Ln³⁺ 4f Energy Levels in CaTiO₃ Analyzed by XPS Measurements

Abstract

The energy levels of Ln 3þ 4f ground states in CaTiO 3 are analyzed using X-ray photoelectron spectroscopy (XPS). The Ln 4f states in the XPS spectra are extracted utilizing large photoionization cross section differences between Ln 4f and O 2p states. The Ln 3þ 4f energy levels referred to the valence band maximum are evaluated to be 0.8 eV for Pr 3þ , À5.0 eV for Gd 3þ , 0.9 eV for Tb 3þ , and À4.6 eV for Lu 3þ from the extracted XPS spectra. Although the obtained values of Gd 3þ and Lu 3þ 4f levels are deeper in the valence band, the values of Pr 3þ and Tb 3þ 4f levels are in good agreement with those reported previously. The difference in the photoluminescence colors between Pr 3þ -doped CaTiO 3 and CaZrO 3 is simply explained from the Pr 3þ 4f energy levels located in the bandgaps.

Energy Diagrams of Lanthanide Energy Levels in Perovskite‐Type Calcium‐Based Double Oxides Examined by X‐Ray Photoelectron Spectroscopy

“…In CaTiO 3 , the Gd 3+ ground level became shallower than that in the previous study because the energy was evaluated referring to the calculated one, which is slightly shallower than the Gd 3+ peak top energy. [ 52 ] The other data for Pr 3+ , Tb 3+ and Lu 3+ in this study agreed well with those in the previous one on the accuracy level within ≈±0.1 eV, even if the samples were newly prepared in this study. The energy of Ln 3+ 4 f levels for the other materials were evaluated in the same way and the values for the Gd 3+ and Tb 3+ 4 f ground levels are shown in Table 1.…”

“…The zigzag curve for Ln 3+ 4 f energy levels referred to the experimental Tb 3+ 4 f level agreed well with the experimental values for Pr 3+ in CaMO 3 , which is similar to the previous results for CaTiO 3 and YAlO 3 . [ 18,52 ] In addition, the experimental data for the deep energy levels of Gd 3+ and Lu 3+ in this study agreed with the zigzag curves much better than the previous one, [ 52 ] even though slight deviation remained. The improvements were made from both experimental and theoretical aspects.…”

“…Although these luminescent perovskite-type materials are anticipated for various applications, the information of the Ln 4f levels referred to the HLs is scarcely available so far in these materials except for CaTiO 3 . [25,52] In this study, the Ln 4f energy levels in the perovskite-type Cabased double oxides, CaMO 3 (M ¼ Ti, Sn, Zr, Hf ), were examined systematically to understand the luminescence properties of Ln 3þ ions in these materials. The energy gaps were evaluated from the absorption spectra of the nondoped materials, then the CT energy for Eu 3þ and the 4f-5d transition energy for Pr 3þ or Tb 3þ were estimated from the PLE spectra of the doped materials.…”

“…Although these luminescent perovskite‐type materials are anticipated for various applications, the information of the Ln 4 f levels referred to the HLs is scarcely available so far in these materials except for CaTiO 3 . [ 25,52 ]…”

Host Lattice-Excitation-Enhanced Photoluminescence in Eu3+-Doped LaInO3 Epitaxial Films

“…Photoluminescence (PL) of perovskite-type oxide phosphors is triggered by not only the direct excitation of luminescent center ions but also by indirect excitations due to interband transitions in the host lattice (HL). − The interband transition energy of the HL can be changed in the range of approximately 3–5 eV via the substitution of B -site ions (mainly with Ti, Zr, and Sn) or A -site ions (alkaline earth and lanthanoid metals), , and the wide band gap makes the HL a band insulator. The combination of the electronic structure of the host materials and the 4f energy levels of luminescent center ions such as Eu 2+ , Eu 3+ , Pr 3+ , and Tb 3+ allows perovskite-type oxide phosphors to exhibit various emission colors . For example, numerous perovskite-type oxide phosphors have been reported, such as Pr-doped Ca 0.6 Sr 0.4 TiO 3 (deep-red emitted), O-deficient SrTiO 3 (blue), Tb–Mg-codoped CaSnO 3 (green), , Sm-doped SrZrO 3 (orange), Cr-doped La 2 MgZrO 6 (near-infrared), and Eu- or Tb-doped CaZrO 3 (tricolored) .…”