A. Kahn-Harari

High efficiency of lutetium silicate scintillators, Ce-doped LPS, and LYSO crystals

We have introduced a new scintillator: cerium doped lutetium pyrosilicate Lu/sub 2/Si/sub 2/O/sub 7/ (Ce: LPS). A high light output (average value: 26,300 ph/MeV), a relatively good energy resolution (10%) and a fast decay time (38 ns) without afterglow make this new scintillator very attractive. We compare its properties to those of another recently developed cerium doped lutetium based silicate, Ce: Lu/sub 2(1-x)/Y/sub 2x/SiO/sub 5/ (LYSO).

Spectroscopic properties and laser performances of Yb:YCOB and potential of the Yb:LaCOB material

Abstract In order to increase the compacity of the Yb-doped lasers, YCOB (Ca 4 Y(BO 3 ) 3 ) materials with high ytterbium concentration have been characterized. Large 15 at.% and 35 at.% ytterbium-doped single crystals were grown by the Czochralski pulling method. Spectroscopic and laser properties have been investigated and laser tests performed under titanium sapphire and diode pumping at 976 nm. Low thresholds under Ti:Sa pumping (50 mW) and high slope efficiency under diode pumping (66%) have been obtained. The optical quality and the distribution of Yb 3+ dopant through the highly doped crystals is discussed. First results on the Yb:LaCOB crystals grown by the Czochralski process, containing 46Yb 3+ at.%, are also presented.

Structural and thermal stability of Czochralski grown GdCOB oxoborate single crystals

Properties such as chemical and structural stability, thermal expansion and thermal conductivity are investigated, with the purpose of better characterizing the behaviour of Czochralski grown GdCOB [Ca4GdO(BO3)3], oxoborate single crystals, to be used in optical devices.

Long-lifetime fluorescence and crystal field calculation in Cr4+-doped Li2MSiO4, M = Mg, Zn

Abstract The diffuse reflectance spectra of Cr:Li2MSiO4, M=Mg, Zn, indicate that in these compounds, chromium ions occur in the 4+, 5+, and 6+ oxidation states simultaneously. Under selective excitation in a Cr4+ absorption band, a very long fluorescence decay time is observed for both compounds: ∼110 μs at room temperature and ∼300 μs at 30 K. These are by far the longest fluorescence lifetimes reported for Cr4+ activated materials. In Cr4+:Li2MSiO4, the 1E excited state level lies below the lowest component of the 3T2 level and the fluorescence decay time is dominated by the long-lifetime 1E level for which the transition to the ground state is spin-forbidden. The reverse situation occurs for the other Cr4+ doped compounds and their fluorescence lifetimes, governed by the short-lifetime 3T2 state, are only a few microseconds. A crystal field calculation, performed for Cr4+:Li2MSiO4, confirms the above interpretation and supports the localization of Cr4+ at the silicon site in this compound.

Optical properties and energy levels of Ce3+ in lutetium pyrosilicate scintillator crystal

Cerium doped lutetium pyro-silicate Ce3+:Lu2Si2O7 (LPS) is an inorganic scintillator that displays particularly promising performance. The spectroscopic properties of pure and Ce3+-doped Lu2Si2O7 are investigated. X-ray-excited luminescence, time-resolved excitation and emission spectroscopy, as well as decay time spectra are presented. For better understanding of the scintillation mechanism, several approaches were undertaken to locate the Ce3+ energy levels relative to levels of LPS host. To estimate the energy position of Ce3+ 4f levels with respect to the valence band, x-ray photoemission spectroscopy (XPS) was used. Scintillation properties of LPS: Ce are explained in terms of the relative positions of Ce3+-5d levels and the conduction band.

Nd :GdCOB: overview of its infrared, green and blue laser performances

Abstract GdCOB (Ca4GdB3O10) is a new non-linear optical material which can be grown in large sized crystals by the Czochralski method. In this material, part of the gadolinium ions can be replace by Nd3+ without significant decrease of the crystal quality. Nd:GdCOB single crystals exhibit laser action in the infrared at 1060 and 1091 nm simultaneously. The two transitions involved originating from the two Kramers doublets of the 4F3/2 state, their respective contributions depend upon the temperature of the Nd:GdCOB crystal. By combining the non-linear properties of the GdCOB matrix and the laser emission due to ND3+ ions, it is possible to generate directly by self-frequency doubling 115 mW of green laser light at 530.5 nm under diode pumping at 810 nm. It is also possible to self-double the 936 nm emission of Nd:GdCOB, leading to blue laser emission, but only under pulsed titanium-sapphire laser pumping. However, a CW blue laser beam is obtained in Nd:GdCOB by self sum-frequency mixing of the 1090 nm laser emission and the residual pump beam at ∼812 nm, yielding 1.2 mW of 465 nm laser light, with an optical to optical efficiency of 0.3%. This paper ends with a survey of the Nd:YCOB laser characteristics which are compared to those of Nd:GdCOB.

Optical spectra and crystal field calculations of doped Zircon-type laser hosts (, P, As)

Low temperature absorption spectra of doped , and single crystals, grown by the flux method, are reported. A simulation of the energy level scheme is carried out. The effective Hamiltonian includes elementary interactions such as coulombic, spin-orbit, two- and three-body interactions. The crystal field effect is introduced through the five non-zero crystal field parameters allowed by the symmetry site occupied by the rare earth. A simulation is performed on the 96 (102, 90) experimental energy levels of , (, ) with a good rms standard deviation of 16.2 (15.4, 15.7) . It is noteworthy that the energy level scheme of is reported for the first time. The wave functions of the systems are used for the calculation of the magnetic factor g. These factors are in good agreement with the values deduced from EPR measurements on the lowest level . The crystal field parameters are also compared to the a priori parameters calculated using the simple overlap model and the correlated crystal field strength is also analysed.

CW blue laser generation by self-sum frequency mixing in Nd:Ca4GdO(BO3)3 (Nd:GdCOB) single crystal

Abstract We report here the first evidence of blue light generation in a Nd:Ca 4 GdO(BO 3 ) 3 (Nd:GdCOB) crystal by self-sum frequency mixing. More than 1 mW of cw 465 nm laser emission was achieved with 490 mW of absorbed pump power from a titanium sapphire laser (829.6 nm). The blue emission is nearly TEM 00 , and the laser threshold is very low (a few mW). The performance should be improved by the use of antireflection-coated crystals and suitable mirrors.

X-Ray powder diffraction study of a new vanadium oxide Cr0.11V2O5.16 synthesized by a sol–gel process

The synthesis of the mixed oxide Cr0.11V2O5.16 , which presents interesting electrochemical performances, has been performed from vanadium oxide gels. Its structure, determined by Rietveld refinement, is similar to that of orthorhombic V2O5 , with the formation of CrO6 short chains linking the V2O5 layers. For comparison, the structures of V2O5 (synthesized by the sol–gel route) and Fe0.11V2O5.16 have been also determined by the same method. The position, along the c axis, of the trivalent ion in the plane formed by the four oxygen atoms of the V2O5 slab, is discussed as a function of the ion size and the crystal field stabilization energy.

Crystal growth, characterization and structure refinement of neodymium3+ doped gehlenite, a new laser material [Ca2Al2SiO7]

In order to find new Nd[sup 3+] laser materials pumpable by laser diode, gehlenite (Ca[sub 2]Al[sub 2]SiO[sub 7]) was chosen as a host matrix for neodymium ions. Large single crystals of Ca[sub 2[minus]x] Nd[sub x] Al[sub 2+x] Si[sub 1[minus]x] O[sub 7] (0 < x < 0.3) were obtained by Czochralski and floating zone methods. The main characteristics of these crystals (crystal perfection, thermal and mechanical behavior, optical properties...) were determined. The structure refinement revealed a structural disorder, occurring both on position and distribution of ions around Nd[sup 3+] and resulting in a broadening of the absorption bands. This means that less effort is required for diode laser pumping, and the laser effect has been observed. Therefore, Nd[sup 3+] doped Ca[sub 2]Al[sub 2]SiO[sub 7] appears as a good candidate as diode pumped laser.