Measurement of Oscillator Strengths of “F_2A” Centres in MeF₂:A⁺ (Me = Ca, Sr; A⁺ = Li⁺, Na⁺, K⁺)

Abstract

From combined EPR and optical measurements, the oscillator strengths f are determined of absorption bands of “F2A” centres in CaF2,:Li+ CaF2:Na+ SrF2:Na+ and SrF2:K+. The results are compared with f‐values obtained from the observed lifetimes of the first excited level of the same centres.

Photoluminescence studies of γ-irradiated CaF2:Dy:Pb:Na single crystals

“…One school of thought attributed the absorption bands around 2.07 and 3.26 eV to M A centres [13,15] (also represented as F 2A centres). Later, the absorption band observed around 3.81 eV was also attributed to the same centre with the aid of luminescence and thermal bleaching studies [16]. Another school of thought attributed the three bands to M þ A centres [14,17,18] (also denoted as F þ 2A centre).…”

“…Thus, it would be appropriate to call the centre absorbing at 2.06, 3.28 and 3.75 eV as M Na , which was mentioned earlier [19]. It was already known that the presence of alkali metal ions in CaF 2 whose concentration was greater than 10 À4 % would alter the whole colour centre characteristics, i.e., the nature and content of the colour centres formed in them [16]. The dominating character of Na was vivid in CaF 2 :Dy:Pb:Na.…”

FD-centers in fluorite crystals doped with alkali metals

“…Вiн становить собою F -центр, розмiщений по сусiдству з домiшкововакансiйним диполем. FD-центр виникає при повторному опромiненнi оптично знебарвлених в M + A -смугах поглинання кристалах й утворюється внаслiдок локалiзацiї зонних електронiв на бiвакансiйних комплексах: Загальновiдомо [1][2][3][4][5], що кристали флюоритiв, леґованi лужними металами (кристали CaF 2 − M e i SrF 2 − M e , де M e = Li + , Na + , K + ), легко забарвлюються пiд дiєю йонiзуючої радiацiї. Високу радiацiйну чутливiсть забезпечують наявнi в кристалi домiшково-вакансiйнi диполi (ДВД) типу M e V • a , де M e неґативно заряджений щодо ґратки йон лужного металу, а V • a позитивно заряджена анiонна вакансiя.…”