A systematic study of o-Ps intensity quenching by different wavelength of SWIR light was performed for a set of n-alkanes which form different crystal structures. The maximal wavelength able to quench was determined for two temperatures. The results for odd- and even-numbered alkanes were compared from this point of view. A systematic decrease in the maximal wavelength with shortening the carbon chain was found. Two kinds of traps were observed in the alkanes with chain length exceeding 30 carbon atoms, one kind only in the shorter ones. It was found that in a binary mixture of alkanes the traps are shallower than in the neat ones.