Yu.V. Orlovskii

Multiphonon relaxation rates measurements and theoretical calculations in the frame of non-linear and non-Coulomb model of a rare-earth ion-ligand interaction

The fluorescence kinetics decay from 3F3, 3H5, 3H4, 3F4 multiplets of Tm3+ and 5F5, 5I5, 5S2 + 5F4, 5I6, 5I7 multiplets of Ho3+ ions in Y3Al5O12, Lu3Al5O12 and LiYF4 crystals was directly measured. On the basis of these measurements the multiphonon relaxation (MPR) rates of the transitions were determined. The theoretical dependence of multiphonon relaxation rates on the rare-earth ionic radii was derived using the non-linear (NL) theory of multiphonon relaxation. A good qualitative agreement of this dependence with new and earlier measured MPR rates in rare-earth ions in the row from Tm3+ to Pr3+ in YAG, YLF, and LaF3 crystals was obtained. The dependence of multiphonon relaxation rates on the crystal type is also considered.

High-order multipole interaction in nanosecond NdNd energy transfer

Abstract The nanosecond energy transfer kinetics of the 4 G 7 2 + 2 K 13 2 multiplet of the Nd3 + ion in the LaF3 laser crystal was investigated. The energy transfer rates of electronic excitation from donors (excited Nd3+ ions) (D) to different coordination spheres of acceptors (A) (unexcited Nd3 + ions) were determined considering no energy migration. The predominance of the dipole-quadrupole (dq) mechanism against dipole-dipole (dd) was found from the analysis of these rates for the donor-acceptor distances from 6.05 A and up to 17 A. For the distances in the range from 4.1 to 4.4 A the mechanism of donor-acceptor interaction differes from that for the longer donor-acceptor distances. It was shown that a high rate and predominance of the dipole-quadrupole interaction is correlated with the larger value of the square of the low rank reduced matrix element U(2) in comparison with those of the high rank U(4) and U(6) for one of the transition involved in the process of energy transfer. We point out that the dipole-dipole nonradiative energy transfer from the 4 F 3 2 metastable level of Nd3+ ion is usually realized because of the small values of (U(2)2) in comparison with (U(4)2) and (U(6)2) for both transitions involved in the quenching process.

Multiphonon relaxation of the electronic excitation energy of rare-earth ions in laser crystals

The paper discusses both the linear and nonlinear mechanisms of multiphonon relaxation (MR) transitions in trivalent rare-earth (RE) ions in crystals. In the first well-known case, the linear terms of electron-phonon interaction (EPI) with respect to vibronic coordinates are responsible for MR transitions. In the last case, the nonlinear part of EPI induces the multiphonon relaxation. The expression for total rate of the MR transition due to both mechanisms taken into account was obtained.

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

Abstract 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 4 D 3/2 manifold of the Nd3+ ion were measured in CeF3 crystals. As a result the temperature dependence of energy transfer kinetics from the 4 D 3/2 manifold of the Nd3+ donor ions to the 2 F 7/2 manifold of the acceptor Ce3+ ions in the ordered practically 100% filled CeF 3 :Nd 3+ (0.056 wt %) crystal lattice was determined for 13– 55 K . 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 55 K is found to be almost 3 orders of magnitude from 9.0×104 to 2.84×10 7 s −1 . In a CeF 3 :Nd 3+ (0.63 wt %) crystal a significant contribution of the Nd→Nd resonance energy transfer to the 4 D 3/2 manifold quenching is found for 20– 40 K 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.

First-principles study of the local structure and crystal field of Yb2+ in sodium and potassium halides

The local coordination structures around the doping Yb2+ ions in sodium and potassium halides were calculated by using the first-principles supercell model. Both the cases with and without the charge compensation vacancy in the local environment of the doping Yb2+ were calculated to study the effect of the doping on the local coordination structures of Yb2+. Using the calculated local structures, we obtained the crystal-field parameters for the Yb2+ ions doped in sodium and potassium halides by a method based on the combination of the quantum-chemical calculations and the effective Hamiltonian method. The calculated crystal-field parameters were analyzed and compared with the fitted results.

Relaxation of Mid- IR Transitions of ND3+ in Laser Crystals With “Short” Phonon Spectra

The kinetics of fluorescence decay of the 4G7/2 manifold of Nd3+ is directly measured in the row of fluoritc type crystals like PbF2, BaF2, SrF2, and CdF2 as well in the CaGa2S4 and PbCl2 crystals with “short” phonon spectra. Based on the measured kinetics the radiative and multiphonon relaxation rates of the 4G7/2 manifold were determined. The lead fluoride crystals demonstrate the smallest nonradiative losses for the 4G7/2→ 4G5/2; 2G7/2 mid- IR transition of Nd3+ among the tested fluoride crystals. But much smaller nonradiative losses are found for CaGa2S4: Nd3+ and practically no losses are found for the PbCl2: Nd3+ crystal. The increased rates of radiative decay in comparison with fluoride and oxide Nd3+ doped crystals were found in the sulfide and the chloride crystal. Based on these results the decay times of the 4I15/2; 4I13/2; and 4I11/2 manifolds perspective as initial laser levels for mid- IR generation were estimated in all studied crystals.