Spectral characteristics and energy transfer from Ce$^{3+}$ to Tb$^{3+}$ in compounds Lu$_{1-x-y}$Ce$_{x}$Tb$_{y}$BO$_{3}$

The structure, IR absorption spectra, morphology, and spectral characteristics of compounds Lu$_{1-x-y}$Ce$_{x}$Tb$_{y}$BO$_{3}$ have been investigated. It has been shown that the Tb$^{3+}$ luminescence excitation spectrum of the Lu$_{1-x-y}$Ce$_{x}$Tb$_{y}$BO$_{3}$ compounds is dominated by a broad band coinciding with the excitation band of Ce$^{3+}$ ions, which clearly indicates energy transfer from the Ce$^{3+}$ ions to the Tb$^{3+}$ ions. The spectral position of this band depends on the structural state of the sample: in the structures of calcite and vaterite, the band has maxima at $\sim$339 and $\sim$367 nm, respectively. By varying the ratio between the calcite and vaterite phases in the sample, it is possible to purposefully change the Tb$^{3+}$ luminescence excitation spectrum, which is important for the optimization of the spectral characteristics of Lu$_{1-x-y}$Ce$_{x}$Tb$_{y}$BO$_{3}$ when it is used in light-emitting diode sources. An estimate has been obtained for the maximum distance between Ce$^{3+}$ and Tb$^{3+}$ ions, which corresponds to electronic excitation energy transfer. It has been shown that the high intensity of Tb$^{3+}$ luminescence in these compounds is due to the high efficiency of electronic excitation energy transfer from the Ce$^{3+}$ ions to the Tb$^{3+}$ ions as a result of the dipole–dipole interaction.