Photon emission from defects are generally associated with [1]:
         i) forward and reverse biased pn junctions,
         ii) transistors in saturation,
         iii) dielectric breakdown.

[1] Barton DL, Tangyunyong P, Soden JM, Liang AY, Low FJ, Zaplatin AN, Shivanandan K, Donohoe G, "Infrared Light Emission from Semiconductor Devices", Proc Int Symp Testing & Failure Analysis (ISTFA 1996), 18-22 Nov 96, Los Angeles, California, USA, pg 9-17, 1996.