ESR Detection of Self‐Trapped Holes in AgCl

Abstract

Ag2+ centres are produced in doped and appropriately treated AgCl crystals by irradiation with blue light a t 20 OK. It is shown that the only purpose of the preceding treatment is to create a high concentration of electron traps. I n chalcogen doped crystals (AgCl :S, Se, Te) electron traps are formed by pre-irradiation with blue light above 120 " K ; in iron doped crystds the incorporated Fe2+ ions are converted to Fe3+, acting as traps, either by irradiation a t 20 "C or by annealing in chlorine gas. As the paramagnetic data of the localized Ag2+ centres are independent of the kind of the impurity, one must conclude that the hole is trapped in the undisturbed lattice.Ag2+-Zentren werden in dotierten und geeignet behandelten AgC1-Kristallen durch Bestrahlung mit blauem Licht bei 20 O K erzeugt. Es wird gezeigt, daB die Aufgabe der Vorbehandlung allein darin besteht, eine hohe Konzentration von Elektronenfallen zu schaffen.I n chalkogen-dotierten Kristallen (AgC1: S, Se, Te) wird die Bildung von Elektronenfallen durch Vorbestrahlung mit blauem Licht oberhalb von 120 OK bewirkt ; in eisen-dotierten Kristallen werden die eingebauten Fez+-Ionen entweder durch Bestrahlung bei 20 "C oder durch Tempern in Chlorgas in Fe3+ umgeladen, das als Fanger dient. Da die paramagnetischen Daten der lokalisierten Agz+-Zentren unabhangig von der Art des Zusatzes sind, muB man auf einen Einfang der Defektelektronen im ungestorten Gitter schlieSen.

Stability and Polaronic Motion of Self-Trapped Holes in Silver Halides: Insight through DFT+UCalculations

“…These results thus support that STHs can be spontaneously produced in irradiated AgCl. Moreover, they are consistent with experimental EPR and ENDOR data on this compound proving the formation of elongated AgCl6 4-complexes with the hole placed in the antibonding x 2 -y 2 orbital 19,23,25,27,35 .…”

“…Indeed for AgCl6 4-complexes in alkali chlorides, as well as in AgCl, the elongated geometry with a hole in the x 2 -y 2 orbital is energetically favorable with respect to a compressed one with the hole in 3z 2 -r 2 ( Fig. 2) as demonstrated by EPR data 19,21,23,[36][37] . Along this line theoretical calculations carried out on KCl:Ag 2+ and NaCl:Ag 2+ reveal that the energy difference between compressed and elongated conformations is equal to 127 meV and 62 meV, respectively 53 .…”

“…As the energy of such a transition, denoted as E(z 2 ), would be zero if the 23 octahedral AgCl6 4-complex is placed in a cubic lattice 90 it depends on the tetragonal distortion in the complex reflected in the Rax -Req = 3 quantity. As in a JT system E(z 2 )  4EJT 41 This luminescence is well observed in AgCl crystals doped with copper and grown in a chlorine atmosphere where self-trapped holes and electrons trapped as Cu + are both simultaneously formed 21,27 .…”

LUMINESCENCE AND TRAPPING CENTRES IN PURE AND Cd DOPED SILVER CHLORIDE CRYSTALS

“…This result is further in good agreement with the occurrence of strong glow peaks at T z 40 K. Therefore it is safe to assume that the electron traps responsible for the glow curves -namely Ag, centres -at least contribute to the stabilization of the Ag2+ centres. M. Hohne and M. Stasiw [26] also mentioned a possible participation of Ag, centres as electron traps in ESR measurements. Moreover the lack of Ag, centres could be the reason for the fact that some workers could detect the Ag2+ centres on pure crystal only by optical absorption and not by ESR measurement.…”

An electron spin resonance study of photoproduced trivalent iron and divalent vanadium in silver chloride

“…Single crystal and polycrystalline specimens of the doubly-doped silver chloride were irradiated with blue light for about 4 I n the dark both the A and B, resonances decayed a t the same rate with a half life of a few minutes. I n some specimens, after B, had decayed to zero, a small A resonance remained which decayed with a half life of a few days.…”