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In this article, we describe our high-pressure infrared (IR) spectroscopy techniques for studying the electronic structures of materials at high pressures. High pressure of up to 20 GPa is applied to a sample using a diamond anvil cell (DAC). To accurately perform IR spectroscopy in the limited sample space of a DAC, synchrotron radiation is used as a bright IR source. Our techniques allow reflectance studies of a single crystal sample and determination of the optical functions of the sample such as dielectric function and optical conductivity. To illustrate the capability and usefulness of our techniques, some actual results of high-pressure IR studies on rare-earth compounds are described.

Infrared synchrotron radiation (IR-SR) is a highly brilliant white light source. We are developing an infrared near-field spectroscopy system with an IR-SR light source. The near-field spectroscopy system previously reported comprised an atomic force microscope (AFM) and a commercial Fourier transform infrared (FTIR) spectrometer. In the present study, the configuration of the FTIR interferometer has been modified to an asymmetric one. In the asymmetric interferometer, one beam split by a beamsplitter is focused onto the tip of an AFM probe, and the other beam goes to a movable mirror. The scattered light from the probe and the light reflected by the movable mirror interfere with each other. The near-field signal is extracted by a modulation method with an AFM oscillation frequency. The signal-to-noise ratio has been improved 6-fold and the signal-to-background ratio is improved 8-fold compared with those observed in the previous system.

We embedded CdSe nanocrstallites into a porous glass with a diffusion process. Using picosecond time resolved luminescence spectrum technique, we investigated the electron dynamics in the CdSe microcrystallites in porous glass. The luminescence decay of our sample has a fast component decay sensitive to temperature. For a sample of CdSe microcrystallites with an average size of 25 Å diameter, the fast decay is 50 ps at 77 K, and is 100 ps at 2 K. With a simple three level model, the luminescence decay is simulated. The temperature dependence of luminescence decay results from nonradiative process.