Relaxed excited state structure and luminescence of thallium-doped caesium chloride and bromide

Abstract

Four bands, all belonging to the main thallium centres, have been detected in the emission spectra of CsCl:Tl and CsBr:Tl crystals. Their spectral, polarization and kinetic characteristics have been studied from 0.45 up to 360 K. It has been shown that the new model proposed by us recently for the relaxed excited state (RES) structure of the luminescence centre in CsI:Tl crystals is valid for CsCl:Tl and CsBr:Tl crystals as well. Two ultraviolet emission bands excited mainly in the A absorption band of centres are ascribed to electronic transitions from trigonal and tetragonal Jahn - Teller minima of the triplet RES of . Two visible bands excitable mainly in the higher energy absorption bands of CsCl:Tl and CsBr:Tl are connected with two different off-centre configurations of self-trapped exciton perturbed by the ion. The parameters of the corresponding excited state minima have been calculated. The mixing of the impurity and halogen excited states has been shown to decrease markedly in the sequence of anions .

Evaluation of Scintillation and Thermally Stimulated Luminescence Properties of Cs2CdCl4 Single Crystals

“…In the emission spectrum of the Cs 2 CdCl 4 :Tl crystal recorded at λ ex = 250 nm, a narrow peak and a broad peak are observed at 350 and 490 nm, respectively. Considering that the wavelengths of the emission peaks are similar to those of CsCl:Tl, (32)(33)(34)(35) the narrow peak (350 nm) and the broad peak (490 nm) are ascribed to the Figure 3 shows the X-ray-induced RL (XRL) spectra of the undoped, Sb-doped, and Tldoped Cs 2 CdCl 4 crystals. In the case of undoped Cs 2 CdCl 4 , three narrow peaks at 320, 360, and 400 nm, a weak band at 450 nm, and a broad peak with a maximum intensity at 600 nm are observed.…”

Optical properties of the Tl+ center doped in NH4Cl crystals with the CsCl structure

“…Luminescence bands due to the perturbed self-trapped exciton are observed in addition to the A X and A T luminescence bands [11,12]. These differences of the optical properties have been tentatively ascribed to that of the ion arrangements around the Tl þ ion [11][12][13][14]. That is to say, though the Tl þ ion doped in NaCl-and CsCl-type alkali halides has the same O h symmetry, the ion is surrounded by six and eight nearest halogen ions, respectively.…”

“…There is no absorption band having features of the B and C absorption bands in the Tl þ center doped in the CsCl-type cesium halides [8][9][10]. Luminescence bands due to the perturbed self-trapped exciton are observed in addition to the A X and A T luminescence bands [11,12]. These differences of the optical properties have been tentatively ascribed to that of the ion arrangements around the Tl þ ion [11][12][13][14].…”

Dynamical processes on relaxed excited states in NH4Cl:Tl+ single crystals

“…The energy order of the A T and A X bands in NH 4 Cl:Tl + is reversed with respect to that of the Tl + centers doped in NaCl-type alkali halides, but is the same as that of the Tl + centers doped in CsCl-type cesium halides [22,24,25]. The A T and A X luminescence bands in NH 4 Cl:Tl + exhibit the blue-shift of the peak energy and the narrowing of the halfwidth with increasing temperature.…”

“…Optical properties of the Tl + ion surrounded by eight nearest halogen ions have been investigated in the Tl + center doped in cesium halides [20][21][22][23]. In the Tl + center doped in cesium halides, the complex luminescence spectra including the luminescence bands due to perturbed self-trapped excitons are observed [22,[24][25][26]. Therefore, it is difficult to discuss the detailed dynamical behaviors on the A T and A X APES.…”