Vladimir I. Makarov

EXTERNAL MAGNETIC FIELD ACCELERATION OF RADIATIONLESS PROCESSES IN THE A STATE OF GASEOUS OXALYL FLUORIDE

Fluorescence excitation spectra of (COF)2 (A ← [Xtilde]) have been observed in the 32 350–33 150 cm-1 spectral region under various magnetic fields below 10 kG. Fluorescence intensity and decay of (COF)2 vapour have been measured as functions of external magnetic field strength with excitation of the different vibrational bands belonging to the A ← [Xtilde] transition. It is found that fluorescence intensity is reduced considerably by magnetic fields below 1 kG, and the magnetic field quenching is saturated at about 1 kG (the maximum reduction being 43% for the 00 0 band and 69% for the 52 071 1 + 51 081 0 band). The magnetic fluorescence quenching increases with increase in excess vibrational energy and decreases with increase in collision frequency. The fluorescence decay and the fluorescence yield in magnetic fields show that the magnetic quenching of the fluorescence of (COF)2 may be considered by the ‘indirect’ mechanism in a frame of the ‘low’ level density approximation.

Study of S–T conversion induced by an external magnetic field in gaseous oxalylfluoride excited to the 00-level of the state

Abstract The fluorescence intensity and decay of gaseous oxalylfluoride ((COF)2) excited to the 1 A u (00) level by the A←X transition were measured as a function of an external magnetic field. On excitation to this level, the dynamics in zero field may be described in the small-molecule limit, with the fluorescence exhibiting an almost exponential decay. However, at increasing field strength the initial fluorescence decay becomes faster, the decay profile becoming biexponential at higher fields. Thus, a magnetic field-induced change of dynamics occurs in the A 1 A u state from that of a small molecule to that of the intermediate case. The fast-component decay rate constant Kf=(2.36±0.19)×107 s−1 is independent of the (COF)2 gas pressure and magnetic field strength, while the slow-component lifetime depends on both. We find that the magnetic field effect on the slow component grows at lower gas pressures. An increase of the integrated (COF)2 phosphorescence was observed at higher magnetic fields; consequently an external field accelerates singlet–triplet transitions in the excited (COF)2. Time-resolved measurements of the effect of a microwave field on the fluorescence demonstrated that the slow-component amplitude and lifetime are additionally reduced by an external microwave field, at νMW=9400 MHz, B=0.3295 T, and P=30 mTorr; and the fast-component amplitude increases at constant lifetime. We also find an additional phosphorescence intensity increase with subsequent saturation at higher microwave intensities. Experimental data are interpreted using the indirect mechanism theory in the low level density limit.

Microwave field effect on the fluorescence of (COF)2 excited to the 000 band of the Ã1Au state

Abstract The effect of a microwave field ( λ MW = 3 cm) in the presence of an external magnetic field has been observed on the fluorescence of (COF) 2 excited to the vibrationless level of the A 1 A u state. The microwave field results in additional resonance quenching of the (COF) 2 fluorescence in the 0.33 T region. This effect corresponds to the optically detected EPR spectrum of the excited vibrational levels of the a 3 A u state and it proves that magnetic quenching of the (COF) 2 fluorescence is realized by the indirect mechanism.

Magnetic and microwave field effects for single rotational levels of the 000-band of oxalylfluoride in cooled jet conditions

Fluorescence intensity and decay in oxalylfluoride vapors ((COF)2), excited to single rotational levels (SRLs) of the 1 Au(00) state of the A 1Au←A 1Ag transition, were measured as a function of an external magnetic field. On excitation to these levels, dynamics in zero field may be described in the small-molecule limit, with fluorescence exhibiting an almost exponential decay. However, at increased field strength B the initial fluorescence decay becomes faster, the decay profile becoming biexponential at higher fields. Thus, a magnetic field-induced change of dynamics occurs in the A 1Au state, from that of a small molecule, to the intermediate case. The decay rate constant of the fast component was measured for different SRLs, being independent on the magnetic field strength, while the slow component lifetime is field dependent, increasing at higher fields. Both the fast and slow decay lifetimes depend on the studied SRL. At higher fields, the slow component amplitude decreases, while that of the fast c...

Time-resolved experiments on external microwave field action in gaseous oxalylfluoride excited to the 00 0—band of the μ1Au state

Time-resolved measurements of the microwave field effect using optically detected EPR (ODEPR) have demonstrated that the amplitude and lifetime of the slow component of fluorescence are additionally reduced by an external microwave field, at a microwave frequency of 9400 MHz, a constant magnetic field of 0.3295 T and an oxalylfluoride pressure of 30 mTorr. This is accompanied by an increase in the fast component amplitude, at a constant decay rate of (2.36 × 0.19) 107 s−1. The fluorescence intensity was found to decrease, and phosphorescence intensity to increase, with subsequent saturation at higher microwave intensities. The experimental data are interpreted using the indirect mechanism theory in the limit of low-level density.

Improving cytotoxicity against cancer cells by chemo-photodynamic combined modalities using silver-graphene quantum dots nanocomposites

The combination of chemotherapy and photodynamic therapy has emerged as a promising strategy for cancer therapy due to its synergistic effects. In this work, PEGylated silver nanoparticles decorated with graphene quantum dots (Ag-GQDs) were tested as a platform to deliver a chemotherapy drug and a photosensitizer, simultaneously, in chemo-photodynamic therapy against HeLa and DU145 cancer cells in vitro. Ag-GQDs have displayed high efficiency in delivering doxorubicin as a model chemotherapy drug to both cancer cells. The Ag-GQDs exhibited a strong antitumor activity by inducing apoptosis in cancer cells without affecting the viability of normal cells. Moreover, the Ag-GQDs exhibited a cytotoxic effect due to the generation of the reactive singlet oxygen upon 425 nm irradiation, indicating their applicability in photodynamic therapy. In comparison with chemo or photodynamic treatment alone, the combined treatment of Ag-GQDs conjugated with doxorubicin under irradiation with a 425 nm lamp significantly increased the death in DU145 and HeLa. This study suggests Ag-GQDs as a multifunctional and efficient therapeutic system for chemo-photodynamic modalities in cancer therapy.

Time-resolved fluorescence of NO2 in a magnetic field

The influence of a magnetic field on the fluorescence of NO2 has been studied by time-resolved experiments. It has been found that the magnetic field quenched the pre-exponential of the fluorescence signal but did not alter its lifetime. A simple model based on an expanded two-level approximation has been proposed. The model has qualitatively accounted for the observed experimental results.

Photoconductivity of the TiO2+Fullerene-C60 bilayers: steady-state and time-resolved measurements

Abstract Photoconductivity of TiO2+Fullerene-C60 bilayers was studied. The fullerene layer conductivity increased significantly in presence of radiation with wavelengths below 300 nm incident onto TiO2. The sample response time was shorter than 20 ns.

Spin-polarized state transport from ferromagnetic to conductive material: Signal amplification by ferromagnetic layer

We continue the work on the quantum filter of spin polarized states induced by magnetic field in an iron nanolayer. Properties of a three-layer ferromagnetic (Fe)–dielectric (SiO2)–conductor (Au) device performing selective transport of spin polarized states were investigated. Reduced diameter of the input magnetic core and thinner conductive layer improved the filter resolution. Output signal amplitude decayed exponentially with the thickness of the dielectric layer. The filter properties were analyzed and explained using the previously developed theoretical approach, based on exchange interaction of the electronic energy levels located in the ferromagnetic and conductive layers. We also studied a five-layer Fe–SiO2–Au–SiO2–Fe sandwich system. Here the transmitted signal structure was more complex than that in a three-layer device. Theoretical model for the five-layer spin state filter device was proposed, based on an extension of that for the three-level device.

Observation of spin-polarized state transport from a ferromagnetic to a conductive material

In the present study, a quantum filter of spin-polarized states induced by magnetic fields in an iron nanolayer was assembled and experimentally studied. We found the device to pass certain spin-polarized states from the iron nanolayer to a conductive gold nanolayer through a dielectric silicon dioxide nanolayer. A theoretical model developed earlier was successfully applied to qualitatively interpret the experimental data.