Ground rules defining design of triboluminescent (TL) materials are currently missing, in part since the triboluminescent efficiency is the product of the efficiency of excited-state formation and the efficiency of radiative relaxation from these excited-states. In order to de-couple these two processes, we have measured, for the first time, the solid-state photoluminescent quantum yield of various triboluminescent materials. The measurements highlighted: (i) some triboluminescent materials possess near-optimised radiative yields; (ii) structurally similar triboluminescent compounds can exhibit widely varying yields and (iii) some triboluminescent materials, which appear to the eye as reasonably efficient, possess low radiative yields, allowing possible triboluminescent enhancement.