AbstractLow temperature (from 4.2 up to 30 K) photoluminescence spectra of InSe crystals containing macroscopic inclusions of neutral slightly soluble impurities (gadolinium, anthracene, fluorene etc.) are studied. The inclusions are of 0.1 to 0.5 μm in size. A substantial rise (by one or more orders in magnitude with respect to the initial spectrum of undoped crystals) of the exciton luminescence intensity is observed at relatively moderate doping doses (the impurity concentration less than 0.5 wt%) in the region of longitudinal exciton frequency ωL. To explain this effect a model is developed, which takes into account the scattering of lower branch polaritons at macroinclusions and their transformation into polaritons of the upper branch without changes in energy. The calculated temperature and frequency dependences of upper polariton branch luminescence are close to those measured experimentally despite of the practically non‐parametric way of the calculati