Electrooptically stimulated exchange between impurity ion and vacancy in divalent anion doped alkali halide crystals

Abstract

A simple mechanism is proposed which qualitatively explains the occurrence of the phenomenon of photoinduced polarization a t lower temperatures. It is suggested that a t lower temperatures the impurity ion and vacancy exchange their positions under the influence of the presence of the electric field and the simultaneous photon irradiation. The exchange between impurity ion and vacancy during photon irradiation is found to take place only in the presence of the electric field and hence is named electrooptically stimulated exchange between impurity ion and vacancy. The mechanism suggested also explains successfully the disappearance of the phenomenon of photoinduced depolarization a t lower temperatures. Es wird ein einfacher Mechanismus vorgeschlagen, der das Auftreten des Phanomens der photoinduzierten Polarisation bei niedrigenTemperaturen qualitativ erklart. Es wird vorgeschlagen, daD bei tieferen Temperaturen das Storstellenion und die Leerstelle ihre Positionen unter dem EinfluD eines elektrischen Feldes und der gleichzeitigen Photoneneinstrahlung austauschen. Der Austausch zwischen Storstellenion und Leerstelle wahrend der Lichteinstrahlung findet nur bei Anwesenheit eines elektrischen Feldes statt und wird deshalb elektrooptisch stimulierter Austausch zwischen Storstellenion und Leerstelle genannt. Der vorgeschlagene Mechanismus erkliirt auch erfolgreich das Verschwinden des Phanomens der photoinduzierten Depolarisation bei tiefen Temperaturen.

Effect of ultraviolet irradiation on Se2−‐anion vacancy dipoles in potassium iodide

“…The results of Fig. 10 suggest the absence of the latter mechanism during P I D which has also been established in the case of KI:S2- [24]. P I D starts to appear only a t 160 K when thermal disorientations through ees become active.…”

“…, 231 and electro-optically stimulated exchange (EOSE) between Se2-and anion vacancy [24]. It would be worth mentioning that the irradiation in the presence of a n electric field in the 371 nm absorpbion band is found to be ineffective for studying the phenomenon of PIP.…”

“…It has been observed that mechanism (ii) is absent when the crystal is irradiated in the absence of the electric field as discussed in the next section. It suggests, therefore, that a limiting value of the electric field is required to activate mechanism (ii) [24]. It is proposed [23] that the limiting value of the electric field for the occurrence of PIP and mechanism (ii) is the same.…”

Photo‐chemical reaction and photo‐induced polarization studies in sulphur‐doped potassium bromide

“…It has been assumed that the phenomena of PIP and P I D t,ake place via ees where the activation energy for the orientation of I V dipole is less than that required in the electronic ground state (egs). The PIP-and P I D results rnent)ioned above can largely be explained [ll] by the following mechanisms: (i) Thermally activated orientation of IV dipoles via ees in accordance with t,he bistable niodel [12] and (ii) electrooptically stimulated exchange between the divalent impurity ion and its respective anion vacancy [13]. It has been proposed Gorakhpur 273001, India.…”