Module VI
Optical Spectroscopy
Learning Objectives
Optical characterization methods
Photoluminescence set up
Energy levels in nanoparticles
Absorption spectrometry
Spectroscopic ellipsometry Introduction
• The term “spectroscopy” was first coined in 1666, when Sir Isaac Newton demonstrated the dispersal of white light through a prism into different colors. Contemporaries thought they were looking at ghosts and called themselves “ghost watchers.”
• “Ghost” in Latin is spectrum, while “watcher” in Greek” is scopos – hence the term
“spectroscopy.”
• Spectroscopy is basically the measurement of the interaction of light with various materials. By analyzing the amount of light absorbed or emitted by a sample, we can determine what it’s made of and how much of it there is.
Technique Synopsis Solid State Physics
Absorption spectrometry Scan λin , measure intensity of transmission.
Optical absorption, band gap, energy level spacing
Photoluminescence (PL) Fixed λin (laser), scan λout Optical recombination transitions.
Photoluminescence Excitation (PLE) Fix λout , scan λin (tunable laser or monochromator)
Sensitive to transitions that
“pump” optical emissions.
Raman scattering Laser in, scan λout very close to λin
Stokes/anti-Stokes peaks provide information about phonon energies.
