The structure, IR absorption, luminescence, and luminescence excitation spectra of La0.99xYxEu0.01BO3 orthoborates (0 ≤ x ≤ 0.25) synthesized at 970°С were studied at 0 ≤ x ≤ 0.99. An increase in х leads to a sequential change of the structural state of these compounds. At 0 ≤ x ≤ 0.1, the samples are single-phase and have the aragonite structure. Within the range of 0.1 < x ≤ 0.8, the samples are two-phase: the vaterite phase is observed along with the aragonite structure. At 0.8 < x ≤ 0.99, the samples are single-phase and have the vaterite structure. Correspondence between the structure and spectral characteristics of these compounds was established. It is demonstrated that with an increase in the Y3+ concentration, the vaterite phase is formed first in the bulk of microcrystals having the aragonite structure and then in the entire sample. It is shown for the first time that a band with the maximum of 469 nm is observed in the luminescence excitation spectrum (LES) of samples having the vaterite structure and is absent in samples having the aragonite structure. It is revealed that a band in the luminescence spectrum, corresponding to the 5D0→7F0 electron transition, as well as 469-nm-band in the LES, can be an indicator of the structural state of the sample.

The structure, IR absorption and luminescence spectra, and morphology of Lu0.99xSmxEu0.01BO3 (0 ≤ x ≤ 0.99) orthoborates synthesized at 970°С were studied. With an increase in the Sm3+ concentration, a successive change of five structural states is observed: calcite (0 ≤ x ≤ 0.1) → calcite + vaterite (0.1 < x < 0.3) → vaterite (0.3 ≤ x ≤ 0.95) → vaterite + a triclinic phase (0.95 < x ≤ 0.98) → a triclinic phase (0.98 < x ≤ 1). A wide range of Sm3+ concentrations at which the vaterite phase (0.3 ≤ x ≤ 0.95) exists and a very narrow region of triclinic phase formation (0.98 < x ≤ 1) are important distinctive features of this system. Correspondence between the structure and spectral characteristics of these compounds was established. It is shown that the vaterite phase appears in the bulk of the microcrystals of the samples that have a calcite structure.