Pb valence in iron garnets

Abstract

A model for the incorporation of Pb in garnets is presented in which self-compensation occurs via the formation of Pb2+ and Pb4+ and allows an explanation of the following observations: high levels of Pb substitution achievable, the temperature dependence of Pb incorporation, lattice mismatch behavior of epitaxial films of Pb-doped iron garnets, the Pb-induced uniaxial anisotropy behavior in EuIG : Pb, the electrical conductivity type, and the high Pb-induced optical absorption. Spectroscopic evidence for the simultaneous existence of Pb2+ and Pb4+ in Y3Ga5O12 (YGG) is given and analyzed in terms of Pb2+, Pb4+ impurity levels lying respectively 1.1 eV above the valence band and 2.36 eV below the conduction band. Intervalence transition between Pb2+ and Pb4+ occurs at 18 000 cm−1 (2.23 eV) in YGG : Pb. Using the separation of Pb2+ and Pb4+ levels determined in YGG and a simple energy-band model for YIG the Pb-induced absorption processes in YIG : Pb are enumerated and shown to give a qualitative explanation of the absorption spectrum of YIG : Pb.

Luminescence of dimer lead centers in aluminium perovskites and garnets

“…Pb 2+ ions. In [25], it was concluded that in this case the charge and volume of a Pb 2+ ion in the garnet lattice are both compensated by a much smaller Pt 4+ ion located in the Al 3+ site, and, hence, no other defects would be necessary to compensate the Pb 2+ , this being provided by the Pt 4+ . However, recent ESR studies [26] have shown that trivalent Pt 3+ ions are incorporated into the garnet lattice at a concentration of about several hundreds ppm which is comparable with the total Pt content in the SCF studied.…”

“…Pb 2+ -based centers of the type of {Pb 2+ -Pb 4+ } In the SCF of garnets with a very large lead content, Pb 4+ ions can also exist [25]. The Pb 2+ and Pb 4+ ions can be localized in dodecahedral positions of the garnet lattice, and in this case they have ionic radii 1.29 Å and 0.94 Å, respectively [24].…”

“…The sum of their ionic radii (2.33 Å) exceeds the sum of the radii of two Lu 3+ (1.96 Å) or Y 3+ (2.03 Å) ions, thus, the total excess volume remains uncompensated. According to [25], a wide (FWHM ≈ 1 eV) absorption band of Y 3 Ga 5 O 12 :Pb with a large lead content, arising from the charge-transfer transitions in the 〈111〉-type {Pb 2+ -Pb 4+ } pairs, is located in the visible spectral range (at 2.23 eV). However, no such band is detected in the YAG and LuAG SCF studied.…”

Time-resolved luminescent spectroscopy of YAG:Ce single crystal and single crystalline films

“…2) consist: (i) the band peaked at 7.95 eV related to the onset of YAG interband transition (Zorenko et al, 2007a); (ii) the dominant bands peaked in 6.67-6.885 eV range, corresponding to the formation of exciton bound with the Ce 3þ ions; (iii) the band peaked at 5.67 eV, related to 4f-5d( 3 T 2g ) transition of Ce 3þ ions; (iv) the band peaked 4.74 eV, caused by the 1 S 0 / 3 P 1 transition of Pb 2þ flux dopant in the SCF (Scott and Page, 1977). Due to Y Al AD presence and formation of Ce-AD coupled centers, the excitation spectra of Ce 3þ luminescence in YAG:Ce SC (Fig.…”

Bi3+–Ce3+ energy transfer and luminescent properties of LuAG:Bi,Ce and YAG:Bi,Ce single crystalline films

“…As the result of ADs elimination, the YAG:Ce and LuAG:Ce SCF phosphors show considerably better timing characteristics under excitation in the range of interband transition with respect to their bulk SC analogues [11,12]. At the same time, at the preparation of SCF by LPE method usually from PbO-based fluxes, lead ions are also introduced into the garnet lattice [16,17] and can influenced on the luminescent and scintillation properties of rare-earth doped SCF phosphors. Namely, the influence of Pb-related centers on the luminescence of Ce 3+ and Pr 3+ ions in YAG and LuAG SCF, grown from PbO-based flux, were investigated in details in our previous works [17][18][19][20].…”