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When doing a Photoluminescence measurement on a Cu2O material with band gap 2.1 eV, a peak is obtained at 2.1 eV and around 1.95 eV. The exciton binding energy of Cu2O is 150 meV.

Is the 1.95 eV peak coming from the free exciton recombination? If so, what is the 2.1 eV peak due to? Can that still be due to band to band recombination if we assign 1.95 eV peak to free excitons?

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Above the band gap energy, semiconductor possess fairly spectrally broad absorption. This is because there are many electronic states which can couple to the photon that preserve energy and momentum.

The exciton peak will be much narrower than the band to band transitions because it is essentially a single energy state; although it is broadened by various processes.

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