21 research outputs found
Extensive studies on CeF crystals, a good candidate for electromagnetic calorimetry at future accelerators
Fluorescence Processes and Scintillation of CeF Crystal Excited by UV and X-Ray Synchrotron Radiation
Photoluminescence properties of CeF have been investigated. Two kinds of emitting centers have been identified: regular Ce sites exhibiting two close emission bands (285 and 300 nm) and a fast fluorescence (20 ns) and several physically different perturbed Ce 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
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+ â Nd3+ energy transfer in YAG : Nd, Ce crystals for the used concentrations.On Ă©tudie, Ă basse tempĂ©rature, les mĂ©canismes de transfert d'Ă©nergie entre les ions Ce3+ et Nd3+ incorporĂ©s dans des cristaux de grenat d'aluminium-yttrium (YAG) en utilisant comme source d'excitation sĂ©lective un laser Ă colorant Ă impulsion et accordable permettant de pomper dans la premiĂšre bande d'absorption de Ce3+. On observe des transferts d'Ă©nergie aussi bien radiatifs que non radiatifs. Les courbes de dĂ©clin de la fluorescence des ions Ce3+ sont enregistrĂ©es pour diverses concentrations en Ce3+ allant de 0,003 Ă 0,02 at. % et des concentrations en Nd3+ habituellement utilisĂ©es dans les barreaux laser YAG : Nd (~ 0,73 et 0,88 at. %). Etant donnĂ© qu'aucune diffusion n'a lieu parmi les ions Ce3+, il est possible de dĂ©crire les courbes de dĂ©clin Ă l'aide de la thĂ©orie d'Inokuti-Hirayama. Le meilleur accord est obtenu pour une distance critique moyenne R0 ~ 1,1 nm aussi bien pour des couplages du type dipĂŽle-dipĂŽle que dipĂŽle-quadrupĂŽle. Ceci signifie que ces deux couplages contribuent au transfert d'Ă©nergie non radiatif Ce3+ â Nd3+ dans les cristaux YAG : Nd, Ce pour les concentrations considĂ©rĂ©es