Measuring Metal Oxide Luminescence

When talking about the band gaps of metal oxides the assumption is that the crystal goes on forever. Since this is never the case the transition metal oxides hold inherent defects in their electron movement which results in a mid gap state. In two crystals, lanthanum aluminate (LaAlO3) and strontium titanate  (SrTiO3), these unexpected energy levels cause these semiconductors to be photoluminescent. A quick look at these metal oxides show that they are of similar form: AMO3, in which A and M both represent cations, and the transition metal part, M, is surrounded by the oxygen. To be able to understand how these crystals energy levels are laid out we can use the photoluminescence to map out the levels and sub levels inside the structure. The light being emitted in the near infrared with each photon having a wavelength of about 70 micrometers (70×10-6 m). It has also been discovered that this luminescence undergoes quite a change with both temperature and external magnetic field alterations. The Zeeman effect is also observed; this is when the emission spectra get split by the magnetic field so two wavelengths appear. The stronger the magnetic field the greater the difference between these wavelengths represented two diverging lines on a graph. What is also interesting is that temperature has the opposite effect on the two metal oxides. LaAlO3 has the emission wavelength decrease at increased temperature while SrTiO3 is the reverse with greater temperatures resulting in even greater wavelengths. This research could be used to develop sensors for recording things like the magnetic field given these effect and also helps us understand more about these defect levels in crystals.


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