C. Pedrini

Time-resolved luminescence of CeF3 crystals excited by X-ray synchrotron radiation

Abstract Under X-ray synchrotron radiation (SR) of storage ring VEPP-3 excitation time-resolved luminescence spectra and decay curves for two different CeF 3 crystals have been measured. The temperature dependence of the decay kinetics of emission at 300 nm of new pure CeF 3 crystal has been studied. The maximum of the intensity of this emission was observed at 390 K under SR X-ray excitation. The results are compared with data obtained under UV SR excitation and are discussed in terms of two models of luminescence quenching.

Luminescence properties of GdAlO3: Ce powders. Dependence on reduction conditions☆

Abstract The influence of the preparation method on the luminescence efficiency of GdAlO 3 (GAP): Ce crystalline powders has been studied. Due to the segregation coefficient of Ce 3+ in GAP, there is always a second absorption band in the UV, next to the 4f–5d absorption of Ce 3+ in these crystalline powders. This absorption band ranges up to 400 nm, i.e. the area where the Ce 3+ emission transition is situated and this absorption will therefore hamper the efficiency of the Ce 3+ emission, independent of the excitation source. However, GAP: Ce crystalline powders can be used to study the scintillator characteristics of this material because the conversion and transfer proceses are not necessarily influenced.

Excited state absorption and looping mechanism in Yb3+-Tm3+- Ho3+-doped Gd3Ga5O12 garnet

Abstract Conversion of infrared laser light (near 753 nm) into green emission has been obtained in Gd3Ga5O12:Yb:Tm:Ho by two-step process: absorption from the fundamental states of the ions followed by a looping mechanism. The latter is composed by an absorption from the 5I7(Ho) excited state and by a positive feedback process. A two-ion model to describe the dynamics is given and the gain and losses of the loop are evaluated.

Synthesis and properties of Lu2O3 sol–gel films

Abstract Lutetium oxide films have been prepared by the sol–gel method and the dip-coating technique. Transparent and crack free coatings are obtained. Differential Thermal Analysis and Infrared spectroscopy were conducted on the dried sol–gel solution in order to determine the structure dependence of the material with temperature. The film microstructure was studied by Raman microscopy and X-ray diffraction. The crystallization of the lutetium oxide phase occurs at 600°C. Opto-geometrical parameters were determined depending on the annealing temperature. After heat treatment at 1000°C, very dense lutetium oxide films are obtained exhibiting a refractive index around 1.8 at 543.5 nm and a thickness of 410 nm.

Fluorescence of Ce3+ in LiREF4 (RE=Gd, Yb)

Abstract Optical absorption, emission and excitation spectra of Ce3+-doped LiYbF4 and LiGdF4 crystals are presented. Vibrational structures were observed and the vibrational modes were described through Raman spectra. Ce3+ and Gd3+ energy level schemes were determined and the influences of various processes on the Ce3+ luminescence intensity are discussed qualitatively. The luminescence efficiency of Ce3+ is strongly decreased by either electron transfer (LiYbF4) or energy migration over the Gd3+ sublattice to impurities (LiGdF4).

Kinetics of transfer and back transfer in thulium-holmium-doped Gd3Ga5O12(Ca, Zr) garnet

Abstract The kinetics of the forward and backward 3 F 4 (Tm)↔ 5 I 7 (Ho) energy transfers in the Gd 3 Ga 5 O 12 (Ca, Zr) garnet are described using the fluorescence “transfer function” method. The fitting parameters are compared with values calculated from spectroscopic data. Despite a rather good agreement between the model and the experimental data we show that further theoretical progress to treat the energy diffusion are necessary in the case of heavilydoped samples.

Single crystal growth and characterization of LaLuO3

Abstract Wide shoulder and fast lateral growth are characteristics of LaLuO 3 during crystallization onto an iridium rod in Czochralskis configuration. Under careful temperature control, necking in and further low-speed pulling provided for single-crystal growth, but spontaneous separation of the growing crystal from the melt is a strongly limiting factor for production of large boules. Ce- and Pr-doped single crystals of up to 0.5 cm 3 were obtained and used in measurements of the X-ray data, density, melting point and optical properties and in annealing studies.

Effects of Ca2+Zr4+ ion pairs on spectroscopic properties of Cr3+ multisites in Cr3+‐doped Gd3Ga5O12 garnets

Some disorder exists in Gd3Ga5O12 (GGG) garnets because of a partial occupation of the octahedral sites by the Gd3+ ions. The luminescence of the Cr3+ ions introduced as dopant in the material is then affected. The situation is worse in (Ca,Zr)‐substituted GGG due to a great deal of Ca‐Zr defects introduced in large quantity in order to have a congruent composition. A simple model based on the local dilatation of the lattice around each defect is presented in order to describe the Cr3+ luminescence at any temperature. The influence of Ca‐Zr ion pairs on the average Cr3+→Tm3+ energy transfer is also studied.

A new microwave resonant technique for studying rare earth photoionization thresholds in dielectric crystals under laser irradiation

Abstract A new technique is presented for measuring the location of the rare earth energy levels with respect to the host conduction band in rare earth doped insulators. This technique is based on the detection of microwave absorption by the rare earth doped crystal inserted in a resonant microwave cavity and irradiated by photons of sufficient energy to induce the rare earth photoionization. The results obtained with CaF2:Sm2+ and Lu2(SiO4)O:Ce3+ indicate photoionization thresholds at 380 nm (3.3 eV) and 400 nm (3.1 eV), respectively.

Bandwidth and time evolution of the Cr3+ fluorescence in (Ca, Zr)-substituted Gd3Ga5O12

Abstract The (Ca, Zr)-substituted Gd 3 Ga 5 O 12 is a disordered laser crystal. The fluorescence of Cr 3+ ion is strongly crystal field dependent and has been studied by decay time analysis and time-resolved spectroscopy. We present detailed investigations of the spin-orbit and electron-lattice couplings in the different Cr 3+ sites leading to a good description of the experimental spectroscopic data.