Structural, electronic, and optical studies of BaRE₂Ge₃O₁₀ (RE = Y, Sc, Gd–Lu) germanates with a special focus on the [Ge₃O₁₀]⁸⁻ geometry

Abstract

A new series of BaRE2Ge3O10 trigermanates crystallizing in the monoclinic system (S.G. P21/m) has been characterized by various methods.

Structural, electronic and optical properties of BaRE6(Ge2O7)2(Ge3O10) (RE = Tm, Yb, Lu) compounds and BaYb6(Ge2O7)2(Ge3O10):Tm3+ and BaLu6(Ge2O7)2(Ge3O10):Yb3+,Tm3+ phosphors: potential applications in temperature sensing

“…According to the literature data, the geometry of the [Ge 3 O 10 ] unit may change significantly in different compounds. 35 In most cases, it is distorted and asymmetric, as, for example, in the structures of CaRE 2 Ge 3 O 10 (RE = Y, La-Yb), Ag 8 Ge 3 O 10 , and Ca 4 (Ge 3 O 10 )•H 2 O. [36][37][38] However, for a number of compounds, including BaRE 2 Ge 3 O 10 (RE = Y, Sc, Gd-Lu), K 2 B 2 Ge 3 O 10 , Rb 2 Ga 2 Ge 3 O 10 , and Ca 7.96 Cu 0.04 Ge 5 O 18 , the presence of a 2-fold rotation axis or mirror plane, residing on the central germanium atom of the [Ge 3 O 10 ] group, has been reported.…”

BaYb2 – xErxGe3O10 and BaY2 – 10yYb9yEryGe3O10: Luminescent Properties and Prospects for Applications in Remote Temperature Determination

“…4. The numerical values of the energies of excited states were calculated using the published results of measurements of the diffuse reflectance spectra for the BaYb 2 Ge 3 O 10 and BaEr 2 Ge 3 O 10 samples [19]. According to the above diagram, the conversion of optical radiation with λ ex = 980 nm proceeds in accordance with the model proposed by Auzel in 1966 [24] and is determined by summation of several primary electronic excitations of Yb 3+ ions on Er 3+ ions emitting light quanta with higher energy.…”

“…20.3exp(-1272.9/T); thus, the ΔE 21 value of for BaY 1.75 Yb 0.225 Er 0.025 Ge 3 O 10 is 884.5 cm -1 . This value corresponds to the difference between the 2 H 11/2 and 4 S 3/2 energy levels, which was previously determined as ΔE 21 = 872 cm -1 from the results of spectroscopic studies of BaEr 2 Ge 3 O 10[19], and indicates the establishment of thermodynamic equilibrium in the populations of these levels.The sensitivity of a temperature sensor is among the most important characteristics showing the relative change in the ratio of fluorescence intensities when the temperature changes by one degree. The absolute and relative temperature determination sensitivities with the BaY 1.75 Yb 0.225 Er 0.025 Ge 3 O 10 germanate can be estimated from the following equations[16,25]:…”

“…In this study, the upconversion characteristics of the BaYb 2 -x Er x Ge 3 O 10 (x = 0.1-0.3) and BaY 2 -10y Yb 9y Er y Ge 3 O 10 (y = 0.015-0.15) solid solutions were investigated for the first time. The choice of germanates with the above compositions as objects of study is not accidental: the results of earlier studies of the BaR 2 Ge 3 O 10 family (R = Y, Sc, and Gd-Lu) [19] showed that these compounds exhibit high chemical and thermal stability, are wide-gap semiconductors E g = 3.0-3.4 eV), and the phonon energy ( ) in them is 836-857 cm -1 . All the above allows us to consider the possibility of creating promising luminescent materials based on them, including those for various upconversion applications.…”

“…The structure was refined by the Rietveld method using the GSAS software package [20,21]. Data on the crystal structure of BaR 2 Ge 3 O 10 (R = Y, Er, and Yb) [19] were used as an initial model for refining the X-ray diffraction profile of the synthesized germanates.…”