We report the measurement of the variation of the value of the linewidth of
an excitonic transition at 4 K in InyGa1-yAs1-xNx alloys (1% and 2% nitrog
en) as a function of hydrostatic pressure using photoluminescence spectrosc
opy. We find that the value of the excitonic Linewidth increases as a funct
ion of pressure until about 100 kbar after which it tends to saturate. This
change in the excitonic linewidth is used to derive the pressure variation
of the exciton reduced mass using a theoretical formalism based on the pre
mise that the broadening of the excitonic transition is caused primarily by
compositional fluctuations in a completely disordered alloy. The variation
of this derived mass is compared with the results from a nearly first-prin
ciples approach in which calculations based on the local-density approximat
ion to the Kohn-Sham density-functional theory are corrected using a small
amount of experimental input.