The nature and morphology of titanium dioxide films play a significant role in determining the overall efficiency of dye-sensitized solar cell (DSSCs). In this work, the preparation of nanostructured titania particles by sol-gel method (SG-TiO?) and its characterization were investigated for the application of DSSCs. The samples were characterized by XRD, XPS, FE-SEM, BET and FT-IR analysis. The energy conversion efficiency of SG-TiO? was approximately 8.3 % under illumination with AM 1.5 (100 mW/cm2) simulated sunlight. DSSCs made of SG-TiO? nanocrystalline films as photoanodes achieved better energy conversion efficiency compared to those prepared using commercially available Degussa P25.

Ba5Al3F19:Eu2+ blue-emitting phosphors were synthesized by the solid state reaction in a reductive atmosphere. The crystal structure of Ba5Al3F19: Eu2+ phosphors were characterized by using the X-ray powder diffraction (XRD) measurement. The luminescence properties are investigated systematically based on the crystal structure. Emission and excitation spectra of the Ba5Al3F19:Eu2+ phosphor along with the decay curves were characterized. Under the excitation of UV light, the phosphor exhibits a broad band emission around 410 nm ascribed to the allowed 4f(6)5d -> 4f(7)(S-8(7/2)) transition, together with a sharp line at 360 nm corresponding to the forbidden 4f(7)(P-6(7/2)) -> 4f(7)(S-8(7/2)) transition of the Eu2+ ions. The temperature dependent emission spectra and decay curves were measured to investigate the origins of the emission and the thermal stabilities of the as-prepared phosphors. The as-prepared Ba5Al3F19:Eu2+ phosphors display interesting and stable luminescence properties, which can act as promising blue-emitting phosphor candidates. (C) 2017 Elsevier B.V. All rights reserved.

Mn4+-doped Y2MgTiO6 phosphors are synthesized by the traditional solid-state method. Powder X-ray diffraction, scanning electron microscope, and energy-dispersive X-ray spectrometer are employed to characterize the samples. The Mn4+-doped Y2MgTiO6 phosphors show the far-red emission at ∼715 nm, which is assigned to the 2Eg → 4A2 spin-forbidden transition of Mn4+. The temperature-dependent luminescent dynamics of Mn4+ is described by a complete model associated with electron-lattice interaction and spin-orbit coupling. The noncontact optical thermometry of Y2MgTiO6:Mn4+ is discussed based on the fluorescence intensity ratio of thermally coupled anti-Stokes and Stokes sidebands of the efficient ∼715 nm far-red emission in the temperature range of 10-513 K. The maximum sensor sensitivity of Y2MgTiO6:Mn4+ is determined to be as high as 0.001 42 K-1 at 153 K, which demonstrates potential applications for the optical thermometry at low-temperature environments.

Series of Mn4+-activated LiLa2NbO6 red emitting phosphors were prepared by the solid state method. The structural and luminescence properties are investigated on the basis of X-ray diffraction (XRD), emission and excitation spectra, and luminescence decay curves. The LiLa2NbO6 :Mn4+ phosphors can be efficiently excited by near-UV to blue light and exhibit bright red emission at around 712 nm, which can be assigned to the E-2(g) -> (4)A(2g) transition of the 3d(3) electrons in [MnO6] octahedra. Temperature dependent emission spectra and decay curves from 10 to 480 K are analyzed to understand the luminescence mechanism of Mn4+ in LiLa2NbO6 lattice. Notably, such a novel red emitting phosphor shows special anti-thermal quenching behavior. (C) 2018 Elsevier B.V. All rights reserved.

Eu3+-doped Gd10(1-x)Eu10xV2O20 (x = 0 – 1) phosphors were synthesized via the sol-gel process. The formation of a single phase compound was verified through the X-ray diffraction studies. Luminescence properties of Gd10V2O20:Eu3+ are investigated by optical and laser excitation spectroscopy. The emission and excitation spectra, luminescence decays were measured in the temperature region 7–300K. The strong emission due to the vanadate group of Gd10V2O20:Eu3+ is observed at low temperature. The charge transfer transition of Eu3+ depends strongly on the Eu3+-concentration in Gd10V2O20:Eu3+. The emission intensity as a function of Eu3+ concentration under excitation of charge transfer band is inconsistent with that of the 4f7 states (the 5L6 state) of Eu3+. The energy transfer occurs between two Eu3+ ions at low Eu3+ concentration (< 10mol%), while energy diffusion dominates at high Eu3+ concentration.

An analytic absorption function was derived to investigate the dynamics of photoisomerization in a poly(methyl methacrylate) thin film doped with disperse orange 3 (DO3). The temporal absorption measured using the pump-probe method was well-behaved, following an analytic function with a single exponential term. The isomerization and thermal-relaxation rates were evaluated by curve-fitting. The analytic absorption function was validated by measuring the thermal-relaxation rates with the pump separately on and off. Using this function, an analytic method for determining the photoisomerization parameters was demonstrated: for DO3 in poly(methyl methacrylate), the photoisomerization quantum yields for trans-cis and cis-trans processes were determined to be ϕTC=0.12±0.01 and ϕCT=0.77±0.06, respectively. The absorption cross section for the cis isomer was measured to be σC=(0.92±0.03)×10−16cm2. This analytic method can thus be used to characterize the dynamics of photoisomerization in dye doped thin films.

Eu3+-doped NaGd(WO4)(2) nanophosphors were synthesized via a facile one-step hydrothermal method without any surfactants or a further heat treatment. X-ray powder diffraction (XRD), scanning electron microscope (SEM), fourier transform infrared spectroscopy (FT-IR), the photoluminescence (PL) excitation and emission spectra, and decay curves were used to characterize NaGd(WO4)(2):Eu3+ phosphors. The results show that the Eu3+-concentration has little influence on the structure and morphology of the as synthesized samples. However, pH value plays a vital role on the structure and morphology of NaGd(WO4)(2). The well-crystallized sheet-like NaGd(WO4)(2) phosphors can be obtained only at pH = 5-7. On the basis of the time -dependent synthesis, a possible growth mechanism of sheet-like architectures is proposed. The luminescence properties of NaGd1-x ELx(WO4)(2))2 (0 <= x <= 1) are investigated. It is found that the charge transfer band of Eu3+ shifts to lower energy and broadens with increasing the Eu3+concentration. (C) 2017 Elsevier B.V. All rights reserved.

The luminescence properties and site occupation of NaScP2O7:Ce 3þ and KScP2O7:Ce 3þ phosphors are reported for the first time. Two principal Ce3þ sites [Ce (I) and Ce (II)] are observed. One of the Ce3þ centers is found to be produced by the direct substitution of the dopant ion for Naþ/Kþ without a local charge compensation. Another center is ascribed to an associate of a Ce3þ ion and a cation vacancy. The zero-phonon line E0 and Stokes shift are calculated. & 2016 Elsevier B.V. All rights reserved.

La 2 W 3 O 12 :Dy 3+ phosphors were synthesized by using a high-temperature solid-state reaction. The Dy 3+ concentration in the La 2 W 3 O 12 lattice was varied from 0.01 to 100 %. The crystalline phases of the samples were confirmed by using an X-ray diffraction analyses. Emission and excitation spectra and decay curves of Dy 3+ ions in the La 2 W 3 O 12 lattices were measured at room temperature. The two charge-transfer (CT) bands that overlapped in the wavelength region 210 - 320 nm were identified as being due to the CT transitions of O 2− -Dy 3+ and WO 4 2− . The decay times of the 4 F 9/2 emission were shortened with increasing Dy 3+ concentration, and the decay curves were slightly nonexponential even at low Dy 3+ concentration. The decay curves were well fitted by the Inokuti-Harayama model based on the energy-transfer process between two Dy 3+ ions at concentrations lower than 10 mol%. On the other hand, the energy diffusion among Dy 3+ ions dominate the energy-transfer process at higher Dy 3+ concentrations up to 100 mol%.

The luminescence properties and site occupation of NaScP2O7:Ce3+ and KScP2O7:Ce3+ phosphors are reported for the first time. Two principal Ce3+ sites [Ce (I) and Ce (II)] are observed. One of the Ce3+ centers is found to be produced by the direct substitution of the dopant ion for Na+/K+ without a local charge compensation. Another center is ascribed to an associate of a Ce3+ ion and a cation vacancy. The zero-phonon line E0 and Stokes shift are calculated.

Europium- (Eu-) doped BaNb(2)V(2)O(11)powders with layered mixed -anion structure were prepared through the solid state method successfully. The obtained powders were characterized using X-ray powder diffraction (XRD), structural refinement, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), ultraviolet visible (UV-vis) absorption spectra, and photoluminescence (PL) measurements. The experimental results demonstrate that BaNb2V2O11 powders could absorb the UV-vis light effectively with the band gap energy of 2.219 eV. The introduction of Eu5 in the host contributes to the decrease of the band gap energy (2.137 eV). Moreover, the photocatalytic activities of the obtained powders were evaluated through the photocatalytic degradation of the methylene blue (MB) solutions under visible light irradiation as a function of time. All the results indicate that the BaNb2V2O11 powders can be used as a potential visible -light -driven photo catalyst. Notably, due to the introduction of Eu3+, the photocatalytic degradation rate of MB solutions could be improved dramatically. The influence of the existence of Eu3+ on the photocatalytic properties is further discussed in detail based on the crystal structure characteristic.

Lanthanum tritungstates, La2W3O12, were prepared by using a conventional high-temperature solid-state reaction. The formation of a single-phase compound with the monoclinic structure of La2W3O12 was verified through X-ray diffraction (XRD) studies. The luminescence propeities of La2W3O12 were investigated by using optical and laser-excitation spectroscopy. The excitation and the emission spectra and the decay curves were measured in the temperature range 7 − 300 K. The charge-transfer transition of WO42− was identified in the excitation and the emission spectra under excitation by ultraviolet radiation. A strong green luminescence was observed at 500 nm with a bandwidth of 4240 cm −1 at temperatures lower than 60 K; then the thermal quenching occurred with increasing temperature. The thermal quenching behaviors of the luminescence intensity and the decay time could be explanined by using a simple thermal quenching model.

New potassium gadolinium phosphate [K3Gd5(PO4)(6)] doped with Eu3+, Ce3+, Tb3+ and co-doped with Ce3+ and Tb3+ phosphors were prepared by high temperature solid state synthesis. Phase purity of the powders was checked by X-ray powder diffraction. Luminescence and excitation spectra of samples were reported. In particular, the interaction mechanism between Eu3+ ions was investigated in terms of the Inokuti-Hirayama model; it was found that the interactions between Eu3+ can be assigned to dipole-dipole interaction. K3Gd5(PO4)(6):Eu3+ could act as a candidate for solid state lighting due to its strong absorption band in the near-UV region (350-400 nm). The energy transfer from Ce3+ to Tb3+ was confirmed and the mechanism was studied using Dexter's theory; it is concluded that electric dipole-dipole interaction predominates in the energy transfer process from Ce3+ to Tb3+ in the K3Gd5(PO4)(6) host. The energy transfer efficiency and critical distance were also investigated. (C) 2016 Elsevier B.V. All rights reserved.

Eu3+-doped Na4La2(CO3)5 rod-like nanophosphors were prepared by a hydrothermal method, and the photoluminescence excitation and emission spectra, the concentration quenching of the phosphors, the luminescence color chromaticity and the activation energy for thermal quenching were measured. The results indicate that all samples possess the pure monoclinic phase. Na4La2−2xEu2x(CO3)5 (x=0–1) phosphors exhibit reddish luminescence with the dominant 5D0→7F2 transition of Eu3+ at 617nm. Na4Eu2(CO3)5 has the strongest emission without luminescence quenching, which is benefited from its structural characteristics: long distance between Eu3+ ions and the average La–O–La bond angle of 128.10°. Moreover, the activation energy of thermal quenching and quantum efficiency of Na4Eu2(CO3)5 nanophosphors are 0.356eV and 13.5%, respectively.

A new red-emitting phosphor of Eu3+-doped Na3La8V3O21 was successfully synthesized by the high-temperature solid state reaction. The phase formation was confirmed by X-ray powder diffraction (XRD) analysis. The morphology of the phosphor was analyzed by scanning electron microscopy (SEM). The optimal doping concentration of Na3La8V3O21:Eu3+ is about 20mol%. The detailed luminescence properties, e.g., the excitation spectra, the luminescence spectra and quantum efficiency under the excitation of near-UV, and decay lifetimes were reported. The phosphors can be efficiently excited by near-ultraviolet light and exhibit a bright red luminescence around 618nm ascribed to the forced electric dipole transition 5D0→7F2 of Eu3+ ions. The thermal stabilities and the absolute luminescence quantum efficiency (QE) were reported. The phosphors of Eu3+-activated Na3La8V3O21 have been discussed as a candidate for white solid state lighting indicating.

Na4La2−2xTb2x(CO3)5 (x=0–0.5) nanophosphors were prepared via hydrothermal method, and the photoluminescence, concentration quenching, luminescence color chromaticity and thermal activation energy of samples were measured. The results indicate that samples with x values of 0–0.5 possess the pure monoclinic phase with an absorption edge at 250nm. Na4La2−2xTb2x(CO3)5 (x=0–0.5) phosphors exhibit green luminescence, attributed to the 5D4→7FJ (J=6, 5, 4, 3) transitions of Tb3+. The concentration quenching takes place at about x=0.3, but no decreased luminescence intensity is observed; moreover, the activation energy of thermal quenching of Na4LaTb(CO3)5 nanophosphor was calculated to be 0.116eV. The luminescence properties of Na4La2−2xTb2x(CO3)5 are benefited from its structural characteristics: long distance between Tb3+ ions and the ordered distribution of Tb3+ ions.

Nanosized particles of strontium bismuth vanadate SrBi3VO8 were prepared via the Pechini method on the base of citrate‐complexation route. The samples were characterized using X‐ray powder diffraction (XRD), scanning electron microscope (SEM), energy dispersive X‐ray spectra (EDX), X‐ray photoelectron spectroscopic (XPS), and UV–vis absorption spectrum. This bismuth‐containing vanadate presents an efficient absorption in the UV–visible light wavelength region with a narrow band‐gap energy of 2.36 eV and an indirect allowed electronic transition. It is well‐known that hybridization of the 6s and 6p orbitals of Bi3+ could result in lone electron pair and yield some very interesting properties. The photocatalytic activities of SrBi3VO8 nanoparticles were evaluated by the photodegradation of methylene blue (MB) under visible light irradiation in air atmosphere. These results indicate that SrBi3VO8 could be a potential photocatalyst driven by visible light. To understand the charge generation and separation process, the luminescence as well as the decay lifetimes was investigated in the same samples for photocatalysis.

A series of Ce3+ doped Ca3B2O6 phosphors with different doping concentration were prepared by using a high-temperature solid-state reaction technique. The luminescence properties under UV excitation were studied. From the photoluminescence (PL) excitation and emission spectra we conclude that two Ce3+ sites (Ce I and Ce II) exist in host crystal. The tunable emission properties of Ce3+-doped Ca3B2O6 phosphors are analyzed by using Ce3+ ions occupancy probability between Ce I and Ce II and possible energy transfer between Ce I and Ce II center.