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Single crystals of CsI, CsI:Tl, and CsI:Tl, Bi were grown by the vertical Bridgman method. We studied the effect of Bi3+ codoping on the CsI:Tl X-ray-induced afterglow. Thermally stimulated luminescence measurements were carried out in order to investigate the role of traps. The results showed a remarkable reduction of afterglow, of about an order of magnitude, and of trap concentration by Bi codoping. These improvements could be related to a possible role of Bi in the compensation of intrinsic nonstoichiometry defects. (c) 2012 The Japan Society of Applied Physics

In the blue colored sapphires of metamorphic origin and Verneuil synthetic studied here, the absorption-emission properties in the VIS-NIR range are largely determined by Cr3+ and Ti3+, as we have been able to demonstrate recently. In that work a sharp radioluminescence band occurring at 870 nm in Verneuil blue sapphires was left unattributed: here we give evidence for the attribution of that band to the E-2 emission transition of V2+, and for the existence of such an emission also in natural samples of metamorphic origin. After such a result, we accurately evaluated by EDXRF the V concentrations in various samples and found the ion more ubiquitous than foreseen. We then searched for and found, weak but diagnostic spin forbidden transitions and phonon sequencies in the absorption spectra of samples sufficiently rich in V. The experimental results just mentioned allowed us to discuss the effects of the overlap of V3+ and Cr3+ spin-allowed absorption bands on the spectrum of the varieties of corundum under study. To complete the updating of the interpretation, we spent a further effort to strengthen the attribution of the absorption band at 14500 cm(-1) (currently interpreted as an IVCT (Fe2+ -> Fe3+)) to the E-5 -> T-5(2) transitions of Cr2+.

Optical absorption and luminescence spectra of yellow corundum have been analyzed, both in magmatic and metamorphic materials, looking at the role of localized electronic transitions of transition metal ions at substituted Al sites. By the aid of energy dispersed x-ray fluorescence (EDXRF) elemental analysis and electron paramagnetic resonance (EPR) measurements, the results confirm that Fe3+ is the dominant impurity ion. However, the results also evidence that Cr3+ and Ti3+ contribute in determining the optical absorption and emission properties of this variety of gem-quality corundum, as we have recently found in Type 1 blue sapphires of metamorphic origin. Furthermore, preferentially but not exclusively in samples of metamorphic origin, Mn plays a role never evaluated up to now. Here we show how few ppm of Mn - below the detection limit of EDXRF, not revealed in the optical absorption spectra, but barely detected by EPR spectroscopy as Mn2+ ion -are active in photoluminescence, showing up with the characteristic emissions of Mn2+, Mn3+ and Mn4+.

Doubly-doped BaY2F8:Tm, Nd scintillation crystals were grown by modified micro-pulling-down method. Nd co-doping was chosen to enhance the energy transfer from the host lattice to the Nd3+ luminescence center via the 5d-levels of Tm3+, due to the overlap of Tm3+ 5d-4f emission spectrum with the Nd3+ 4f-5d absorption. The energy transfer was clearly evidenced in the BaY2F8: Tm, Nd. This process is not complicated by an energy migration to killer centers and/or cross-relaxation. The radioluminescence process is complicated by an energy transfer from the host lattice exciton states to the lower f-levels of Tm3+ ion.