Correlation between Refractive Index Dispersion Parameters and Cation Coordination Numbers in Fluoride Crystals

— Refractive index dispersion parameters of optical crystals of MF n (M n + = Na + , K + , Ca 2+ , Sr 2+ , Ba 2+ , Cd 2+ , Pb 2+ , La 3+ , Ce 3+ , Pr 3+ , Nd 3+ ) binary fluorides have been shown to correlate with the cation coordination numbers in their structures. Using this correlation, I have demonstrated that, with increasing LaF 3 concentration, the cation coordination number in Sr 1 − x La x F 2 + x ternary fluoride crystals (fluorite structure) increases from 8 to 11.