studies were conducted using the Judd-Ofelt theory, revealing a trend of Omega(2) > Omega(4) > Omega(6), which indicates a highly asymmetric local environment around the Dy3+ ions. A prominent emission peak at 574 nm corresponding to the F-4(9/2) -> H-6(13/2) transition was observed in all glass samples. Structural analysis revealed the presence of GeO6 and GeO4 units, 3-membered ring structures, and Q(3) germanate networks, all of which influence the luminescence properties. The absolute photoluminescence quantum yield (PLQY) was measured under 350 nm excitation, showing values of 6.4 f 0.4 %, 13.0 f 0.6 %, 18.2 f 0.8 %, and 25.2 f 0.8 % for Dy, DG, DGF, and DGO glasses, respectively. Energy transfer efficiency was also evaluated, with the DGO sample exhibiting up to 25 % efficiency. Radioluminescence studies demonstrated that these glasses exhibit significant scintillation in the visible range. Overall, the findings suggest that Dy3+-doped germanate glasses have strong potential for white light-emitting applications under various excitation sources.

Water-soluble organic luminophores based on 3-(1,3-benzothiazol-2-yl)-4-hydroxybenzenesulfonic acid were studied both experimentally and by density functional theory for the first time. Because of peculiarities in chemical structure, one of them has a large Stokes shift, which results from excited state intramolecular proton transfer.

A method for the determination of pore orientation in metal-organic framework structures by polarized Raman spectra is proposed. The method involves sensitivity of the line intensity of Raman scattering to the geometry of propagation in a crystal. The operability of the method is shown by DUT-8 (Ni, Co) crystals. The obtained results are interpreted based on analysis of symmetry and direction of vibrations within periodic calculations of the electron density functional theory. The simultaneous approach allowed us to describe the vibrations and to find the principal crystal orientation collinear to the pore direction. The information on the pore orientation is necessary for problems of adsorption and design of complex multicomponent materials based on metal-organic framework.

The temperature sensitivity of photoluminescence (PL) of synthesized composites based on differently charged biopolymers with colloidal quantum dots CdSe/ZnS and erythrosin B dye was investigated. The dynamic range of the analytical signal of the intensity of quantum dot photoluminescence broadens under the combined action of temperature quenching and the resonance energy transfer from the quantum dots to the dye, which can be used to create dynamic temperature sensors.

In this work, we considered the influence of viscogenic agents (glycerol, sucrose) as well as the temperature on the fluorescent characteristics of fluorescein at pH 6.5 in order to describe the acid-base status of local environment in terms of a spectrally detectable dianion-anion equilibrium. The protolytic equilibrium of fluorescein was found to depend on the solvent viscosity in a complex way. Whereas in the presence of sucrose the ratiometric signal of fluorescein (I488/I435) remains rather unchanged, the addition of glycerol (up to 40% w/w) results in the increase of the signal (up to 19%), that can be attributed to the different mechanisms of cosolvents effects on dye molecules in the ground state. Molecular dynamics of the dye in the presence of glycerol and sucrose revealed that the cosolvents preferentially interact with fluorescein monoanion and dianion, displacing water molecules from the local environment which in turn reduces the average number of the hydrogen bonds between xanthene ring of the dye and water molecules. The ratiometric signal demonstrates linear growth with the temperature in the range of 10–80 °C regardless of the presence of viscogenic agents. A linear correlation between the temperature sensitivity of the ratiometric signal and the change in the molar enthalpy of the proton dissociation reaction in buffer and viscous media was determined.

In the work, the priority among a number of temperature mechanisms affecting the fluorescence ratiometric signal of fluorescein in the pH range of 5.5÷7 was revealed. The kinetic model at the monoanion-dianion dissociation step with temperature-dependent constants was applied to analyze the experimental data. It was shown that the major contribution to the sensitivity of the ratiometric signal on temperature provides the perturbation of the ionic equilibrium in the ground state. The thermometric characteristics of ratiometric signal were found and the temperature resolution of 7°C was achieved. Temperature resolution can be improved up to 2°C by optimization of the experimental conditions.

An approach to the study of the porous structure of metal-organic frameworks (MOF) using guest luminescent molecules with specially selected spectral characteristics as acceptors of electronic excitation energy was suggested. If such molecules are adsorbed in MOF pores with sizes comparable to the Förster radius, Förster resonance energy transfer (FRET) from photoexcited linkers occurs. In this case quenching of luminescence of the linker can serve as analytical signals indicating open pore structure of the MOF. The developed approach was demonstrated by the example of DUT-8(Zn) MOF and Coumarin 1 as guest molecules by time-resolved luminescence methods.

New water-soluble supramolecular complexes are synthesized from the ammonium salt of arabinogalactan sulfate and rhodamine dyes via ion exchange. Stable fluorescent complexes exhibit fluorescence quantum yields sufficient for visualization (10–20%). The molecular content of the polymer is two orders of magnitude above that of the dye in supramolecular complexes. The high concentration of functional sulfo groups of arabinogalactan allows the complexes to be used in drug delivery systems.

The protolytic equilibrium of the excited states of fluorescein depends not only on the equilibrium in the ground state, but also on the efficiency of photoexcitation, relaxation, and proton transfer in the excited state. Due to rate-competing radiative and non-radiative processes occurring in a mixture of protolytic forms, there is still a problem of identifying the fluorescent characteristics of individual forms of fluorescein. In this work, the steady-state distribution of the concentrations of the ground and excited states of the cation, a number of tautomers of the neutral form, monoanion, and dianion of fluorescein under continuous photoexcitation was simulated. The pH values of the predominant existence of individual protolytic forms in the excited states were determined, which were confirmed by steady-state fluorescence measurements. Possible reasons for the discrepancies in the published data on the fluorescent properties of individual protolytic forms of fluorescein are discussed and refined data on the spectral shapes and lifetimes of the quinoid and monoanion of fluorescein are obtained.

In the work, a system with effective (up to 90%) F8rster resonance energy transfer is implemented. The system includes thin gelatin films with embedded CdTe quantum dots (donors) and rose bengal xanthene dye (acceptor). The energy transfer mechanism revealed to be possible due to the high local concentration of fluorophores as well as careful selection of donor and acceptor spectral characteristics. The energy transfer was confirmed by the quench-ing of the donor photoluminescence in both steady-state and time-resolved measurements. The Stern-Volmer formalism and the F8rster theory were used to estimate the constants and efficiency of energy transfer. It was shown that the photoluminescence spectrum of the system can be driven by changing the ratio of the donor-to-acceptor concentration.

The behaviours of the open pore (op) and closed pore (cp) phases of the flexible Ni2(ndc)2(dabco) (ndc - 2,6-naphthalene dicarboxylate, dabco - 1,4-diazabicyclo[2.2.2]octane, DUT-8(Ni)) metal-organic framework under high hydrostatic pressures up to 10 GPa in isopropanol and silicone oil were studied by Raman spectroscopy. Ab initio simulations of vibrational spectra were performed for the open and closed pore phases, which allowed us to disclose the characteristic vibrational modes affected by the structural transitions under pressure. Analysis of theoretical and experimental Raman data suggests that the op-cp transition involves gateway vibrations at 25 and 67 cm-1, corresponding to trampoline/rotational motions of aromatic linkers. The experiments reveal the formation of new distorted cp phases at pressures higher than 2 GPa, which are formed without amorphisation. The transition between the cp phase and the distorted cp phase is reversible. The experiments also reveal the pivotal role of the pressure transmitting medium on the phase transition behaviour.

Calibration curves for determining the constant of fluorescein equilibrium in the excited state were obtained by decomposing the emission spectrum into separate dianion and anion contours. It is shown that the photoinduced proton transfer at the step of dianion‒anion dissociation competes with radiative processes, and its efficiency increases with the concentration of phosphate ions acting as proton acceptors. The change in apparent dissociation constant ΔpKapp2 during photoexcitation into the absorption band of the fluorescein dianion (488 nm) was found to be close to limit value ΔpKa = −0.71 determined according to the Förster cycle.

Positively charged polyelectrolyte complexes (PECs) were synthesized from two polysaccharides chitosan and arabinogalactan sulfate by self-assembly method as potentially efficient adsorbents for medical and environmental purposes. The obtained PEC particles of submicron size were comprehensively characterized by dynamic and electrophoretic light scattering, FTIR spectroscopy and scanning electron microscopy. The adsorption properties of the synthesized PECs were determined by optical methods using eosin Y as a model anionic dye. A temporal evolution of dye absorption spectra was revealed during the equilibration process in the eosin Y-PEC system; the decay can be described by three characteristic times with maximal value of 35 min. The adsorption within the pH range of 3.0–5.6 can be appropriately described by Langmuir-Freundlich model with the maximal adsorption capacity of 500 mg g−1. The increase of ionic strength has no significant effect on adsorption capacity of PECs, however it results in the increase of the heterogeneity factor from 0.82 up to 2.35. The revealed relationships were discussed in terms of predominantly electrostatic adsorbate-adsorbent interactions. The synthesized PECs demonstrated high colloidal stability along with a high removal efficiency of dye at low pH values that makes them very attractive eco-friendly dye adsorbent with improved biocompatibility.

Recently, there has been an increased interest in natural polysaccharides, in particular, chitosan, which are widely used in medicine and industry. Chitosan labeled with fluorescein dyes acquires additional optical properties that can be used in sensing and delivery systems. Mechanism of binding of a polymer to a label largely determines the field of its possible applications. The quantum chemical calculation using the B3LYP/aug-cc-pVDZ theory level has been made in order to contribute to the understanding of intermolecular interactions. The geometry of fluorescein, eosin Y, and erythrosin B in the dianionic, monoanionic, and neutral quinoid forms interacting with chitosan has been optimized and the absorption spectra have been calculated using the time-dependent density functional theory taking into account the solvent. The comparison of the calculated absorption spectra with the experimental data has shown a major role of the electrostatic mechanism in binding of anionic dyes to the protonated chitosan groups.

Experimental determination of the fluorescence quantum yield and spectral profile for a variety of protolytic forms of fluorescein is challenged by their simultaneous co-existence in aqueous solutions as well as the excited-state proton transfer (ESPT). Different methods of fluorescence spectroscopy (both steady-state and time-resolved) were applied to investigate aqueous solutions of fluorescein containing sulfuric and hydrochloric acids (pH < 3.5). The obtained emission spectra were decomposed by Alentsev-Fok method to separate spectral contributions for cationic and neutral quinoid forms. The resolved individual fluorescence spectra were used for the estimation of the excited-state dissociation constant of the cation-quinoid equilibrium (pka*=-0.5) as well as fluorescence quantum yield for the quinoid form (0.42). An almost total fluorescence quenching of the cationic fluorescein was observed in the solutions with high concentration of the hydrochloric acid whereas quantum yield for this form remains considerable (0.92) in the solutions containing sulfuric acid at similar pH. The obtained results bring new insights to the understanding of the role of the ESPT and counter-ion of the acid in the relaxation of the excited states of fluorescein in acidic media.

Interpolymer complexes based on chitosan and arabinogalactan with a different degree of sulfation (7.7–40.8%) stable for 30 days are synthesized. The resulting complexes are characterized by scanning electron microscopy, IR spectroscopy, dynamic light scattering, and ζ-potential electrophoretic measurements. The main mechanism of complex formation is considered in terms of the electrostatic bonding of polyions. New complexes show promise as biosorbents and drug delivery systems.

Abstract In this paper, a new method for the synthesis of the sulfated starch-casein complex is proposed. The resulting new complex was characterized by FTIR and UV-spectroscopy. It has been shown by FTIR spectroscopy that both nitrogen atoms and the carboxyl group of amino acid residues are protonated in casein. The sulfated starch-casein complex obtained in this work may have biological activity, as well as its analogues isolated from plants, fungi, and microorganisms, as well as synthesized in laboratory conditions.

Multistage dissociation of fluoroscein dyes, widely used in biological labeling, yields a variety of ionic and tautomeric forms in a wide range of pH values. In contrast to well-studied absorption spectra, the emission spectra are not quite readily interpreted due to their strong overlapping and proton transfer in electronically excited states. The least studied are the fluorescent properties of eosin and erythrosin dyes containing heavy atoms (Br, I), in which the characteristics of the dianionic form only are reliably determined. In the framework of the density functional theory using the B3LYP-functional including nonequilibrium solvation, the geometries of the series of ionic forms of eosin and erythrosin in the ground and excited states are found, and the electronic spectra are calculated. Based on the identified linear regression of the calculated and experimental data for the earlier resolved electronic spectra, for the first time, the emission spectrum maxima of the monoanionic, neutral quinoid, and cationic forms of the dyes are determined. The spectral peculiarities (Stokes shifts) are discussed in terms of variation of the molecule and ion geometries in the ground and excited states.

In contrast to the well-studied absorption spectra of different protolytic forms of fluorescein, the complex structure of the fluorescence spectra in a wide pH range is not completely understood because of the interplay between emission and photoinduced proton transfer in the electronic excited states. We provide insight into this interplay through a combined analysis of the experimental data, obtained by absorption and steady-state fluorescence spectroscopy at pH 0.3-10.5, and the time-dependent density functional theory (TD-DFT). The TD-DFT based computational model is validated on dianion and used to model the spectra of other protolytic forms. The protolytic/tautomeric forms of fluorescein are classified according to the partial charges on the triple chromophore ring, and electronic transitions are analyzed in terms of changes in molecular geometries and orbitals. A linear regression analysis between the calculated and experimental results based on both absorption and well-understood dianionic and cationic fluorescence peaks is used to assign the monoanionic (496 nm), neutral quinoid (550 nm) and neutral zwitterionic (483 nm) fluorescence peaks, whose positions were not clear prior to this work. The values of the excited-state dissociation microconstants pk(a)*for different forms of fluorescein are calculated by means of the Forster cycle in conjunction with the spectroscopic measurements and computational data.