Investigation of Luminescence Spectroscopy for Mineral Characterisation in Planetary Exploration

Kurzfassung

Spectroscopic methods such as Raman spectroscopy are widely used for mineral characterisation in planetary exploration. In the case of Raman spectroscopy, when used on natural samples, the Raman signal may be overlaid by luminescence caused by impurities in the mineral. Therefore, in this scenario, luminescence is usually seen as an unwanted contribution. However, luminescence can also be specific, in most cases for the impurities, but sometimes also the mineral matrix. The goal of this thesis is to investigate in a laboratory study whether the luminescence signal might give additional information that can be useful in mineral characterisation. Four minerals were chosen for their spectroscopic signals and comparable impurities: a ruby that is known for characteristic luminescence of Cr3+ impurities and calcite, svabite and tremolite, three minerals showing luminescence of Mn2+. The minerals were analysed using Raman spectroscopy and laser-induced breakdown spectroscopy as well as plasma-induced luminescence and a setup for time-resolved luminescence spectroscopy. For ruby, the expectation of characteristic luminescence could be confirmed. The luminescence signal could be observed with all spectroscopic methods. For ruby, the characteristic Cr3+ luminescence in form of rather sharp peaks could be observed in all spectroscopic measurements. In this case, the luminescence signal alone was su!cient to confirm the presence of ruby, which would not have been possible using LIBS or Raman spectroscopy alone. For the other tree minerals, broad luminescence features of Mn2+ could be observed at di”erent wavelengths. For calcite, impurities of manganese could only be identified using the luminescence because the concentration was lower than the limit of detection of LIBS. With svabite and tremolite, manganese emission lines were observed with LIBS confirming that the luminescence was caused by impurities of this element. Overall, luminescence was found to provide useful additional information about the investigated mineral samples. In most cases, the combination with the other techniques Raman spectroscopy and LIBS was necessary for a complete characterisation including the mineral matrix as well as impurities.