Congruently melting Ca0.77Sr0.07La0.16F2.16 and Ca0.70Sr0.11Ce0.19F2.19 fluorite solid solutions crystals in the CaF2–SrF2–RF3 (R = La, Ce) systems have been grown from melt by the Bridgman technique in a fluorinating atmosphere. Their optical, mechanical, electrophysical, and thermophysical characteristics have been studied. The crystals are transparent in a wide spectral range; their refractive indices are nD = 1.468 (R = La) and 1.479 (R = Ce), and their microhardness (НV ∼ 5.0 GPa) and ionic conductivity (σ ∼ 3 × 10–3 S/cm at 823 K) exceed significantly the corresponding values for CaF2 and SrF2 crystals. The materials under study are promising isomorphic-capacious crystalline matrices for various applications in photonics and solid-state ionics.