EFFECT OF SODIUM DOPING ON THERMOLUMINESCENCE AND OPTICAL-PROPERTIES OF BARIUM BORATE (BAB2O4) SINGLE-CRYSTALS

Thermoluminescence (TL) emission from undoped and sodium doped alpha- and beta-BaB2O4 (BBO) crystals has been investigated. A single TL glow peak is observed for the undoped crystals of both phases. The glow pe ak temperatures found for alpha- and beta-BBO crystals over the temper ature range 35-300 degrees C are 104 and 80 degrees C, respectively. T he presence of minute amount of sodium ions in the lattice gives rise to a glow peak around 200 degrees C. For impurity concentrations highe r than 0.02% (by wt), additional glow peaks around 123 and 240 degrees C are also observed. The ratio of the TL intensities corresponding to the first and 200 degrees C peaks is observed to increase with impuri ty concentration. This fact provides an easy and sensitive method of d etecting the presence of sodium ions in BBO lattice. The results also show that sodium ions go substitutionally into the lattice and act as charge traps. The optical absorption in the ultra violet region and th e crystal hardness towards ionizing radiations are found to be adverse ly affected by the presence of this impurity. (C) 1998 Elsevier Scienc e B.V. All rights reserved.