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The disclosure relates to a method of detecting a change in a chemical composition by contacting a doped oxide material with a monitored stream, illuminating the doped oxide material with incident light, collecting exiting light, monitoring an optical signal based on a comparison of the incident lig

The disclosure relates to a method of detecting a change in a chemical composition by contacting a doped oxide material with a monitored stream, illuminating the doped oxide material with incident light, collecting exiting light, monitoring an optical signal based on a comparison of the incident light and the exiting light, and detecting a shift in the optical signal. The doped metal oxide has a carrier concentration of at least 1018/cm3, a bandgap of at least 2 eV, and an electronic conductivity of at least 101 S/cm, where parameters are specified at a temperature of 25° C. The optical response of the doped oxide materials results from the high carrier concentration of the doped metal oxide, and the resulting impact of changing gas atmospheres on that relatively high carrier concentration. These changes in effective carrier densities of conducting metal oxide nanoparticles are postulated to be responsible for the change in measured optical absorption associated with free carriers. Exemplary doped metal oxides include but are not limited to Al-doped ZnO, Sn-doped In2O3, Nb-doped TiO2, and F-doped SnO2.

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1. A method of a detecting a change in a chemical composition of a gas stream comprising: placing a doped oxide material in the gas stream, where the gas stream has a temperature of at least 100° C., and where the doped oxide material comprises a doped metal oxide, where the doped metal oxide has a

1. A method of a detecting a change in a chemical composition of a gas stream comprising: placing a doped oxide material in the gas stream, where the gas stream has a temperature of at least 100° C., and where the doped oxide material comprises a doped metal oxide, where the doped metal oxide has a carrier concentration of at least 1018/cm3, a bandgap of at least 2 eV, and an electronic conductivity of at least 101 S/cm at a temperature of 25° C.;contacting the doped metal oxide with a monitored stream, where the monitored stream is at least a portion of the gas stream, and where the monitored stream has a temperature of at least 100° C.;illuminating the doped metal oxide with a light source emitting incident light;collecting exiting light, where the exiting light is light that originates at the light source and is transmitted, reflected, scattered or a combination thereof by the doped metal oxide;monitoring an optical signal based on a comparison of the incident light and the exiting light using optical spectroscopy; anddetecting a shift in the optical signal, thereby detecting the change in the chemical composition, and thereby monitoring the chemical composition of the gas stream. 2. The method of claim 1 where the doped metal oxide has an empirical formula MaOb where M comprises one or more elements and where O comprises an oxygen anion. 3. The method of claim 2 where the doped metal oxide has an empirical formula AyBxOz, where A is a first element and B is a second element. 4. The method of claim 3 where the first element, the second element, and the oxygen anion form a crystalline structure having a crystalline lattice, where the crystalline lattice is cubic, hexagonal, tetragonal, rhombohedral, orthorhombic, monoclinic, or triclinic, and where the first element, the second element, and the oxygen anion occupy special positions within crystalline lattice. 5. The method of claim 4 where the doped metal oxide comprises Zn1-xAlxO3, In2-xSnxO3, Ti1-xNbxO2 or mixtures thereof. 6. The method of claim 2 where the gas stream has a temperature of at least 200° C., and where the monitored stream has a temperature of at least 200° C. 7. The method of claim 6 where the optical signal is a signal-averaged optical signal, and where the shift in the optical signal is detected when an observed signal-averaged optical signal is at least 0.1% greater or lesser than an initial signal-averaged optical signal. 8. The method of claim 6 where the change in the chemical composition is an increased concentration of a reducing gas, and where the shift in the optical signal is an increase in transmission at a specific wavelength. 9. The method of claim 6 where the exiting light has an optical signal edge between 250 and 550 nanometers, and where the shift in the optical signal comprises a shift in the optical signal edge. 10. The method of claim 6 where the exiting light has an optical signal edge between 1000 and 3750 nanometers, and where the shift in the optical signal comprises a shift in the optical signal edge, and where the change in the chemical composition is an increased concentration of a reducing gas, and where the shift in the optical signal edge is a shift to a lower wavelength. 11. The method of claim 6 where the doped oxide material has an rms surface roughness of at least 15 nanometers. 12. The method of claim 6 where the change in the chemical composition a change in the concentration of a reducing gas, where the reducing gas comprises H2, CO, NH3, a hydrocarbon, or mixtures thereof. 13. The method of claim 6 where the change in the chemical composition is a change in the concentration of an oxidizing gas, where the oxidizing gas comprises O2, O3, NOx, SOx, a halogen, a halogen compound, a sulfuric acid, a nitric acid, a nitrate, or mixtures thereof. 14. The method of claim 2 where the gas stream is comprised of a molecular gas constituent, and further comprising: utilizing a barrier layer, where the barrier layer material has a first surface and a second surface, where the first surface and the second surface are separated by at least some portion of the barrier layer; andcontacting the first surface of the barrier layer and the gas stream, and withdrawing the monitored stream from the second surface of the barrier layer. 15. The method of claim 2 further comprising: providing a waveguide comprised of a core material;placing the doped oxide material in contact with the core material; andemitting the incident light from the light source into the core material and illuminating the doped metal oxide, thereby illuminating the doped metal oxide with the light source emitting the incident light. 16. A method of determining a concentration of a chemical species in the monitored stream using the method of claim 1, further comprising: placing a sensing head of an instrument in the monitored stream, where the doped oxide material comprises the sensing head and where the doped oxide material is in fluid communication with the monitored stream, thereby contacting the doped metal oxide with the monitored stream;emitting incident light using an interrogator in optical communication with the doped oxide material comprising the sensing head and illuminating the doped oxide material, and gathering exiting light using the interrogator in optical communication with the doped oxide material, and comparing the optical signal based on a comparison of the incident light and the exiting light with optical spectroscopy using the interrogator, thereby illuminating the gas sensing oxide material with the light source emitting incident light, collecting exiting light, and comparing the incident light and the exiting light using optical spectroscopy;generating a measurand using the interrogator based on the comparing the incident light and the exiting light, and communicating the measurand to a meter in data communication with the interrogator;receiving the measurand at the meter and displaying a meter reading on the meter based on the measurand, and observing the meter reading, thereby generating an observed meter reading, and thereby monitoring the optical signal based the comparing the incident light and the exiting light;evaluating a difference between the observed meter reading and a reference meter reading; andassigning a value to the concentration of the chemical species in the monitored stream based on the difference between the observed meter reading and the reference meter reading, thereby determining the concentration of the chemical species in the monitored stream. 17. A method of a detecting a change in a concentration of a reducing gas in a gas stream comprising: generating the gas stream, where the gas stream comprises the reducing gas, and where the gas stream has a temperature of at least 200° C.;placing a doped oxide material in a gas stream, where the doped oxide material comprises a doped metal oxide, where the doped metal oxide has an empirical formula MaOb where M comprises one or more elements and where O comprises an oxygen anion, and here the doped metal oxide has a carrier concentration of at least 1019/cm3, a bandgap of at least 2 eV, and an electronic conductivity of at least 102 S/cm at a temperature of 25° C.;contacting the doped metal oxide with a monitored stream, where the monitored stream is at least a portion of the gas stream, and where the monitored stream comprises the reducing gas, and where the monitored stream has a temperature of at least 200° C.;illuminating doped metal oxide with a light source emitting incident light;collecting exiting light, where the exiting light is light that originates at the light source and is transmitted, reflected, or a combination thereof by the doped metal oxide;monitoring an optical signal based on a comparison of the incident light and the exiting light using optical spectroscopy; anddetecting a shift in the optical signal, thereby detecting the change in the concentration of the reducing gas in the gas stream. 18. The method of claim 17 where the doped metal oxide has an empirical formula AyBXOz, where A is a first element and B is a second element, where the first element, the second element, and the oxygen anion form a crystalline structure having a crystalline lattice, where the crystalline lattice is cubic, hexagonal, tetragonal, rhombohedral, orthorhombic, monoclinic, or triclinic, and where the first element, the second element, and the oxygen anion occupy special positions within the crystalline lattice. 19. The method of claim 18 where the doped metal oxide is a non-stoichiometric oxide. 20. The method of claim 18 where the where doped metal oxide has a carrier concentration of at least 1019/cm3, a bandgap of at least 2 eV, and an electronic conductivity of at least 102 S/cm at a temperature of 25° C. following an elevated temperature reducing treatment, where the elevated temperature treatment comprises contacting the doped metal oxide for a period of at least one hour with a gaseous mixture having a composition of 4 vol. % H2/balance N2, where the gaseous mixture is at a temperature of at least 100° C.