Eu concentration dependence of the structural, physical and optical properties of NaCl:Eu crystals grown in air

Abstract

The NaCl:XEu (with X = 0.0, 0.002, 0.004, 0.006, 0.008, 0.01, 0.02 and 0.04) crystals have been grown in air by the melt (Czochralski) method and have investigated the Eu concentration dependence of the structural, physical and optical (optical absorption, photoluminescence and thermo-luminescence) properties by using the available characterization techniques. X-ray diffraction and photoluminescence (PL) studies on the doped crystals have confirmed the presence of Eu ions (existing as Eu2+ and Eu3+ ions) in the NaCl crystal matrix. Hardness measurement has shown that the Eu doped crystals belong to the hard material category and the hardness and elastic stiffness constant decrease with the load increase and increase with the Eu concentration increase. Optical absorption spectra have revealed that five new peaks appear on doping with Eu ions. PL spectra have shown increase in emission intensity with the increase in concentration of Eu2+ and Eu3+ ions. Thermo-luminescence (TL) glow curves exhibit two peaks at ~103.7 and ~199.9 ℃. The TL peak intensities observed for the Eu doped NaCl crystals are much larger than the pure NaCl crystal. NaCl:XEu crystal with X = 0.008 has been found to possess the optimal luminous (both PL and TL) properties. The TL parameters calculated prove that the activation energy (E) values vary with the Eu concentration and the trap concentration (n0) values of the high temperature peak are larger than that for the low temperature peak.