The undoped and Cr3+-doped NaCe(PO3)4 metaphosphates were synthesized by the modified Pechini method and obtained as the crystalline powders. They were characterized by means of X-ray diffraction, ...vibrational and optical spectroscopy to clarify the structure and mechanism of Cr3+ emission in NaCe(PO3)4. This phosphor crystallizes in the monoclinic P121/n1 structure with an infinite (PO3)n chain. The Cr3+ ions can substitute the C1 symmetry site occupied by cerium ions. They can also occupy the tunnels formed in the anionic layer. Spectroscopic properties of the Cr3+ and Ce3+ ions were discussed in terms of structure of the studied crystalline powders. IR and Raman data confirm the predicted structure and indicate C1 site symmetry of the Cr3+ active ions. The Cr3+ ions appear in the distorted octahedral environment of the weak crystal field. Optical studies were confirmed by EPR results carried out in the temperature range of 4–293K. In addition, the magnetic measurements were performed up to 305K. The Cr3+ ions reveal negligible ferromagnetic interactions while the Ce3+ ions change their magnetic interactions from slightly antiferromagnetic to significantly ferromagnetic above 20K.
•NaCe(PO3)4:Cr3+ crystalline powders were synthesized by the modified Pechini method.•The optical and magnetic properties of the NaCe(PO3)4:Cr3+ crystalline powders were investigated.•Cr3+ ions replacing Ce3+ ions in the unit cell are in the distorted octahedral environment.•Cr3+ ions reveal ferromagnetic interactions, that strength depends on temperature.
Nanoparticles of bismuth layered Aurivillius phase, Bi2W2O9, have been synthesized by annealing of precursor prepared by high energy milling in ball mill. The obtained powders have been investigated ...using the XRD, TEM, SEM, diffuse reflectivity, Raman and infrared spectroscopy. The results show that mechanochemical activation allows obtaining Bi2W2O9 at much lower temperatures than those required in a conventional solid state reaction or synthesis through a complex organic precursor. As a result, material with smaller grain size can be obtained. Therefore this synthesis method is the best route to enhance photocatalytic activity of Bi2W2O9. Our results also show that milling time has great impact on the crystallization mechanism. Bi2W2O9 crystallizes easily already at 600AC from precursor milled by 8h. However, prolong milling time results in stabilization of an unknown phase or phases, which crystallize below 700AC, and transform into the well-known Bi2W2O9 phase after annealing at 750AC.
Polarized Raman, IR, optical and dielectric studies of RbNd(WO
4)
2 single crystal have been performed. Symmetries of the observed Raman and IR modes have been established and their assignment to ...respective motions of atoms has been proposed. We have shown that the phonon properties of RbNd(WO
4)
2 are very similar to the phonon properties of KGd(WO
4)
2 but significantly different from properties of isostructural KLu(WO
4)
2 and KYb(WO
4)
2. The intensity parameters determined for RbNd(WO
4)
2 by means of the Judd–Ofelt theory are the most similar to those reported for KLu(WO
4)
2:Nd
3+. Dielectric measurements have revealed that this crystal exhibits low DC conductivity with the activation energy 1.02
eV up to 773
K and 1.22
eV at higher temperatures.
New europium complexes of picolinic acid
N-oxides have been synthesised and introduced into sol–gel matrices. Their application as UV-light sensors has been considered. The sequence of the electronic ...levels for Eu
3+ ions has been determined from the absorption and emission studies and assigned to the respective electron transitions. The lifetimes of the excited states have been detected and analysed. The role of the CT transition inside the picolinic ligand and its influence on the ligand to metal charge transfer (LMCT) have been discussed.
Research on the phase equilibria in one of the cross-sections of a CaO–Nd2O3–Nb2O5 ternary oxide system, i.e. the Ca2Nb2O7–Nd3NbO7 binary system, has shown the existence of a new solid solution with ...the general formula (Ca2Nb2)2xNd3NbO14x+7 (0 < x < 1) and a homogeneity range between Nd3NbO7 and Ca4Nd3Nb5O21 end-members. The dependence of the powder XRD patterns, as well as IR and Raman, emission and excitation spectra and luminescence decay times on mixture composition has been reported. XRD and spectroscopic studies show a continuous change of the substrates’ interaction within the existence limit of a new solid solution. Significant improvement of the luminescence properties was obtained by dilution of the optically active Nd3+ ions by gadolinium and lanthanum in the Ca4Nd3Nb5O21 end-member of the new solid solution. The spectroscopic measurements were used to propose the depopulation mechanism of the Nd3+ electron excited states in the studied materials. The optical band gaps of Ca2Nb2O7, Ca4Nd3Nb5O21 and Nd3NbO7 were calculated using Tauc plots.
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•(Ca2Nb2)2xNd3NbO14x+7 solid solution is formed in Ca2Nb2O7–Nd3NbO7 system.•Texturing process within the existence limit of a new solid solution takes place.•Ca4Nd3Nb5O21 niobate shows perspective luminescent properties.•Dilution of Nd3+ ions by Gd3+ or La3+ in Ca4Nd3Nb5O21 improves the decay time.
► Polycrystalline Cd0.25RE0.5□0.25MoO4 solid solutions were prepared (RE=Pr–Dy). ► The cationic vacancies influence the phonon and electronic properties. ► The structural parameters depend on RE3+ ...atomic mass and ionic radii. ► RE3+ mass affects the strengths of phonon coupling.
Cadmium-rare earth Cd0.25RE0.5□0.25MoO4 molybdates, where RE=Pr–Dy, have been prepared and characterised by powder XRD analysis and spectroscopic studies. IR and Raman spectra at room temperature have been measured in the MIR and FIR ranges. The correlation between the lattice parameters and spectroscopic data has been discussed in terms of factor group analysis. The dependences between the RE3+ ionic radius, atomic mass and IR and Raman wavenumbers have been discussed.
Polarized Raman scattering spectra of the NaY(WO4)2 (NYW) single crystal have been measured. Its structure is described in the tetragonal space group isomorphic to CaWO4 scheelite. The Ag, Bg and Eg ...spectra were made and discussed in terms of factor group analysis. These spectra are compared to those of monoclinic KY(WO4)2 (KYW) single crystals whose structure differs from the other crystal. The NYW unit cell comprises of the isolated WO4 tetrahedra whereas the KYW structure is built from the WO6 octahedra joined by WO2W double bonds and WOW single bridges. The vibrational characteristics of the bridge bond systems are proposed. On this basis, the role of the vibronic transitions for the KYW crystal doped with Eu3+ ions is discussed.
Raman scattering and polarised infrared spectra of the potassium rare-earth double molybdates and tungstate (KLnxTm1−x(MO4)2, where LnLa,Y,Lu, MMo,W) were measured at ambient temperature in the ...range of 40–1000 cm−1. The assignment of the observed bands to the respective internal and external vibrational modes is proposed. The X-ray structural analysis of the yttrium thulium molybdate and lanthanum thulium tungstate crystals is reported. The crystal structure of the compounds studied depends on the type of cation and changes from monoclinic (for the lanthanum-thulium molybdate) to orthorhombic (for the yttrium- and lutetium-thulium molybdates). The character of the coordination sphere around the molybdenum atom changes from octahedral to tetrahedral.
A high-temperature solid-state reaction method was used to successfully synthesize a series of Pr3+-doped lead molybdato-tungstates, namely Pb1-3x▯xPr2x(MoO4)1-3x-y(WO4)3x+y, where x = 0.0455, ...0 = y ≤ 0.7635, and ▯ represents vacancy. X-ray diffraction method together with Raman spectroscopy results confirmed the formation of single, tetragonal scheelite-type phases with space group I41/a. The assignment of the observed bands to the internal and external modes was proposed. The absorption, emission, and excitation spectra of the studied solid solutions were measured and analyzed. When the composition parameter y, and concentration of the WO4 groups, were increased, all detected emission bands exhibited blue-shifts of 43–58 cm−1. Due to the concentration quenching, there was no recorded emission originating from the 1D2 level. The Mo content had a significant impact on the lifetime of the 3P0 multiplet.
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•The solid solution Pb1-3x▯xPr2x (MoO4)1-3x-y (WO4)3x + y (x = 0.0455, 0 = y ≤ 0.7635) was prepared.•The structural and phonon properties are analyzed as a function of y.•The impact of the MoO4/WO4 ratio on the optical properties of Pr3+ ions is discussed.
