New optical transitions of colour centres in CaF2 : Na+

Abstract

2014 Nous mettons en évidence de nouveaux centres colorés dans CaF2 : Na+ par leurs spectres optiques d'absorption, d'émission et d'excitation. Le centre que nous appelons f est responsable d'une bande de fluorescence qui culmine à 573 nm, d'une bande d'excitation à 510 nm et d'une raie à zéro-phonon à 541,8 nm. Le centre que nous appelons g a des bandes d'émission et d'excitation respectivement centrées à 681 et à environ 562 nm. De nombreuses raies fines apparaissent dans les spectres d'absorption et de fluorescence; les unes sont des raies à zéro-phonon de centres connus, ou leurs satellites vibrationnels, tandis que les autres ne sont pas encore attribuées. Abstract 2014 New colour centres are detected in CaF2 : Na+ by their absorption, emission and excitation optical spectra. The so-called f centre accounts for a fluorescence band peaking at 573 nm, an excitation band at 510 nm and a zero-phonon line at 541.8 nm. The so-called g centre has emission and excitation bands respectively centred at 681 and approximately 562 nm. A number of sharp lines appears in the absorption and fluorescence spectra, some of which are zero-phonon lines of known centres, or their vibrational satellites, while others are still unidentified

Colour Centres in Alkali Metal Doped SrF2

“…It is accompanied by vibrational satellites a t 541.3 nm in absorption, a t 550.2 and 554.6 nm in emission, all of them corresponding to a vibrational quantum of 148 + 4 cm-l. This is close to the 143cm-l observed both in emission and absorption for the ''F3a" centre in CaF2: Na+ [6], which suggests that the associated local vibrational mode does not entail a sizeable motion of the ''FiA" centre's alkali impurity (either Na+ or Li+). Fig.…”

“…The 562.8 nm zero phonon line of f centres is accompanied by satellites: 558.7 nm in absorption, 567.8 and 573.2 nm in fluorescence. Different frequencies thus appear in absorption and in emission, contrary to the case of f centres in CaF,:Na+ for which the same quantum 151 cm-l is observed in both spectra [6].…”

“…Thus f has emission and absorption transitions shifted by nearly the same quantity toward greater wavelengths with respect t o ''FiA4": 17 nm for the maximum of the absorption band and for the zero phonon line, 1 9 n m for the maximum of the emission spectrum. I n the analogous case of CaF,: Na+, the corresponding shifts are of comparable magnitude: 20, 20, and 25 nm, respectively [6].…”

“…As its genuine ixicroscopic structure does not seem t o have been yet reliably determined, we shall call this CC from here on " F Z A " . Similarly, we shall write "FiA7' for another conspicuous CC which has been identified by Rauch [5] as being FiA, but from somewhat inconclusive argumenh6) By measurements of optical absorption and emission spectra, we discovered some new CC's in CaF,:Na+ [6]. We also studied the E P R of FA and "FzA" centres both in CaF,: Na+ and CaF,: Li+ [7], from which we obtained the oscillator strengths of optical absorption bands of the " F~A " centres [8].…”

“…Doualan et al [6] have shown that besides the ' ' F i A " centre described by Rauch [5] with absorptions at 317 and 490 nm and emission at 548 nm, there exists a similar CC, which they called f , with absorption a t approximately 510 nm and emission a t 573 nm. Both " F i A " and f centres are obtained from " F Z A " centres by thermal evolution in the dark a t room temperature, but f centres are much favoured if one heats the sample a t N 100 "C. From the MCD work of Doualan et al [4], the ''FiA'' centre is known to have a non-degenerate ground level, but a degenerate or nearly degenerate first excited level.…”