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This work explores the size-induced lattice modification and its relevance to photoluminescence properties of tetragonal zircon-type GdVO(4):Eu(3+) nanostructures. GdVO(4):Eu(3+) nanoparticles with crystallite sizes ranging from 14.4 to 24.7 nm were synthesized by a hydrothermal method using sodium citrate as a capping agent. Regardless of the reaction temperatures, all samples retained an ellipsoidal-like morphology. Nevertheless, as the crystallite size reduces, there appears a tensile strain and lattice distortion, which is accompanied by a lattice expansion and a decreased symmetry of structural units. These lattice modifications could be associated with the changes in the interior chemical bonding due to the interactions of surface defect dipoles that have imposed an increased negative pressure with crystallite size reduction. Furthermore, crystallite size reduction also led to a significant increase in the amounts of surface hydroxyl groups and citric species, as well as the concentration of the surface Eu(3+) ions. When Eu(3+) was taken as a structural probe, it was found that the asymmetric ratio (I(02)/I(01)) of Eu(3+) gradually declined to show a remarkable decrease in color chromaticity as crystallite size reduces, which could be interpreted as due to the change of local environments of Eu(3+) ions from the interior to the surface of the nanoparticles.

A facile strategy was initiated to fabricate large-scale uniform brookite TiO2 nanospindles preferentially grown along the [001] direction, which were highly thermally stable and exhibited superior electrical conductivity, about two orders of magnitude higher than those of anatase and rutile counterparts.

This work reports on the kinetic control over the crystallinity and defect chemistry of YVO 4 nanoparticles for the optimization of their photocatalytic performance. YVO 4 nanoparticles were prepared at room temperature via a precipitation method and then annealed in air at selected temperatures Յ 500°C to tune their crystallinity and defect features. By systematic evaluation of the sample characterizations, it has been found that the as-prepared samples crystallized in a pure tetragonal zircon-type structure, and the surfaces of the particles are hydrated. Upon annealing, all YVO 4 nanoparticles became dehydrated, which increased the crystallite sizes and improved the crystallinity of the samples. In con-

In this work, BiPO4/Eu of different polymorphs was prepared using a simple hydrothermal method. It is found that a hexagonal phase (HP) was formed at 100 °C, which transformed to a low-temperature monoclinic phase (LTMP) when hydrothermal temperature was increased to 160 °C. This LTMP transformed reversely to HP when the temperature increased beyond 180 °C. This phase evolution is quite distinct from those when using high-temperature calcinations (CrystEngComm201113). Accompanying this phase evolution, sample morphology varied from homogeneous rodlike shape to prismlike shape, while the lattice strain features changed from tensile to compressive, and then to tensile, as followed by a decrease in symmetry of tetragonal PO4 groups from pseudo-T d to C 1. These variations were closely related to the reaction mechanism in solution chemistry, in which two interfacial processes were indicated, differing from the ionic diffusion process during calcination. As a consequence, luminescence properties become sensitive to polymorphs. All Judd–Ofelt parameters (Ωλ, λ = 2, 4, 6) were calculated to evaluate the asymmetric nature for the polymorph-sensitive luminescence. It is found that the Ω2 value for HP was 1.66 × 10–20 cm2, which increased to 2.10 × 10–20 cm2 for LTMP; meanwhile, the quantum efficiency increased from 9.33% for HP to 36.09% for LTMP. These results demonstrated that BiPO4 of different polymorphs can be obtained through the hydrothermal method, which may enrich the significance of solution chemistry in preparing advanced materials of tailored functionalities.

In this work, preparation of cereal-like architectures Y V O(4) and Y V O(4):Ln(3 + ) (Ln = Eu, Sm, Dy, Tb) was initiated using a hydrothermal method. During the formation reaction, Na(3)C(6)H(5)O(7).2H(2)O was used to effectively adjust the concentration of Y(3 + ) species necessary for cereal-like architectures. Phase structure, surface chemistry, morphology, and photoluminescence were characterized by x-ray powder diffraction, Fourier transformed infrared spectra, scanning electron microscopy, transmission electron microscopy, and photoluminescence spectra. All samples crystallize in a tetragonal zircon structure, stably showing a homogeneous cereal-like morphology. This special morphology was constructed by self-assembly of tiny primary particles with a dimension of 31-32 nm. With increasing atomic number of Ln(3 + ), the lattice dimension of the cereal architectures became monotonously enlarged. This cereal-like architecture is proved unique in significantly improving the quantum efficiencies: the internal quantum efficiencies of (5)D(0) for Ln = Eu and (4)F(9/2) for Ln = Dy were 14.6% and 11.4%, respectively, which are all superior over those of the counterparts of nanoparticles reported in the literature. The average lifetime of the (5)D(0) level for Ln = Eu was calculated to be 98 micros, which is longer than that of 50 micros of the (4)F(9/2) level for Ln = Dy. The strong photoluminescence might be the consequence of the effective energy transfer due to the greatly reduced defect centers from this special self-assembly structure.