Interconfigurational d-f luminescence of Pr³⁺ ions in praseodymium doped Li₆Y(BO₃)₃ single crystals

Luminescence properties of undoped Li₆Y(BO₃)₃ (LYB) crystals grown by the Bridgman method as well as undoped and praseodymium doped LYB crystals grown by the Czochralski method were studied under excitation by ultraviolet light, synchrotron radiation and electron beam in the temperature region of 5–300 K. The emission bands peaking at 4.8, 3.76 and 2.95 eV were found in undoped Czochralski-grown crystals, while the band at 3.34 eV was dominant in the Bridgman-grown crystals. These bands are presumably ascribed to excitons localized at regular and defect-perturbed lattice sites. Intense emission bands peaking at 4.75, 4.50, 4.17 and 3.98 eV were discovered in Pr doped crystals at low temperatures and related to the interconfigurational 4f¹5d¹ → 4f² radiative transitions in Pr³⁺ ions. The structure of the emission spectrum is shown to be determined by the ³H₄, ³H₅, ³H₆, ³F₂, ³F₃, ³F₄ terms of the Pr³⁺ ion. The characteristic decay time of the 4f¹5d¹ → 4f² emission is τ = 24 ns at low temperatures, however, it shortens to 9 ns by room temperature due to a strong thermal quenching. The study of glow curves and spectra of thermostimulated luminescence in Li₆Y(BO₃)₃:Pr crystal irradiated by 10-keV electron beam shows that Pr³⁺ ions do not participate in an electron-hole recombination process.