D. Vivien

Preparation, structure, optical, and magnetic properties of lanthanide aluminate single crystals (LnMAl11O19)

Rare‐earth aluminates having the general formula LnMAl11O19 with Ln3+ = La, Pr, Nd, Sm, Eu, Gd, and M2+ = Mg, Ni, Co, Mn, Fe have been synthetized. This paper is devoted to mixed compounds of the series La1−xNdx Mg Al11O19 of which large single crystals have been obtained by the flame fusion method. A full refinement of the pure lanthanum compound (x = 0) having a quasimagnetoplumbite structure has been performed (final R = 0.039). Spectroscopic investigations of the (La, Nd) aluminate have allowed the measurement of fluorescence yield and lifetime of Nd3+ in the host lattice as a function of the neodymium content. Additional results have been obtained on the magnetic anisotropy, from susceptibility measurements performed on the Nd3+ aluminate in the temperature range 4–300 K.

Yb3+ to Er3+ energy transfer and rate-equations formalism in the eye safe laser material Yb:Er:Ca2Al2SiO7

Rate equations formalism is used to predict the population ratio of the Er3+ 4I132 levels involved in the 1.55 μm laser transition in the Yb:Er:CAS laser materials. An effective Yb → Er energy transfer, favourable to the Er3+ 1.55 μm laser emission, is demonstrated in this laser host. Indeed, the Yb → Er transfer and the Er → Yb back transfer rates are calculated to be 6 x 10−16 and 0.45 x 10−16 cm3 s−1, respectively. Attempts of codoping the system with Nd3+, Eu3+ and Ce3+ have been realised in order to increase the population of the Er3+ 4I132 laser emitting level. Best results are obtained with Ce3+ ion since in the sample containing 6 x 1020 Ce3+/cm3, the Er3+ 4I112 level lifetime is divided by a factor of 3 while the Er3+ 4I132 fluorescence lifetime remains unaffected. On the contrary, codoping with Nd3+ or Eu3+ ions simultaneously decreases the Er3+ 4I112 and 4I132 kinetics parameters. The role of the other parameters such as Yb/Er concentrations ratios is also discussed.

Spectroscopic properties and laser performances of Yb:YCOB and potential of the Yb:LaCOB material

Abstract In order to increase the compacity of the Yb-doped lasers, YCOB (Ca 4 Y(BO 3 ) 3 ) materials with high ytterbium concentration have been characterized. Large 15 at.% and 35 at.% ytterbium-doped single crystals were grown by the Czochralski pulling method. Spectroscopic and laser properties have been investigated and laser tests performed under titanium sapphire and diode pumping at 976 nm. Low thresholds under Ti:Sa pumping (50 mW) and high slope efficiency under diode pumping (66%) have been obtained. The optical quality and the distribution of Yb 3+ dopant through the highly doped crystals is discussed. First results on the Yb:LaCOB crystals grown by the Czochralski process, containing 46Yb 3+ at.%, are also presented.

Spectroscopic studies of Yb3+-doped rare earth orthosilicate crystals

Infrared transmission and Raman scattering have been used to study Raman active phonons and crystal-field excitations in Yb3+-doped yttrium, lutetium and scandium orthosilicate crystals (Y2SiO5 (YSO), Lu2SiO5 (LSO) and Sc2SiO5 (SSO)), which belong to the same C2h6 crystallographic space group. Energy levels of the Yb3+ ion 2F5/2 manifold are presented. In the three hosts, Yb3+ ions experience high crystal field strength, particularly in Yb:SSO. Satellites in the infrared transmission spectra have been detected for the first time in the Yb3+-doped rare earth orthosilicates. They could be attributed to perturbed Yb3+ sites of the lattices or to magnetically coupled Yb3+ pairs.

Synthesis, ESR investigation, and optical properties of the potential vibronic laser material LaMgAl11−xCrxO19

Cr/sup 3 +/ doped LaMgAl/sub 11/O/sub 19/ single crystals have been grown. The ESR spectra and the optical properties of this matrix with magnetoplumbite structure have been studied. Three kinds of isolated sites have been identified by the /sup 2/E ..-->.. /sup 4/A/sub 2/ transition associated with the Cr/sup 3 +/ ion doped into the 4f antiprism site, the regular 2a octahedral site, and the 12k octahedral site. Additional lines in ESR and fluorescence spectra arise from the occurrence of 4f-4f pairs even for low doping levels. The presence of the /sup 4/T/sub 2/ ..-->.. /sup 4/A/sub 2/ broad band of fluorescence makes this material a possible candidate for a red of near-infrared emitting vibronic laser.

Resonance paramagnetique electronique du manganese divalent dans l'alumine β

Abstract Single crystals of β alumina doped with manganese ions have been prepared by high frequency induction melting and slow cooling, followed by Na + - Mn 2+ exchange in molten MnCl 2 . EPR study shows that Mn 2+ ions occupy two kinds of sites. The first one, with an axial zero field tensor corresponds to the tetrahedral positions in the spinel blocks, close to the sodium planes. This seem to indicate that aluminium vacancies in β alumina are partly located in this site. The other, with an orthorhombic zero field tensor, and high D and E values, belongs to the conduction planes.

Electron‐spin resonance and fluorescence investigation of LaMgAl11O19:Ti3+, a potential tunable laser material

Single crystals of LaMgAl11O19:Ti (LMA:Ti) have been grown from the melt by the Verneuil (flame fusion) process. As‐grown crystals contain titanium in both 3+ and 4+ oxidation states. Ti4+ ions can be reduced into the 3+ state by annealing at 1200 °C under hydrogen atmosphere. The crystals exhibit a broadband fluorescence extending from ∼600 to 1200 nm and peaking around 775 nm. The fluorescence lifetime is found to be ∼6 μs at 10 K against ∼4 μs at 300 K; it does not depend significantly on the emission wavelength, this indicating that fluorescence originates mainly from one type of Ti3+ active ions. Electron‐spin‐resonance (ESR) investigations reveal that Ti3+ ions are distributed among the three octahedral sites of the magnetoplumbite structure of the host, with a marked predominance for the regular octahedral site (2a), which contains about 90% of the titanium detected by ESR. Crystal field splitting of the t2g level has been estimated for the three sites and it is proposed that Ti3+ in the (12k) site...

Optical spectra and crystal field calculations of doped Zircon-type laser hosts (, P, As)

Low temperature absorption spectra of doped , and single crystals, grown by the flux method, are reported. A simulation of the energy level scheme is carried out. The effective Hamiltonian includes elementary interactions such as coulombic, spin-orbit, two- and three-body interactions. The crystal field effect is introduced through the five non-zero crystal field parameters allowed by the symmetry site occupied by the rare earth. A simulation is performed on the 96 (102, 90) experimental energy levels of , (, ) with a good rms standard deviation of 16.2 (15.4, 15.7) . It is noteworthy that the energy level scheme of is reported for the first time. The wave functions of the systems are used for the calculation of the magnetic factor g. These factors are in good agreement with the values deduced from EPR measurements on the lowest level . The crystal field parameters are also compared to the a priori parameters calculated using the simple overlap model and the correlated crystal field strength is also analysed.

Optimization by energy transfer of the 2.7 μm emission in the Er:SrLaGa3O7 melilite crystal

Abstract A laser emission in the 3 μm range may find various interesting applications, for instance, in surgery, spectroscopy and LIDAR. This paper reports the spectroscopic study of the 4 I 11 2 → 4 I 13 2 transition of Er3+ ions which occurs at ~ 2.7 μm in SrLaGa3O7 (SLG). The emission cross section calculated at the maximum of the band is 0.65 × 10−20cm2. The lifetime of the 4 I 11 2 emitting level is quite long, due to a low active phonon energy (560 cm−1). The 2.7 μm emission corresponds to a self-terminating transition since τ( 4 I 13 2 ) > τ) 4 I 11 2 ) (5.8 ms and 780 μs, respectively). In this paper, the influence of various parameters is analysed to determine how to increase the population inversion by depopulating the 4 I 13 2 terminal level. Codopant ions presenting energy levels in good resonance with the Er3+ 4 I 13 2 one can be used. Three codopants (Eu3+, Nd3+, Pr3+) were investigated but only Pr3+ decreases drastically the 4 I 13 2 level lifetime without significantly affecting the 4 I 11 2 one, leading to a good potentiality to achieve the 4 I 11 2 4 I 13 2 population inversion.

EPR and optical study of Yb3+-doped β-PbF2 single crystals and nanocrystals of glass-ceramics

β-PbF2 single crystals doped with YbF3 (0.2% and 2%) were studied by x-ray diffraction (XRD), electron paramagnetic resonance (EPR) and optical spectroscopy. EPR revealed the presence of only one kind of paramagnetic ion Yb3+, in a cubic symmetry site. The optical absorption, emission and excitation spectra enabled us to identify the transitions attributed to Yb3+ in the cubic site and to determine its energy level diagram. Site-selective laser spectroscopy also evidenced the presence of another type of Yb3+ ions, undetectable by classical EPR. This second type, which dominates in the 2%-doped crystal and exhibits cooperative luminescence, was attributed to Yb3+ ions forming clusters. Transparent oxyfluoride glass-ceramics, containing β-Pb1−yYbyF2+y nanocrystallites, were also synthesized and studied by XRD, EPR and optical spectroscopy. Two types of Yb3+ ions were found, as in β-PbF2 single crystals. The optical properties of the oxyfluoride glass-ceramics turn out to be similar to those of ytterbium activated β-PbF2 single crystals. Moreover, the Yb environments found in PbF2 single crystals seem to already occur in the parent glass. Therefore, these materials are expected to be good laser media, like the rare-earth doped fluorite crystals, either in bulk or fibre form.