Optical photons not traveling through boundary

I am trying to implement scintillation, but I cannot get the optical photons to leave the volume in which they are created. My understanding is that optical surfaces are not needed as long as all materials have had their rindex specified, but the photons either get reflected or stop entirely at the boundary of my scintillator.
Running /process/optical/boundary/verbose 2 shows that every photon that hits a boundary and is not reflected has an interaction length of 1.79769e+307 cm, and the message at the end says StepTooSmall

Is there something else I need to specify? I have abslength, rindex, scintillation properties.