Luminescence characterization of ultrathin MgO films of high crystallinity prepared by pulsed laser deposition

Abstract

Thin MgO films with thicknesses ranging from 127 to 35 nm were prepared by pulsed laser deposition on Si substrates. The crystalline films were smooth (rms roughness 0.6-1.2 nm) with an average density of 3.5 g/ cm 3 . Cathodoluminescence study revealed emissions peaked at 7.65 eV and ascribed to the edge emission of large radius exciton states as well as luminescence due to the F and F + colour centres in the range of 2-4 eV. This luminescence is efficiently excited in the absorption band peaked at 6.2 eV and in the intrinsic absorption with the onset at 7.4 eV via energy transfer processes.

Luminescence spectroscopy of nanocrystalline MgO

“…This is also confirmed by the excitation spectrum of 3.0 eV emission recorded from nano-powders (not shown), which has a broad maximum near 6 eV and it is practically not excited in the intrinsic absorption region of MgO. We note that this excitation spectrum resembles an analogous one recorded from thin MgO films [6], and it is assigned to the excitation of five-coordinated oxygen sites (i.e. oxygen ions on the surface) in several experimental and theoretical papers [14,15].…”

“…The UV part of the spectra consists of broad bands peaked at 5.1 eV in the bulk and new emissions observed in the nano-samples are blue shifted up to 5.8 eV. The 5.1 eV band originates from recombination of electrons and holes near V Al -centres [6]. In the long wavelength range, wellknown luminescence bands due to F and F + centres with maxima at 2.4 and 3.15 eV, are clearly seen in undoped MgO nanoceramics of 80 nm crystallite size.…”

“…Also self-trapping of surface excitons of MgO has been predicted with a related luminescence band at 5.7 eV [5]. Recently we have applied luminescence spectroscopy along with other methods of structural and surface characterization in investigation of properties of electronic excitations of thin ultra-smooth MgO films prepared by pulsed laser deposition [6]. The goal of the present study was to reveal effects due to crystallite size on the evolution of electronic excitations in pure and Al-doped MgO nanopowders and nano-ceramics using energy transfer to wellknown V Al -centres emitting at ~5 eV [7], as well as analyzing emissions of different origin to study the relaxation processes.…”

Photoluminescence from screen printed ZnO based nanocrystalline films

“…Any direct relation between PL spectra and the crystallite size which varies between 33 and 47 nm is not seen. However, the role of more complicated defects like bivacancies cannot be ruled out [47] as the occurrence of bivacancies along with monovacancies is also energetically favorable in certain circumstances [48].…”

Structure-Dependent CO2 Gas Sensitivity of La2O2CO3 Thin Films

“…Pure CO 2 or O 2 /10% CO 2 background gas at 10 −2 or 10 −1 mbar pressure was used during the deposition process. The substrate temperature was varied between 300 and 700 ∘ C. Other details of the deposition process are described elsewhere [15]. Two types of annealing procedures were used for after-growth processing of the films: (a) ex situ annealing or (b) in situ annealing process.…”