C. Garapon

Elaboration and scintillation properties of Eu3+-doped Gd2O3 and Lu2O3 sol–gel films

Abstract High-resolution X-rays imaging requires thin films of dense materials with high light yield under X-ray excitation. Polycrystalline films of europium-doped gadolinium and lutetium oxide have been prepared by sol–gel method. The scintillation performances of these compounds for X-rays imaging are presented and discussed.

Optical properties of europium-doped Gd2O3 waveguiding thin films prepared by the sol–gel method

Abstract Recently, there has been a growth of interest in the preparation of new phosphor films for high-resolution X-ray imaging systems. Europium activated gadolinium oxide is very interesting because of its scintillation properties especially as a red component. The sol–gel method has been used to synthesize europium-doped gadolinium oxide films. The films present waveguiding properties and this special feature is used to study their microstructure by Raman spectroscopy in waveguiding configuration. Structural results, confirmed by X-ray diffraction (XRD) and transmission electron microscopy (TEM) observations, show that the crystallization in the cubic phase occurs at 700 °C. Opto-geometrical parameters were determined with respect to the annealing temperature. After annealing at 1000 °C, very dense europium-doped gadolinium oxide films are obtained with a thickness of 390 nm and a refractive index of 1.88 at 632.8 nm. Spectroscopic results constituted by emission spectra (UV and X-ray excitation) and decay measurements are presented.

Optical and structural analysis of Eu3+-doped alumina planar waveguides elaborated by the sol–gel process

Abstract Eu 3+ ion-doped Al 2 O 3 waveguiding thin films were dip-coated by the sol–gel route. Crack-free films were obtained, about 880 nm thick for 15 layers. According to the results of grazing incidence X-ray diffraction analysis and transmission electron microscopy (TEM), the film contains γ-Al 2 O 3 nanocrystals in an amorphous surrounding. The refractive index determined by m-lines spectroscopy is 1.582 at 543.7 nm. A good agreement between film thicknesses determined by m-lines spectroscopy measurements and TEM observation is obtained. The propagation is good (propagation losses less than 2 dB/cm) and waveguide fluorescence spectroscopy (WFS) could be used to register the Eu 3+ fluorescence spectrum, which shows disordered environment for Eu 3+ ions.

Luminescence properties of CsPrP4O12 and RbPrP4O12

Abstract Single crystals of CsPrP 4 O 12 and RbPrP 4 O 12 cyclotetraphosphates have been grown using the flux method. Selective excitations in the Pr 3+ (4f 2 ) 3 P 0 and 3 P 2 levels using an excimer-pumped dye laser mainly result in intense line emissions in both materials. Although originating from transitions within the Pr 3+ 4f 2 ground configuration, these emissions have very short decay times, of the order of 50xa0ns. Both compounds also exhibit intense ultraviolet band emissions in the 200–300xa0nm spectral range when using either a xenon lamp or an X-ray source for optical excitation. The decays of these emissions under pulsed X-ray excitation were measured using the start–stop technique. They exhibit a main fast component (decay time τ f ) and a minor slower one (decay time τ s ), the decay times of which are τ f ≅9 and 5xa0ns, τ s ≅30 and 20xa0ns, in the Cs and Rb compounds, respectively.

Optical spectroscopy of A Cr3+-doped (Gd, Ca)3(Ga, Mg, Zr)2Ga3O12 garnet

Abstract In a gadolinium gallium garnet GGG crystal substituted by different cations (Ca 2+ , Mg 2+ , Zr 4+ ) we have studied the optical properties of Cr 3+ -doping ions and compared them with those of Cr 3+ -doped Gd 3 (Ga, Sc) 2 Ga 3 O 12 (GSGG). At room temperature the 4 T 2 → 4 A 2 band is observed with a maximum at 7500 A. At 4.4 K the 2 E → 4 A 2 line and the 4 T 2 → 4 A 2 band are superposed. The important inhomogeneous broadening of the line and non-exponential fluorescence decays as well as excitation and FLN spectra show that the Cr 3+ ions are located in multisites of different intermediate crystal field strengths.

Site-selective optical spectroscopy of Cr3+ doped non-stoichiometric green spinel MgO–2.6 Al2O3

Abstract Site-selective laser spectroscopy at low-temperature is used to analyse the fluorescence of Cr3+ in the non-stoichiometric green spinel MgO–2.6 Al2O3. Four main kinds of sites are characterized: several more or less distorted strong crystal field sites responsible for 2 E→ 4 A 2 emission lines around 690 nm with lifetimes of 20 to 5 ms and 2 E splitting of 26 to 120 cm−1, Cr3+ pairs emitting at about 710 nm, and medium and weak crystal field sites responsible for 4 T 2 → 4 A 2 broad band emissions at about 750 nm and 910 nm, respectively.

Excited-state absorption in Tm3+ doped LiNbO3: MgO and Gd3Ga5O12 and looping mechanism

Abstract Two different mechanisms for the red excitation of Tm3+ leading to up-converted fluorescence have been observed under pulsed laser excitation. In LiNbO3:MgO the ground state 3H6→3F2 absorption is followed during the same laser pulse by an excited state absorption from the 3H4 level which leads to a 1D2 violet emission. In Gd3Ga5O12 a looping mechanism constituted by an excited state absorption and a cross-relaxation progressively feeds the long-lived 3F4 level during successive pulses, leading to blue fluorescence from the 1G4 level. We describe a model for the dynamics and we calculate the gain and the losses of the loop.

Dynamics of looping mechanisms in laser crystals

Abstract 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.

Rare Earth Doped Gallium Gadolinium Orthogallate Films Prepared by Pulsed Laser Deposition

The decomposition of Gd3Ga5O12 single crystal target induced by a KrF excimer laser pulse during the deposition process was observed. This phenomenon was studied ex situ by EDX analyse of ablated target and in situ by Optical Emission Spectroscopy of the laser plasma. The decomposition process depends mainly on the absorption coefficient of the target on the corresponding laser wavelength and oxygen partial pressure in the deposition chamber during laser ablation. Taking into account the differences between absorption coefficients of Pr:Gd3Ga5O12 and Yb:Gd3Ga5O12 targets the Pr:GdGaO3 and Yb:GdGaO3 thin films were successfully fabricated at different oxygen pressures of 1 Pa and 2.5 Pa, respectively. The structural properties of the fabricated films were studied by RBS and XRD.