CsI Tl Crystals Research Articles

F centre production in CsI and CsI–Tl crystals under Kr ion irradiation at 15 K

We present results of simultaneous in situ luminescence and optical absorption studies in scintillator CsI and CsI–Tl crystals, exposed to very dense electronic excitations induced by 86Kr ions (8.63 MeV/amu). Irradiation at 15 K leads to the formation of the prominent F absorption band. In addition, several other features of the broad absorption between exciton and F bands were ascribed to an anion vacancy, α centre (240 nm), self-trapped hole, Vk centre (410 nm) and interstitials, H centres (560 nm). We have found that low doping of thallium (∼1017 cm−3) causes the F centre formation to proceed more rapidly than in pure crystal. On the other hand, we were not able to create any amount of F centres in heavily doped CsI–Tl. We have shown that point defects created by heavy ions manifested themselves in luminescence ageing.

Photo- and thermo-stimulated luminescence of CsI—Tl crystal after UV light irradiation at 80 K

Thermo- and photo-stimulated luminescence are studied for CsI—Tl crystal after the irradiation with the UV light at 80 K. Creation spectrum of the photostimulated luminescence coincides with the D absorption band of Tl+ ions. Nature of the defects created by UV light at low temperatures is discussed basing on the correspondence between the thermostimulated glow curve peaks and thermal evolution of the photostimulation spectra observed after irradiation in the D absorption band. Three bands at 1400, 950 and 580 nm have been observed in the stimulation spectrum at 80 K. The 1400 and 950 nm stimulation bands are presumably explained as the optical transitions in the Tl0 centre forming the spatially correlated defect pair with Vk centre while the 580 nm stimulation band is connected with the unperturbed Tl0 centres. It is concluded that the Tl+ luminescence at low temperature is connected with the electron recombination with the Tl2+ centre.

Relaxation of the conductivity of CsI-Tl after excitation by subnanosecond electron pulses

The pulsed conductivity is investigated for a CsI-Tl crystal having a Tl+ concentration N=8×1017cm−3 and excited by an electron beam (0.2 MeV, 50 ps, 102–104A/cm2). It is shown that the amplitude of the conduction current pulse is almost an order of magnitude lower than for “pure” CsI crystals irradiated under like conditions. The conduction current relaxation time is preserved up to τ=100 ps in this case. Under the experimental conditions, therefore, the lifetime of electrons in the conduction band is controlled by trapping at Tl+ centers. The electron capture cross section at a Tl+ center is determined: σ=7×10−16 cm2, which agrees in order of magnitude with estimates of the capture cross section for a neutral trapping center.

Time-resolved luminescence of CsITl crystals excited by pulsed electron beam

Results of the time-resolved measurements of CsITl crystal luminescence under electron pulse excitation at room temperature are reported. The rise and decay times of both 400 and 500 nm emission bands have been measured. The results obtained show that the main mechanism of the luminescence excitation is hole recombination luminescence which is due to self-trapped hole migration toward Tl 0 centres. Stimulation spectra of photostimulated luminescence of CsITl are also analyzed.