The nature of photochromism in chlorosodalites from optical data

Abstract

Methods have been devised for the preparation of pure and doped (S, Se, Te) chlorosodalites. Optical data are presented which are at variance with the accepted mechanism for photochromism in these materials (i.e. the presence of an S22- ion). Intrinsic and extrinsic mechanisms which depend upon the formation of an F centre in conjunction with an O2- ion on a chlorine vacancy site are proposed. Similar mechanisms involving S, Se and Te may occur, and it is possible that more complex ions are involved.

Luminescence and tenebrescence of natural sodalites: a chemical and structural study

“…Yellow-orange PL, which is observed in sodalites investigated in this study, has been ascribed to the disulphide anion S 2 2− (Kirk 1955;Ballentyne and Bye 1970;Warner 2011) or the radical anion (Taylor et al 1970;Warner 2011;Kaiheriman et al 2014). Different luminescence centres, e.g.…”

“…S n 2− ) being trapped in adjacent vacant cages (Armstrong and Weller 2006;Williams et al 2010). Ballentyne and Bye (1970) showed that Se and Te substituting for S can create tenebrescence in synthetic chlorosodalites. Vacancies in sodalite cages can form by the substitution of two Cl − by one S n 2− , leaving an empty cage (Williams et al 2010).…”

“…We have not performed Mössbauer spectroscopy on our samples, and therefore, we solely base our assumption that Fe is trivalent on the fact that the luminescence of HF_B has a typical Fe 3+ emission (Finch et al 2016). Ballentyne and Bye (1970) showed that Se and Te can cause tenebrescence. We did not analyse for these elements as Bailey et al (2001) showed that Se in sodalite from Ilímaussaq is <1 ppm, and Te has never been described in any amounts in silicates in Ilímaussaq.…”

Raman scattering studies of sodalite for crystal structure and coloration mechanism

“…Various attempts have been made to understand the coloration and erasure mechanisms as this would allow the optimization of the devicerelated properties. Electron spin resonance measurements [1][2][3] have estabilished the trapping of F-centre electrons at the halogen ion-vacancies at the centres of sodalite cage. However, Annersten et al [4] have shown by conductivity and ESR measurements the arising of the blue colour due to the presence of metal particles of colloidal nature.…”

“…Optical spectroscopy of colourless sodalite shows absorption band at 530 nm upon Xray irradiation when a sample develops a pink or magenta colour [14,15]. This band was supposed to arise from F-centres as concluded by Hodgson et al [16] and McLaughlan [17] from their electron spin resonance studies.…”