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Nonlinear optical characteristics of chemically prepared silver selenide (Ag2Se, 3.7 nm) and lead selenide (PbSe, 6.3 nm) colloidal quantum dots (QDs) are investigated using the 1030 nm femtosecond pulses. Ag2Se QDs demonstrated two-photon absorption followed by saturable absorption. PbSe QDs initially showed the saturable absorption at small intensities of 1030 nm probe pulses, followed by reverse saturable absorption at stronger excitation. The difference in the positive nonlinear optical absorption mechanisms in these two QD colloids is attributed to their different bandgaps. The studied QD colloids exhibited the Kerr-induced positive nonlinear refraction. Transient absorption studies of the QDs showed that photoexcitation creates a hot exciton that forms band-edge exciton within 1.2 ps after excitation. Most of the electron-hole pairs further recombine through band-to-band recombination with a time constant of 1490 ps. Furthermore, the results from the transient absorption studies indicate the contribution of trap-assisted recombination occurs on a time scale exceeding that of the experimental time window. [ABSTRACT FROM AUTHOR]

The possibilities for changing the direction of energy transfer in hybrid associates of colloidal Ag2S quantum dots (QDs) and thionine molecules are analyzed. The studies were performed by transmission electron microscopy, absorption and luminescence spectroscopy, PL decay study (time correlated single photon counting). An increasing of the average QDs size from 1.8 nm to 5.5 nm, and also a shift of the luminescence band from 630 nm to 950 nm, were found at using of TGA molecules and sodium sulfide as a sulfur precursor. Hybrid association of QDs (1.8 nm) with TH+ molecules leads to quenching of QDs luminescence with a simultaneous reduction of the luminescence lifetime from 13.7 to 6.5 ns. An association of QDs with a luminescence band maximum of 950 nm with TH+ molecules leads to quenching of TH+ luminescence and a reduction in its lifetime of luminescence from 0.43 to 0.3 ns. It was concluded that the reduction of lifetime of luminescence caused by the resonant nonradiative energy transfer between the components of the associates. An increasing in the average size of QDs leads to a change in the direction of energy transfer between the components of the associates.

We study the features of the nonlinear optical response of silver nanoparticles (Ag NPs) of spherical and triangular shapes synthesized using a citrate-borohydride approach and their mixtures with methylene blue (MB+). The Z-scans at the wavelengths of 532 nm using 10 ns pulses were used to analyze the nonlinear optical absorption of MB+ solutions, Ag NPs of different morphology, particularly, the concurrence of saturable and reverse saturable absorption in the solution of triangular Ag NP and MB+. We show the significant contribution to the increasing in the normalized transmittance accomplished by photochemical degradation of the non-spherical Ag NPs (extinction maximum of 600 nm) and transformation into the spherical ones (extinction maximum of 400 nm). The nonlinear light scattering is also analyzed, which showed the contribution to the variation of the sample transmission when it approaches the focal plane. It is shown that the nonlinear optical response is not additive in the mixture of Ag NPs and MB+. The increasing of the nonlinear absorption is probably due to both a change in the population of the triplet states of the dye and the efficiency of photochemical degradation of NPs in the presence of MB+.

Hybrid associates formed from colloidal Zn0.5Cd0.5S quantum dots, passivated with thioglycolic acid, europium tenoyltrioteracetonate and methylene blue molecules, absorption, luminescence, IR and time-resolved spectroscopy technique are studied. The shift of the IR absorption bands of COO- and C=O groups of thioglycolic acid and europium thenoyltrifluoroacetonate has been detected. An increase in the efficiency of excitation of europium luminescence and a simultaneous increase lifetime of its luminescence upon adsorption on Zn0.5Cd0.5S quantum dots were found. Addition of methylene blue (thionine) molecules leads to quenching of the trap state luminescence of Zn0.5Cd0.5S and intracentric luminescence of Eu3+. A conclusion about the adsorption of Eu3+ on the surface of Zn0.5Cd0.5S quantum dots and the nonradiative energy transfer to methylene blue molecules was made.

The article presents a method for the construction of a new tricyclic system of imidazo[1,2‐b]pyrido[4,3‐e][1,2,4]triazin‐6(7Н)‐ones based on subsequent reactions of the obtained 1,2‐diamino‐4‐phenylimidazole ethyl ether of 3‐methyl‐6‐phenylimidazo[1,2‐b][1,2,4]triazin‐2‐carboxylic acid with dimethylformamide dimethyl acetal and primary amines. The structures of the obtained compounds were confirmed using the data obtained from 1Н and 13С NMR, HRMS, and XRD analyses. We analyzed the dependence of the absorption and photoluminescence spectra on the structure of the compounds obtained using quantum chemistry methods. The theoretical results were compared with the data from a real experiment. The article suggests a range of practical applications for imidazo[1,2‐b]pyrido[4,3‐e][1,2,4]triazin‐6(7Н)‐ones. [ABSTRACT FROM AUTHOR]

This work presents studies of IR luminescence sensitization of Indocyanine Green dye (ICG), observed during association with colloidal Ag2S quantum dots with an average size of 2.2 nm passivated with thioglycolic acid (Ag2S/TGA QD). The opportunity of enhancing the dye monomer luminescence (peak at 820 nm) by 4–6 times under excitation of 660 nm in the presence of Ag2S/TGA QDs (2.2 nm) was shown. At the same time, Ag2S/TGA QDs luminescence intensity does not change. quantum yield (QY) luminescence of ICG increases by 5 times. The luminescence lifetime obtained with use of luminescence decay analysis at wavelength of 820 nm increases by 2.2 times. The observed changes in ICG luminescent properties during its conjugation with Ag2S/TGA QDs are result of a decrease in the mobility of the dye polymethine chain due to coordination interaction with Ag2S/TGA QDs, which decreases the efficiency of non-radiative transitions. [ABSTRACT FROM AUTHOR]

The possibilities of changing the direction of electronic excitations transfer in hybrid associates are analyzed. Studies of hybrid associates of colloidal Ag2S quantum dots (QDs), stabilized with thioglycolic acid (TGA) with thionine (TH+) molecules, were realized by transmission electron microscopy, absorption and luminescence spectroscopy, and photoluminescence decay studies (time correlated single photon counting). The increase in the average size of QDs from 1.8 to 5.5 nm, as well as shift of QDs luminescence peak from 630 to 950 nm were observed, when TGA molecules together with sodium sulfide was used as a sulfur precursor. The hybrid association of QDs (1.8 nm) with TH+ molecules leads to quenching of QDs luminescence in the luminescence band with peak at 630 nm and simultaneously decreases in luminescence lifetime from 13.7 to 6.5 ns. In the case of QDs association with a luminescence peak at 950 nm with TH+ molecules, it leads to quenching of TH+ luminescence and decrease in its luminescence lifetime from 0.43 to 0.3 ns. It is concluded that the decreasing in the luminescence lifetime is caused by nonradiative resonance energy transfer between components of associates. An increase in the average size of QDs leads to a change in the direction of energy transfer between associate components. [ABSTRACT FROM AUTHOR]

The article presents a method for the construction of a new tricyclic system of imidazo[1,2-b]pyrido[4,3-e][1,2,4]triazin-6(7Н)-ones based on subsequent reactions of the obtained 1,2-diamino-4-phenylimidazole ethyl ether of 3-methyl-6-phenylimidazo[1,2-b][1,2,4]triazin-2-carboxylic acid with dimethylformamide dimethyl acetal and primary amines. The structures of the obtained compounds were confirmed using the data obtained from 1 Н and 13 С NMR, HRMS, and XRD analyses. We analyzed the dependence of the absorption and photoluminescence spectra on the structure of the compounds obtained using quantum chemistry methods. The theoretical results were compared with the data from a real experiment. The article suggests a range of practical applications for imidazo[1,2-b]pyrido[4,3-e][1,2,4]triazin-6(7Н)-ones., (© 2022 John Wiley & Sons Ltd.)

A technique of obtaining plexitonic structures based on Ag 2 S quantum dots passivated with l-cysteine (Ag 2 S/l-Cys QDs) in the presence of Au nanorods passivated with cetyltrimethylammonium bromide molecules (Au/CTAB NRs) with controlled luminescence properties has been developed. The structural and luminescence properties of Ag 2 S/l-Cys QDs with Au/CTAB NRs are studied. The effect of plasmonic Au/CTAB NRs on IR trap state luminescence (750 nm) is considered. It has been found that the direct interaction between the components of the plexcitonic nanostructure leads to a significant luminescence quenching of Ag 2 S/l-Cys QDs, with the luminescence lifetime being constant. This is the evidence for photoinduced charge transfer. The spatial separation of the components of plexcitonic nanostructures due to the introduction of a polymer - poly(diallyldimethylammonium chloride) (polyDADMAC) provides a means to change their mutual arrangement and achieve an increase in the IR trap state luminescence intensity and a decrease in the luminescence lifetime from 7.2 ns to 4.5 ns. With weak plexcitonic coupling in the nanostructures [Ag 2 S QD/l-Cys]/[polyDADMAC]/[Au/CTAB NRs], the possibility of increasing the quantum yield of trap state luminescence for Ag 2 S QDs due to the Purcell effect has been demonstrated. In the case of formation [Ag 2 S QD/l-Cys]/[polyDADMAC]/[Au/CTAB NRs] a transformation of shallow trap state structure was established using the thermostimulated luminescence method., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

In this paper, we present the results on photoinduced formation of colloidal Ag 2 S quantum dots with sizes of 1.5-3 nm passivated by 2-mercaptopropionic acid (Ag 2 S/2-MPA) in the presence of ethylene glycol. The synthetized colloidal Ag 2 S/2-MPA QDs have NIR recombination luminescence with its maximum near 800 nm. The control of absorption and luminescence properties of the QDs is achieved by photoactivation. It is shown that photoexposure of colloidal solution of Ag 2 S/2-MPA QDs leads to an increase in the QD size and monodispersity along side with the growth of the luminescence quantum yield from 1% to 7.9%. Enhancement of the luminescence quantum yield is accompanied by an increase in the average luminescence lifetime up to 190 ns, which is due to the blocking of the nonradiative recombination channel with the radiative recombination rate being (3-5.5) × 10 5 s -1 . It is shown that the purification of the Ag 2 S/2-MPA solution by a dialysis membrane from regenerated cellulose leads to an increase in the sample monodispersity, as well as stops the photoinduced growth of QDs, and also reduces the degradation of their photoluminescence., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)