X-ray damage characterization in BaLiF3,KMgF3 and LiCaAlF6 complex fluorides

Two-inch sized KMgF₃,BaLiF₃ and LiCaAlF₆ (LiCAF) single crystals were grown by the Czochralski method under a CF₄ atmosphere. X-ray irradiation was used to carry out a comparative study of induced optical absorption phenomena and colour centre creation in the ultra-violet and visible spectral regions. The integral of the induced absorption spectra is significantly lower in LiCAF with respect to the other studied materials. It is found that the amplitude of the F-absorption band is suppressed more than a factor of 3 by Mg-doping. For Mg-doped crystals, the optimum doping concentration is about 0.2 mol% of Mg²⁺.     

Large‐Scale Synthesis of Helicene‐Like Molecules for the Design of Enantiopure Thin Films with Strong Chiroptical Activity

Helicenes are fascinating molecules owing to their unusual properties and applications in many fields from catalysis to organic electronics. Herein, we report a straightforward pathway for the synthesis of helicene‐like molecules on a gram scale in an enantiopure form. Thin‐film materials with good propagating optical properties and very high chiroptical responses have been grown by using pulsed laser ablation without altering the structure or the enantiopurity of the molecules. Moreover, electronic and vibrational circular dichroism spectroscopies coupled with theoretical calculations enabled some dependences of the chiroptical properties with the structure to be highlighted, for example, effects of rigidification, aromatization, or the state of matter (liquid versus solid).     

From optical spectroscopy to a concentration quenching model and a theoretical approach to laser optimization for Yb3+-doped YLiF4 crystals

A spectroscopic characterization was carried out to identify crystal-field levels for magnetic-dipole transitions of Yb³⁺ ions located in the Y³⁺ dodecahedral S₄ crystallographic site in YLiF₄ (YLF) crystals which were grown either by the Czochralski technique or by the laser heated pedestal growth (LHPG) technique. The concentration dependence of the measured decay time of the ²F_5/2 excited level of Yb³⁺ was analysed in order to understand relevant concentration quenching mechanisms. Under Yb³⁺ ion infrared pumping, self-trapping and up-conversion non-radiative energy transfer to trace rare-earth impurities (Er³⁺, Tm³⁺) has been observed over the visible region and interpreted by a limited-diffusion process within the Yb³⁺ doping ion subsystem to the impurities. The principal parameters useful for a theoretical approach for potential laser applications of Yb³⁺-doped YLiF₄ crystals have also been given.     

Excited-state dynamics of Yb in LiCaAlF6 single crystal

Single crystals of Yb²⁺-doped LiCaAlF₆ were grown by the Czochralski technique under CF₄ atmosphere. Photoluminescence, thermally stimulated luminescence and decay kinetics of Yb²⁺ centre in the LiCaAlF₆ host were measured in the 4–300 K temperature interval. Phenomenological two excited-state-level model is introduced to obtain quantitative characteristics of the excited state dynamics of Yb²⁺. The role of Yb²⁺ centre in trapping processes is discussed. Moreover, defect centres related to LiCaAlF₆ host were found.     

Study of effects of polishing and etching processes on Cd1−xZnxTe surface quality

The effect of surface preparation on CdZnTe properties was investigated. Surface etching using bromine solutions enhances Te elemental composition, resulting in a Te rich surface layer that is prone to oxidize. This oxidation degrades the performance of the fabricated CZT gamma detector. Roughness results were identical for samples polished with 1 and 3 μm and subsequently etched in 2% Br-MeOH. The optimal concentration of etching was 2% Br-MeOH.     

The effect of etching time on the CdZnTe surface

The surface quality of CdZnTe plays an important role in the performance of sensors based on this material. In this paper the effect of chemical etching on Cd_0.9Zn_0.1Te sensor performance was examined. Sample surfaces were treated with the same concentration 2% Br-MeOH for different etching times (30 s, 2, 4, 6, 8 min). The surfaces were characterized by Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), and I-V Measurement. These results demonstrate that the best surface quality can be obtained by chemical etching for 30 s. Under these experimental conditions, the surface composition Te/Cd + Zn approaches 1, the roughness is lower than 3 nm, and the leakage current shows a value lower than 10 nA.     

X-ray induced color centres in pure and doped LiYF 4 AND LiLuF 4 single crystals

YLiF 4 and LuLiF 4 pure and doped with Yb 3+ ion were grown by the Czochralski technique under CF 4 atmosphere. X-ray irradiation was used to carry out a comparative study of the induced optical absorption phenomena and color center creation in the ultraviolet and visible spectral regions. The F-center absorption band at 315 and 340 v nm in LLF and YLF, respectively, is the dominating induced absorption feature. The amplitude of the induced absorption is reduced by more than a factor of 10 in Yb-doped crystals compared to the undoped ones.