Enrico Bovero

Optical spectroscopy of BaY2F8:Dy3+

The optical spectra of the BaY2F8:Dy3+ laser crystal have been investigated in the 5000–30 000 cm−1 range. The Judd–Ofelt parametrization scheme has been applied to the analysis of the room temperature absorption spectra. The calculated radiative lifetime of the 4F9/2 state is 1.48 ms. Decay curves of the visible emission have been measured as a function of the temperature for two different Dy3+ concentrations (0.5 and 4.4%). In the case of the diluted crystal the emission profiles are single exponential with decay times consistent with the radiative lifetime. The decay curves of the concentrated crystal are not exponential and they obey the Inokuti–Hirayama model for energy transfer for an electric dipole–dipole interaction in the absence of diffusion among the donors. The emission cross section at 575 nm has been estimated using the integral β–τ method in order to assess the potentialities of this compound as a solid state laser material in the yellow region.

Study of the visible spectra of Ca3Sc2Ge3O12 garnet crystals doped with Ce3+ or Pr3+

Abstract We have measured the absorption, the visible emission spectra and the lifetimes of Ca3Sc2Ge3O12 single crystals activated with Ce3+ or Pr3+. The crystals were grown by the ‘flux growth’ method. The optical spectra of the Ce3+-doped crystal consist of broadbands as a consequence of the strong electron–phonon coupling in the 2D(5d1) excited level, the emission band being located in the blue-green region with maximum at about 480 nm. The spectroscopic properties of CaSGG:Pr are affected by inhomogeneous broadening arising from the presence of non-equivalent optical centres. The spontaneous transition probabilities, the branching ratios and the radiative lifetimes have been calculated in the framework of the Judd–Ofelt Theory and compared with the experimental results for the 3P0 and 1D2 levels. The emission cross-sections of the transitions originating from the 3P0 level were calculated and compared with those reported for other Pr3+-doped crystals of technological interest.

Optical spectroscopy of SrWO4 : Nd3+ single crystals

The optical properties of SrWO4 crystals doped with Nd3+ have been investigated at temperatures ranging from 10 to 300 K. The scheme of the energy levels up to 20 000 cm−1 has been deduced from low temperature measurements and reproduced by theoretical calculations based on a parametric Hamiltonian including Coulombic, spin–orbit and crystal field terms. The spontaneous transition probabilities, the branching ratios and the radiative lifetime have been calculated in the framework of the Judd–Ofelt theory and compared with the experimental results for the 4F3/2 emitting level. The optical bands are broadened because of crystal field inhomogeneities caused by charge compensation processes accompanying the substitution of Nd3+ for Sr2+. This fact and the high emission cross section values obtained for the emission from the 4F3/2 multiplet indicate Nd:SrWO4 as a possible active medium for tunable laser operation.

Optical spectroscopy and crystal-field analysis of YAl3 (BO3)4 single crystals doped with dysprosium

YAl3 (BO3)4 crystals doped with Dy3+ were grown from a potassium trimolybdate flux. Their absorption and visible emission spectra and decay curves were measured at temperatures ranging from 10 to 298 K. The complete energy level scheme has been deduced from the low temperature measurements and reproduced by theoretical calculations based on a parametric Hamiltonian including coulombic, spin–orbit and crystal-field terms. The Judd–Ofelt parametrization scheme has been applied to the analysis of the room temperature absorption spectra. The calculated radiative lifetime of the 4F 9/2 state is 344 μs; this value is reasonably consistent with the experimental data.

Cr3+→Nd3+ energy transfer in the YAl3(BO3)4 nonlinear laser crystal

The energy transfer between Cr3+ and Nd3+ ions in Cr3+, Nd3+:YAl3(BO3)4 (YAB) codoped crystals has been investigated by means of steady-state and time-resolved laser spectroscopies. The mainly nonradiative character of the energy transfer has been evidenced from the comparison between the emission spectra and the donor fluorescence decays. The analysis of the donor decay profiles has been used to determine the main dipole–dipole character of the transfer, in excellent agreement with the predictions made from the Dexter [J. Chem Phys. 21, 836 (1953)] model, as well as with the dependence of the energy-transfer rates on the acceptor concentration. The temperature behavior of the transfer rate has been analyzed considering the thermal-induced population redistribution between the E2 and T24 states of Cr3+ ions and the existence of the phonon-assisted energy transfer. We have obtained that 80% of the Cr3+→Nd3+ energy transfer in YAB is taking place without the assistance of lattice phonons whereas almost 20% ...

Effects of neodymium incorporation on the structural and luminescence properties of the YAl3(BO3)4?NdAl3(BO3)4 system

The luminescence of Nd(3+) ions in Nd(x)Y(1-x)Al(3)(BO(3))(4) (Nd:YAB) single crystals has been investigated as a function of the neodymium concentration in order to evidence the relation between the structural and spectroscopic properties in this nonlinear laser system. The analysis of the experimental data allowed us to individuate four different composition ranges. For moderate concentrations (x<0.2) the lattice parameters are nearly constant, and the emission spectra arise from Nd(3+) ions in unperturbed crystal sites. For concentrations in the 0.2<x<0.75 range the lattice parameters notably depend on the neodymium content, and a concomitant variation of the luminescence features is observed. In the 0.75<x<0.9 range a hexagonal to monoclinic phase transition takes place: the structural disorder is evidenced well by the broadening of the emission lines and by discontinuities in the concentration behaviour of other indicators such as the crystal-field strength, energy transfer parameters, etc. Finally, for x>0.9 the final formation of the NdAl(3)(BO(3))(4) (NAB) monoclinic phase is complete, and a new local ordering around Nd(3+) is very evident in the spectral features.

Single longitudinal mode laser oscillation from a neodymium aluminium borate stoichiometric crystal

We report on single mode 1.06μm laser oscillation from a 882nm pumped NdAl3(BO3)4 stoichiometric crystal. When operating in continuous wave regime, laser slope efficiencies in excess of 50% have been obtained from a 250μm thick cavity. Additionally, stable single mode nanosecond (2ns) and subnanosecond (200ps) pulses have been generated by Q-switching the microchip cavity with semiconductor saturable absorbed mirrors. In this way peak powers in excess of 500W have been obtained while keeping single mode oscillation.

Optical spectroscopy of Yb3+-doped Ca3Sc2Ge3O12 garnet crystal

Good quality Ca3Sc2Ge3O12 garnet crystals activated with Yb3+ have been grown by means of the flux growth method and characterized using optical spectroscopy techniques. The low-temperature absorption and emission spectra give evidence of the presence of nonequivalent optical centers, as a consequence of the distribution of the Yb3+ ions in different lattice sites. The effect of codoping with Na+ or Mg2+ on the Yb3+ site distribution has been investigated. The energy-level schemes of the most important centers have been determined on the basis of site-selective spectroscopy experiments. Cooperative luminescence has also been observed and reliably compared with the self-convolution of the NIR luminescence.