Doping symmetry

Finally we recall that in the Sr-doped system the maximum Tc is achieved for a Sr content of 0.15, which corresponds to a formal valence per Cu of 2.15 (i.e., 0.15 holes per Cu). In the Ce-doped system the maximum in Tc (24K) is achieved for a Ce content of 0.15, which corresponds to a formal valence per Cu of 1.85 (i.e., 0.15 electrons per Cu). Thus, a maximum Tc occurs in the n-type materials at the same electron concentration as the hole concentration in the p-type materials which produces a maximum Tc and indicates a doping symmetry. The symmetry between the n-type and p-type materials is further reflected in Figure 4 where we have shown that... 

For the alkali metal doped Cgo compounds, charge transfer of one electron per M atom to the Cgo molecule occurs, resulting in M+ ions at the tetrahedral and/or octahedral symmetry interstices of the cubic Cgo host structure. For the composition MaCgg, the resulting metallic crystal has basically the fee structure (see Fig. 2). Within this structure the alkali metal ions can sit on either tetragonal symmetry (1/4,1/4,1/4) sites, which are twice as numerous as the octahedral (l/2,0,0) sites (referenced to a simple cubic coordinate system). The electron-poor alkali metal ions tend to lie adjacent to a C=C double... 

The two extremes of ordering in solids are perfect crystals with complete regularity and amorphous solids that have little symmetry. Most solid materials are crystalline but contain defects. Crystalline defects can profoundly alter the properties of a solid material, often in ways that have usefial applications. Doped semiconductors, described in Section 10-, are solids into which impurity defects are introduced deliberately in order to modify electrical conductivity. Gemstones are crystals containing impurities that give them their color. Sapphires and rubies are imperfect crystals of colorless AI2 O3, red. 

The determination of the electronic structure of lanthanide-doped materials and the prediction of the optical properties are not trivial tasks. The standard ligand field models lack predictive power and undergoes parametric uncertainty at low symmetry, while customary computation methods, such as DFT, cannot be used in a routine manner for ligand field on lanthanide accounts. The ligand field density functional theory (LFDFT) algorithm23-30 consists of a customized conduct of nonempirical DFT calculations, extracting reliable parameters that can be used in further numeric experiments, relevant for the prediction in luminescent materials science.31 These series of parameters, which have to be determined in order to analyze the problem of two-open-shell 4f and 5d electrons in lanthanide materials, are as follows. 

Although symmetry considerations often permit g- and hyperfine matrix principal axes to be non-coincident, there are relatively few cases of such noncoincidence reported in the literature. Most of the examples discussed by Pilbrow and Lowrey in their 1980 review36 cite cases of transition metal ions doped into a host lattice at sites of low symmetry. This is not to say that matrix axis non-coincidence is rare but that the effects have only rarely been recognized. 

Okubo et al. have used Stark spectroscopy to study the unusual trinuclear complex salt (76) which has pseudo D3h symmetry and contains tetrahedral Cu1 centers and a symmetrical hexa-azatriphenylene-derived radical anionic ligand.139 The x responses of PMMA thin films doped with (76) are enhanced by an intense, broad MLCT transition which has a maximal absorbance in the NIR region.139... 

Finally, we note that, to the best of our knowledge, only one report exists about EPR spectra of non-Kramers lanthanide ions in molecular magnets. In 2012, Hill and coworkers [51] performed a multifrequency study on powder and single crystal samples of NagHofWgOj H20, in both the pure form and when doped into the isostructural Y3+ derivative. While crystallizing in a triclinic unit cell, the symmetry of the lanthanide ion in this family is very close to Did. For this reason, susceptibility data had been previously fitted by a purely axial Hamiltonian [50]. 

Eu3+-doped LaCl3 (C3h or D3h), LaA103 (D3) and La203 (C3v) have also been studied (145). In LaCl3, there are no off-diagonal elements between/-orbitals (in the pseudo-symmetry D3h) in the other compounds, two off-diagonal elements arise. 

Yttrium aluminum borate, YAlj (603)4 (abbreviated to YAB), is a nonlinear crystal that is very attractive for laser applications when doped with rare earth ions (Jaque et al, 2003). Figure 7.9 shows the low-temperature emission spectrum of Sm + ions in this crystal. The use of the Dieke diagram (see Figure 6.1) allows to assign this spectrum to the " Gs/2 Hg/2 transitions. The polarization character of these emission bands, which can be clearly appreciated in Figure 7.9, is related to the D3 local symmetry of the Y + lattice ions, in which the Sm + ions are incorporated. The purpose of this example is to use group theory in order to determine the Stark energy-level structure responsible for this spectrum. 

Measurements on single crystals of lower symmetry doped with NpO or PuOl" " should remove this uncertainty but no such experiment has been performed so far. However, the distinction between configurations (a) and (b) has been possible in an electron paramagnetic resonance study at 20 K on a single uniaxial crystal of RbU02(N03)3 doped with plutonyl ions. This study conclusively showed that the ground state is H4 with gy = 5.4 and g = 0 28). 

When KMnO is mixed with MnCl2,4H20 in cone. HCl followed by the addition of [Co(en)3]Cl3 at — 10"C, [Co(en)3][MnCl ],H20 is formed. Spectroscopic and magnetic properties = 4.94 BM at 293 K) have been reported. Polarized crystal spectra of MnClj" have been reported. The results indicate 2, symmetry for (bipH2)[MnCl5] (bipH2 = bipyridinium ion) and symmetry when Mn is doped into (Et N)2lnCl5. ... 

Alexandrite, the common name for Cr-doped chrysoberyl, is a laser material capable of continuously tunable laser output in the 700-800 nm region. It was established that alexandrite is an intermediate crystal field matrix, thus the non-phonon emitting state is coupled to the 72 relaxed state and behaves as a storage level for the latter. The laser-emitted light is strongly polarized due to its biaxial structure and is characterized by a decay time of 260 ps (Fabeni et al. 1991 Schepler 1984 Suchoki et al. 2002). Two pairs of sharp i -lines are detected connected with Cr " in two different structural positions the first near 680 nm with a decay time of approximately 330 ps is connected with mirror site fluorescence and the second at 690 nm with a much longer decay of approximately 44 ms is connected with inversion symmetry sites (Powell et al. 1985). The group of narrow lines between 640 and 660 nm was connected with an anti-Stokes vibronic sideband of the mirror site fluorescence. 

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