Time Resolved Raman Experiment
About the Equipment:
The set up includes two lasers, which deliver short pulses of intense light to a sample. The first is used to push the material into its excited state and the second to analyse its structure and properties. The time lapse between the two pulses can be adjusted to probe different points during the material’s relaxation back to its rest state. Times can be pinpointed with nanosecond resolution. The wavelengths of the two lasers can also be adjusted separately to allow each to resonate with excited states in different materials. The CCD detector used to record the Raman signal has a shutter to block out unwanted light from the first laser or fluorescence. This ensures a very good signal to noise ratio.
Otago chemist Keith Gordon is researching Organic Light Emitting Diodes (OLED’s) – organic molecules that emit light. They show great potential for applications such as flexible efficient light sources which could be painted on to large walls or surfaces to give gentle diffuse light. To improve the light emitting properties of OLED’s it is essential to understand their excited state. Now the group can track every slight change in structure and electronic behaviour as the molecules relax back into their ground state. The data you get out of the time resolved Raman experiment is extremely complicated but the group’s expertise in computational chemistry allows them to unlock its meaning. Keith believes that their new capability will fast forward the research process, assist in funding applications and help the group produce more papers.
With the strong combination of time resolved Raman spectroscopy, computational chemistry and synthesis, the group now has a powerful set of skills to offer collaborators. The new equipment spurred a collaboration with a group in Queensland who were trying to improve the properties of a solar cell material without success. With the new equipment, Keith was able to confirm their suspicions that the key excited state structure was different from that generally thought to be important. By giving them the correct structure he put them on the right track. “Having this new equipment definitely helps keep students here,” says Keith. “They see that it is new and that there’s the expertise and time to use it – a situation often rare in overseas labs.” Keith suggests that because the set-up is complicated and fiddly to use and the chance of blowing a hole in the sample or your eye is quite good, it is easier if people send them the samples to analyse. However, if someone is interested in using the technique as a major part of their project, the group will be happy to train them.