Why do the PL spectra of indirect band gap semiconductor (for example Sb2S3） have to be tested at low temperatures?
PL normally at low temperature for semiconductors are easily resolved for the band to band transitions, specifically on the band edges. As temperature increases, PL becomes broaden and difficult to distinguish the peaks.
There are many references which you could find out the reasons. Hope it helps.
PL from indirect bandgap semiconductors involves phonons since there is a momentum mismatch between the crystal momentum at the band extrema and photon momentum.
At low temperatures you expect the phonon population to be low and hence the indirect bandgap PL is expected to be weaker than say at room temperature. However, the PL spectra are usually better resolved at low temperatures due to suppression of thermal broadening. Also at higher temperatures one may have other thermally activated non-radiative recombination processes. Thus, one may have to select an optimum temperature depending on the material, to best observe the indirect bandgap PL.
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