Etude des propriétés structurales et optiques des matrices cristallines KCl et KBr dopées par les agrégats des terres rares Er, Ce et Lu

Abstract

The aim of this work is to develop and characterize the single crystals of alkali halide (KCl and KBr) doped with rare earth elements (Er, Ce and Lu) using the crystal growth technique from melt phase according to the principle of the Czochralski method. The single crystals obtained are on cylindrical morphology. For the purposes of their characterization, the single crystals are cut by pellet cleavage whose plane faces are perpendicular to the growth axis which is parallel to the crystallographic axis of KCl or KBr. Structural studies on elaborated materials using X-ray diffraction, FT-IR and Raman spectroscopies have shown that the KCl and KBr monocrystals (pure and doped) have a monocrystalline character, and in these crystalline matrices theaggregates of rare earths elements (ErCl3, CeCl3 and Lu2O3) are incorporated. The presence of these aggregates induced stresses in the crystal lattice of the matrices KCl and KBr. Certain impurities such as H2O and CO2 have also been revealed and their come from the environment during the growth operation (uncontrolled atmosphere) or the characterization of the samples. Optical investigations by absorption, photoluminescence and radioluminescence were carried out to demonstrate the optical properties of KCl and KBr single crystals doped with rare earth elements Er, Ce and Lu and also to confirm the presence of dopants in the host matrices. Observation of the optical absorption spectra shows that all the samples studied are transparent in the IR domain but have an important absorption in the UV-VIS domain. Bands corresponding to the absorption by the doping elements and to the colored centers present in the matrices KCl and KBr are also visible on the spectra. The photoluminescence of the samples shows an emission bands due to radiative electronic transitions of the rare earth elements, demonstrating that the matrices studied can be considered as luminophores. The relatively high concentration of the doping elements leads to a decrease in the intensity of the observed luminescence bands; this decrease may be due to a mutual influence of the rare earth atoms incorporated in the KCl and KBr matrices. The analysis by radio-luminescence shows intense emission bands and shows that the elaborated materials can be used as scintillators for the detection of X-rays. Mots clés: chlorure de terre rare (ErCl3, CeCl3), oxyde de terre rare Lu2O3, Czochralski, DRX, FT-IR, μ-Ramn, absorption UV-visible, photoluminescence, radio-luminescence