1.As a result of the search for new materials for solid state diode pumped lasers operating in the mid infrared region at room temperature, a family of low symmetry crystals of double halides of an alkali metal and lead APb 2 Cl 5 (where A = K, Rb) was found. These crystals feature chemical stability, low hygroscopicity, narrow phonon spectrum, and possible activation by rare earth ions.The space group of these crystals is P2 1 /c (P12 1 /c1); according to [1,2], the APb 2 Cl 5 structure contains two inequivalent lead ion sites with triclinic symmetry (C 1 ). The nearest environment of one site (Pb2 in the notation of [1]) is a "tricapped" trigonal prism with a coordination number (CN) of 9 (Fig. 1a). The other site (Pb1) is in the distorted bicapped octa hedron (CN = 7). In [3], as a result of the study of the KPb 2 Cl 5 structure, it is proposed to represent the envi ronment of these two lead sites (Pb2, Pb1) as bicapped (due to remoteness of one of ligands) (CN = 8) and monocapped (CN = 7) trigonal prisms. The authors of [4] attribute only six chlorine ions with R < 0.3 nm to the nearest environment of Pb1 in KPb 2 Cl 5 and con sider the coordination number of Pb2 to be equal to 7 ("umbrella" of five chlorine ions with R ≈ 0.3 nm and two ions with distances of 0.315 and 0.321 nm). Taking into account the ratio of ionic radii and charge states of a rare earth element, lead, and rubidium, it can be expected that exactly the lead site will be substituted with rare earth ions.The authors of the optical study of KPb 2 Cl 5 :Nd 3+ [4] and measurements of the high frequency EPR of Tb 3+ ions in KPb 2 Cl 5 [5] assume that rare earth ions are mostly localized at Pb1 sites. In this case, in [5], it was considered that the substitution of lead at the site Pb1 with the Tb 3+ ion is accompanied by the forma tion of a vacancy of one of the nearest K + ions.The authors of [6] studied RbPb 2 Cl 5 with dyspro sium and bismuth impurities in order to determine localization of rare earth ions and mechanisms of their charge compensation using broadband EPR spectroscopy. These measurements did not allow a final conclusion about the Dy 3+ localization in RbPb 2 Cl 5 .2. In the same samples (RbPb 2 Cl 5 :1.0 wt % DyCl 3 ), we detected an EPR spectrum of high spin (S = 7/2) rare earth Gd 3+ ion (Fig. 2), existing in the crystal as an uncontrolled impurity (<0.01%). The single crys tals under study were grown by the Bridgman method in quartz ampules [7]. Measurements were performed using a Bruker EMX Plus spectrometer operating in the 3 cm range at room temperature.As seen in Fig. 2, the spectrum of Gd 3+ centers is well described by the strong magnetic field approxima tion. The weak satellites observed near seven allowed (Δm = 1, m is the electron spin projection) transitions can be caused by both sample mosaicity and twinning. Similar satellites are observed in other magnetic field orientations. The orientation behavior of the positions of the main spectrum transitions in three crystallo graphic planes is shown in Figs. 3-5. Splittin...
1.In the recent study [1] of Pb 5 (Ge 1 -x Si x ) 3 O 11 solid solution crystals doped with gadolinium, it was found that the trigonal electron paramagnetic reso nance (EPR) spectrum of single Gd 3+ ions observed in Pb 5 Ge 3 O 11 is split into four spectra with strongly broadened lines. It was shown that these spectra are associated with the triclinic Gd 3+ -Si dimer centers; the Gd 3+ ions of these complexes substitute for the Pb 2+ ions; and the Si 4+ ions are located in the positions of the nearest germanium spheres. Models of the localization of silicon ions were proposed for all the observed Gd 3+ -Si centers. It is obvious that the pres ence of silicon ions in more distant germanium spheres also disturbs the spectrum of Gd 3+ ions. It is the existence of a large number of variants of the sub stitution Si 4+ Ge 4+ in these spheres that is respon sible for the strong broadening of the transitions of the triclinic dimer centers.In [1], it was ignored that the EPR spectrum in the region of the resonances -1/2 +1/2 of Gd 3+ -Si centers in the vicinity of the orientation B || C 3 (B is the magnetic induction) demonstrates an anomalous shape and behavior with a deviation from B || C 3 and that, in a wide vicinity of the coincidence of the tran sitions ±1/2 ±3/2, there is an additional signal [2][3][4][5]. This work is devoted to the study of the aforemen tioned features in the EPR spectrum of Gd 3+ centers in single crystals of the Pb 5 (Ge 0.85 Si 0.15 ) 3 O 11 solid solu tions.2. We studied Pb 5 (Ge 0.85 Si 0.15 ) 3 O 11 single crystals grown by the Czochralski method from the charge containing 0.01 mol % gadolinium [1]. The fraction of silicon in the charge during the growth coincided, within the limits of experimental error, with the results of comparison of the peak intensities of the X ray luminescence lines of lead and germanium in crystals with silicon and without it. The structure of the Pb 5 Ge 3 O 11 single crystal, which undergoes a second order ferroelectric structural transition P3 at a temperature of 450 K, was investigated in [6,7]. The EPR spectra were recorded on a Bruker EMX Plus X band (3 cm) EPR spectrometer at temperatures in the range from 100 to 450 K. The temperature of the sample was measured and maintained constant with an accuracy of ±1 K. 3.The change in the shape of the first derivative of the absorption spectrum in the region of the transi tions -1/2 +1/2 of Gd 3+ -Si centers with a devia tion from the orientation B || C 3 is illustrated in Fig. 1. The character of the orientation changes of the spec trum does not depend on the microwave power, even though at a power higher than 1 mW the saturation effects similar to those observed in other transitions become noticeable. It should be noted that, in the magnetic field range shown in Fig. 1, there are unre solved transitions -1/2 +1/2 of four triclinic cen ters (Gd Si 1, Gd Si 2, Gd Si 3, and Gd Si 4 in the notation used in [1]), each represented by three signals of the structurally equivalent but differently oriented com plexes. T...
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