B. Blanzat

Excited state absorption mechanisms of red to UV and blue conversion luminescence in Tm3+ doped fluorophosphate glass

Abstract Characteristics and ion-ion interaction processes important in the optical dynamics of UV and blue upconversion luminescence in Tm 3+ doped fluorophosphate glass have been investigated by exciting Tm 3+ ions into the 3 F 2 level with a DCM dye laser tuned at 657 nm. Two emission bands centered at 363, 451 nm from the 1 D 2 level and one emission band centered at 478 nm from the 1 G 4 level were observed. The 451 nm emission was stronger than the 478 nm emission. The excitation power dependence of all the upconverted emissions were found to be quadratic, conforming the two photon nature of these transitions. The mechanism leading to these emissions was attributed to the excited state absorption (ESA) from the 3 F 4 and 3 H 4 levels for the emissions of the 1 D 2 and 1 G 4 levels, respectively. The loss mechanism due to ion-ion interaction in the 3 F 4 level therefore was studied as function of temperature by measuring the spectral overlap between emission and absorption spectra of this level. From this data relevant microscopic interaction parameters that give a measure of Tm-Tm coupling have been calculated. Optical properties of the intermediate and the final levels involved in the upconversion processes were studied using the Judd-Ofelt theory. This theory was also used to determine radiative transition rates and the fluorescence quantum efficiencies of the excited levels, and the excited state absorption coefficient for the 3 F 4 → 1 D 2 and 3 H 4 → 1 G 4 transitions when the excitation was fixed at 657 nm. Lower excited state absorption coefficient of the former transition explains why the 478 nm emission intensity is weaker than 451 nm emission intensity in this glass. According to the rate equation model temperature dependence of the upconverted emission intensities from the 1 D 2 level was controlled by the temperature dependence of the excited state absorption coefficient corresponding to the 3 F 4 → 1 D 2 transition.

Optical properties of Cs2NaBiCl6

Abstract Luminescence properties of Cs2NaBiCl6 are reported. Absorption, excitation, steady and pulsed fluorescence spectra have been investigated over a wide temperature range. The temperature dependences of the integrated fluorescence intensities and lifetimes versus temperature were obtained under selective excitation in the main absorption bands. Absorption processes are described using a molecular orbital scheme. The behaviour of the absorption (intensity and splitting) with the temperature provide evidence of a strong interaction with the lattice as shown in alkali halides doped with mercury-like ions. Emission processes are discussed. The lifetime measurements do not agree with the classical three-levels scheme generally proposed for luminescent processes in Bi3+ centres. Absorption and emission results seem to support the hypothesis of a strong coupling with the vibrational modes. In addition, the behaviour of the decay times at low temperatures are consistent with migration and trapping sites effects.

Synthesis, characterization and optical properties of bismuth germanate doped with trivalent europium

Abstract Bismuth germanate single crystals doped with trivalent europium were grown by the Czochralski method. Procedures and results of synthesis experiments are reported. Microprobe analysis reveals the segregation of doped rare-earth elements. Spectroscopic studies of Eu 3+ ions suggests C 3v point symmetry for the cationic site. Oscillator strengths and τ λ parameters for Eu 3+ were calculated.

Luminescence properties of Ni2+ in CsCdBr3

Spectroscopic properties of Ni2+ ions substituted in the unidimensional compound CsCdBr3 were investigated from 9 to 300 K. The structured features of the absorption spectrum have been interpreted on the assumption of a trigonal distortion of the Ni2+ site. Four emissions were observed and assigned to the 1T2 →3T2,3T1,1E and to the 3T2 →3A2 transitions in order of decreasing energy. Energy‐level calculations were performed in the usual cubic model and the results compared to the values obtained in a trigonal‐field framework. The lifetimes have been measured and fitted by the Mott law and using the Struck and Fonger model.

Etude spectroscopique et R.P.E. du pentaphosphate de cerium

Under ultraviolet excitation cerium pentaphosphate CeP/sub 5/O/sub 14/ shows emission with a quantum efficiency almost independent of the Ce/sup 3 +/ concentration and temperature. Energy transfer between the Ce/sup 3 +/ ions is not efficient. Decay measurements have been performed and Ce/sup 3 +/ decays with tau 1 = 13 10/sup -9/s and tau 2 = 41 10/sup -9/s independently of Ce/sup 3 +/ concentration and temperature. The electron spin resonance spectra of Gd/sup 3 +/ in Ce/sub 1-x/Gd/sub x/P/sub 5/O/sub 14/ twin-free crystals are reported and the angular variations of the absorption lines have been fitted to the spin Hamiltonian correspondng to Cs symmetry Twin-free crystals, selected by EPR measurements, exhibit only the tau 2 lifetime, tau 1 can be induced mechanically in the course of the crash of the initially twin-free crystal.

Synthese et etude des proprietes spectrales de monocristaux de vanadate a structure grenat Ca2NaMg2V3O12 active par l'europium trivalent

Abstract Single crystals of garnet-type vanadates Ca 2−2x Na 1+x Eu x Mg 2 V 3 O 12 have been obtained by the flux and Czochralski methods. Spectroscopic studies of Eu 3+ ion in these single crystals confirm the precedent results obtained on powdered samples especially the lowering of the D 2 point symmetry of the dodecahedral site.

Influence du lithium sur les propriétés optiques de l'orthophosphate de lanthane dopé avec Eu3+, Tb3+, Ce3+−Tb3+

Abstract The presence of monovalent lithium ions in the lanthanum orthophosphate La PO 4 strongly increases the luminescence intensity of trivalent rare earths doped with Eu 3+ , Tb 3+ , Ce 3+ _____ Tb 3+ . The introduction of the lithium ions significantly favours the direct transfer Ce 3+ _____ Tb 3+ which is still efficient at high temperature.

Effect on pressure on trivalent chromium photoluminescence in fluoride garnet Na3In2Li3F12

Abstract This compound shows at one atmosphere only fluorescence from the 4 T 2 band, the pressure leading to a blue shift of 14.8 cm−1/kbar. A new emission attributed to 2 E level and its phonon satellites appears at 40 kbar and gains intensity with compression up to 125 kbar. The increase in the exponential lifetime of the 4 T 2 emission from 310 μm at 1 Atm. to 580 μs at 125 kbar reflects the low crystal field—high crystal field transition.

Crystallographic and spectroscopic studies of europium trivalent doped garnet type germanates

Abstract Luminescent garnet-type calcium yttrium germanates activated by trivalent europium of general formula Ca 3 Y 2−x Eu x Ge 3 O 12 have been synthetized. Spectral properties give evidence of the localization of Eu 3+ in both dodecahedral and octahedral cationic sites of the garnet structure.

Emission bands of CsCdBr3

Optical properties of CsCdBr3 crystals have been investigated. Three emission bands peaking at 3.3, 2 and 1.8 eV are induced by ultraviolet excitation. Correlation with intrinsic luminescence properties of alkali halides leads to the assignment of the bands to emission from Br22- centres.