Spectroscopic study of the TbAl3(BO3)(4) single crystal: Raman and luminescence spectroscopy

The vibrational and luminescence properties of the TbAl₃(BO₃)₄ single crystal were studied in the temperature range of 5–300 K. Raman spectra of the single crystal revealed 5 of 7 A₁ and all E phonon modes predicted by the group-theory analysis. The splitting energy between the LO and TO components of polar E phonons is determined. A group of intense bands associated with the ⁵D₄ → ⁷F₀ electronic transition was observed in the energy range of 14520–14680 cm⁻¹ of the luminescence spectra. The intensity of these bands decreases upon heating. At the same time, the bands which can be assigned with ⁵D₄ → ⁷F₆, ⁵D₄ → ⁷F₅, and ⁵D₄ → ⁷F₄ transitions were revealed in luminescence spectra at room temperature. The intensity of these bands is comparable to the intensity of the Raman spectrum of TbAl₃(BO₃)₄. The observation of luminescence from the ⁵D₄ multiplet (20600–20750 cm⁻¹) upon excitation at λ_exc = 632.8 nm (15803 cm⁻¹) and λ_exc = 532 nm (18797 cm⁻¹) indicates strong nonlinear properties of the studied crystal. The structure of the main ⁷F₆ multiplet of Tb⁺³ in the TbAl₃(BO₃)₄ single crystal has been studied at 5 K by Raman spectroscopy. The energies of the electronic levels of ⁷F₆ and ⁵D₄ multiplets were determined from the luminescence spectra measured at 300 K.