The effects of chemical etching in KI solution, heating, and vacuum exposures of HgI2were individually studied by low‐temperature photoluminescence (PL) spectroscopy. Each of these processing steps is important in the manufacturing of mercuric iodide detectors and may be responsible for the incorporation of carrier traps both in the near‐surface region and in the bulk. The results of etching experiments showed that the near‐surface region has a different defect structure than the bulk, which appears to result from iodine deficiency. Bulk heating at 100 °C also modifies the defect structure of the crystal. Vacuum exposure has an effect similar to chemical etching, but it does not cause significant degradation of the stoichiometry for recently KI‐etched specimens. These studies suggest that some features in the PL spectra of HgI2are associated with stoichiometry of the specimens.