Luminescence properties of zirconium oxide films

Various luminescence techniques have been applied in the characterisation of the zirconium oxide film formed on the metal matrix. Our investigation shows that some alloying elements in the zirconium alloys show characteristic emissions which could be used to study their distribution in the zirconium oxide. While the origin and detailed mechanism of luminescence in the zirconium oxide system is not well established, cathodoluminescence (CL) and thermoluminescence results from this study support the theory that oxygen vacancies in complexes with impurities are responsible for the intrinsic luminescence in the oxide system. The specific oxygen vacancy and impurity complex is reported in literature as the T-defect, having an energy of 2.2 eV. To aid in interpretation of the CL data, optical transmission properties of the oxides were also measured. The latter investigation showed the thickness of the oxide illuminated by the CL technique is greatly dependent on the optical transmission properties of the oxide, and it ranges from 20 μm for pure zirconium or low-alloyed zirconium oxides to less than 3 μm for oxides of alloys with more absorbing, or higher alloying element concentrations. The 20 μm depth of illumination is significantly deeper than the electron penetration depth, which suggests a secondary source of excitation, possibly characteristic X-rays emitted by the specimen. These combined properties of the oxide and technique can result in CL images showing structural contrast not easily seen during SEM or optical microscopy of oxidised surfaces.