The luminescence of NaxEu(2-x)/33+MoO4 scheelites depends on the number of Eu-clusters occurring in their incommensurately modulated structure (original) (raw)
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Crystal Structure and Luminescent Properties of R 2– x Eu x (MoO 4 ) 3 (R = Gd, Sm) Red Phosphors
Chemistry of Materials, 2014
The R 2 (MoO 4 ) 3 (R = rare earth elements) molybdates doped with Eu 3+ cations are interesting red-emitting materials for display and solid-state lighting applications. The structure and luminescent properties of the R 2−x Eu x (MoO 4 ) 3 (R = Gd, Sm) solid solutions have been investigated as a function of chemical composition and preparation conditions. Monoclinic (α) and orthorhombic (β′) R 2−x Eu x (MoO 4 ) 3 (R = Gd, Sm; 0 ≤ x ≤ 2) modifications were prepared by solid-state reaction, and their structures were investigated using synchrotron powder X-ray diffraction and transmission electron microscopy. The pure orthorhombic β′-phases could be synthesized only by quenching from high temperature to room temperature for Gd 2−x Eu x (MoO 4 ) 3 in the Eu 3+ -rich part (x > 1) and for all Sm 2−x Eu x (MoO 4 ) 3 solid solutions. The transformation from the α-phase to the β′-phase results in a notable increase (∼24%) of the unit cell volume for all R 2−x Eu x (MoO 4 ) 3 (R = Sm, Gd) solid solutions. The luminescent properties of all R 2−x Eu x (MoO 4 ) 3 (R = Gd, Sm; 0 ≤ x ≤ 2) solid solutions were measured, and their optical properties were related to their structural properties. All R 2−x Eu x (MoO 4 ) 3 (R = Gd, Sm; 0 ≤ x ≤ 2) phosphors emit intense red light dominated by the 5 D 0 → 7 F 2 transition at ∼616 nm. However, a change in the multiplet splitting is observed when switching from the monoclinic to the orthorhombic structure, as a consequence of the change in coordination polyhedron of the luminescent ion from RO 8 to RO 7 for the αand β′-modification, respectively. The Gd 2−x Eu x (MoO 4 ) 3 solid solutions are the most efficient emitters in the range of 0 < x < 1.5, but their emission intensity is comparable to or even significantly lower than that of Sm 2−x Eu x (MoO 4 ) 3 for higher Eu 3+ concentrations (1.5 ≤ x ≤ 1.75). Electron energy loss spectroscopy (EELS) measurements revealed the influence of the structure and element content on the number and positions of bands in the ultraviolet−visible−infrared regions of the EELS spectrum.
Influence of the Structure on the Properties of Na x Eu y (MoO 4 ) z Red Phosphors
Chemistry of Materials, 2014
Scheelite related compounds (A′,A″) n [(B′,B″)O 4 ] m with B′, B″ = W and/or Mo are promising new materials for red phosphors in pc-WLEDs (phosphor-converted white-light-emittingdiode) and solid-state lasers. Cation substitution in CaMoO 4 of Ca 2+ by the combination of Na + and Eu 3+ , with the creation of A cation vacancies, has been investigated as a factor for controlling the scheelite-type structure and the luminescent properties. Na 5 Eu(MoO 4 ) 4 and Na x Eu 3+
Inorganic chemistry, 2018
The oxonitridosilicate oxides RE26Ba6[Si22O19N36]O16:Eu2+ (RE = Y, Tb) were synthesized by high-temperature reaction in a radiofrequency furnace starting from REF3, RE2O3 (RE = Y, Tb), BaH2, Si(NH)2, and EuF3. The structure elucidation is based on single-crystal X-ray data. The isotypic materials crystallize in the monoclinic space group Pm (no. 6) [Z = 3, a = 16.4285(8), b = 20.8423(9), c = 16.9257(8) Å, β = 119.006(3)° for RE = Y and a = 16.5465(7), b = 20.9328(9), c = 17.0038(7) Å, β = 119.103(2)° for RE = Tb]. The unique silicate layers are made up from Q1-, Q2-, and Q3-type Si(O/N)4- as well as Q4-type SiN4-tetrahedra, forming three slightly differing types of cages. The corresponding 3-fold superstructure as well as pronounced hexagonal pseudosymmetry complicated the structure elucidation. Rietveld refinement on powder X-ray diffraction data, energy-dispersive X-ray spectroscopy and infrared spectroscopy support the findings from single-crystal X-ray data. When excited with UV...
Theoretical and Experimental Chemistry, 2012
Nanosized solid-state solutions of Sc 1-x Eu x (CH 3 CO 2) 3 (x = 0.01-0.1) have been obtained and their morphology, structure, vibrational and luminescence properties studied. The experimental IR and Raman spectra are in accord with the structures assigned to these compounds. A spectroscopic study showed that scandium acetate doped with 10 at.% Eu 3+ holds interest as a potential luminescent material active in the visible spectrum. Solid-state solutions of Sc 1-x Eu x (CH 3 CO 2) 3 can be used as precursors for obtaining nanosized oxides Sc 2-2x Eu 2x O 3 with specified particle morphology.
Journal of Fluorescence, 2011
SrMoO 4 doped with rare earth are still scarce nowadays and have attracted great attention due to their applications as scintillating materials in electro-optical like solid-state lasers and optical fibers, for instance. In this work Sr 1−x Eu x MoO 4 powders, where x=0.01; 0.03 and 0.05, were synthesized by Complex Polymerization (CP) Method. The structural and optical properties of the SrMoO 4 :Eu 3+ were analyzed by powder X-ray diffraction patterns, Fourier Transform Infra-Red (FTIR), Raman Spectroscopy, and through Photoluminescent Measurements (PL). Only a crystalline scheelite-type phase was obtained when the powders were heat-treated at 800°C for 2 h, 2θ=27.8°(100% peak). The excitation spectra of the SrMoO 4 :Eu 3+ (λ Em. =614 nm) presented the characteristic band of the Eu 3+5 L 6 transition at 394 nm and a broad band at around 288 nm ascribed to the charge-transfer from the O (2p) state to the Mo (4d) one in the SrMoO 4 matrix. The emission spectra of the SrMoO 4 :Eu 3+ powders (λ Exc. =394 and 288 nm) show the group of sharp emission bands among 523-554 nm and 578-699 nm, assigned to the 5 D 1 → 7 F 0,1and 2 and 5 D 0 → 7 F 0,1,2,3 and 4 , respectively. The band related to the 5 D 0 → 7 F 0 transition indicates the presence of Eu 3+ site without inversion center. This hypothesis is strengthened by the fact that the band referent to the 5 D 0 → 7 F 2 transition is the most intense in the emission spectra.
Chemistry of Materials, 2013
Scheelite related compounds (A′,A″) n [(B′,B″)O 4 ] m with B′, B″ = W and/or Mo are promising new light-emitting materials for photonic applications, including phosphor converted LEDs (light-emitting diodes). In this paper, the creation and ordering of A-cation vacancies and the effect of cation substitutions in the scheelite-type framework are investigated as a factor for controlling the scheelitetype structure and luminescent properties. CaGd 2(1−x) Eu 2x (MoO 4) 4(1−y) (WO 4) 4y (0 ≤ x ≤ 1, 0 ≤ y ≤ 1) solid solutions with scheelite-type structure were synthesized by a solid state method, and their structures were investigated using a combination of transmission electron microscopy techniques and powder X-ray diffraction. Within this series all complex molybdenum oxides have (3 + 2)D incommensurately modulated structures with superspace group I4 1 /a(α,β,0)00(−β,α,0)00, while the structures of all tungstates are (3 + 1)D incommensurately modulated with superspace group I2/b(αβ0)00. In both cases the modulation arises because of cation-vacancy ordering at the A site. The prominent structural motif is formed by columns of A-site vacancies running along the c-axis. These vacant columns occur in rows of two or three aligned along the [1̅ 10] direction of the scheelite subcell. The replacement of the smaller Gd 3+ by the larger Eu 3+ at the A-sublattice does not affect the nature of the incommensurate modulation, but an increasing replacement of Mo 6+ by W 6+ switches the modulation from (3 + 2)D to (3 + 1)D regime. Thus, these solid solutions can be considered as a model system where the incommensurate modulation can be monitored as a function of cation nature while the number of cation vacancies at the A sites remain constant upon the isovalent cation replacement. All compounds' luminescent properties were measured, and the optical properties were related to the structural properties of the materials. CaGd 2(1−x) Eu 2x (MoO 4) 4(1−y) (WO 4) 4y phosphors emit intense red light dominated by the 5 D 0 − 7 F 2 transition at 612 nm, along with other transitions from the 5 D 1 and 5 D 0 excited states. The intensity of the 5 D 0 − 7 F 2 transition reaches a maximum at x = 0.5 for y = 0 and 1.
Crystal structure and luminescence properties of SrxCa1-xAlSiN3:Eu2+ mixed nitride phosphors
Journal of Alloys and Compounds, 2009
LiYP 4 O 12 polyphosphate doped with Ce 3+ ions was prepared by the melt solution technique. The crystal structure, interatomic distances, and atom coordination numbers were determined using x-ray powder diffraction. A study of the spectral-kinetic luminescent properties was performed employing excitation with pulsed radiation from a synchrotron (UV-VUV range) and a laboratory x-ray source. The characteristics of Ce 3+ luminescence, namely the emission doublet maxima at 3.97 and 3.72 eV and the 4f-5d excitation maxima at 4.20, 5.11, 5.40, 5.65 and 6.55 eV, are discussed in terms of crystal field splitting in a low-symmetry site of the LiYP 4 O 12 host lattice. The location of the Ce 3+ energy levels with respect to the valence and conduction bands of the LiYP 4 O 12 host is estimated from the temperature dependence of the decay time measured for Ce 3+ 5d-4f luminescence.
Inorganic Chemistry Communications, 2007
The R 2 (MoO 4 ) 3 (R = rare earth elements) molybdates doped with Eu 3+ cations are interesting red-emitting materials for display and solid-state lighting applications. The structure and luminescent properties of the R 2−x Eu x (MoO 4 ) 3 (R = Gd, Sm) solid solutions have been investigated as a function of chemical composition and preparation conditions. Monoclinic (α) and orthorhombic (β′) R 2−x Eu x (MoO 4 ) 3 (R = Gd, Sm; 0 ≤ x ≤ 2) modifications were prepared by solid-state reaction, and their structures were investigated using synchrotron powder X-ray diffraction and transmission electron microscopy. The pure orthorhombic β′-phases could be synthesized only by quenching from high temperature to room temperature for Gd 2−x Eu x (MoO 4 ) 3 in the Eu 3+ -rich part (x > 1) and for all Sm 2−x Eu x (MoO 4 ) 3 solid solutions. The transformation from the α-phase to the β′-phase results in a notable increase (∼24%) of the unit cell volume for all R 2−x Eu x (MoO 4 ) 3 (R = Sm, Gd) solid solutions. The luminescent properties of all R 2−x Eu x (MoO 4 ) 3 (R = Gd, Sm; 0 ≤ x ≤ 2) solid solutions were measured, and their optical properties were related to their structural properties. All R 2−x Eu x (MoO 4 ) 3 (R = Gd, Sm; 0 ≤ x ≤ 2) phosphors emit intense red light dominated by the 5 D 0 → 7 F 2 transition at ∼616 nm. However, a change in the multiplet splitting is observed when switching from the monoclinic to the orthorhombic structure, as a consequence of the change in coordination polyhedron of the luminescent ion from RO 8 to RO 7 for the αand β′-modification, respectively. The Gd 2−x Eu x (MoO 4 ) 3 solid solutions are the most efficient emitters in the range of 0 < x < 1.5, but their emission intensity is comparable to or even significantly lower than that of Sm 2−x Eu x (MoO 4 ) 3 for higher Eu 3+ concentrations (1.5 ≤ x ≤ 1.75). Electron energy loss spectroscopy (EELS) measurements revealed the influence of the structure and element content on the number and positions of bands in the ultraviolet−visible−infrared regions of the EELS spectrum.
Journal of Solid State Chemistry, 2012
Autoclaving the rare-earth nitrate/NH 4 OH reaction system under the mild conditions of 120-200 1C and pH 6-13 have yielded four types of well-crystallized compounds with their distinctive crystal shapes, including Ln 2 (OH) 5 NO 3 Á nH 2 O (Ln¼Y and Eu) layered rare-earth hydroxide (hexagonal platelets), Ln 4 O(OH) 9 NO 3 oxy-hydroxyl nitrate (hexagonal prisms and microwires), Ln(OH) 2.94 (NO 3) 0.06 Á nH 2 O hydroxyl nitrate (square nanoplates), and Ln(OH) 3 hydroxide (spindle-shaped microrods). The occurrence domains of the compounds are defined. Ammonium nitrate (NH 4 NO 3) as a mineralizer effectively widens the formation domains of the NO 3 À containing compounds while leads to larger crystals at the same time (up to 0.3 mm). Crystallization mechanisms of the compounds and the effects of NH 4 NO 3 were discussed. Optical properties (PLE/PL) of the four phases were characterized in detail and were interpreted from the different site symmetries of Eu 3 þ. The compounds convert to cubic-structured (Y 0.95 Eu 0.05) 2 O 3 by annealing at 600 1C while retaining their original crystal morphologies. The resultant phosphor oxides of diverse particle shapes exhibit differing optical properties, in terms of luminescent intensity, asymmetry factor of luminescence and fluorescence lifetime, and the underlying mechanism was discussed.