We have observed at 4.2 K the emission of biexcitons in CuCl (the $M$ emission) created via two-photon absorption under a weak excitation condition by means of a high-repetition-rate (82-MHz) picosecond-tunable uv light source obtained by sum frequency generation. The spectral shape and the time response are measured. The results are quite different from the previous work measured under stronger excitation conditions and show that the lifetime of the biexcitons is short, about 30 ps, and they experience no momentum relaxation at this temperature.

• Received 9 February 1989

DOI:https://doi.org/10.1103/PhysRevB.39.12973