VUV-UV excited luminescent properties of LnCa_4O(BO_3)_3:RE~(3+) (Ln = Y, La, Gd; Re = Eu, Tb, Dy, Ce)

摘要

Calcium lanthanide oxyborate doped with rare-earth ions LnCa_4O(BO_3)_3:RE~(3+) (LnCOB:RE, Ln = Y, La, Gd, RE = Eu, Tb, Dy, Ce) was synthesized by the method of solid-state reaction at high temperature. Their fluorescent spectra were measured from vacuum ultraviolet (VUV) to visible region at room temperature. Their excitation spectra all have a broadband center at about 188 nm, which is ascribed to host absorption. Using Dorenbos' and Jorgensen's work [P. Dorenbos, J. Lumin. 91 (2000) 91, R. Resfeld, C.K. Jorgensen, Lasers and Excite States of Rare Earth [M], Springer, Berlin, 1977, p. 45], the position of the lowest 5d levels E(Ln, A) and charge transfer band E_(ct) were calculated and compared with their excitation spectra. Eu~(3+) and Tb~(3+) ions doped into LnCOB show efficient luminescence under VUV and UV irradiation. In this system, Ce~(3+) ions do not show efficient luminescence and quench the luminescence of Tb~(3+) ions when Tb~(3+) and Ce~(3+) ions are co-doped into LnCOB. GdCOB doped with Dy~(3+) shows yellowish white light under irradiation of 254 nm light for the reason that Gd~(3+) ions transfer the energy from itself to Dy~(3+) . Because of the existence of Gd~(3+), the samples of GdCOB:RE~(3+) show higher excitation efficiency than LaCOB:RE~(3+) and YCOB:RE~(3+), around 188 nm, which indicates that the Gd~(3+) ions have an effect on the host absorption and can transfer the excitation energy to the luminescent center such as Tb~(3+), Dy~(3+) and Eu~(3+).