Optical properties of coloured LiF crystals with given content of oxygen, hydroxyl and metal impurities

Abstract

Optical absorption and emission spectra have been studied in LiF crystals containing oxygen, hydroxyl and metal impurities, and coloured with γ-rays at room temperature with doses up to 83 kGy. Welldefined bands in absorption and emission spectra of uncoloured samples have been attributed to impurities. Colouring of the same crystals adds new spectroscopic features, which are related to various colour centres, but at the same time depends strongly on the impurity content, especially as far as their formation efficiency is concerned. The connection between impurities and colour centres will be discussed on the basis of optical spectra of uncoloured and coloured, and also pre-annealed and bleached crystals.

Thin‐film layers and multilayer nano‐structures with controllable properties

“…(The non-irradiated and γ-irradiated substrates remain non-absorbing in the above spectral range.) According to the literature [22][23][24], besides impurities, Mg colloids with the absorption band peaked at 4.4-4.6 eV, the low-wavelength absorption band at 3.6-4.1 eV related to formation of more large Mg colloids or intrinsic Li colloids, are reliably distinguished in non-irradiated LiF nanostructures and initital LiF crystals γ-irradiated with various doses and bleached by annealing after irradiation [13,25] (Fig. 4a, insert).…”

“…The substrates were kept at room temperature (RT) on a copper holder, and the vacuum pressure in the evaporation chamber was about 10 -6 Torr. Crystals and films produced in standard ways were used as reference samples [10][11][12][13]. After the growth some samples were γ-irradiated at RT [14].…”

Enhanced photo-response of thin-film structures with nanocrystals

“…Lithium fluoride is a well-known material which, after irradiation by electrons, X-rays, g-rays, or laser light, is characterized by F-CC aggregates and metal colloids formation sensitive to the content of oxygen, hydroxyl and divalent metal ions in initial crystals [15,16,19,20]. Clusters of F-CCs (lithium colloids) and impurity colloids can be created in LiF at temperatures where diffusion of point defects and impurities is possible [18][19][20].…”

“…Ion implantation [17], thermal treatments [18] and ionising radiation bombardment (combined with special annealing [15,16,19,20]) are established tools for metal nanoparticles formation in solids. Understanding the structural evolution during the preparation of nanocomposites can be of great help in understanding how to control the characteristics of the final products.…”

“…Unfortunately, not only bulk, but boundary (surface) states of nanocrystals affect strongly their physical properties as their size reduces [14]. The properties of thin layers and nanocrystals as prepared and post-growth processed by different methods can be affected by the presence of impurities, crystal defects and aggregation of impurities and intrinsic defects to the colloids in the bulk and surface regions [13,[15][16][17][18][19][20] related to the used preparation technique.…”