CaSO4:Dy and CaSO4:Tm are highly sensitive phosphors used in the thermoluminescence (TL) dosimetry of the ionizing radiations. It is shown that, by using P, Mo or SO3 as co-dopants, the TL sensitivities can be increased by 40-100%. The increase in sensitivity originates in various processes, which are discussed. P acts as a charge compensator, allowing the incorporation of Dy in higher concentration without causing quenching. Mo increases the efficiency of trap filling. It is claimed that use of Mo as a co-dopant will improve the sensitivities without disturbing the other dosimetric characteristics.

CaF2:n~ and CXO~:RE are important phosphors. The phosphors corresponding to RE E Dy and Tm find applications h thermoluminescence dosimetry using ionizing radiations. Although these phosphors have been in use for several yeus. the mechanism of thermoluminescence in these phosphors is not well understood. The role of RE ions in emission has been clearly indicated. Two types of model have been proposed. In model I it is assumed that a hole recombines with a RE'' ion to convert it into RE3+. Model Z proposes that the energy of electron-hole recombination is mansferred to the RE ion. Experimental results on c1sOd:Eu and CaF2:Eu are presented which show that model 2 is closer lo reality.

Single crystals of Bis(thiourea) cadmium chloride (BTCC), and Tris(thiourea) zinc sulphate (TZnS) have been grown from saturated aqueous solution by slow evaporation method at room temperature. The laser b a n and FT-IR spectra on these crystals are recorded in the frequency range 50-4000cm-'. The spectral data of BTCC and TZnS are interpreted on the basis of thiourea crystal vibrational data. The vibrational frequencies in the FT-IFt &d Raman spectra of BTCC and TZnS establish that ZnSOr and CdClz metal complex are coordinated with thiourea by the metal to sulfur bonds. The effect of the metal complexation on thiourea molecule and nature of bands due to different vibrational modes have been discussed. The lattice vibrational frequencies changes have also been observed and analyzed.

phosphors find applications in dosimetry of ionizing radiations. Phosphors having Dy or Tm activators are high-sensitivity thermoluminescence dosimetry materials, while the phosphors with Eu or Sm activators are the proposed materials for radio-photoluminescence dosimetry. Mechanisms of several processes related to various luminescence phenomena, however, are not yet properly understood. Usually, all phosphors are prepared under identical conditions and comparative studies are carried out. It is shown here that the form in which the impurity is incorporated and the nature of defects produced is quite different in than in . The results presented throw light on the mechanism for thermoluminescence, radio-photoluminescence, incorporation of the impurity and conversion.

The transport and magnetic studies of a series of compounds having the general formula La 0.7 Ca 0.3 Mn 1−x Co x O 3 (0.1x < 0.9) have shown that Co 3+ can exist both in high spin and low spin states (diamagnetic state). This is found to affect greatly the transport and magnetic properties of the system at low temperature by varying the strengths of both double-exchange (DE) and superexchange (SE) interactions. The introduction of cobalt changes the mobile carrier concentration, so even with 10% of Co concentration the strength of DE is found to decrease considerably. For x 0.25 there is a clear spin transition at low temperature from the high to the low spin state of trivalent cobalt and this leads to change in ferromagnetic (FM) and antiferromagnetic (AFM) phases. For x 0.25 there are two transitions for each value of x: the upper one gives the FM and AFM spin arrangement depending upon whether the DE or the SE dominates; the lower one is obtained due to the transition from the high to the low spin state of the trivalent cobalt ion.