Site Dependence of Tb³⁺ Luminescence in Double Perovskite-Type Alkaline Earth Lanthanum Tantalates

Abstract

Tb 3+ doped alkaline earth lanthanum tantalates with the B-site-ordered double perovskite-type structure (AA')[BB']O 6 (namely (CaLa 1-x Tb x)[CaTa]O 6 (CLTO:Tb 3+) and Ba 2 [La 1-x Tb x Ta]O 6 (BLTO:Tb 3+) with x =0.01, 0.10) were prepared and their Tb 3+ photoluminescence (PL) properties were examined and explained based on the occupied crystal sites (A or B sites). The location of Tb 3+ activators were elucidated by analyzing powder X-ray diffraction patterns and X-ray absorption near edge structure at the Tb L III edge. Tb 3+ ions are located at A sites in the CLTO:Tb 3+ and at B sites in the BLTO:Tb 3+ as indicated in the nominal compositions. Both CLTO:Tb 3+ and BLTO:Tb 3+ exhibited intense PL excitation (PLE) peaks in the UV region due to the 4f−5d excitation for Tb 3+. The PLE peak of Tb 3+ in BLTO:Tb 3+ showed a marked red shift compared to that in CLTO:Tb 3+ primarily because of the larger crystal field at the B sites than at the A sites. The main PL peaks associate with the 4f−4f transitions from 5 D 4 to 7 F 5 states are also influenced by the crystal field and the splitting of the PL peaks for Tb 3+ at B sites in BLTO:Tb 3+ is more pronounced than for Tb 3+ at A sites in CLTO:Tb 3+. In addition, owing to a downshift of the Tb 5d orbitals, the PL in the blue region derived from 5 D 3-7 F J transitions are quenched for Tb 3+ in BLTO:Tb 3+ .

Site-Dependent Eu3+ Photoluminescence in Double Perovskite-Type Alkaline Earth Lanthanum Tantalates

“…The decay curves for CLTO:Eu 3+ are not largely dependent on the temperatures between RT and LNT, whereas those for BLTO:Eu 3+ showed conspicuous temperature dependence implying that the Eu 3+ PL from B sites is largely influenced by the lattice vibrations. Although these results are similar to the Tb 3+ doped samples reported previously, 51 the temperature dependence for the present Eu 3+ doped samples is notably larger than the one for the Tb 3+ doped samples.…”

Site-Dependent Luminescence from Pr3+ in Double-Perovskite-Type Alkaline Earth Lanthanum Tantalates

“…To understand site-dependent Pr 3+ PL systematically, Pr 3+ ions were directly excited through the 4f−5d transitions in Pr 3+ in both CLTO:Pr 3+ and BLTO:Pr 3+ as previously done in Tb 3+ -doped HLs. 39 Although the PL spectra on the HL excitation (λ ex = 220 and 230 nm) were also measured at 298 K, they were very similar to those on the 4f− 5d excitation except the PL intensities, indicating that the energy transfer from the HLs to Pr 3+ occurred smoothly at 298 K.…”

“…The overall spectral features between CLTO:Pr 3+ 1% and CGTO:Pr 3+ 1% or between BLTO:Pr 3+ 0.2% and SGTO:Pr 3+ 0.2% were almost unchanged because of the same crystal structure of the HLs and the same Pr 3+ locations. To understand site-dependent Pr 3+ PL systematically, Pr 3+ ions were directly excited through the 4f–5d transitions in Pr 3+ in both CLTO:Pr 3+ and BLTO:Pr 3+ as previously done in Tb 3+ -doped HLs . Although the PL spectra on the HL excitation (λ ex = 220 and 230 nm) were also measured at 298 K, they were very similar to those on the 4f–5d excitation except the PL intensities, indicating that the energy transfer from the HLs to Pr 3+ occurred smoothly at 298 K.…”

“…The features of the PLE spectra for Pr 3+ -doped CLTO and BLTO were very similar to those for Tb 3+ -doped ones. 39 The PLE peak for the 4f−5d excitation in BLTO:Pr 3+ was obviously red-shifted against that in CLTO:Pr 3+ . Because the ground energy levels of Pr 3+ and Tb 3+ are usually analogous to each other in the electronic structure of similar HLs, 50−53 the PLE spectral features will be also understood as reported in Tb 3+ -doped cases.…”

“…We previously examined PL from Eu 3+ and Tb 3+ at not only A sites but also B sites utilizing double-perovskite-type oxides, (AA')[BB']O 6 , and observed the site-dependent luminescence. 39,40 Ta]O 6 (x = 0.00, 0.002, 0.005, 0.01, 0.10), respectively. The powders of the starting materials were weighed in the stoichiometric amount, and they were mixed in an agate mortar with ethanol and dried.…”