Publication Date

8-1970

Advisor(s) - Committee Chair

William Buckman, George Moore

Degree Program

Department of Physics and Astronomy

Degree Type

Master of Science

Abstract

Over the past decade the luminescence properties of sapphire (∝-AL2O3) and ruby (Al2O3:Cr2O3) have been the subject of many investigations because of their importance in materials technology. Sapphire and ruby are at present used as lasing materials, radiation dosimeters, and as optical windows. In order that these operations may be made more efficient, and that other useful luminescent properties may be systematically explored and developed, much attention has been given to understanding the luminescent mechanisms from the standpoint of the physics of the solid state. However, mechanisms have not yet been proposed that describe in detail the known luminescent properties of sapphire and ruby.

The luminescence experiments which have been previously reported in the literature on sapphire and ruby fall into two classes: experiments in which the exciting energy is stored in the crystal by some defect mechanism and subsequently released by perturbing the crystal, and experiments in which the luminescence is observed while the crystals are being excited. Thermoluminescence, in which energy is stored in the crystals by exposing it to ionizing radiation and subsequently released by raising the temperature of the crystal, is the most extensively used technique of the former class. The facts concerning the thermoluminescence of sapphire and ruby are well documented. (11,12) Numerous experiments in the latter class have been reported in which the exciting radiation was in the visible or ultraviolet energy region. (16, 17) These latter experiments have a disadvantage; the amount of exciting energy absorbed is not independent of two important parameters, temperature and chromium concentration.

It was the primary intent of these investigations to resolve the difficulty of the dependence of the absorbed energy by exciting sapphire and ruby crystals with x-rays. Because the energy of the x-ray photons incident on and within the crystal is more than an order of magnitude more energetic than is necessary to produce highly mobile or free electrons within the crystal, the number of such electrons produced is independent of the temperature and chromium concentration over the range that these parameters were varied.

The program of experiments reported herein was designed to answer the following questions: (1) How does the intensity of the total luminescence depend on the temperature? (2) How does the emission spectrum depend on temperature and chromium concentration? (3) How does the luminesce yield depend on temperature? The answers to these questions were obtained by observing the luminescence of sapphire and ruby, subjected to continuous x-ray excitation, as a function of temperature and chromium concentration. The total x-ray-induced luminescence and emission spectra of two crystals, one nominally pure sapphire and the other sapphire containing 0.005% Cr2O3, were observed as the temperature of the crystals was raised and lowered between 25°C and 400°C. The results for other chromium concentrations (0.05% and 0.5% Cr2O3) may be found in Mr. Wayne Cooke’s masters’ thesis (21) The thermoluminescence total emission and emission spectra were observed between 25°C and 400°C after x-ray exposure at room temperature.

It should be noted that there is one experiment in the literature in which the x-ray-induced luminescence of ruby was observed as a function of temperature.(19) The investigators observed the luminescence as the temperature increased; hence, much of the emission as the temperature decreases because the energy stored in a crystal at a particular temperature has a decreasing probability of being released at lower temperatures.

Disciplines

Astrophysics and Astronomy | Physics

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