Synthesis and crystal structure of Ln2M2+Ge4O12, Ln=rare-earth element or Y; M=Ca, Mn, Zn

Structural chemistry and magnetic properties of Ln MnFeGe 4 O 12 ( Ln = Y, Eu, Lu)

“…The bond-valence sums around Ln in the germanates are calculated to be 3.46, 3.53 and 3.28, again suggesting that these cations are in relatively compressed environments; the degree of "over-bonding" increases with the ionic radius of Ln 3+ . This is consistent with the failure of ourselves and others [17] to prepare isostructural germanates containing Ln 3+ cations larger than Eu 3+ . The near-constancy of the Ge -O and mean Mn/Fe -O bond lengths, see Table 2, might lead to a description of the structure as a framework of fixed-size octahedra and tetrahedra with Ln 3+ cations occupying a set of 8coordinate holes.…”

Experimental and computational study of the magnetic properties of ZrMn2−xCoxGe4O12

“…The principal phase apparent in the XRPD pattern of every sample could be indexed in the tetragonal space group P4/nbm; the refined unit cell parameters are listed in Table 1. The intensity distribution in the XRPD, exemplified by that of ZrCo2Ge4O12 in Figure 3, was consistent with the crystal structure previously assigned to Y2CaGe4O12 22 with the 2b site now occupied by Zr 4+ and the 4f site by a disordered distribution of divalent transition-metal cations. The XRPD patterns collected from samples of ZrCo2Ge4O12 and ZrMn0.5Co1.5Ge4O12 contained weak Bragg peaks, see Figure 3, from a CoGeO3 impurity phase.…”

Upconversion luminescence in Er3+/Yb3+ codoped Y2CaGe4O12

“…One of the ways to effect the emission, caused by lower excitation energy, is the use of multiphonon-assisted processes originating from inelastic scattering on vibrations in a host matrix. This effect has been found in many rare-earth doped systems [ [19], Ca [20], Mn [21], Zn [22]. Pow-0925-8388/$ -see front matter © 2010 Elsevier B.V. All rights reserved.…”

“…Y2CaGe4O12, Er2CaGe4O12 and Yb2CaGe4O12 powder samples were synthesized by the traditional high-temperature solid state reaction as described elsewhere [20,22], the starting materials were Ln2O3, Ln = Er, Yb, Y (99.99%), CaCO3 (99.9%), and GeO2 (99.99%). The quality of erbium and ytterbium oxides was proved by optical absorption spectra in visible and near-infrared (NIR) range.…”

“…Recently synthesized compounds of the new group of calcium tetrametagermanates Ln 2 CaGe 4 O 12 , Ln = Y, Eu, Gd, Dy-Lu, crystallize in S.G. P4/nbm, Z = 2, keeping the similar cycles in the structure. Layers of discrete [Ge 4 O 12 ] 8− cycles alternate with layers of metal ions (1/2Ca + 1/2Ln) in distorted octahedral coordination, and lanthanide ions are in square antiprism coordination [22].…”