Real-Time Identification of Oxygen Vacancy Centers in LiNbO3 and SrTiO3 during Irradiation with High Energy Particles

Abstract

Oxygen vacancies are known to play a central role in the optoelectronic properties of oxide perovskites. A detailed description of the exact mechanisms by which oxygen vacancies govern such properties, however, is still quite incomplete. The unambiguous identification of oxygen vacancies has been a subject of intense discussion. Interest in oxygen vacancies is not purely academic. Precise control of oxygen vacancies has potential technological benefits in optoelectronic devices. In this review paper, we focus our attention on the generation of oxygen vacancies by irradiation with high energy particles. Irradiation constitutes an efficient and reliable strategy to introduce, monitor, and characterize oxygen vacancies. Unfortunately, this technique has been underexploited despite its demonstrated advantages. This review revisits the main experimental results that have been obtained for oxygen vacancy centers (a) under high energy electron irradiation (100 keV–1 MeV) in LiNbO3, and (b) during irradiation with high-energy heavy (1–20 MeV) ions in SrTiO3. In both cases, the experiments have used real-time and in situ optical detection. Moreover, the present paper discusses the obtained results in relation to present knowledge from both the experimental and theoretical perspectives. Our view is that a consistent picture is now emerging on the structure and relevant optical features (absorption and emission spectra) of these centers. One key aspect of the topic pertains to the generation of self-trapped electrons as small polarons by irradiation of the crystal lattice and their stabilization by oxygen vacancies. What has been learned by observing the interplay between polarons and vacancies has inspired new models for color centers in dielectric crystals, models which represent an advancement from the early models of color centers in alkali halides and simple oxides. The topic discussed in this review is particularly useful to better understand the complex effects of different types of radiation on the defect structure of those materials, therefore providing relevant clues for nuclear engineering applications.

‘Horror Vacui’ in the Oxygen Sublattice of Lithium Niobate Made Affordable by Cationic Flexibility

“…Using high-energy irradiation by electrons or heavier particles at 220 • C in vacuum, absorption bands persisting well above room temperature may be detected. This was demonstrated by Hodgson et al [52] and revisited in the present Special Issue [1]. Apart from a superficial comparison between LN and SrTiO 3 disregarding the deep constitutional differences between these matrices, Ref.…”

“…In most simple oxides, defect generation processes by thermal reduction or irradiation are dominated by defects of the oxygen sublattice. Originally, the same was also assumed for LiNbO 3 (LN), and most authors did not (and many still do not) have any doubts about simply postulating vacant oxygen sites (V O ) capable of trapping one or two electrons (F + and F-centers, respectively) in discussions of their experiments and proposed applications (see, e.g., [1,2]). The controversy about the availability of oxygen vacancies manifests in the reviews of Sánchez-Dena et al [3,4], is touched upon by some topical reviews [5,6], and is also closely related to the topics of other papers [7][8][9][10][11] of the present Special Issue, and deserves a clarifying discussion.…”

New Trends in Lithium Niobate: From Bulk to Nanocrystals

“…The editors also initiated the clarification of the highly disputed issue of defects in the anionic sublattice of LN, but this only resulted in a repetition of earlier unconfirmed or refuted interpretations based on a superficial comparison disregarding the deep constitutional differences between LN and SrTiO 3 such as the extreme instability of the Li positions compared to the rigid Sr sublattice [5]. This forced the editors to present a review of their own on defect generation and annealing mechanisms in LN [6].…”

Tendencies in ABO3 Perovskite and SrF2, BaF2 and CaF2 Bulk and Surface F-Center Ab Initio Computations at High Symmetry Cubic Structure

“…The V 0 is the most frequent point defect in ABO 3 perovskites [23][24][25][26][27]. Bearing in mind the technological relevance of ABO 3 perovskite matrixes, as well as quantity of F-centers, which unavoidably exist in these materials and deteriorate their quality, the number of F-center studies is still insufficient [28][29][30][31][32][33][34][35]. In order to save the computer time, we performed bulk and (001) surface F-center ab initio computations in ABO 3 perovskites in their high-symmetry cubic phase.…”