Fluorescence Processes and Scintillation of CeF3\text{}_{3} Crystal Excited by UV and X-Ray Synchrotron Radiation

Photoluminescence properties of CeF$\text{}_{3}$ have been investigated. Two kinds of emitting centers have been identified: regular Ce$\text{}^{3+}$ sites exhibiting two close emission bands (285 and 300 nm) and a fast fluorescence (20 ns) and several physically different perturbed Ce$\text{}^{3+}$ sites giving rise to a broad emission band near 340 nm and a longer fluorescence (30-40 ns) the decay time of which varies with wavelength. An energy transfer occurs between these two kinds of centers. Scintillation properties have been studied under UV and X-ray excitation. The additional fast decay always observed at short time under ionizing radiation is interpreted by a temperature dependent luminescence quenching phenomenon due to high excitation density

Influence of looping mechanisms in up-conversion processes in Yb-Tm-Ho doped Gd3Ga5O12

Two looping mechanisms are studied in Tm and Tm-Ho-Yb doped Gd3Ga5O12 (GGG). The first one is obtained under pulsed laser excitation, the second one under continuous laser excitation. The gain, losses and condition of stability of the loop are given

Energy transfer mechanisms between Ce3+ and Nd3+ in YAG : Nd, Ce at low temperature

The energy transfer mechanisms between Ce3+ and Nd3+ are studied at low temperature (T = 4.4 K) in Ce codoped YAG : Nd crystals using selective pulsed dye laser excitation to pump into the first Ce3+ absorption band. Both radiative and nonradiative energy transfers are observed. Ce3+ fluorescence decay curves are measured for various Ce3+ concentrations ranging from 0.003 to 0.02 at. % and typical Nd3+ concentrations used in YAG: Nd laser rods (~ 0.73 and 0.88 at. %). Since no diffusion occurs among Ce3+ ions, the Ce3+ decay curves are fitted according to Inokuti-Hirayama's theory. The best agreement is obtained for a average critical distance R 0 ~ 1.1 nm for dipole-dipole as well as quadrupole-dipole couplings. This means that both couplings contribute to nonradiative Ce3+ → Nd3+ energy transfer in YAG : Nd, Ce crystals for the used concentrations.On étudie, à basse température, les mécanismes de transfert d'énergie entre les ions Ce3+ et Nd3+ incorporés dans des cristaux de grenat d'aluminium-yttrium (YAG) en utilisant comme source d'excitation sélective un laser à colorant à impulsion et accordable permettant de pomper dans la première bande d'absorption de Ce3+. On observe des transferts d'énergie aussi bien radiatifs que non radiatifs. Les courbes de déclin de la fluorescence des ions Ce3+ sont enregistrées pour diverses concentrations en Ce3+ allant de 0,003 à 0,02 at. % et des concentrations en Nd3+ habituellement utilisées dans les barreaux laser YAG : Nd (~ 0,73 et 0,88 at. %). Etant donné qu'aucune diffusion n'a lieu parmi les ions Ce3+, il est possible de décrire les courbes de déclin à l'aide de la théorie d'Inokuti-Hirayama. Le meilleur accord est obtenu pour une distance critique moyenne R0 ~ 1,1 nm aussi bien pour des couplages du type dipôle-dipôle que dipôle-quadrupôle. Ceci signifie que ces deux couplages contribuent au transfert d'énergie non radiatif Ce3+ → Nd3+ dans les cristaux YAG : Nd, Ce pour les concentrations considérées

Energy Transfer Mechanisms and Excited State Dynamics of Yb3+\text{}^{3+}, Tm3+\text{}^{3+} and Ho3+\text{}^{3+} Doped Gd3\text{}_{3}Ga5\text{}_{5}O12\text{}_{12} Single Crystals

The transfer mechanisms occurring in ytterbium, thulium and holmium doped gadolinium gallium garnet crystals are presented. Various models are used to modelize the up- and down-conversion processes. They lead to a good description of the excited state dynamics and provide information about the efficiencies of the transfers