Thermoluminescence, optical absorption and photoluminescence studies on γ-irradiated single crystals

Thermoluminescence (TL) glow, TL emission (TLE), Optical Absorption (OA) and Photoluminescence (PL) studies were made on γ-irradiated CaF2:Dy:Pb:Na single crystals (Dy-0.005 at%, Pb-0.188 at% and Na-0.007 at%). The TL glow curve (after 206 Gy dose) exhibited three glow peaks around 394, 445 (shoulder) and 536 K. The first peak was found most intense for lower doses (<∼3680 Gy) and beyond this dose the second peak was dominanting. The growth of this peak could be exploited in this system to measure the radiation doses (at least upto ∼8 kGy) as it was at a higher temperature compared to the first peak. The TLE spectra were recorded under each glow peak and found to be the characteristic Dy3+ emission. The γ-irradiated crystal showed OA bands around 2.06, 3.28, 3.75 (shoulder) and 2.48 eV. The first three bands could be attributed to MNa centre. The thermal bleaching of the OA spectrum was observed. The excitation spectrum for the Dy3+ emission around 2.15 eV was very broad peaking around 3.55 eV. This consisted of a few overlapping bands originated from different colour centres (CCs) formed after γ-irradiation and MNa was one such centre. The intensiy and shape of the excitation spectrum changed with temperature indicating the decay and conversion of different CCs taking part in the PL process. The probable TL mechanism was suggested for the present system.