Investigations on the Temperature‐Dependent TPA Linewidth of the Z3‐Exciton in CuCl

The two‐photon absorption (TPA) line of the longitudinal Z3(1s) exciton in CuCl is studied in the temperature region between 4.6 and 185 K. The longitudinal exciton component has a Lorentzian‐like lineshape in the quoted temperature interval. The halfwidth of the narrow absorption line, which is approximately 0.14 meV below 10 K, increases rapidly for temperatures above 60 K (14 meV at 185 K). The steep increase is correlated with the number of thermally excited LO phonons. The temperature‐dependent halfwidth, which can be fitted by a Bose function with the energy of the LO phonon mode (26.3 meV), is found to be proportional to the LO phonon density. From this it is concluded that the lifetime of the Z3‐exciton is mainly determined by an intraband scattering process caused by the absorption of a longitudinal optical phonon.