Yttrium Germanate Research Articles

Study on luminescence properties and anti-counterfeiting application of Sr3Y2Ge3O12 doped Mn2+ long afterglow materials

Traditional anti-counterfeiting materials have the characteristics of static display of anti-counterfeiting patterns and are easy to be disturbed by background patterns. Consequently, the development of novel luminous materials represents an imperative objective. As a novel class of matrix material, Sr3Y2Ge3O12 has demonstrated considerable potential for application in the field of anti-counterfeiting. In this study, strontium yttrium germanate doped manganese ion long afterglow material was prepared by the high temperature solid phase method, and its afterglow performance and dynamic anti-counterfeiting application were studied. The experimental results show that the sample exhibits excellent luminescence characteristics. It is observed that the sample excited at 260 nm shows an emission band centred at 634 nm and a high-energy turning point at 578 nm. Using screen printing technology, design a variety of anti-counterfeiting labels. The prepared samples after ultraviolet excitation can maintain the pattern for a long time, and with the passage of time, the pattern shows dynamic attenuation, which is important in enhancing the anti-counterfeiting effect and improving product safety.

Polymorphic transformations of NaYGeO4 olivine under high pressure and high temperature

Two new high-pressure modifications of sodium yttrium germanate NaYGeO4 are described. A reversible pressure-induced phase transition of olivine-type NaYGeO4 to new phases has been studied in the pressure range of 4–10 GPa at temperatures from 400 to 1000°C. It was shown that NaYGeO4 olivine is stable at 400–600°C up to 10 GPa. A high-pressure polymorph of NaYGeO4 with NaNdSiO4 crystal structure is formed at 800°C starting from 6 GPa. Along with this polymorph, another new high-pressure modification of NaYGeO4 with NaSmSiO4 crystal structure was found in small amount. In addition, a yet undescribed polymorph of Y2Ge2O7 with pyrochlore-type structure was isolated at 8 GPa and 800°C. The crystal structures of the new phases were determined by X-ray powder diffraction. The results of DFT calculations confirmed the experimental crystallography and gave a preliminary insight into the relative thermodynamic stability and electronic properties for all three new compounds.

Структура и динамика решетки тетрагональных германатов R-=SUB=-2-=/SUB=-Ge-=SUB=-2-=/SUB=-O-=SUB=-7-=/SUB=- (R=Tb-Lu, Y): ab initio расчет

Within the framework of density functional theory, an ab initio calculation was carried out to study the crystal structure, phonon spectrum and elastic constants of a series of rare-earth germanates, including yttrium germanate R2Ge2O7 (R = Tb-Lu, Y) with tetragonal structure. The frequencies and types of fundamental vibrations as well as the intensities of the IR and Raman modes were determined. The degree of participation of ions in each mode was determined from the analysis of the displacement vectors obtained from the ab initio calculation. The calculations were performed for the first time. The corresponding experimental data for the entire series, with the exception of the IR and Raman spectra of yttrium germanate, are absent. The calculations made it possible to interpret and supplement available in the scientific articles results of measurements of the IR and Raman spectra of yttrium germanate Y2Ge2O7.

Why Do Relative Intensities of Charge Transfer and Intra-4f Transitions of Eu3+ Ion Invert in Yttrium Germanate Hosts? Unravelling the Underlying Intricacies from Experimental and Theoretical Investigations.

The dominant intensity of parity-forbidden intra-4f transitions of europium(III) over O → Eu charge-transfer band (CTB) intensity is against common perceptions, yet this trend is observed in many germanate hosts and has not been rationalized so far. In search of a plausible explanation for this unusual trend, present work reports an experimental and theoretical investigations in conjunction on two sibling germanate host, namely, Y2GeO5 and Y2Ge2O7 having dopant Eu3+ in their respective YO7 polyhedra. Whereas for Y2GeO5:Eu3+, the CTB is more intense than the intra-4f transitions in the excitation spectrum, in the case of Y2Ge2O7:Eu3+, the relative intensities of CTB and intra-4f transitions are reversed. Comparative structural analysis reveals that Eu3+ present in YO7 of Y2GeO5 has a greater number of tetra-coordinated oxygen (Otetra) and yttrium atom as first and second neighbors, respectively (Eu3+-Otetra-Y3+ linkages). Conversely, in Y2Ge2O7 host, the Eu3+ ion mostly has tricoordinated oxygen (Otri) as its nearest neighbor and germanium ions next to Otri (Eu3+-Otri-Ge4+ linkage). Theoretical calculations reveal that while Y2GeO5:Eu has Otetra(4Y) dominating at the Fermi level and the 4f state of Eu3+ remains inert toward mixing, in Y2Ge2O7:Eu, the Fermi level has major contribution from Otri(2Y + 1Ge) with significant mixing with 4f states of Eu. The dominant control of Eu3+-Otri-Ge4+ linkages in geometrical and electronic structure of Y2Ge2O7:Eu owing to the GeO4 surrounding has been attributed to relative poor intensity of O → Eu CTB. Siege of Eu3+ by GeO4 and subsequent occurrence of Eu3+-Otri-Ge4+ linkages play a dual role: First, it induces electronic rigidity to hinder excitation of electron at bridging (Otri) oxygen by highly charged small Ge4+ cation; second, the covalent character in Eu-O bond is achieved by intermixing of Eu's 4f and Otri 2p orbital which facilitates relaxing of the parity-selection rule thus enhancing the probability of intra-4f transitions. The inferences drawn remain valid when extrapolated to other inorganic oxides having EuOx polyhedra surrounded by covalent units like PO4, SiO4, etc. and have a prevailing number of low-coordinated oxygen atoms and highly charged small cation in the first and second coordination shells, respectively. The optical basicity concept is also found to endorse our explanation. These remarkable generic inferences will pave the rational way for designing efficient phosphors for solid-state lighting.

Color tuning dependence on cross-relaxation effect of Pr3+ activated yttrium germanate phosphor

Phosphors are important photoluminescence (PL) materials that are widely used in the lighting and display fields. The PL tricolor of phosphors is commonly obtained by doping different kinds of the emitters in phosphors. In this work, we first report the multicolor PL of Pr3+ single activated Y2GeO5 phosphor. Excited at 254 nm, the PL color of the phosphor can be tuned from red to yellow, green and even blue by changing the Pr3+ content. It reveals that this observation is due to the cross-relaxation effect of Pr3+ in a low phonon energy host. On the basis of this multicolor phosphor, a multicolor luminescent image is fabricated for anticounterfeiting application.

Synthesis and High-Temperature Heat Capacity of Y2Ge2O7

Yttrium germanate Y2Ge2O7 was prepared by solid-phase synthesis from a stoichiometric Y2O3–GeO2 mixture under multistage calcination in air within a temperature range of 1273–1473 K. The molar heat capacity of polycrystalline samples was measured by differential scanning calorimetry (DSC), and the C P = f(T) dependence was used to calculate the thermodynamic properties of yttrium digermanates, such as the enthalpy and entropy changes and the reduced Gibbs energy.

Platinum-assisted post deposition annealing of the n-Ge/Y2O3 interface

The impact of annealing temperature and annealing duration on the interface properties of n-Ge/Y2O3/Pt MOS-capacitors is investigated employing an ultrathin catalytically acting Pt-layer. X-ray photoelectron spectroscopy analysis has been used to verify an enhanced growth of GeO2 and thermally stabilizing yttrium germanate at the n-Ge/Y2O3 interface induced by an oxygen post deposition annealing (PDA). Especially at 500 °C and 550 °C high quality Ge/Y2O3 interfaces have been achieved resulting in very low interface trap density of 7.41*1010 eV−1 cm−2. It is shown that either a short oxygen annealing at higher temperatures (550 °C) or a long time annealing at lower temperatures (450 °C) are appropriate to realize low interface trap density (Dit). It turns out that a Pt-assisted PDA in combination with a final PMA are needed to reduce hysteresis width significantly and to bring flat band voltages toward ideal values.

Improving the ALD-grown Y2O3/Ge interface quality by surface and annealing treatments

Metal Oxide Semiconductor capacitors are investigated, employing ALD grown Y2O3 as gate dielectric, and n-type (100) germanium as channel substrate. The effect of post deposition annealing (PDA) in oxygen and forming gas atmosphere using a thin catalytically acting platinum (Pt)-layer on the Y2O3/Ge interface is electrically analyzed for buffered hydrofluoric (BHF) and thermally pre-treated Ge-surfaces.The Pt-assisted PDA ensures even for BHF pre-treated samples very low values for the interface trap density Dit of 1.55×1011eV−1cm−2 and low leakage current densities J of <7×10−9A/cm2 outperforming conventional PDA treatments. The interfacial formation of GeO2 and yttrium germanate after PDA is proven by using X-ray Photoelectron Spectroscopy measurements.

Effective reduction of trap density at the Y2O3/Ge interface by rigorous high-temperature oxygen annealing

The impact of thermal post deposition annealing in oxygen at different temperatures on the Ge/Y2O3 interface is investigated using metal oxide semiconductor capacitors, where the yttrium oxide was grown by atomic layer deposition from tris(methylcyclopentadienyl)yttrium and H2O precursors on n-type (100)-Ge substrates. By performing in-situ X-ray photoelectron spectroscopy, the growth of GeO during the first cycles of ALD was proven and interface trap densities just below 1 × 1011 eV−1 cm−2 were achieved by oxygen annealing at high temperatures (550 °C–600 °C). The good interface quality is most likely driven by the growth of interfacial GeO2 and thermally stabilizing yttrium germanate.

Interfacial-layer-free growth of yttrium oxide on germanium by understanding initial surface reactions

In this study, we investigate the surface and interfacial reactions involved in the growth of yttrium oxide through the oxidation of yttrium metal on germanium. Our combined understanding of the oxidation and interfacial reactions allows us to introduce a layer-by-layer method to grow an interfacial-layer-free yttrium oxide on germanium at room temperature, which has previously proven to be difficult. During initial growth, we show evidence that yttrium germanide provides the lowest kinetic pathway in the formation of the yttrium germanate interfacial layer and explain how this pathway can be avoided using our layer-by-layer method. This method can possibly be used to achieve interfacial-layer-free growth for other metal oxides on semiconductors.

Interaction of oxygen vacancies in yttrium germanates

Forming a good Ge/dielectric interface is important to improve the electron mobility of a Ge metal oxide semiconductor field-effect transistor. A thin yttrium germanate capping layer can improve the properties of the Ge/GeO(2) system. We employ electronic structure calculations to investigate the effect of oxygen vacancies in yttrium-doped GeO(2) and the yttrium germanates Y(2)Ge(2)O(7) and Y(2)GeO(5). The calculated densities of states indicate that dangling bonds from oxygen vacancies introduce in-gap states, but the system remains insulating. However, yttrium-doped GeO(2) becomes metallic under oxygen deficiency. Y-doped GeO(2), Y(2)Ge(2)O(7) and Y(2)GeO(5) are calculated to be oxygen substoichiometric under low Fermi energy conditions. The use of yttrium germanates is proposed as a way to effectively passivate the Ge/dielectric interface.

Preparation of Mn-activated yttrium germanate phosphor thin films for electroluminescent devices

Manganese (Mn)-activated yttrium germanate phosphor thin films were prepared by conventional r.f. magnetron sputtering. The phosphor thin films prepared with a Y 2O 3 content of 33, 50 and 67 mol.% and postannealed above approximately 950 °C were crystallized and identified as Y 2Ge 2O 7, Y 2GeO 5 and Y 4GeO 8, respectively, whereas all as-deposited thin films were found to be amorphous. Thin-film electroluminescent (TFEL) devices were fabricated using the postannealed phosphor thin films. The obtainable electroluminescent (EL) characteristics were considerably affected by the Mn content and the postannealing temperature of the phosphor thin-film emitting layers. High luminances for yellow photoluminescence and EL emissions were obtained in TFEL devices using these ternary compound phosphors activated with Mn and postannealed at 1020–1045 °C. Maximum luminance of 2590, 3020 and 2500 cd/m 2 were obtained in 1 kHz-driven TFEL devices using Y 2Ge 2O 7:Mn, Y 2GeO 5:Mn and Y 4GeO 8:Mn thin-film emitting layers, respectively.

The crystal structure of InYGe2O7 germanate

Abstract A new indium yttrium germanate presenting the thortveitite structure with symmetry described by the space group C2/m (No. 12) has been prepared by high temperature solid state reaction as polycrystalline powder material. This crystallizes in the monoclinic system, with cell parameters a = 6.8286(1) Å, b = 8.8836(2) Å, c = 4.9045(1) Å, β= 101.8340(7)º, V = 291.195(9) Å3 and Z = 2. The structure was characterized by X-ray powder diffraction and Rietveld refinement of the diffraction pattern. The In3+ and Y+3 cations occupy the same octahedral site forming a hexagonal arrangement on the ab planes. In their turn, the hexagonal arrangements of InO6/YO6 octahedral layers are held together by sheets of isolated diorthogroups constituted by a double tetrahedra sharing a common vertex. In this compound, the Ge2O7 diorthogroup shows the C2h symmetry implying a Ge-O-Ge angle of 180º, being an important feature of the thortveitite structure, which has been controversial in some reported papers. A remarkable photo-luminescence effect (in comparison with glass) was observed when the sample was irradiated with α-particles beam during the RBS experiments employed to analyze the chemical stoichiometry.

Crystal Structure and Low-Temperature Magnetic Ordering in Rare Earth Iron Germanates RFeGe2O7, R = Y, Pr, Dy, Tm, and Yb

Polycrystalline samples of iron and rare earth germanates, RFeGe2O7 (R = Y, Pr, Dy, Tm, and Yb), have been prepared. Depending on the size of R, they present two different monoclinic crystal structures, described either in space group P21/c (no. 14) for R = Pr or in P21/m (no. 11) for the smaller rare earths R = Y, Dy, Tm, and Yb. The results of crystal structure refinements from room-temperature high-resolution neutron powder diffraction (NPD) data are given. Magnetization measurements between 350 and 1.6 K reveal the existence of one maximum, at 3 or 38 K for the praseodymium or yttrium germanate, respectively, and two separate anomalies for the remaining materials, which appear at T1 and T2 (T2 < T1), where T1 ≈ 40 K and T2 = 24, 6, and 5 K, for R = Dy, Tm, and Yb, respectively, indicating transitions to antiferromagnetically (AF) ordered states. Judging from low-temperature NPD data, three-dimensional (3D) AF ordering is established for all compounds, with simultaneous ordering of the R3+ and (or) Fe3...