Author

Xu Ouyang

Date of Award

5-1995

Degree Type

Thesis

Degree Name

Doctor of Philosophy (PhD)

Department

Materials Engineering

Supervisor

Dr. A.H. Kitai

Abstract

The cathodoluminescence of various thin films deposited on (111)Si substrates was systematically studied for the first time. The best dopants for red, green and blue (RGB) phosphor films are Eu, Tb and Ce, respectively. A program was developed for the calculation of chromaticity coordinates from the luminescent spectra. High luminescence can only be achieved by post-annealing thin films above 900°C for yttrium silicates or above 850°C for zinc silicates. The band-gaps of the thin films were measured by UV absorption spectroscopy.

Rare earth (Ce³⁺, Pr³⁺, Nd³⁺, Sm³⁺, Eu³⁺, Gd³⁺, Tb³⁺, E³⁺) doped Y₂SiO₅, Y₂Si₂O₇, Y₄.₆₇(SiO₄)₃O and Mn²⁺ doped Zn₂SiO₄ thin films were prepared by magnetron sputtering. Their compositions were studied by Rutherford backscattering and X-ray diffraction. Sputtering parameters such as magnetic field, pressure, target-substrate distance and substrate temperature were studied. The chromaticity coordinates and brightness of thin film phosphors were compared with their powder counterparts. These films show potential for practical applications.

Electroluminescence was found only in Zn₂SiO₄:Mn²⁺ and Y₂SiO₅:Ce³⁺ thin film phosphors. The devices of ITO/Zn₂SiO₄:Mn²⁺ (or Y₂SiO₅:Ce³⁺)/BaTiO₃/Al and multi-insulated phosphor thin films were prepared and their electroluminescent (EL) response under different voltages, frequencies and pulse widths, and their decay curves and transferred charges were studied. With the same chromaticity coordinates as Sylvania powder CL samples, Zn₂SiO₄:Mn²⁺ (2% mole) thin films are shown to have very good EL performance with a brightness as high as 80 foot lambents (fL) excited by 400 Hz a.c. pulses, with a short decay time of 0.6 ms and with an efficiency of 0.78 lumin/watt.

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