Abstract <p>Subsolidus phase equilibria in the La₂O₃–Y₂O₃–SrO system at temperatures up to 1350°C were studied. The La_{1 –} _<i>x</i>Sr_<i>x</i>YO_{3 – δ} (<i>x</i> = 0–0.26) solid solutions and SrY₂O₄-base solid solutions extending between 0 and 15 mol % La₂O₃, between 28 and 50 mol % Y₂O₃, and between 50 and 70 mol % SrO were found to exist in the system. The phase equilibria in the La₂O₃–Y₂O₃–SrO system are comparable to those known to occur in its boundary binary systems. Vibrational spectra and X-ray luminescence spectra (XLS) of La_{1 –} _<i>x</i>Sr_<i>x</i>YO_{3 – δ} solid solutions were recorded. The IR spectra featured the existence of OH^– groups captured by the crystal lattice in La_{1 –} _<i>x</i>Sr_<i>x</i>YO_{3 – δ} samples. <i>F</i> centers were shown to be formed in the perovskite structure, and the luminescence spectral characteristics of these centers were considered. The X-ray luminescence intensity of <i>F</i> centers is proposed as a criterion to estimate the extent of capture of OH groups by the perovskite lattice.</p>