Two- and three-dimensional restricted geometry case of luminescence quenching

We present general analytical expression for two and three-dimensional cases of static energy transfer kinetics in doped nanoparticles (of round, spherical and cylindrical shape). A series of numerical experiments has been performed using Monte-Carlo simulation. The analytical expressions have shown very good coincidence with the computer simulation.     

Picosecond stimulated Raman scattering in crystals

The comparative values of the peak and integral cross sections of spontaneous Raman scattering and the optical dephasing time of molecular vibrations were determined for several oxide crystals by spontaneous Raman spectroscopy. The spectral, time, and energy parameters of stimulated Raman scattering (SRS) were measured for ten crystals using picosecond YLF: Nd laser pumping with a radiation wavelength of 1047 nm. An analysis of the experimental dependence of the threshold energy of pumping SRS on the integral and peak cross sections of spontaneous Raman scattering showed that the SRS gain increment explicitly depended on the integral cross section and was independent of the peak cross section of spontaneous Raman scattering as the ratio between the pumping pulse width (11 ps) and the time of optical dephasing of molecular vibrations changed from 0.42 to 9.3. The gain coefficients of steady-state stimulated Raman scattering under threshold stimulated Raman scattering conditions were determined for all the crystals studied on the basis of the measured threshold SRS pumping energies, the duration and width of the spectrum of pulses, the nonlinear interaction length, the intensity of pumping, and the theoretical dependences that relate the steady-state and transient SRS gain increments. The steady-state SRS gain coefficients obtained in this work fitted well a linear dependence on the peak cross sections of spontaneous Raman scattering, which substantiated the correctness of our analysis and measurements.     

Theoretical analysis of the static quenching of optical excitations in luminescent nanoparticles

A compact analytical expression has been obtained for the kinetics of the donor-acceptor transfer of the energy and the quenching of optical excitations in spherical nanoparticles with luminescent impurities. A series of numerical experiments simulating the process have been performed using the Monte Carlo method for nanoparticles of various sizes and concentrations of acceptors. The analytical expression well describes the numerical simulation results.     

Direct nanosecond Nd→Ce nonradiative energy transfer in cerium trifluoride laser crystals

Using third harmonics of LiF:F₂⁺ tunable color center laser excitation and selective fluorescence detection the temperature and concentration dependencies of fluorescence decay curves of the high-lying manifold of the Nd³⁺ ion were measured in CeF₃ crystals. As a result the temperature dependence of energy transfer kinetics from the manifold of the Nd³⁺ donor ions to the manifold of the acceptor Ce³⁺ ions in the ordered practically 100% filled crystal lattice was determined for 13-. Based on the temperature dependence the mechanisms and the channels of the Nd→Ce nonradiative energy transfer have been recognized. The net growth of the resonance Nd→Ce energy transfer rate in the temperature range from 25 to is found to be almost 3 orders of magnitude from 9.0×10⁴ to .In a crystal a significant contribution of the Nd→Nd resonance energy transfer to the manifold quenching is found for 20- and its channel and mechanism are suggested.Discussion of the possibility of subpicosecond and picosecond nonradiative energy transfer in rare-earth doped laser crystals is provided.     

Two-photon polarization spectroscopy of LiF crystals with F 2 laser color centers

The paper reports on a measurement and calculation of the dependence of LiF: F ₂ luminescence polarization and intensity on the polarization of high-power laser radiation (λ_ex=1064 nm) producing two-photon excitation of F ₂ centers. It is shown that the two-photon transition results in the excitation of a previously unknown electronic level of F ₂ centers of the A _1g symmetry.     

Cooperative luminescence quenching on many-particle acceptors in disordered media

Many-body cooperative energy transfer is an important process in biology, medicine, photosynthesis, rare-earth-doped laser materials, responsible for up- and down-conversion of energy, optical excitation sensitization and relaxation. We present an analytical solution for long-time asymptotic of static luminescence quenching kinetics due to cooperative energy transfer to ensembles of acceptors comprised of two-, three-, and more particles. For cooperative energy transfer and cooperative luminescence quenching to n-body acceptors we have discovered a new law of power d/(nS−(n−1)d)$d/(nS-(n-1)d)$ time dependence (d=1,2,3$d=1,2,3$ is the space dimension, S=6,8,10$S=6,8,10$ is the multipolarty of interaction: dipole–dipole, dipole–quadrupole, or quadrupole–quadrupole). The detailed numerical simulation of cooperative quenching by Monte-Carlo method confirms the theoretical result.     

Radiative properties of lanthanide and transition metal ions in nanocrystals

We examine the physical factors that influence the radiative transitions of small-radius optical centers in ellipsoidal nanoparticles. The main objective of this work is to reveal to the extent to which changes in the phonon subsystem and electron-phonon interaction caused by spatial confinement effects affect the radiative characteristics of optical centers in nanocrystals.     

SRS generation under phase matching conditions for four-wave interactions of SRS components in birefringent Raman-active crystals

The possibilities of efficient four-wave SRS generation in the schemes of cavity and cavity-amplifier SRS converters with the implementation of phase matching conditions for four-wave mixing of different SRS radiation components at an appropriate orientation of birefringent SRS crystals have been considered based on a numerical simulation. The threshold characteristics and achievable energetic parameters of the SRS generation of different frequency radiation components have been analyzed under the conditions of implementation of phase matching for four-wave mixing. Conditions have been found for a low-threshold SRS-four-wave mixing generation of an anti-Stokes wave with a conversion efficiency of up to 40%, as well as of the first, second, and third Stokes SRS components with conversion efficiencies of up to 90, 80, and 30%, respectively.     

Cooperative quenching kinetics:Theory and Monte-Carlo simulation

Analytic expression is given for the static cooperative quenching kinetics in crystals with arbitrary acceptor concentration and arbitrary multipolarity of interaction. For the quenching by two acceptors, the results of Monte-Carlo simulation are also presented which can be approximated in the long-time domain by the nonexponential law I(t)?exp[?(wt)^k], with k=0.41, 0.3, and 0.25 for the multipolarities S=6, 8, and 10, respectively.