The absorption spectra of Nd3+ in pure anhydrous neodymium chloride crystals and in anhydrous praseodymium chloride crystals (containing 0.1% NdCl3) have been examined systematically examined. The structures of the groups of their absorption lines are found to be similar to those of Nd3+ in NdCl3 crystals diluted by LaCl3 (containing 2% NaCl3 in LaCl3), except for a shift of the spectrum towards the long wave side. The shifts (relative to the ground state) of these corresponding sub-levels are proportional to the length of unit cell of the single crystals.