Biexciton luminescence from CuGaS2 bulk single crystals

New photoluminescence from CuGaS2 appeared at the lower energy side of the free exciton luminescence under high excitation. The time-resolved spectrum of this luminescence at 0–20 ps after the excitation fits quite well with the calculated spectrum of the luminescence from the biexciton with the binding energy of 4.5±0.5 meV. Its time-integrated luminescence intensity was proportional to the excitation intensity to the power of ∼2.