Shujuan Han

Morphology control and luminescence properties of YAG:Eu phosphors prepared by spray pyrolysis

Starting from nitrate aqueous solutions with citric acid and polyethylene glycol (PEG) as additives, Y3Al5O12:Eu (YAG:Eu) phosphors were prepared by a two-step spray pyrolysis (SP) method. The obtained YAG:Eu phosphor particles have spherical shape, submicron size and smooth surface. The effects of process conditions of the spray pyrolysis on the crystallinity, morphology and luminescence properties of phosphor particles were investigated. The emission intensity of the phosphors increased with increasing of sintering temperature and solution concentration due to the increase of the crystallinity and particles size, respectively. Adequate amount of PEG was necessary for obtaining spherical particles, and the optimum emission intensity could be obtained when the concentration of PEG was 0.10 g/ml in the precursor solution. Compared with the YAG:Eu phosphor prepared by citrate-gel (CG) method with non-spherical morphology, spherical YAG:Eu phosphor particles showed a higher emission intensity.

A New Deep-Ultraviolet Transparent Orthophosphate LiCs2PO4 with Large Second Harmonic Generation Response

LiCs2PO4, a new deep-ultraviolet (UV) transparent material, was synthesized by the flux method. The material contains unusual edge-sharing LiO4-PO4 tetrahedra. It exhibits a very short absorption edge of λ = 174 nm and generates the largest powder second harmonic generation (SHG) response for deep-UV phosphates that do not contain additional anionic groups, i.e., 2.6 times that of KH2PO4 (KDP). First-principles electronic structure analyses confirm the experimental results and suggest that the strong SHG response may originate from the aligned nonbonding O-2p orbitals. The discovery and characterization of LiCs2PO4 provide a new insight into the structure-property relationships of phosphate-based nonlinear optical materials with large SHG responses and short absorption edges.

Sr4B10O18(OH)2·2H2O: a new UV nonlinear optical material with a [B10O23]16− building block

A new ultraviolet (UV) nonlinear optical (NLO) crystal Sr4B10O18(OH)2·2H2O has been synthesized using the hydrothermal method. It crystallizes in the triclinic space group P1 (no. 1) with lattice constants a = 6.4991(6) A, b = 6.5059(6) A, c = 11.3175(11) A, α = 88.458(6)°, β = 86.019(5)°, γ = 61.351(5)°, Z = 1. The fundamental building block of the structure is a [B10O23]16− unit which consists of two stereo-isomeric configurations of [B5O12]9− groups. The structure exhibits a ∞[B10O18]6− three dimensional network with 9-membered tunnels along the b-axis where the Sr cation, OH anion and H2O molecule are located. Powder second harmonic generation (SHG) measurements indicate that Sr4B10O18(OH)2·2H2O is type-I phase-matchable and displays a SHG response of about 2 × KH2PO4. The UV-Vis-NIR diffuse reflectance spectrum shows that its cutoff edge is lower than 190 nm. Density functional theory (DFT) calculations on electronic structures and SHG coefficients confirm the experimental results.

Ba2B10O17: a new centrosymmetric alkaline-earth metal borate with a deep-UV cut-off edge

A new centrosymmetric alkaline-earth metal borate, Ba2B10O17, has been successfully synthesized through high-temperature solid-state reactions. The single-crystal X-ray structural analysis shows that Ba2B10O17 crystallizes in the triclinic space group P1[combining macron]. The parameters of the triclinic unit cell are a = 6.7128(3) Å, b = 9.8698(4) Å, c = 9.9998(4) Å, α = 76.860(3)°, β = 83.200(3)°, γ = 73.332(3)°, and Z = 2. The title compound features a [B10O17]∞ three-dimensional anionic framework with infinite channels in which the Ba(2+) cations are located. Ba2B10O17 possesses a large experimental band gap of 6.29 eV and a short cut-off edge lower than 180 nm proved by the transmission spectrum on a single crystal sample 0.5 mm in thickness. The calculated band structures and the density of states of Ba2B10O17 suggest that its indirect energy gap is 5.97 eV which agrees with the experimental result. The thermal behavior and the IR spectrum of Ba2B10O17 are also reported in this work.

KPb2(PO3)5: a novel nonlinear optical lead polyphosphate with a short deep-UV cutoff edge

It is a challenge to explore deep-ultraviolet (DUV) nonlinear optical (NLO) crystals in a Pb-containing system due to the red-shift caused by the Pb atom. Here, three new NLO crystals APb2(PO3)5 (A = K, Rb and Cs) were synthesized. Their single-crystal X-ray diffraction patterns indicate that they are isostructural and crystallize in the asymmetric space group of Pn (No. 7). Interestingly, KPb2(PO3)5 displays moderate powder second harmonic generation (SHG) intensities (0.5× KDP) in type I phase matching behaviors with a short UV cut-off edge of 177 nm, which is the shortest UV cut-off edge among Pb-containing NLO crystals. To better understand the blue-shift of the band gap of KPb2(PO3)5, the theoretical calculations by density functional theory were done. In addition, RbPb2(PO3)5 shows a SHG response of 0.3× KDP and is phase matchable. According to first-principles calculations, compared with RbBa2(PO3)5, KPb2(PO3)5 has a noticeable enhancement in birefringence (0.021 and 0.009 at 1064 nm for KPb2(PO3)5 and RbBa2(PO3)5, respectively). Furthermore, the relationship between its structure and NLO properties was also discussed by calculation of dipole moments.

Borate Fluoride and Fluoroborate in Alkali-Metal Borate Prepared by an Open High-Temperature Solution Method

By incorporation of the largest-electronegativity F atoms into borate, two novel halogen-containing borates, Li6RbB2O6F and K3B3O3F6, have been synthesized. Interestingly, Li6RbB2O6F is the first borate fluoride in alkali-metal borate. Meanwhile, K3B3O3F6 appears to be the first confirmed alkali-metal fluoroborate crystal grown by a high-temperature solution in air.

Ba4(BO3)3(SiO4)·Ba3X (X = Cl, Br): new salt-inclusion borosilicate halides as potential deep UV nonlinear optical materials

Based on the combination of two different anionic groups (SiO4 and BO3) and the utility of a XBa6 (X = Cl, Br) polar template, two new salt-inclusion compounds, Ba4(BO3)3(SiO4)·Ba3X (X = Cl, Br) have been successfully synthesized by the high-temperature solution method for the first time. They are isostructural and their structures feature the ∞3[Ba4(BO3)3(SiO4)] framework with 1D channels along the c axis, in which resided the polar ∞1[Ba3X] chains. It is worth noting that they are the first alkaline-earth metal borosilicate halides to be used as nonlinear optical (NLO) materials. The second harmonic generation (SHG) measurements show that they have SHG responses similar to that of KH2PO4 (KDP) and are type-I phase-matchable. In addition, they melt congruently and exhibit a wide transparent region with the UV cut-off edge below 190 nm. These properties make Ba4(BO3)3(SiO4)·Ba3X potential deep UV NLO materials.

Effect of the [Ba2BO3F]∞ Layer on the Band Gap: Synthesis, Characterization, and Theoretical Studies of BaZn2B2O6·nBa2BO3F (n = 0, 1, 2).

Two new zincoborate fluorides with the common formula BaZn2B2O6·nBa2BO3F (n = 1, 2) have been successfully synthesized for the relationship study between the band gaps and crystal structures in zinc-containing borate fluorides. Ba3Zn2B3O9F with n = 1 in the common formula belongs to the orthorhombic space group Pnma (No. 20), and Ba5Zn2B4O12F2 with n = 2 in the common formula crystallizes in the monoclinic space group C2/c (No. 62). They can both be seen as compounds with the n[Ba2BO3F]∞ (n = 1 or 2) layer inserted in the structure of BaZn2B2O6. UV-vis-near-IR diffuse-reflectance spectra show that the band gaps of BaZn2B2O6·nBa2BO3F (n = 0, 1, 2) gradually increase with more [Ba2BO3F]∞ layers inserted. The first-principles calculation indicates that the inserted n[Ba2BO3F]∞ layers play a positive effect in increasing the band gaps of zincoborate fluorides. Furthermore, the IR spectra, thermal behaviors, and refractive indices of these compounds are also studied.

Effect of halogen (Cl, Br) on the symmetry of flexible perovskite-related framework.

The perovskite structure is a good candidate for the design of functional materials. On the basis of the combination of B6O13 groups and XM6 (X = Cl, Br; M = alkali metals) octahedra, three new perovskite-related crystals Na3B6O10Cl, RbNa2B6O10Cl, and RbNa2B6O10Br have been synthesized by a high-temperature solution method for the first time. Na3B6O10Cl and RbNa2B6O10Cl are isostructural and crystallize in the noncentrosymmetric (NCS) space group P212121 (No. 19), while RbNa2B6O10Br belongs to the centrosymmetric (CS) space group Pnma (No. 62). The phenomenon that Cl-containing borates are not isostructural with corresponding Br-containing borates is extremely rare among borates. Detailed structure analysis suggests that the difference is owing to the effect of the halogen (Cl, Br) on the symmetry of the flexible perovskite-related framework. In addition, thermal analyses, IR spectroscopy, the UV-vis-NIR diffuse reflectance spectrum, and first-principles theoretical studies have also been performed on the three compounds.

New type of complex alkali and alkaline earth metal borates with isolated (B12O24)12− anionic group

Compounds with isolated anionic groups often exhibit special linear and nonlinear optical properties and possess potential applications such as birefringence, second harmonic generation and stimulated Raman scattering crystals. In this paper, two new alkali and alkaline earth mixed-metal borates, Li3KB4O8 and LiNa2Sr8B12O24F6Cl, with isolated (B12O24)(12-) anionic groups have been successfully synthesized by spontaneous crystallization. Their structures were determined by single crystal X-ray diffraction and they both crystallize in the same space group, R3[combining macron]. More interestingly, further structure comparison shows that the discovered anhydrous borates with the (B12O24)(12-) groups also crystallize in the same space group R3[combining macron], which is related with the local symmetry of the (B12O24)(12-) groups. These structural features suggest that the crystal structures of the family of compounds depend more on their anionic groups. In addition, the property characterizations of the two new borates were investigated by TG-DSC, IR and UV-vis-NIR diffuse reflectance.