G.D. Patra

Growth and optical properties of partially transparent Eu doped CaF2 ceramic

Partially transparent ceramic of 2 at.% Eu doped CaF2 have been grown preferentially towards [111] direction. For this purpose, Eu doped CaF2 nanoparticles (size∼12 nm) obtained by a low temperature solution growth method has been pressed at 1000°C under vacuum. The preferentially grown ceramic shows 15% transparency within the visible range of spectrum. As confirmed by the X-ray diffraction result, the hot pressed ceramic exhibits reduced lattice volume than the nanopowder. It indicates Eu3+ as the dominant substituting ions at the Ca2+ sites of CaF2 lattice in the hot pressed ceramic material. It is corroborated by the photoluminescence results of hot pressed ceramic which shows strong red emission corresponding to Eu3+ sites. However, photoluminescence of nanopowder exhibits intense peak in the blue region of the spectrum which is characteristics of Eu2+ sites.

Synthesis of optically transparent ceramic of CaF2 doped with Mn and Ce for thermoluminescent dosimetry

Nano-particles of CaF2: Mn were synthesized by a co-precipitation method. Optically transparent ceramics were obtained by vacuum hot-pressing at 1000°C under 20 MPa pressure for 2 h. The duration of pressure and dehydration of the initial powder was found important to achieve the transparency. 50% transparency was observed for a polished disc of 1 mm thickness. SEM micrographs revealed the absence of voids in hot pressed samples. These samples were found to be highly sensitive and linear for TLD and can measure doses from mGy to kGy.

Effect of film thickness on luminescence property of CsI: Tl

Thin films of thallium activated cesium iodide (CsI: Tl) have been deposited on silicon substrates using a thermal evaporation technique. The films were found to have similar luminescence properties as bulk single crystals and the Tl ion concentration could be controlled by varying the film thickness. These can be used with P-I-N photodiodes in the radiation detection applications.

Exciton localization in films of ZnO nanoparticles

Temperature dependent photoluminescence (PL) spectroscopy has been employed to study the exciton localization in ZnO nanostructures of various sizes. Low temperature (LT) near-band-edge UV emission from ZnO nanostructures of size less than 100 nm show signature of free exciton (FE), bound exciton and longitudinal-optical phonon replica of FE lines. Free and bound excitonic emission deviates from the Varshni equation at LT and exhibits S-shaped temperature dependence due to the exciton localization effect. Deviations of the measured data from the Varshni equation directly provide the exciton localization energies, ELoc. It was found that ELoc increases and dELocalization due to thermal activation occurs at higher temperature for smaller nanoparticles.

Epitaxial growth of Eu doped CaF2 thin film on CaF2 (111)

Epitaxial films of 2 at.% Eu doped CaF2 have been grown on (111) plane of CaF2 by a low temperature solution growth method. The CaF2: Eu films when grown on Si (111) and glass substrate show random orientation having higher degree of surface roughness. As confirmed by the X-ray diffraction and photoluminescence results, Eu (II) ions substitute the Ca sites of CaF2 lattice. Excitation spectrum shows two broad peaks at 282 and 366 nm, which correspond to the allowed transitions of 4f7 to 4f65d1 (eg) and 4f65d1 (t2g) of Eu2+, respectively. Photoluminescence of Eu (II) doped CaF2 films exhibit intense and sharp peak in the blue region of the spectrum.