S V Moharil

Luminescence of Pb2+ in Some Aluminates Prepared by Combustion Synthesis

Pb 2+ is a low cost activator which can provide strong absorption of UV and an efficient conversion to longer wavelengths. Considering that aluminate hosts are used in some lamp phosphors, Pb 2+ luminescence in these hosts is studied. This paper reports results on the luminescence of Pb 2+ in aluminates. It was found that the position of Pb 2+ emission can be manipulated by selecting the size of the host cations. The findings are important in context of the role of Pb 2+ as a sensitizer.

Cu+ emission in LiF

Abstract Cu + is known to exhibit characteristic luminescence corresponding to 3 d 9 4 s ↔ 3 d 10 transition. Data for excitation and emission of Cu + in alkali halides have been published. Earlier works report failure to dope Cu + in lithium fluoride. However, we discovered photoluminescence in LiF: Mg, Cu, P, a commercial TL phosphor. A peculiar synthesis led to similar emission in LiF: Cu. The emission and excitation spectra for LiF: Cu and the comparison with LiF: Mg, Cu, P, are presented. It is claimed in this communication that the emission is due to Cu + .

Additive coloration of microcrystalline powders of potassium halides

The additive coloration of potassium halide powders is reported. The optimum coloration temperature decreases with decreasing particle size. The stability of coloration was profoundly reduced in the powders in comparison with that in single crystals. The reduced stability of coloration is interpreted as due to the interaction of F centres with mobile dislocations whereas the decrease in the optimum coloration temperature is attributed to surface effects.

Correlation between microhardness, dislocation mobility and the isothermal stability of coloration in microcrystalline powders of KCl

Stable colour centres can be introduced in single crystals of alkali halides using electrolytic coloration. The powders obtained by crushing these single crystals lose colour very rapidly. Mobile dislocations which are present in far greater abundance in the powders are responsible for the reduced stability. Results on some KCl samples showing a correlation between microhardness, dislocation mobility and the stability of coloration are presented.

Isothermal decay of colour centres in microcrystalline powders of KBr:KI

Colour centres in single crystals are stable. The crystals can be stored in the dark for several months without any appreciable loss of colouration. The colouration of the microcrystalline powders, on the other hand, was found to decay very fast. This fast decay has been attributed to the defects inherent in the microcrystallites. The microcrystalline powders of the mixed crystals of KBr:KI could, surprisingly, retain their colouration for several days.

On the trapping centres in LiF TLD-100

Abstract Most of the TL in TLD-100 originates from the defects responsible for the optical absorption bands at 310 and 380 nm. Different models have been suggested for these defects and TL mechanism in TDL-100. These models are viewed critically in this paper

Isothermal decay of colour centres in microcrystalline powders of alkali bromides

Abstract The bleaching of F-centres on storing in darkness of electrolytically coloured single crystals and microcrystalline powders of solid solutions of KBr with other alkali bromides is reported. The colouration of the microcrystalline powders decays isothermally while that of single crystals is comparatively stable. The decay proceeds slower in the powders of mixed crystals than in the pure materials. A tentative explanation is suggested.

Colloid formation in microcrystalline powders of alkali halides

It is reported that the growth of colloids in NaCl powders is easy as compared with that in single crystals. This ease is attributed to the availability of more nucleation sites in the powders and to the motions of the colour centres being aided by dislocations. It is suggested that the study of colloids in microcrystalline powders provide information on such motions.

Role of peak IV in the sensitisation of LiF TLD-100

Peak IV in LiF TLD-100 is different from the rest of the glow peaks (I-V) in that it does not appear in the glow curves of sensitised samples or in photo-transferred TL glow curves. This behaviour is discussed in the light of a recently suggested model for the TL process in this material.

On the mobile interstitial model for TL in LiF-TLD 100

In recent years, Alvarez Rivas and co-workers (1972, 1974) have proposed a model for thermoluminescence in alkali halides in which the mobile entity is an interstitial, and not a hole or an electron as assumed in the conventional models. Recently, Sagastibelza and Alvarez Raivas (1981) have extended the model to LiF-TLD 100. In this paper some anomalies are pointed out. It is suggested that the model has to be suitably modified to remove such anomalies before it can be generally accepted.