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

Abstract

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.