A hyperlinear increase of radiative quantum efficiencies of poly(para-phenylene)-type ladderpolymer in the blue–green region as a function of subpicosecond excitation intensity is reported. The light emission in the range from 485 to 495 nm undergoes a change from linear behavior to a second order response; the two regimes are separated by a distinct threshold of 3.1mJ/cm2.Above this threshold, investigation by femtosecond excitation–correlation measurements indicate that the hyperlinear blue emission is associated with a characteristic excitonic depopulation of 2 ps. ©1997 American Institute of Physics.