A series of potassium lanthanum praseodymium ternary chlorides, K 2 La 1Àx Pr x Cl 5 , (0.02 6 x 6 0.15) single crystals was grown with Bridgman techniques. The structures of the mixed crystals were found isotypic with that of K 2 PrCl 5 and K 2 LaCl 5 . The high resolution absorption, luminescence and excitation spectra were recorded at 4, 77 and 293 K. Broad band emission of Pr 3+ reabsorbed by the 3 H 4 ! 3 P J , 1 D 2 transitions was observed simultaneously with the emission from the 3 P 0 level after excitation in the UV region. The 4f 1 5d 1 level scheme derived from the absorption, excitation spectra and from VUV synchrotron excitation was partly established. The 4f 2 energy level scheme of the Pr 3+ ion in K 2 PrCl 5 consisting of 86 (out of 91) Stark components determined from the absorption and emission spectra was simulated by using a phenomenological crystal field model. The model including eight free ion and nine crystal field parameters (according to the C 2v symmetry) yielded a rms deviation of 17 cm À1 between the experimental and calculated energy level schemes. Magnetic susceptibility measurements were carried out between 2 and 298 K. Good agreement was obtained between the experimental and calculated paramagnetic susceptibilities as a function of temperature by using the van Vleck formalism and the energies and wave functions derived from the spectral data.