Effects of Codoping on Site-Dependent Eu³⁺ Luminescence in Perovskite-Type Calcium Zirconate and Hafnate

Abstract

The single doping of Eu3+ and codoping with Ga3+ or La3+ into perovskite (ABO3)-type CaZrO3 and CaHfO3 were carried out to investigate the effect of codoping on the photoluminescence (PL) features of Eu3+, attempting the site-selective Eu3+ doping at either A or B sites. To comprehend the Eu3+ PL features, the accurate locations of Eu3+ were examined by X-ray absorption near edge structure (XANES) and the proportions of Eu3+ located at A or B sites (Eu3+(A) or Eu3+(B); EuCa • or EuZr ′/EuHf ′) were analyzed. No considerable differences in the XANES spectra and in the proportions of Eu3+(A) and Eu3+(B) were observed in the single-doped samples. On the other hand, the shape of the XANES spectra and the Eu3+ proportion markedly differed in the codoped samples. Ga3+ codoping (GaZr ′/GaHf ′) achieved Eu3+(A) proportions of more than 90%, and La3+ codoping (LaCa •) resulted in the largest Eu3+(B) proportions of approximately 40%. In both PL and PL excitation spectra, the site-dependent spectral features were changed depending on the proportion of Eu3+(A) and Eu3+(B), especially the PL peaks at 595 nm were intensified most in the La3+ codoped samples. Consequently, the site-dependent Eu3+ PL features in CZO and CHO were found to become more conspicuous by the effect of Ga3+ or La3+ codoping. The results also revealed that the codoped ions work not only to compensate for the charge of aliovalent Eu3+ but also to drive Eu3+ to the intentional doping sites.

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

“…In the single-doped samples, Eu 3+ ions were located at both A and B sites and Eu 3+ (A) was found to be dominant not only in SMO:Eu 3+ (A) but also in SMO:Eu 3+ (B). Although the A-site preference of Eu 3+ remained slightly in SMO:Eu 3+ (B), it was not so strong as observed in CMO:Eu 3+ (B) . The results verified that the self-compensation occurred in the single-doped samples by some Eu 3+ moving to antisites unintentionally.…”

“…Because both the proportions of Eu 3+ (A) in the Ga 3+ -codoped samples and those of Eu 3+ (B) in the La 3+ - or Nb 5+ -codoped samples exceeded 90%, almost complete site-selective doping of Eu 3+ was demonstrated in the HLs of SZO and SHO. The results were in contrast to those for Eu 3+ -doped CZO and CHO . The locations of the Eu 3+ ions were also compared with those for Eu 3+ -doped LaLuO 3 because the Eu 3+ locations in SMO were controlled by not only the ionic size but also the valence.…”

“…However, two different spectral shapes of photoluminescence (PL) were obtained probably because the charge compensation by La 3+ and B-site doping of Eu 3+ were not satisfactory. Similar difficulties in the site-selective doping of Eu 3+ were also reported in BaHfO 3 . , Therefore, the actual occupation sites of Eu 3+ ions and the accurate PL properties and efficiencies have not been understood sufficiently. − Because Eu 3+ ions are often incorporated at either A or B sites unintentionally in the perovskite-type zirconates, − highly controlled site-selective doping of Eu 3+ is essential to obtain the expected high luminescence efficiency.…”

“…Actually, two types of Eu 3+ were observed in BZO even though B-site doping was carried out with La 3+ codoping at A sites for charge compensation . We lately attempted site-selective doping of Eu 3+ in CZO and found that Eu 3+ were located at both A and B sites with A-site preference in Eu 3+ single-doped CZO . Although almost complete A-site doping of Eu 3+ was achieved by Ga 3+ codoping, B-site doping was incomplete in spite of La 3+ codoping.…”

“…7 We lately attempted siteselective doping of Eu 3+ in CZO and found that Eu 3+ were located at both A and B sites with A-site preference in Eu 3+ single-doped CZO. 14 Although almost complete A-site doping of Eu 3+ was achieved by Ga 3+ codoping, B-site doping was incomplete in spite of La 3+ codoping. The insufficient B-site doping of Eu 3+ in CZO and BZO is attributed to much smaller and larger sizes of Ca 2+ and Ba 2+ ions, respectively, which change not only the space of A sites but also some interstitial space between ions.…”