Host and defect-related luminescence in Rb 2 KTiOF 5 oxyfluoride crystals irradiated by fast electrons

The paper presents a comparative analysis of RKTF crystals (full name single crystals Rb 2 KTiOF 5 ), and RKTF + e crystals, single crystals irradiated on a cyclotron by fast electrons Rb 2 KTiOF 5 . The crystals were grown by slow solidification method. The study was conducted at a temperature from 7 to 400 K for various types of optical and radiation effects. Spectra of photoluminescence (PL) and X-ray excited luminescence (XRL) in region of 1.5-5.5 eV, time-resolved pulse cathode-luminescence (PCL) spectra, the temperature depending of the XRL, luminescence decay kinetics were studied. Single crystal RKTF are transparent from microwave up to the edge of the long-wave fundamental absorption (near UV range). We detected three luminescence bands for RKTF, in the visible spectral region, that were attributed to radiative annihilation of intrinsic excitons (2.25 eV), recombinaion-type luminescence (2.1 eV) and luminescence of higher TiOF 5 complexes (1.9 eV), for all emission bands characterized by great (∼1.5-1.8 eV) Stokes shift. The exponential component with lifetime of approximately 19 μs was found in the PCL decay kinetics at 2.25 eV. In the crystal RKTF + e we detected new luminescence bands 2.6 eV and 3.2 eV and the disappearance of the RKTF luminescence bands. Stokes shift of the band 3.2 eV of the RKTF + e crystal is much smaller and is equal to 0.7 eV. Excitation of the band 3.2 eV occurs in the field of crystal transparency, which indicates the defective nature of the glow. PCL decay kinetics at 2.0 and 2.5 eV has a complex nature and consists of at least two components with a life time of 0.5 ms and 6 ms, that significantly more in comparison with RKTF. Irradiation by fast electrons of crystals Rb 2 KTiOF 5 led to entirely new optical properties and suppression of self-luminescence of the crystals. © Published under licence by IOP Publishing Ltd.This work has been partially supported by the Ministry of Education and Science of the Russian Federation – basic part of the government mandate (project No. 3.8302.2017/8.9) and Act 211 Government of the Russian Federation (contract No. 02.A03.21.0006, the Center of Excellence “Radiation and Nuclear Technologies”) and COST Action TD1401 "FAST”. The authors thank to Dr. S. Omelkov (University of Tartu, Estonia) for help in PCL experiments and M. Sarychev (UrFU) for support in low temperature measurements