Enlarged Site Determination Signals of Eu³⁺ for Tracking Structural Phase Transition in Terbium-Rich TbSc₃(BO₃)₄ Borate

Phase transitions exert profound effects on luminescent behavior, while conversely, luminescence can serve as an effective probe for monitoring phase transitions. Trivalent europium ions (Eu3+) are well-known lattice probes since their nondegenerate 5D0–7F0 transition directly reflects the number of nonequivalent crystallographic sites in host materials. However, the emission intensity of the 5D0–7F0 transition in general compounds is typically too weak for reliable detection under ambient conditions. Herein, La3+ and Eu3+ codoped terbium-rich TbSc3(BO3)4 phosphor was prepared and studied for the first time. Through efficient energy transfer from Tb3+ to Eu3+, the newly generated peak of Eu3+ occupying the LaSc3(BO3)4 phase can be distinctly observed in lattice site resolution spectra, evidencing the phase transition induced by the small amount of La3+. Considering that a small amount of Eu3+ in the LaSc3(BO3)4 phase can hardly give detectable emission intensity of the 5D0–7F0 transition, the enlarged site resolution ability can be ascribed to an efficient Tb3+→Eu3+ energy transfer inside the LaSc3(BO3)4 phase. In other words, the phase tolerance of TbSc3(BO3)4 by LaSc3(BO3)4 prompts the enlarged site resolution ability of Eu3+ in this terbium-rich inorganic compound. This discovery may propose a complementary spectroscopic approach for tracking structural transformations.