Investigations of Defect Centres in Alkali Halides Doped with Trivalent Cations. Part 1: Bismuth in NaCl, KCl and RbCl Crystals

Abstract

A correlated set of experiments was performed with a view to study the effect of trivalent bismuth upon some properties of NaCl, KCI and RbCI crystals. For NaCI the effect of BiO+ ions was also investigated. It was stated that: 1. The hydrolytic properties of bismuth are responsible for the formation of BiO+ centres also in crystals doped with BP+ ions. 2. During all experiments performed, the dopant remains in the form of trivalent cations. 3. Optical absorption spectra of bismuth are similar to those characteristic of other heavy metal ions with the s 2 electronic configuration. 4. The charge excess of BP+ ions is compensated by cation vacancies whereas for BiO+ ions the preferential bonding between Iii"" and O 2-serves for the charge compensation.

RES structure of Bi3+ centres in KCI: Bi, S and CaO:Bi crystals

“…The positions of absorption bands (in eV) and the oscillator strength ratio R = C / A for KC1 : Bi at 77 K [GI The concentration of Bi3+ was 6 x cm3 in [5], 2.5 to 13.5 mol ppm in [7], and 400 ppm in [8] expected such as associates of a Bi3+ ion with one or two cation vacancies (v;), with impurity anions (02-, S2-), etc.…”

Investigations of Defect Centres in Alkali Halides Doped with Trivalent Cations. Part 2: The NaCl:Cr3+Crystals

“…With increasing c 3+ the association of vacancies occurs at temperatures at which the intrinsic conductivity takes place. Similar to the bismuth doped alkali halides [1], the number of cation vacancies, induced by each Cr3+ ion, is larger than one. The migration and association energies, obtained from the lg(σT) vs. 1/T plot for AR samples, are listed in Table II; for comparison, experimental data for NaCl crystals doped with other transition metal ions are also presented.…”

“…The temperature dependence of ionic conductivity was measured in the same way as it has been described in Part 1 [1]. Figure 1 shows the conductivity σ versus inversion of temperature 1/T for AR samples doped with various amounts of chromium.…”

“…The present series of papers, devoted to alkali halides (AH) doped with "small" trivalent cations (Me 3 +), began with characterization of bismuth centres in NaCl, KCl and RbCl crystals (Part 1 [1]). Although some evidences for the presence of impurity-vacancy-vacancy (I.V.V.)…”