Kheirreddine Lebbou

Synthesis and luminescent properties of sub-5-nm lanthanide oxides nanoparticles

Abstract We introduce a new method for the synthesis of luminescent nano-sized particles. Ultrafine, equiaxed and monodisperse rare-earth oxide particles with an average grain diameter in the range 2–5xa0nm have been prepared by applying direct precipitation from high-boiling polyalcohol solutions. Colloidally stable suspension of luminescent nanoparticles is formed. The lanthanide doped nanoparticles are easily, quantitatively and reproducibly prepared. The materials have been characterized by using high-resolution TEM, absorption spectroscopy and luminescence spectroscopy. A very significant modification of the luminescent properties is observed. Lanthanide sesquioxides Ln2O3 and doped Ln3+ yttrium or gadolinium oxides are presented (Ln=Eu, Tb, Nd).

Crystal growth, Yb3+ spectroscopy, concentration quenching analysis and potentiality of laser emission in Ca1−XYbXF2+X

Ca1−XYbXF2+X crystals were grown by two different methods: simple melting under CF4 atmosphere and the laser heated pedestal growth (LHPG) method under Ar atmosphere. Spectroscopic characterization (absorption, emission, Raman spectroscopy and decay curves) was carried out to identify Stark levels of Yb3+ transitions in the different crystallographic sites of the cubic structure in Ca1−XYbXF2+X crystals. The Yb3+ concentration dependence of the experimental decay time was analysed by using concentration gradient fibre in order to understand involved concentration quenching mechanisms. Under Yb3+ ion infrared pumping, self-trapping and up-conversion non-radiative energy transfer to unexpected rare earth impurities (Er3+, Tm3+) has been observed in the visible region and interpreted by a limited diffusion process within the Yb3+ doping ion subsystem towards impurities. The main parameters useful for a theoretical approach of laser potentiality have been given as τrad = 2.05 ms, N0 = 7.47 × 1021 cm−3 (32 mol%) and Nm = 6.39 × 1021 cm−3 (26.5 mol%).

Synthesis and characterization of Gd2O3:Eu3+ phosphor nanoparticles by a sol-lyophilization technique

Abstract The characterization and luminescence properties of nanostructured Gd 2 O 3 :Eu 3+ phosphors synthesized by a sol-lyophilization process are presented. After preparation of gadolinium-based sols from gadolinium nitrate and ammonium hydroxide, the so-prepared sols were freeze dried at −10°C and calcinated at different temperatures. For temperatures lower than 1300xa0K, highly crystalline samples with the cubic structure can be obtained without concomitant grain growth of the particles ( 3+ with C 2 symmetry and present two major features: an increase of the luminescence efficiencies of the phosphors in comparison with that obtained by solid-state reaction and the presence of an additional peak at about 609xa0nm at the vicinity of the 5 D 0 → 7 F 0…4 transition.

Growth and spectroscopic analysis of Yb3+-doped Y3Al5O12 fiber single crystals

Two major fiber crystal growth methods have been applied for the synthesis and spectroscopic characterizations of Yb3+-doped Y3Al5O12 (Yb:YAG) to show the feasibility of a flexible single crystal fiber laser. One is the micropulling-down (μ-PD) method and the other is the laser heated pedestal growth (LHPG) method. 500 mm length fiber with no Yb segregation has been grown by the μ-PD method. A detailed analysis of Yb:YAG spectroscopy is made to contribute to the discussion on the determination of energy levels. On the other hand, a combinatorial chemistry approach has been applied on concentration gradient crystal fibers grown by the LHPG method allowing the measurement of the intrinsic radiative lifetime and the analysis of concentration quenching processes of Yb3+ ions in YAG.

Growth and optical properties of Yb doped new scintillator crystals

Abstract Single crystal of heavily Yb3+-doped Lu3Al5O12 (Yb:LuAG) were grown by the micro-pulling-down method. Radio- and photoluminescence spectra of the Yb:LuAG were studied. Two bands peaking round 340–350 and 480–500 nm could be ascribed to charge transfer (CT) luminescence of Yb3+, as their position nearly coincide with the Yb3+-related CT emission in YAG matrix. The highest emission intensity was observed for Yb concentration of 5% with respect to the Lu site. Temperature dependence of photoluminescence spectra of the Yb: LuAG (5%) was measured and points to remarkable thermal quenching above liquid nitrogen temperature.

Synthesis, crystal growth and second harmonic generation properties of trivalent rare-earth-doped non-linear tungsten–bronze-type structure Ba2Na1−3xRExNb5O15 (RE=Sc, Y, La, Gd, Yb and Lu)

Abstract A new compound filled tungsten–bronze-type structure Ba 2 Na 1−3 x RE x Nb 5 O 15 (trivalent rare-earth ions: RE 3+ =Sc 3+ , Y 3+ , La 3+ , Gd 3+ , Yb 3+ and Lu 3+ , with x =0.02) has been prepared by selecting RE 3+ ions without any absorption in the visible range. The effect of rare-earth addition on micro-twin formation, that is to say, tetragonal–orthorhombic ferroelastic phase transition in barium sodium niobate was investigated and micro-twin formation could be suppressed by doping of smaller RE 3+ ions such as Yb 3+ and Lu 3+ . All the samples exhibit an intense second harmonic generation signal under tunable IR pumping laser source, due to both the high values of the non-linear optical coefficients and the absence of absorption of additional RE ions in the visible range.

Evaluation of Fiber-Shaped LYSO for Double Readout Gamma Photon Detection

Recently, the development of the micro pulling-down method has allowed the growth of single inorganic scintillation crystals with a uniform fiber shape. The dimensions may vary from 0.3 to 3 millimeters in diameter with length up to 1 meter. This paper presents an experimental set up built in order to study the scintillation light propagation within fiber shaped crystals. The interaction position of a gamma photon in the fiber is determined by a coincidence method. Light yields measured by photomultipliers at both sides of the fiber are correlated to the photon interaction position and the scintillating properties of the crystals. X-ray excited luminescence experiments were also performed to study the process of light attenuation along the fibers. X-ray and gamma ray measurements are in good agreement. Two cerium doped lutetium yttrium orthosilicate Lu2(1-x)Y2x SiO5:Ce3+ fibers have been studied. The first was a cylindrical crystal fiber of 6.9 cm in length and of 1 mm in diameter obtained by the micro pulling-down technique. The second was a squared shaped fiber crystal of 1times1times43 mm3 obtained from a bulk after cutting and polishing. The interaction localization can be determined with a precision from 4 to 12 mm depending on the fiber shape

Search for impurity phases of Nd3+:YVO4 crystals for laser and luminescence applications

Structural investigation of the Y 2 O 3 —V 2 O 5 system was undertaken with the aim of characterizing possible segregated phases appearing during the synthesis of pure and doped yttrium vanadate. Nd3‘ : YVO 4 single crystals obtained by LHPG and flux growth techniques were studied by high spatial resolution micro-Raman probe (up to 1 lm in the X—‰ plane) spectroscopy. The confocality of microscope coupled to the Raman microprobe allowed us to select the in-depth resolution of the probe. By mapping several single crystals grown with di⁄erent methods, a segregated phase was identified in the flux grown crystal, about 70 lm below the surface. Micro-Raman maps of powder samples prepared by solid state reaction starting from 4Y 2 O 3 —V 2 O 5 and 5Y 2 O 3 —V 2 O 5 mixtures gave evidence of this phase. The spectral features are very similar to the precipitate found in YVO 4 :N d3‘ single crystal. ( 1999 Elsevier Science B.V. All rights reserved.

Test beam results with LuAG fibers for next-generation calorimeters

For the next generation of calorimeters, designed to improve the energy resolution of hadrons and jet measurements, there is a need for highly granular detectors that require peculiar geometries. Inorganic scintillators can provide good stopping power to allow compact calorimeter designs together with an excellent energy resolution. The micropulling-down technique allows to grow crystal fibers with high aspect ratio providing good granularity. Designs based on dual-readout could also be considered since the host matrices of extrinsic scintillators behave as a Cherenkov radiator in the absence of the scintillating dopant. We report here about results obtained with crystal fibers of 22 cm length and 2 mm diameter of lutetium aluminium garnet (LuAG, Lu3Al5O12). The response of such fibers in a high energy physics environment has been investigated through a test beam campaign at the CERN PS facility using electrons in the 50?150 GeV energy range. The results, proving the potential of LuAG fibers for calorimetry applications, have been used to validate a Geant4 simulation which allowed to study different configuration of a fiber-based detector. Possible implementations of the crystal fibers technology into a real calorimeter are also discussed.

SBN single crystal fibers grown by micro-pulling down technique

Abstract SBN fibers single crystal have been grown using micro-pulling down (μ-PD) technique. The grown fibers are oriented along the c -axis or a -axis as a function of initial seed. The diameters are approximately between 500 μm and 1 mm. The preliminary observation show that these fibers appear to be striation and cracks free.