Paramagnetic defects in ZnWO4 single crystals induced by electron irradiation at room temperature

Section: Introductionmentioning

confidence: 99%

and centres in single crystals characterized by ESR and ENDOR spectroscopy

Watterich¹,

Hofstaetter²,

Wuerz³

et al. 1998

“…In undoped ZnWO 4 single crystals electrons are trapped at oxygen vacancies which may be in two positions (named A or B). These intrinsic defects have been created by energetic electron irradiation at ∼300 K, and are denoted as V • O (A) and V • O (B) centres [8], respectively. In the presence of appropriate compensators the electron may be localised on one W or Mo forming essentially a W 5+ or Mo 5+ centre.…”

Section: Introductionmentioning

confidence: 99%

“…The second type of observed defects is of hole-type: the self-trapped hole is essentially an O − ion without any local charge compensation and is stable below 70 K [9]. In other hole-type defects the O − ions were stabilised either by monovalent impurity ions (Li [10]) or nearby V Zn [8], impurity-V Zn complexes (like V Zn -OH − [11] or V Zn -Tm 3+ pairs [12]).…”

Section: Introductionmentioning

confidence: 99%

Al- and OH-related paramagnetic impurity centres in UV- or x-irradiated ZnWO₄single crystals

Watterich

Hofstaetter

Scharmann

et al. 2003

Using electron paramagnetic resonance (EPR) and in one case also electron nuclear double resonance new trapped electron and hole centres are characterised in ZnWO4 single crystals. In undoped and Al-doped ZnWO4 a new W5+-type defect is produced by UV- or x-irradiation at 77 K. The centre is stabilised by a nearby Al3+ impurity that is substituting for Zn2+. In ZnWO4:Al in addition to the above electron-type defect three kinds of hole-type centres created by x-irradiation at 77 K are also studied: one of these is assigned to an O− ion near a VZn–AlZn3+ complex, and the second to an O− ion near a VZn–OH− pair. The - and hydrogen super hyperfine (SHF) tensors of the latter centre have been published previously. Due to the higher concentration in the Al-doped crystal, SHF tensors of two W neighbours could also be determined. The third hole-type defect shows quartet SHF (I = 3/2) with a 100% abundant nucleus and therefore the O− in this centre is most likely stabilised by an Na+ impurity. Complete sets of EPR parameters are compared for trapped electron and trapped hole centres including previously characterised defects.

“…a substitutional OH − ion [10]) reducing the centre symmetry to C 1 . A number of defects like V Zn (Zn vacancy), the Li + (probably also Na + ) impurity on the Zn site and the V Zn -OH − pair were shown to trap holes, forming very similar colour centres [9,11,12]. Under high-energy electron irradiation at 300 K, electrons are captured by oxygen vacancies creating V • O centres [11].…”

Section: Introductionmentioning

confidence: 99%

Electron spin-resonance (ESR) and electron-nuclear double-resonance (ENDOR) study of the self-trapped hole in ZnWO₄single crystals

Watterich

Kovács

Würz

et al. 2001

After x-ray irradiation at 20 K, an intrinsic O- centre was identified by ESR and ENDOR spectroscopy as the self-trapped hole centre in ZnWO4. Observation of one Zn and two strong W superhyperfine interactions allows us to distinguish between two possible trapping sites: the hole resides at the B-type oxygen position which has one Zn and two W nearest neighbours. Broadening of the ESR lines and averaging of the g-value is observed and explained as due to thermally activated hopping of the hole between two energetically equivalent oxygen positions. The activation energy of this reorientation is found to be 0.016±0.003 eV. The thermal decay of the intrinsic O- centre, and its connection to thermoluminescence, has been studied; it shows that this centre cannot be the luminescence centre for the typical TL emission at ~480 nm in ZnWO4. This emission may be due to an intrinsic electron-type defect.