The need for cleaner energy systems, including CO<
sub>
2<
/sub>
capture technologies, is driving the current development of chemical looping technologies such as chemical looping combustion (CLC) and chemical looping gasification (CLG). Specific processes that are under development for using solid fuels are in-situ Gasification Chemical-Looping Combustion (iG-CLC) and Chemical Looping with Oxygen Uncoupling (CLOU). Chemical looping is based on using oxygen carriers (e.g., iron oxides, copper oxides, calcium sulfates, etc.) to provide the oxygen for the reaction with the fuel. In order to optimize the overall process performance, it is critical that the properties of the oxygen carriers are well-defined and maintained for their specific purpose during the different stages of the CLC process. One of the critical properties of the oxygen carrier is its oxidation state (e.g., content of Fe<
sub>
2<
/sub>
O<
sub>
3<
/sub>
vs. Fe<
sub>
3<
/sub>
O<
sub>
4<
/sub>
) as it affects the fundamental operation of the CLC process. Unfortunately, the ability to make on-line measurements of the oxidation state of oxygen carriers is lacking and new sensors need to be developed. The goal of this project was to evaluate the potential of Raman spectroscopy as a sensor for the on-line analysis of the oxidation state of oxygen carrier particles. Oxygen carrier particles (OCPs) of interest include iron oxides, copper oxides, calcium sulfite, and calcium sulfate, with particle sizes typically less than 0.5 mm diameter. The expected operating conditions of the sensor include OCP temperatures in the range of 800 �C to 1000 �C, and pressures of about 10 atm. We evaluated continuous wave (cw), Quasi cw, pulsed, and time-gated Raman spectroscopy at multiple wavelengths (355 nm, 360 nm, 532 nm, 633 nm, 785 nm). Samples included iron oxides, copper oxides, calcium sulfate, and a custom sample provided by NETL for temperatures beyond 1000 �C. Our findings can be summarized as follows: Calcium sulfate can be detected via cw and pulsed 532 nm Raman spectroscopy at temperatures above 1100 �C. Hematite (Fe<
sub>
2<
/sub>
O<
sub>
3<
/sub>
) Raman spectra can be detected at temperatures of 700 �C via cw 360 nm, 1089 �C with cw 532 nm, 400 �C with cw 633 and 600 �C with cw 785 nm lasers. Magnetite (Fe<
sub>
3<
/sub>
O<
sub>
4<
/sub>
) can be detected via cw 532 nm Raman spectroscopy up to 600 �C. Mixtures of Fe<
sub>
2<
/sub>
O<
sub>
3<
/sub>
and Fe<
sub>
3<
/sub>
O<
sub>
4<
/sub>
can be distinguished for temperatures up to 600 �C using 532 nm. Copper oxides did not yield suitable signals at elevated temperatures. The custom NETL samples did not yield suitable signals at elevated temperatures. Raman spectroscopy would be a suitable approach for calcium sulfate as this material provides a very strong Raman signal at high temperatures. Oxygen carrier particles of higher interest such as metal oxides, however, do not yield a strong-enough signal at elevated temperatures. As such, Raman spectroscopy is not suitable to differentiate the oxidation state of these materials at temperatures above 600 �C.