Dr. ERNEST BEHRINGER
PHOTOLUMINESCENCE SPECTROSCOPY
Background
When light impinges on material objects, scattering or absorption of the incident light may occur. Sometimes the absorption of light can be followed by the emission of light, possibly of a different wavelength (color). By measuring the emitted light, it is possible to gain information about the characteristics of the material -- and this is the basic idea behind photoluminescence spectroscopy. In other words: send light in, measure the light that comes out, and the measurements tell you about the material. The information gained can provide insight on how to improve the material. The materials that I study are semiconductors, which are very important in optoelectronics (e.g., in displays, lighting applications, lasers, etc.).
Experiments
Photoluminescence spectroscopy experiments are carried out in the Modern Optics Lab. The organization of the experiment is as is shown in the figure below [insert jpg]. Light from a source (such as a laser) is directed towards a semiconducting sample that is housed in a small vacuum chamber. The chamber has glass windows to permit light to enter and exit, and also has a central hollow reservoir to contain liquid cryogens (such as liquid nitrogen) to enable the sample to be cooled. (Cooling the sample makes the photoluminescence process more likely.) The emitted photoluminescence is collected by a lens and transported optically to a grating spectrometer. Together with a sensitive detector, the spectrometer enables the amount of photoluminesce to be measured as a function of its wavelength. An example of a photoluminescence spectrum is shown below. This was the first fairly optimized spectrum obtained by an undergraduate student who was using a helium-neon laser to excite a gallium arsenide sample. [insert jpg]
Interested?
If you have approximately 8-10 hours a week to work in the laboratory, you might consider doing an independent study project in which you measure the photoluminescence spectra of various semiconducting samples. It will take a significant portion of a semester to learn the necessary laboratory techniques and experimental procedures. On the other hand, you can expect to obtain significant insight into what it takes to succeed.
