Experimental and theoretical studies of donor–acceptor scintillation from PbI2

Abstract

We report on the scintillation properties of undoped PbI2, and PbI2 doped with La, Cu, Ag, and Te. X-ray luminescence spectra were recorded at 7K and the time responses for 80ps pulses of X-rays were recorded from 14K to 150K. Samples were irregularly shaped crystal pieces that ranged from 300 to 1000μm in size. We found that at 14K the undoped samples had a fast emission at 520nm (0.18eV below the band edge) and a total light output of about 40,000photons/MeV. 10% of this light appears in the first ns, which is 5 times greater than LSO and 1.5 times greater than LaBr3:Ce. 50% of the light appears in the first 100ns. The luminosity decreased dramatically as the temperature was increased above 40K, consistent with a non-radiative path that has an activation energy of 3.8meV. Doping with the donor La3+ only slightly changed these scintillation properties. Doping with the donor La3+ and the deep acceptors Cu+, Ag+, and Te2– produced primarily slow donor–acceptor emissions at peak wavelengths of 605, 653, and 800nm, respectively. The luminosity of the samples doped with La3+ and Cu+ depended strongly on the La3+ concentration, demonstrating its role as an electron donor. First-principles band structure calculations showed (1) that the donor level depth of an isolated iodine vacancy is about 0.8eV, too deep to explain the 520nm emission wavelength, and (2) that a donor–acceptor pair consisting of a spatially associated iodine vacancy donor and a lead vacancy acceptor has shallower donor and acceptor depths that are consistent with the 520nm emission wavelength.