Crystal structure and the optical spectral properties of 0.5 at.% Nd3+, 5 at.% Gd3+-codoped Ca1-xSrxF2 (0 <= x <= 1) crystals grown by the temperature gradient technique (TGT) were investigated. The linear variations of the crystal structure and spectral parameters as a function of Sr2+ proportion (x) were observed and correlated with each other. The results indicated that Sr2+ ions introduced as matrix-substituted ions could regulate the crystal structures and the spectroscopic properties.