HREM and Analytic nanostructural characterization of transparent and luminescent ceramic materials (Progetti)

Type
Label
  • HREM and Analytic nanostructural characterization of transparent and luminescent ceramic materials (Progetti) (literal)
Anno
  • 2012-01-01T00:00:00+01:00 (literal)
Alternative label
  • Thierry Epicier Laura Esposito (2012)
    HREM and Analytic nanostructural characterization of transparent and luminescent ceramic materials
    (literal)
Http://www.cnr.it/ontology/cnr/pubblicazioni.owl#autori
  • Thierry Epicier Laura Esposito (literal)
Http://www.cnr.it/ontology/cnr/pubblicazioni.owl#affiliazioni
  • INSA CNRS Lyon France CNR ISTEC Faenza Italy (literal)
Titolo
  • HREM and Analytic nanostructural characterization of transparent and luminescent ceramic materials (literal)
Descrizione sintetica
  • FRENCH METSA PROJECT (literal)
Abstract
  • The recent development of ceramic, e.g. polycrystalline laser materials is probably the most important innovation in the field of laser material fabrication technology. Large-scale laser materials are necessary for high-power laser systems. Unfortunately, the size of single-crystal is limited. Recently, it has been possible to fabricate large-scale laser materials by using poly-crystals, a so-called ceramic technology, applied on isotropic hosts like cubic garnets (typically, Yttrium-Aluminium-Garnet - YAG -), sesquioxides (e.g. Y2O3), spinels, fluorides. Producers are challenging to make large size ceramics with high optical quality under rods, disks and slabs shapes, and by playing with composites like un-doped and doped ceramics. Doping is usually performed using Rare Earth (RE) elements: RE-doped ceramics constitute a class of very interesting laser materials (transparent Nd: or Yb:YAG), light converters in LEDs (Ce:YAG) and scintillators for medical imaging. Advantages of ceramics are low cost, various sizes, mass production, high content of doping activators and ability to engineer profiles and structures. Laser ceramics have then become very attractive. Strong citation began since 2002 and articles are increasing linearly. It has been demonstrated that to obtain the required high optical quality, links between elaboration conditions, microstructure and optical properties must be established. During the last conference PRE'10 in April 2010 (Firenze, Italy), we have been aware of the work performed by the research group in Lyon on the characterization of Ce-doped ceramics [1,2,3]. It was shown that rare earth concentrations significantly lower than 0.1 at. % could be confidently measured with the help of an EDX detector of the new generation mounted on a FEG-TEM (e.g. a Silicon Drift Detector - SDD -). We are currently working on YAG-based polycrystalline ceramics doped with Yb and/or co-doped with Er and Yb. We know, from our own optical characterization, that sintering conditions (e.g. thermal cycles, additive and/or impurity contents) affect the optical properties (e.g., laser output power and transparency) [4,5]. A detailed SEM and conventional TEM study failed to reveal any significant microstructural differences in several materials exhibiting different optical properties. Clearly the explanation is to be seeked at the nanometric or sub-nanometric level. We aim at undertaking TEM characterization at very high resolution (possibly with Cs-corrected instruments) but strongly believe that, according to the expertise demonstrated by the research group in Lyon at CLYM, a first approach is required, which consists in nano-probe EDX analysis (combined to HREM and conventional STEM-HAADF imaging). The capabilities of the SDD sensitivity allows to plan the detection of possible segregation and/or clustering (if any) in the grains using STEM imaging and analysis with a nanometric or sub-nanometric probe as permitted by the 200 kV FEG-TEM available at CLYM. EELS can also possibly be tried during these experiments, but severe overlap is expected between RE ionization edges (Yb-N near 185 eV, Ce near 200 eV) and the major Y-M peak starting near 160 eV. Results should concern the influence of the sintering conditions on the grain-boundary structure (cleanness, segregation effects) and the grain chemistry (homogeneity of the dopant distribution, impurity concentration). We have already prepared thin foils and expect to characterize two sets of Yb-YAG samples, and one new Er/Yb-YAG co-doped samples, which lead us to ask for a 3 days experiment. This proposal is formulated in anticipation of a joined research project between CNRS-F and CR-Italy, which will contribute ONLY to travel expenses for exchanges between both teams during a two years period. [1] W. Zhao, S. Anghel, C. Mancini, D. Amans, G. Boulon, T. Epicier, Y. Shi, X.Q. Feng, Y.B. Pan, V. Chani, A. Yoshikawa, \"Ce3+ dopant segregation in Y3Al5O12 optical ceramics\", Opt. Materials 33 (2011) 684-687 [2] W. Zhao, C. Mancini, D. Amans, G. Boulon, T. Epicier, Y. Min, H. Yagi, T. Yanagitani, T. Yanagida, A. Yoshikawa, \"Evidence of the inhomogeneous Ce3+ distribution across grain boundaries in transparent polycrystalline Ce3+-doped (Gd,Y)3Al5O12 garnet optical ceramics\", Jap. J. Appl. Phys. (2010), 49 (2, Pt. 1). [3] G. Boulon, T. Epicier, W. Zhao, V. I. Chani, T. Yanagida, A. Yoshikawa, \"Absence of Host Cations Segregation in the (Gd,Y)3Al5O12 Mixed Garnet\", Jap. J. of Appl. Phys., 50, Issue 9, (2011). [4] D. Alderighi, A. Pirri, G. Toci, M. Vannini, L. Esposito, A. L. Costa, A. Piancastelli, M. Serantoni, \"Characterization of Yb:YAG ceramics as laser media\", Opt. Materials, 33 2 (2011), 205-210. [5] L. Esposito, A. Piancastelli, A. L. Costa, M. Serantoni, G. Toci, M. Vannini, \"Experimental features affecting the transparency of YAG ceramics\", Opt. Materials, 33 5 (2011), 713-721. (literal)
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