Dynamic range and dose linearity of the radiophotoluminescence intensity in lithium fluoride crystals irradiated with 2.3 and 26 MeV protons

Abstract

Irradiation of lithium fluoride with protons causes the formation of electronic defects, known as colour centres, in the crystal lattice. Two stable defects among them, the F2 and F3+ aggregate ones, under blue light simultaneous excitation show broad photoluminescence in the red and green visible spectral ranges, respectively, their peculiar characteristics being well known for applications in optically-pumped tuneable lasers, broad-band miniaturized light-emitting photonic devices and passive radiation imaging detectors. Recently, exploitation of their radiophotoluminescence has been successfully proposed for proton-beam advanced diagnostics and dosimetry, even at low dose values typical of radiotherapy. In the present study, lithium fluoride crystals were irradiated with 2.3 MeV protons in the dose range from ∼104 to ∼107 Gy and their dynamic range, that is the capability of detecting the widest possible range of radiophotoluminescence intensity emitted by the colour centres, was found to be 114 dB at the F2 peak emission wavelength of 675 nm under continuous-wave laser excitation at 445 nm. Moreover, after including in the analysis a set of lithium fluoride crystals irradiated with 26.1 MeV protons in the dose range from 0.5 to 48 Gy at a much lower dose-rate, it was found that the radiophotoluminescence intensity of the F2 colour centres shows a linear dependence with dose from 0.5 to ∼2 × 105 Gy.