Spatial structures based on color centers created by electrons in lithium fluoride crystals: Absorption and luminescence characteristics

Abstract

We have shown that in spatial structures based on color centers created by electrons in a lithium fluoride crystal, the distances between centers reach 1.6 nm and 3.6 nm for F 1 and F 2 centers respectively. This suggests considerable potential opportunities for using electron technology to form structures in the crystals with spatial resolution of such an order of magnitude. We measured the decrease in fluorine content on the irradiated surface of the crystal. We found the concentrations of F 1 , F 2 , F 3 + , F 3 (R 2 ), and F 4 (N 1 ) centers. We established that the specific characteristics of color center formation by electrons leads to an increase in the efficiency of creation of F 3 and F 4 centers. We determined the decrease in the average luminescence lifetimes of F 2 and F 3 + centers as a result of concentration quenching. We observed distortion of the luminescence con- tour for F 2 centers as a result of absorption of its short-wavelength portion by other centers and emission of radiation by the latter in its long-wavelength portion.Introduction. Formation processes, properties, and characteristics of nanosized media and structures and also the prospects for development of nanotechnologies are quite timely problems which are widely studied today. In this paper, we study and discuss the possibilities for creating nanostructures in crystals when they are bombarded by electrons. Electron bombardment leads to formation of intrinsic radiation-induced color centers in crystals and crystalline films [1]. Color centers considerably alter the optical and other characteristics of crystals and films at the sites where they are located, which makes it possible to form certain structures by controlling the spatial distribution of centers. In [2,3], it is suggested that technologies based on creating color centers by an electron beam be used for fabrication of optics devices with high spatial resolution: photomask templates for microelectronics, waveguides, etc. A review of the first research steps in this direction is given in [4].The spatial resolution of elements in structures created by the indicated method is limited in principle by the sizes of the color centers and the linear resolution limits attainable in electron optics. The sizes of color centers are equal to a few interatomic distances in the crystal in which they are formed. Thus using color centers to form structures or record information makes it possible to achieve the highest possible spatial resolution, limited by the atomic structure of the solid. For example, the distance between adjacent atoms in lithium fluoride crystals (LiF), which we used to conduct all the experiments in this work, is 0.2 nm. Consequently, the size of a single element of the structure created by the color center is equal to ≈1 nm. This is much greater than the possibilities for all media for image recording known at this time.The limiting linear resolution in optics, including electron optics, is directly proportional to the wavelength of the radiation used. The de Broglie...

Lifetimes of anion vacancies and F 2 + color centers in lithium fluoride following irradiation

“…Usually the concentration of F 1 centers is an order of magnitude greater than the combined concentration of all other color centers in irradiated LiF crystals [10]. Under the irradiation conditions stated above, the excess concentration of F 1 centers is even several times greater [12].…”

Aggregate color center formation processes in lithium fluoride crystals after irradiation

“…Usually the concentration of F 1 centers is an order of magnitude higher than the total concentration of all other color centers in irradiated lithium fluoride crystals [7]. For the irradiation conditions used (T irrad < T v ), this excess increases even more [19].…”

“…Lithium fluoride with color centers is used as an active medium with broadband gain in solid-state lasers in the visible and near-IR ranges of the spectrum [3]. The problems of miniaturization of components based on it and design of structures with high spatial resolution [4][5][6][7] have been studied. New detectors have been proposed in the form of microcrystalline lithium fluoride in a polymer matrix for determining high doses of gamma photons and electrons [8], and also polycrystalline LiF films as neutron sensors [9].…”

Luminescence excitation spectra and characteristics of luminescence centers with overlapping absorption bands

“…For example, when impurity and/or intrinsic defects (arising as a result of technological operations or other external factors) are studied in a solid, samples must be studied containing all existing luminescence centers, each characterized by their own spectra, including overlapping spectra, and their own absorption values. Technological operations in the sample can be carried out at small depths (on the order of a few micrometers), and in this case several types of luminescence centers are created with overlapping absorption spectra and an overall optical density on the order of a few units (see, for example, [3]). In such cases, we need to know the connection between the photoluminescence intensity for the sample and its actual absorption spectrum.…”

“…Consequently, in [5] the methodology of the experiments was incorrect. In [3,6], dips were obtained in the photoluminescence excitation spectra of the F 3 + centers. They were correctly interpreted as the result of the effect of a strong absorption band for the F 2 color centers that was narrower than for the F 3 + centers.…”