Identification of spin wave resonances and crystal field levels in simple chromites RCrO3 (R = Pr, Sm, Er) at low temperatures in the THz spectral region

•Pr3+ non-Kramers in PrCrO3 emerges at 100 K and Zeeman splits.•Absence of spin wave resonances in PrCrO3 attributed to Pr3+ remaining paramagnetic.•Resonances in SmCrO3 harden decreasing temperature and split under applied fields.•In ErCrO3 the Er3+ Kramers doublet is active at about the spin resonance temperature.•Er3+ smaller ion size disrupts the two magnetic sublattice hypothesis.