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Solid solutions K2Bi(PO4)(MoO4):Gd,Eu containing from 0.1 to 30 mole% of europium(III) and 0.1 mole% of gadolinium(III) have been prepared by conventional solid state reaction. The samples are characterized by X-ray powder diffraction method, IR and luminescence spectroscopies. It has been shown that doping with Eu3+ does not affect the symmetry of the layered framework. At room temperature, all the studied samples are characterized by intense red photoluminescence, which is associated with 5D0→7F0-4 emission transitions in Eu3+ ions. Due to the absence of concentration quenching and color characteristics, K2Bi(PO4)(MoO4):Gd,Eu has prominent prospects for application as a red phosphor. [ABSTRACT FROM AUTHOR]

The results of synthesis, crystal structure characterization, and luminescence properties study of pure and Eu3+-doped K0.45Bi0.55Mo0.9V0.1O4 solid solutions have been reported. The obtained powders crystallize in a compact form with an average size of the particles of about 5–10 µm. It was found that doping with europium leads to the transformation of the host from monoclinic to tetragonal scheelite-like phase. The Eu3+-doped samples reveal intensive red luminescence under excitation in ultraviolet and blue spectral regions. Energy transfer from molybdate–vanadate host to Eu3+ ions takes place in the studied solid-solution. Intensity of the red luminescence increases when Eu3+ content increases and no concentration quenching has been found. [ABSTRACT FROM AUTHOR]

Solid solutions of K3Gd(PO4)2:Eu containing 0.1 to 10 mole % of europium(III) were obtained by solid-phase interaction. The obtained micropowders were characterized by X-ray phase analysis, IR, and luminescence spectroscopy. It is shown that doping does not affect the symmetry of the double phosphate framework. All studied samples are characterized by intense red photoluminescence at room temperature, which is associated with the5D0→7F0-4 radiation transitions in Eu3+ ions. The absence of concentration attenuation and color characteristics of the samples indicate the prospects of using the K3Gd0.9Eu0.1(PO4)2 compound as a red phosphor. [ABSTRACT FROM AUTHOR]

The results of synthesis, crystal structure characterization and luminescence properties study of the Pr3+-doped bismuth orthophosphate, BiPO4, polycrystals are reported. It was found that doping of bismuth orthophosphate with praseodymium of concentration more than 1% leads to phase transition of BiPO4 from so-called "high-temperature monoclinic" to "low-temperature monoclinic" structure. At room temperature studied samples revealed intensive red luminescence caused by radiation electronic transitions in the Pr3+ ions under their intrinsic f → f excitation at 3H4→ 3P1+1I6 absorption transition. Influence of phase transformation as well as multi-phonon and cross-relaxation processes on the luminescence of the Pr3+-doped BiPO4 compounds were discussed. [ABSTRACT FROM AUTHOR]

Composite samples based on microcrystalline cellulose matrix incorporated with micro/nanoparticles of La0.7Sm0.3VO4 complex oxide were made by cool pressing procedure. Morphology, crystallinity and characteristic luminescence and dielectric properties of the composites were studied. Their morphology can be described as "ceramics-like" type, as it consists of cellulose plates and embedded oxide particles. Luminescence spectra of the composites covers the range of the whole visible light, 350-750 nm, and comprises both wide band and narrow lines, related with host and oxide luminescence, respectively. Temperature dependences of the dielectric permittivity of composites showed the impact of the oxide particles on the characteristics of the microcrystalline cellulose. An assumption was made that this influence can be affected via water molecules, hydroxyl groups or molecules of the ambient gases. Studied composites can be perspective luminescent materials for transformation of ultraviolet and violet radiation into green-red light. [ABSTRACT FROM AUTHOR]

The investigated La1-xRExVO4 (RE = Eu, Sm) solid solutions are characterized by intensive emission of the RE ions that is excited from the wide spectral range including UV region of intrinsic transitions in the vanadate host. We have carried out comparable analysis of characteristics of the La1-xRExVO4 compounds synthesized by three different methods: solid state reaction, co-precipitation and sol-gel synthesis. The investigation revealed differences in luminescence and excitation spectra of samples obtained by different methods. Spectra of the samples with lower activator concentrations have a more complicated character. They contain exceed number of lines that is caused by formation of two types of RE3+ emission centers. Spectral exhibitions of the second ('at surface') type of centers are observed up to x = 0.05, 0.1 and 0.3 for samples synthesized by solid state, co-precipitation and sol-gel methods, respectively. The presence of the 'at surface' type of centers leads to essential increasing of total intensity of emission. Differences in excitation spectra give us a possibility to suppose that enhancement of luminescence intensity is also due to expanded excitation range caused by 'at surface' centers in UV region. Therefore, 'at surface' centers satisfy better absorption of UV light. (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

The conditions of synthesis and luminescence characteristics of composites Al2O3:Cr3+/NaAl(MoO4)2:Cr3+obtained from molybdate high-temperature solutions have been studied. The composite formation has been achieved by rapid cooling of a Na-Al-Cr-Mo-O molten solution in the range of 1173-820 K. The sizes of the alumina inclusions in the molybdate host range from sub-microns to tenth of microns. The composite material is transparent for light in the visible spectral region, it allows effective excitation of the Cr3+ luminescence in Cr3+- related absorption bands in both NaAl(MoO4)2hosts and Al2O3inclusions. At liquid helium temperature, the Al2O3:Cr3+/NaAl(MoO4)2:Cr3+composite materials simultaneously reveal luminescence of Cr3+ ions in NaAl(MoO4)2(the R-line near 741 nm) and in Al2O3(the R1 line near 693 nm). At room temperature, the Al2O3:Cr3+ inclusions reveal Cr3+-related R1 and R2 lines at 694.2 and 692.8 nm, respectively, whereas the luminescence of Cr3+ ions in the molybdate host is quenched. Testing of Al2O3:Cr3+ fluorescent particles in a scanning thermal microscope reveals potential of using the Cr-doped Al2O3:Cr/NaAl(MoO4)2 nanocomposites for high-resolution mapping of the surface temperature in 300-380 K temperature range. (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

Highlights: [•] Pb2MoO5 single crystals reveal intensive PL band peaking at ∼600nm. [•] Pb2MoO5 is an indirect-gap dielectric crystal. [•] The p states of oxygen atoms belonging to Pb–O chains form the TVB of Pb2MoO5. [•] Main excitation band of the violet PL component of PbMoO4 peaks at 6.2eV. [•] Low-energy peaks in reflectivity of PbMoO4 are formed by band-to-band transitions. [Copyright &y& Elsevier]

Ultraviolet and visible photoluminescence properties of ZrP2O7 crystals are studied under excitation in the region 3.5÷12 eV of incident photon energies. Partial densities of electronic states are calculated with a full-potential linear augmented plane-wave method for both perfect crystals and those containing two types of oxygen vacancies. The UV luminescence is considered as a radiation decay of trapped excitons formed on the basis of [ZrO6]8- polyhedrons. Generation of the excitons is mainly related to charge-transfer electronic transitions between the electronic states Op and Zrd. The visible luminescence and its excitation are associated with processes that occur in polyhedrons containing the oxygen vacancies. [ABSTRACT FROM AUTHOR]

Abstract: The photoluminescence (PL) of ZrP2O7 and KZr2(PO4)3 phosphate crystalline micro-powders grown by spontaneous crystallization method is studied under vacuum ultra-violet (VUV) synchrotron radiation excitations (4–20 eV region of excitation photon energies) in 8–300 K temperature region. The electronic structures (partial densities of states) and optical absorbance spectra of the crystals are calculated by the Full-Potential Linear Augmented Plane Wave Method. Both phosphate crystals reveal PL emission band in the UV spectral region peaking near 300 and 295 nm for ZrP2O7 and KZr2(PO4)3 respectively. The spectral profile of the band weakly depends on temperature. The excitation spectra of the UV emission in each crystal contain intensive excitation band peaking at 189 and 182 nm for ZrP2O7 and KZr2(PO4)3 respectively. The excitation band of the UV emission is related to band-to-band electronic transitions with charge transfer from O 2p to Zr 4d states. The energy band gaps E g of ZrP2O7 and KZr2(PO4)3 are estimated as 6.7 and 6.6 eV respectively. [Copyright &y& Elsevier]

The origin of intrinsic photoluminescence (PL) in the set of Bi-containing phosphate, molybdate and tungstate crystals is analyzed in complex experimental and computational studies. The PL properties of polycrystalline powder samples of BiPO4, K3Bi5(PO4)6, K2Bi(PO4)(MoO4), K2Bi(PO4)(WO4) and K5Bi(MoO4)4 crystals synthesized by spontaneous crystallization method are studied under excitations in the VUV and UV region of photon energies (3.5-14 eV) at T = 8-300 K. The electronic band structures of the crystals are calculated by the Full-Potential Linear Augmented Plane Wave Method. The values of band gaps Eg of studied compounds are estimated from diffuse reflectance and PL excitation spectra. Calculations indicate that all studied crystals except K5Bi(MoO4)4 are indirect-gap materials. It is found that the Bi 6s and Bi 6p states contribute respectively at the tops of the Valence bands and the bottoms of the Conduction bands of all studied compounds. Each studied compound reveals several (at least two) PL emission components which undergo complete quenching below room temperature. Under nitrogen laser excitation with λex = 337.1 nm, all studied crystals reveal single-exponential decay of PL signal with decay constants τ in 3-35 µs range. It is assumed that the high-energy PL components of BiPO4, K3Bi5(PO4)6 and K2Bi(PO4)(MoO4) (peaking in the blue and violet regions) originate from ³P1 → ¹S0 radiative transitions in Bi3+ ions. The red PL components of K2Bi(PO4)(MoO4) and K5Bi(MoO4)4 have the MoO42--related origin. The red PL component of K2Bi(PO4)(WO4) presumably originates from the molybdenum impurities which form MoO42- emission centers in the phosphate-tungstate host. [ABSTRACT FROM AUTHOR]

A narrow-band green emitting K 3 Tb(PO 4 ) 2 phosphor has been synthesized by a novel single-crystal growth approach involving the application of an inert flux. Its structural and spectroscopic peculiarities have been systematically studied by means of single-crystal X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy analysis, and diffuse reflectance, infrared and photoluminescence spectroscopy. The layered framework of the title compound is organized by linking together slightly distorted phosphate tetrahedra with non-condensed TbO 7 polyhedra into [Tb(PO 4 ) 2 ] 3- sheets interconnected by potassium cations. K 3 Tb(PO 4 ) 2 reveals an intense slow green photoluminescence (PL) (decay time constant τ is near 2.6 ms) under excitation in the range from VUV (100 nm) up to blue light (484 nm). Intensive narrow lines of the 5 D 4 → 7 F 6-0 (4f 8 → 4f 8 ) radiative transitions in Tb 3+ ions form the PL spectra. Besides, fast violet PL (time constant τ < 20 ns) occurs under PL excitations in a narrow range from 250 to 325 nm. Dependencies of the PL quantum yield, and the green and violet PL decays on the excitation wavelength have been analyzed taking into account the multi-phonons, cross-relaxation processes and exciting light absorption by the inherent defects in the K 3 Tb(PO 4 ) 2 crystal lattice. The dependency of the complex characteristics of PL quantum yield on the excitation wavelength and violet photoluminescence is ascribed to the formation of Tb 4+ ions. The color coordinates and color purity of the emission were estimated for the cases of PL excitation in the 160-371 nm spectral range. It has been shown that these characteristics are similar to or even better than those reported for conventional commercial green phosphors. The high values of correlated color temperature ( T  > 4863 K) of the emission indicates the potential use of K 3 Tb(PO 4 ) 2 for enhancing cold-light emitting devices.