Experimental and theoretical studies of donor–acceptor scintillation from PbI2

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 7 K and the time responses for 80 ps pulses of X-rays were recorded from 14 K to 150 K. Samples were irregularly shaped crystal pieces that ranged from 300 to 1000 μm in size. We found that at 14 K the undoped samples had a fast emission at 520 nm (0.18 eV below the band edge) and a total light output of about 40,000 photons/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 100 ns. The luminosity decreased dramatically as the temperature was increased above 40 K, consistent with a non-radiative path that has an activation energy of 3.8 meV. 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 800 nm, 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 0.8 eV, too deep to explain the 520 nm 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 520 nm emission wavelength.