# How photoluminescence (PL) spectroscopy works

Photoluminescence (PL) spectroscopy is used to find the energy levels in a compound but how does PL spectroscopy works? After exciting a material with a particular wavelength whether PL machine looks for photons emitted with in a range of wavelenght?

The below image was taken from here.

To get this spectra the $\ce{CeO2}$ was excited at 345 nm and got peaks at 490 and 520 nm(approx) ie 2.53 and 2.38 eV respectively and its band gap is 3 eV. Whats happening here?

• What is the question? The experimental procedure? The theory in general? The reason for the shift? The analysis of CeO2 in particular?
– Greg
Dec 4 '15 at 10:34