Site-Selective Eu³⁺ Doping and Enhanced Luminescence from Eu³⁺ at B Sites in Perovskite-Type Strontium Zirconate and Hafnate

Abstract

To achieve efficient Eu 3+ luminescence, site-selective doping of Eu 3+ was attempted in perovskite-type (ABO 3 ) SrMO 3 (M = Zr, Hf). In contrast to CaMO 3 and BaMO 3 , it was found that the doping sites of Eu 3+ (Eu Sr• or Eu Zr ′ /Eu Hf ′ ) could be highly controlled in SrMO 3 by a codoping technique. This was mainly because the size of Sr 2+ was suitable for the site-selective doping of Eu 3+ in SrMO 3 . The codoping of small Ga 3+ at B sites (Ga Zr ′ /Ga Hf ′ ) was carried out for A-site doping of Eu 3+ , whereas the codoping of large La 3+ at A sites (La Sr• ) or small Nb 5+ at B sites (Nb Zr• /Nb Hf • ) was conducted for B-site doping of Eu 3+ . As a result, the proportion of Eu 3+ at A and B sites became more than 90% by the Asite and B-site doping, respectively, from the analysis of X-ray absorption near-edge structures for the Eu L 3 edge. Eu 3+ ions were driven to intentional sites by codoping due to the dual effects of charge compensation and ionic size balance. The high Eu 3+ proportion at B sites, viz. the almost complete B-site doping, led to the findings of significant enhancement of Eu 3+ luminescence, which was derived from the magnetic dipole transitions from 5 D 0 to 7 F 1 states. The quantum efficiencies of the enhanced luminescence from SrMO 3 doped with Eu 3+ at B sites exceeded 50% at room temperature.

Variable Photoluminescence Intensity Ratio with the Excitation Wavelength in Eu3+-Doped Perovskite-Type Alkaline Earth Zirconates─Possibility of a Unique Visualization of Ultraviolet Light

“…These peaks of the SZO:Eu sample were characterized based on both sets of reference data, and such characterized peaks were also observed for other AZO:Eu samples (Figure S4). Therefore, the obtained XANES spectral features implied that Eu 3+ was located at both the A and B sites in the perovskite-type AZO:Eu samples, consistent with the XANES spectral results for Eu 3+ -doped single perovskite-type oxides reported by Ueda et al , …”

“…For the PLE spectra of site-selective Eu 3+ -doped SrZrO 3 that were prepared by codoping technique, CT bands attributed to Eu 3+ at the B site and the A site were observed at 235 and 305 nm, respectively. 21 Therefore, the obtained band at 230 nm was attributed to the CT band for Eu 3+ located at the B site, and the band at 300 nm was due to CT by Eu 3+ at the A site. In addition, this difference in CT energies for Eu 3+ at the A and B sites was responsible for the observed change in the PL spectra shown in Figure 3.…”

“…Therefore, the CT energy for Eu 3+ at the B site was greater than that for Eu 3+ at the A site, because of the shorter Eu–O bond length at the B site. For the PLE spectra of site-selective Eu 3+ -doped SrZrO 3 that were prepared by codoping technique, CT bands attributed to Eu 3+ at the B site and the A site were observed at 235 and 305 nm, respectively . Therefore, the obtained band at 230 nm was attributed to the CT band for Eu 3+ located at the B site, and the band at 300 nm was due to CT by Eu 3+ at the A site.…”

“…Perovskite-type zirconates AeZrO 3 (Ae: alkaline earth metal) are suitable candidates for the host lattice because AeZrO 3 has band gap energies in the ultraviolet (UV) region that are higher than the CT energies, and the A and B sites are different in terms of the presence or absence of a center of symmetry as well as bond lengths, except for cubic BaZrO 3 . In addition, Eu 3+ could be unintentionally substituted at both sites in CaZrO 3 and SrZrO 3 . , In this study, Eu 3+ -doped AeZrO 3 were prepared via the Pechini method, and the PL and PLE spectra were evaluated at various excitation wavelengths. The results show changes in the PL spectra caused by various excitations via CT of Eu 3+ at both the A and B sites.…”

“…In addition, Eu 3+ could be unintentionally substituted at both sites in CaZrO 3 and SrZrO 3 . 20,21 In this study, Eu 3+ -doped AeZrO 3 were prepared via the Pechini method, and the PL and PLE spectra were evaluated at various excitation wavelengths. The results show changes in the PL spectra caused by various excitations via CT of Eu 3+ at both the A and B sites.…”