Marko Eltermann will defend his PhD thesis "Analysis of samarium doped TiO2 optical and multiresponse oxygen sensing capabilities" (physics) on 30 August 2019.
dr. Sven Lange
dr. Raivo Jaaniso
Dr. Krisjanis Smits (University of Latvia, Latvia)
Photoluminescence (PL) is a process occurring inside a material that results in a change of wavelength of the light that falls on the material. The human eye perceives it as a change of colour of the light. Titanium oxide mixed with a small amount of samarium ions (TiO2:Sm3+) is a material that does emit photoluminescence, when illuminated with ultraviolet (UV) light, converting the invisible UV into a red-orange PL emission that is visible to the naked eye. The properties of TiO2:Sm3+ PL are dependent on the gas composition of its surrounding atmosphere. This raises a rather obvious question whether this material can be applied as an optical gas sensor, where the gas composition could be determined by observing the characteristics of PL. This question forms the basis of this thesis. In this thesis, TiO2:Sm3+ is investigated as an optical oxygen gas sensor. Oxygen serves as a good indicator gas, as sensitivity to oxygen usually indicates sensitivity to other gases as well, inclduing toxic or explosive gases. It will be shown that TiO2:Sm3+ is applicable as an optical oxygen sensor. The sensing principle is simple: the intensity of the PL emission increases as the oxygen concentration increases, so by measuring the intensity of the PL emission it is possible to estimate the oxygen content in gas. The material can sense oxygen in a wide range of concentrations, from 0.01 % to 100 %. At the same time it is fast and stable. The gas sensing mechanism is further analysed and a mathematical model is developed that descibes the processes behind the PL emission. The model is matched with experimental data to understand why is the PL sensitive to oxygen. TiO2 as a gas sensor material is actually much better known as an electrical sensor. In this kind of a sensor, the gas sensitive quantity is electrical conductance. The second half of this thesis combines the electrical and optical gas sensing. It is shown that the material can operate as a 2-in-1 gas sensor where it is simultaneously operating both as an electrical and an optical sensor. Through a more detailed analysis of this 2-in-1 operation it is shown that by combining the electrical and optical signals, it is possible to increase the precision of oxygen concentration measurement by more than two times.