Thermally activated structural changes in KCl crystals containing color centers

Structural changes taking place in the temperature interval 300–750K in KCl crystals additively colored in Na vapor are studied by spectrophotometric and light scattering methods in conjunction with crystal lattice constant measurement.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 39–45, September, 1984.     

Destruction mechanism of color centers and recombination luminescence in NaCl-Cd crystal phosphors

The authors have studied the origin of integral thermoluminescence peaks and the destruction mechanism of color centers during thermal relaxation of X-irradiated NaCl-Cd phosphors. The luminescence spectra have also been studied, and previous similar results are discussed.     

Micron-sized diamond particles containing Ge-V and Si-V color centers

Micron-sized diamond particles containing germanium-vacancy(Ge-V) color centers with a zero-photon line(ZPL)around 602.3 nm are successfully grown using hot filament chemical vapor deposition.The crystal morphology changes from icosahedron to truncated octahedron and decahedron, finally becomes spherical with the growth pressure increase.Due to the chamber containing Si, all diamond particles contain silicon-vacancy(Si-V) color centers.High growth pressure contributes to the formation of Ge-V and Si-V in diamonds.With prolonging growth time, the change in the full width at half maximum(FWHM) of the diamond peak is small, which shows that the concentration of Ge-V and Si-V centers nearly maintains a constant.The FWHM of the Ge-V ZPL is around 4 nm, which is smaller than that reported, suggesting that the Ge-V center has a more perfect structure.Ge-V and Si-V photoluminescence(PL) intensities increase with the prolonging growth time due to the increased diamond content and reduced content of sp~2-bonded carbon and trans-polyacetylene.In summary, increasing the growth pressure and prolonging the growth time are beneficial to enhance the Ge-V and Si-V PL intensities.     

NaF和NaF：Mg^＋＋晶体色心光致电离研究

用337nm、380nm和510nm脉冲激光照射着色NaF和NaF:Mg~(++)晶体,皆能产生大量F_2~+心.在照射过的NaF:Mg~(++)晶体中,观测到了F_2~+ 心向(F_2~+)~*心的转型现象.     

Oscillator strength of electron-type color centers in KCl single crystals irradiated with electrons and protons

The absorption spectra of KCl single crystals irradiated with electrons and protons at energies of 15 and 100 keV and a particle flux ranging from 5×10¹² to 10¹⁵ cm^?2 are investigated. The absorption bands attributed to simple (F, F _a, K) and complex (M, R ₂, R ₄, N) color centers are identified in the spectra. The correlation dependences of the absorption coefficients for M, R ₂, and R ₄ centers on the absorption coefficient of F centers and the correlation dependences of the absorption coefficients for R ₂ and R ₄ centers on the absorption coefficient of M centers are established. The oscillator strengths are calculated for M, R ₂, and R ₄ color centers.     

Peculiarities of absorption and luminescence spectra of nitrogen-vacancy color centers in diamond crystals

We have studied photoluminescence spectra of nitrogen-vacancy (NV) centers upon their pumping by short-wavelength visible and near-UV radiation. We have shown that NV⁰ centers, as distinct from NV^? centers have an absorption line in the UV range. Inversion of the zero-phonon line of NV^? centers has been shown and interpreted.     

Tunneling recombination luminescence in KBr and KCl

The tunneling recombination luminescence bands with maxima at 550 nm in KBr and 500 nm in KCl are due to electron tunneling transitions between the ground states of F and V_k centres. The emission of σ excitons occurs as a result of electron tunneling transitions from an electron centre (presumably an F' centre) to an excited state of the (V_k + electron) system. The KBr tunnel luminescence decay data are consistent with an isolated pair model, below critical X-ray excitation doses and at temperatures ranging from 100 to 150 K.     

A trigonal color center in NaF

Uniaxial stress splitting experiments suggest the 5456 Å zero-phonon line in NaF to be due to a transition of the F ₃ ⁺ center. The line and a number of phonon-assisted peaks are observed in absorption and emission.     

Studies of intrinsic luminescence in KCl

Measurements have been made of the luminescence intensity, lifetime, emission spectra, and thermoluminescence associated with self-trapped exciton states in KCl, at temperatures of 7°K and above. These results indicate the presence of another exciton-like state in addition to the well-known state that decays by emission at 2.32 eV. Thermoluminescence glow peaks and spectra are correlated with F + V_k and F + H recombination processes.     

Short-lived color and luminescence centers in LiNbO3 crystals irradiated by pulsed electron beams

Data on spectra of short-lived optical absorption (SLOA) and luminescence induced in congruent crystals of lithium niobate by a pulsed electron beam (0.25 MeV, 20 ns, 15–160 mJ/cm²) in a temperature range of 80 to 350 K are presented. Anisotropic bands with maxima at 1.6 and 4.0 eV, originating from the capture of one and two conduction electrons by an (Nb_Nb-Nb_Li) complex, respectively, and weakly polarized bands at 2.5 and 3.3 eV due to holes located at Li and Nb vacancies are identified in the structure of SLOA spectra. Cathodoluminescence (CL) of lithium niobate crystals is characterized by fast (τ<4 ns) decay and a broad spectrum, which contains the same bands as the SLOA spectra. It is shown that the change in the initial amount of defects in reduced crystals at 830 K results in an identical change in both the CL and SLOA spectra. A model which treats the luminescence as the result of radiative nonphonon transitions that accompany the thermalization of charge carriers captured into the ground state of a polaron is discussed.     

Build-up of F and M color centers in KCl single crystals under combined electron and proton irradiation

The F and M color-center build-up kinetics in KCl crystals under combined irradiation with electrons of energy 15 and 100 keV and 100-keV protons have been studied in the flux range of 10¹³–10¹⁵ cm⁻² and at a flux density of 3×10¹¹ cm⁻² s⁻¹. It is shown that consecutive irradiation with electrons and protons produces results not obtainable under electron or proton irradiation alone. Fiz. Tverd. Tela (St. Petersburg) 40, 2015–2018 (November 1998)     

Effect ofV K centers on positron annihilation in KCl and Ag-doped KCl

Positron lifetime spectra have been measured at 77 K for KCl and Ag-doped KCl before and after x-irradiation at 77 K and after annealing at room temperature. Radiation at 77 K reduces the intensity of the intermediate lifetime (τ₂) component. Radiation-induced defects were monitored optically and by ESR. The experiment shows that the changes observed in the positron decay are associated with the presence ofV _K centers.