Optical properties of structures obtained by deposition of ZnO microparticles in an electric field

Abstract

This paper considers the photoluminescence (PL) spectra of ultrafine ZnO crystals (UFC) deposited on a substrate in an electric field. Fine ZnO crystals were obtained by separating into fractions in a colloidal solution of K-56 industrial phosphor. The colloidal solution was kept in a test tube for at least two weeks. After that, 1/3 of the solution from the upper part of the tube was used for research. The analysis of the micrograph of the UFC film shows that the size of the crystals ranges from 10 to 40 nm. The samples for the study were deposited on a stainless steel substrate in the form of an aqueous solution of ZnO emulsion, then the water was removed by evaporation. ZnO samples deposited on a substrate, both in the usual way and in an electric field, were investigated. The electric field strength was 105 V/m. The PL spectra for the initial sample have a fairly intensive wide band in the visible region, which, when the original sample is deposited in an electric field, becomes less intensive. The PL spectra for UFC ZnO have a weak intensity of the band in the visible region; while the PL spectra for UDC ZnO deposited in an electric field practically do not have this band In this case, the exciton band with λmax = 401 nm for all the samples remains almost unchanged. To answer the question as to the origin of the spectral line in the visible region and covering the range from 401 to 650 nm the sample of the original ZnO (K-56 industrial phosphor) was treated with 3 kV oxygen ions, for twenty minutes after which the intensity of the PL band (E6) in the visible region increased significantly. After heating the sample to 700 K in vacuum (followed by cooling to room temperature) the ZnO FL spectrum takes on its original appearance, which means that the defects responsible for the line in the visible region of the spectrum (the wavelength at the maximum is λmax ≈ 510-540 nm), are created by oxygen ions