Excited states of modified oxygen-deficient centers and Si quantum dots in Gd-implanted silica glasses: Emission dynamics and lifetime distributions

The emission centers and excited states characteristics in silica glasses implanted with Gd ions were studied by time-resolved pulsed cathodoluminescence. It was found that in the process of ion implantation,...

Разгорание и затухание импульсной катодолюминесценции в монокристаллах и керамиках Nd:ИАГ

The kinetics of pulsed cathodoluminescence of Nd3+ ions in Nd:YAG single crystals and ceramic samples was studied. In these substances, luminescence appears after the ending of exposure by an electron beam with a duration of 2 ns. Optical transitions are observed from the 2F2 5/2 level and manifest themselves in the ultraviolet and visible regions of the spectrum, and from the 4F 3/2 level – in the near infrared region. The kinetics of luminescence is characterized by a rise and a decay and is described by the difference between two exponential functions. It has been determined that the characteristic decay times of luminescence are the lifetimes of the 2F2 5/2 and 4F 3/2 radiative levels, and the time of a rise is determined by the pumping mechanism. Moreover, the pumping of the uppermost Stark component of the 2F2 5/2 level occurs in the process of linear recombination of the ionized neodymium ion with free electrons, and the 4F 3/2 level is due to nonradiative transitions from the upper levels.

Специфика кинетики импульсной катодолюминесценции иона неодима в иттрий-алюминиевом гранате и оксиде иттрия

The kinetics of pulsed cathodoluminescence of Nd3+ ions in single crystals, ceramics, and nanopowders of Nd3+:Y3Al5O12 (Nd3+:YAG) and Nd3+:Y2O3 under excitation by a 2 ns electron beam with average electron energies of 130, 150, and 170 keV was studied. In this case, the luminescence of these substances occurs after the termination of the electron beam. In Nd3+:YAG, there are optical transitions from the 2F25/2 level of the neodymium ion in the ultraviolet and visible regions of the spectrum, as well as from the 4F3/2 level in the near infrared region. In Nd3+:Y2O3, there are not transitions from the 2F25/2 level of the neodymium ion, but infrared luminescence occurs from the 4F5/2 and 4F3/2 levels. The luminescence kinetics is characterized by rise and decay and it is described by the difference of two exponential functions. It is found that the characteristic luminescence decay times are the lifetimes of the 2F25/2, 4F5/2 and 4F3/2 emissive levels, and the rise time is determined by their pumping in recombination and relaxation processes. The rise mechanisms of pulsed cathodoluminescence are substantially different from the mechanisms of "phosphor ignition", which occur during ionization and excitation of the phosphor by an external source.

Спектральные и амплитудно-временные характеристики излучения Черенкова при возбуждении прозрачных материалов пучком электронов

Interest in the study of the characteristics of the Vavilov-Cherenkov (VCR) radiation has increased in connection with the work on the creation of runaway electron (RE) detectors for TOKAMAK-type installations. This review presents the results of studies of the spectral, amplitude-temporal, and spatial characteristics of VCR, obtained mainly in recent years when transparent substances are excited by an electron flux with energies of tens to hundreds of keV. The VCR spectra in diamond (natural and synthetic), quartz glass, sapphire, leucosapphire are given, and the VCR registration in MgF2, Ga2O3 and other transparent samples is reported. A comparison of the spectra and amplitude-time characteristics of the VCR and pulsed cathodoluminescence (PCL) at various electron energies is carried out. For a number of samples, the VCR spectra were calculated taking into account the dispersion of the refractive index, as well as the energy distribution of the beam electrons and the decrease in the electron energy during their deceleration in the sample material. The emission spectrum of polymethyl methacrylate (PMMA), which is used as a material for radiators in Cherenkov detectors and optical fibers transmitting radiation in scintillation dosimeters, as well as a plastic base in organic scintillators, has been investigated.

Излучение Вавилова-Черенкова и импульсная катодолюминесценция в полиметилметакрилате при возбуждении субнаносекундным пучком электронов

The spectral and amplitude-time characteristics of the emission of polymethyl methacrylate upon excitation by electron beams with electron energies up to 300 and 450 keV are studied. Vavilov-Cherenkov radiation and cathodoluminescence pulses were recorded with a subnanosecond time resolution. It is shown that the intensity of pulsed cathodoluminescence radiation in the visible and near ultraviolet spectral regions at electron energies of hundreds of keV exceeds the intensity of Vavilov-Cherenkov radiation.

Люминесценция дефектов F-типа и их термическая стабильность в сапфире, облученном импульсными ионными пучками

Luminescence and thermal stability of defects formed in alpha-Al2O3 single crystals under pulsed ion beam treatment (C+/H+ ions with an energy 300 keV, pulse duration 80 ns) were investigated. This type of irradiation leads to the intensive generation of both single F- and F+-centers and more complex defects (F2-type aggregate centers or vacancy-impurity complexes) in alpha-Al2O3. It was confirmed by the results of optical absorption, photoluminescence, and pulsed cathodoluminescence measurements. The thermal stability of F-type defects formed in alpha-Al2O3 under the pulsed ion beam treatment is comparable to the stability of radiation-induced defects in neutron-irradiated samples.