A Experimental Investigation of Luminescence and Photoconductivity in Single Crystals of Spinel and Sapphire and a Study of Ionic Motion in SODIUM-CHLORIDE:COPPER.
Abstract
Scope of Study. The objective of this dissertation is to investigate the luminescence and photoconductivity in (alpha)-Al(,2)O(,3) and MgAl(,2)O(,4) and to identify the nature of the defects. Also investigated are the optical properties and ionic motion of Cu('-) ions (impurity related defect) in Sodium Chloride. Findings and Conclusions. Isothermal anneal experiments were performed on NaCl crystals containing Cu('-) ions, the samples being bleached with F-light prior to each anneal experiment. The isothermal decay of Cu('-) ions showed a second order kinetics with an estimated activation energy of 0.80 (+OR-) 0.05 eV. The preirradiation state of the crystal (recovery of Cu('+) ions) was achieved in a two stage process. Near 150(DEGREES)C , the absorption spectrum did not show the presence of Cu('+) ions even though all the Cu('-) ions were destroyed at this temperature. Complete preirradiation state of the crystal was achieved near 200(DEGREES)C. Thermoluminescence spectrum of NaCl:Cu('-) samples showed a TL peak at 165(DEGREES)C at which Cu('-)- and F-centers were annealed by possible recombination with holes. UV excitation of thermochemically reduced MgAl(,2)O(,40) single crystals below room temperature produced a luminescence band with peak at 2.69 eV. The excitation spectrum of the emission coincided with the broad F-center absorption band at 5.30 eV. The 2.69 eV band is also emitted in UV -stimulated glow peaks which occurred at 95 and 265K. Photoconductivity maxima were detected at 4.59 and 5.39 eV above 160K, but the 5.39 eV band was readily bleached by UV light. The 2.69 eV band was assigned to be due to F-centers, possibly in a special configuration of the crystal. Optical absorption spectrum of an (alpha)-Al(,2)O(,3) crystal annealed at 1500(DEGREES)C for 12 hours showed a shoulder near 5.6 eV. Absorption due to F-centers at 6.1 eV was not present in the sample. UV excitation of the crystal below room temperature produced a polarized luminescence band at 2.75 eV with a shoulder near 2.95 eV. An (alpha)-Al(,2)O(,3) sample annealed at 1200(DEGREES)C behaved in a similar way. The excitation spectrum of the luminescence in these crystals showed a peak at 5.6 eV which coincided with the broad absorption at 5.6 eV in these samples. Thermoluminescence spectra showed a peak at 260K for (alpha)-Al(,2)O(,3) crystals annealed at 1250(DEGREES)C and 1500(DEGREES)C respectively. An (alpha)-Al(,2)O(,3) crystals annealed at 1200(DEGREES)C exhibited photoconductivity at 80K. The photoresponse of the sample showed a shoulder near 5.0 eV and at higher photon energies, the photoresponse showed a steadily increasing trend. Luminescence bands at 2.75 and 2.95 eV were proposed to be due to perturbed F-centers, the perturbation being caused by heat treatments.
- Publication:
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Ph.D. Thesis
- Pub Date:
- 1985
- Bibcode:
- 1985PhDT.......151B
- Keywords:
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- Physics: Condensed Matter