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Tungsten bronze-type ceramics have been widely investigated as one of the best ferroelectric frameworks. RE-doped Ba2NaNb5O15 phosphors have been reported with unsatisfactory luminescence efficiencies. It is attractive to develop a ferroelectric showing multifunctionality with electric and luminescence performances. In this work, the cation substitutions of (Eu3+ → Ba2+) and (Ti4+ → Nb5+) are realized in tungsten bronze-type Ba2NaNb5O15 to develop optoelectronic ceramics (luminescence + dielectric). The introduction of framework-disturbances is regarded to be an effective strategy on modification of the luminescence and electronic properties. The ceramics were prepared using the high-temperature solid-state reaction. The cation disorder due to Eu3+/Ti4+ co-doping can significantly enhance the luminescence efficiency and thermal stability. Meanwhile, Eu3+/Ti4+ co-doping has a strong influence on the microwave dielectric performances, that is, the dielectric constant (er) values and quality factor (Q × f) were significantly improved. The temperature coefficient of resonant frequency (τf) is optimized. The improvement of optoelectronic effects shows a significant dependence on cation disorder of the ferroelectric framework.

In this work, a series of mixed pyrophosphates (Mg1-xMnx)2P2O7 (x = 0-1.0) were prepared for the first time using a solid-state reaction method, which exhibits two kinds of structural variants, that is, α-(low temperature) and β-(high temperature) phases. The detailed phase-formations were determined via structural Rietveld refinements and the luminescence transitions of 4T1 → 6A1 in Mn2+. The phase-formation of (Mg1-xMnx)2P2O7 (x = 0-1.0) shows a strict dependence on Mn2+ doping contents in the lattices. (Mg1-xMnx)2P2O7 has an α-Mg2P2O7 phase when the Mn2+-doping concentration is lower than x ≤ 0.1. With an increase of Mn2+ substitution above 20 mol% (x = 0.2-1.0), (Mg1-xMnx)2P2O7 presents only the β-phase even at room temperature, while (Mg1-xMnx)2P2O7 (x = 0.15) shows a mixed formation of α- and β-Mg2P2O7 phases. The crystallographic surrounding of the Mn2+ activators in different structures had a strict influence on the spectral profile, luminescence efficiency, and color centers. Interestingly, in this series of phosphors, (Mg1-xMnx)2P2O7 (x = 0.15) with the mixed phases of α- and β-type has overwhelming luminescence abilities such as the best luminescence intensity and high thermal stability. The pyrophosphates were confirmed to qualify for red-emitting LED lamps.

BiVO4 was selected as a model to manipulate the luminescence and photocatalysis by Eu3+ ions incorporation. Eu3+-uniformly doped and surface-localized BiVO4 was prepared by a coprecipitation route ...

Bismuth niobate semiconductors are of considerable interest in both contaminant degradation and H2-generation. However, the wide band gap strictly limits the optical absorption in visible-light wavelength. In this work, a new niobate semiconductor Bi3Nb17O47 was prepared with co-precipitation synthesis. To modify the band structure, Te4+-, Ti4+-, and Te4+/Ti4+-doping were conducted in Bi3Nb17O47 lattices. Rietveld refinements were used to investigate the crystal phase and structure. The UV–vis absorption measurements concluded that Te4+-, Ti4+- doping could greatly modify the band energy of Bi3Nb17O47. The Te4+/Ti4+-doped sample could harvest more visible light in the longer-wavelength region being favorable for photocatalysis performances. This was verified by RhB photodegradation tests under the visible-light irradiation (λ > 420 nm). To discuss the photocatalytic mechanisms, XPS and impedance spectra were measured. The improved photocatalysis was related to the microstructure changes, charge carrier dynamics, oxygen vacancies, and redox couples of multivalent ions. The present work provides a valid route to modify the band structure and to improve the photocatalysis abilities via impurity ions Te4+/Ti4+-doping in bismuth niobate semiconductors.

The Bi3+-containing semiconductors have been widely reported as potential photocatalyst candidates for water-splitting and environmental pollution problems. This work reported a new kind Bi-heterojunction of LiBiO2/Bi2O3, which was synthesized by the facile hydrothermal reactions. The XRD (X-Ray powder diffraction) measurement was applied to investigate the phase formations. The composite crystals developed in the well-crystallized ultrathin nanosheets with the thickness about 320 nm. The UV–visible absorption indicated that LiBiO2/Bi2O3 heterojunction has a similar optical absorption edge to that of LiBiO2 (2.04 eV). This confirms the heterojunction has the actively optical abilities in visible wavelength region. The photocatalytic activities were tested by photo-degradation effects of rhodamine B (RhB) dye and colorless phenol solutions under the visible light irradiation. The experiments suggested that the photocatalysis activities could be greatly improved via coupling Bi2O3 in LiBiO2/Bi2O3 heterojunctions. The migration of light-induced charge-carriers adopts a typical direct Z-scheme in LiBiO2 and LiBiO2/Bi2O3 heterojunctions.

Aluminosilicate with the cordierite structure (Mg2Al4Si5O18) represents a big family of technologically important compounds with typical α- and β-phases. Crystallographic sites for transition metal and rare earth ions in the cordierite structure have always been a controversial topic. In this work, the (Mg1−xMnx)2Al4Si5O18 (x = 0–1.0) solid solution is firstly confirmed via Rietveld structural refinements and luminescence dynamics. The well-crystallized ceramics were prepared by high-temperature solid-state reaction, and then characterized using structural, morphological, luminescence, decays, and thermal quenching measurements. (Mg1−xMnx)2Al4Si5O18 (x = 0–1.0) undergoes structural changes from the orthorhombic β-phase (x = 0–0.2), α-phase (x = 0.3–0.9) and Mn-cordierite (x = 0.95–1.0) (isostructural to β-phase). It is technically meaningful that high-temperature α-phase cordierite Mg2Al4Si5O18 can be stabilized via Mn2+-doping (30–90 mol%). The crystallographic site-occupation of Mn2+ activators is clearly identified. Interestingly, (Mg1−xMnx)2Al4Si5O18 (x = 0.01–1.0) presents tunable colors produced by two distinct luminescence centers, that is, green Mn2+(A) and red Mn2+(B) bands centered at about 530 and 650 nm, respectively. The most efficient excitation wavelengths and decay times of Mn2+(A) are distinct from those of Mn2+(B). The Mn2+(A) green centers are only observed in β-phase cordierite (x = 0.01–0.2) with a dominant emission intensity compared with Mn2+(B), while the Mn2+(B) red centers are observed in all samples (x = 0.01–1.0). The Mn2+(A) center fills in the hexagonal channels, while Mn2+(B) is related to the substitution of Mn2+ for the octahedral Mg2+ site in the cordierite lattices. The luminescence mechanism of Mn2+ in (Mg1−xMnx)2Al4Si5O18 was proposed. The results can be used for basic and application research studies in a wide family of rare earth or transition-metal-doped cordierite materials.

There is a close correlation between the photoluminescence and photocatalysis of a semiconductor because the two processes involve the same electronic transition. Eu3+ is one of the most popular rare-earth ions; it presents efficient luminescence and improved photocatalysis. Usually, the luminescence from the higher states (5D1,2) of Eu3+ can be hardly observed due to cross-relaxation processes. This work demonstrates a particularly developed transition from the 5D1 level of Eu3+ and its significant contribution to the improved photocatalysis of (Bi3Li)O4Cl2via prolonging the decay time of the excited state. Single-phase (Bi3−3xEu3xLi)O4Cl2 (x = 0, 0.01, 0.03, 0.05) was synthesized by the sol–gel method in combination with a solid-state reaction. This is a bismuth layer structure with [(Bi/Li)O2]2+ layers formed by alternative Bi3+ and Li+ stripes. The intrinsic luminescence of (Bi3Li)O4Cl2 (λem = 500 nm) with a decay time of 0.26 μs was detected even at 300 K. Unusually, the phosphor shows a prominent transition from 5D1 in (Bi3−3xEu3xLi)O4Cl2. Moreover, in addition to 5D0 → 7F3, 5D0 → 7FJ (J = 0, 1, 2, 4) is characterized by intense transitions with comparable intensities. The intrinsic emission of (Bi3Li)O4Cl2 has a decay time which involves the band transition of an electron from the valence band to the conduction band. In Eu3+-doped (Bi3Li)O4Cl2, there are midgap states formed by the 5D1 level with a longer lifetime of about 60 μs. The D1 levels of Eu3+ significantly contribute to the separation of light-induced charges by prolonging the decay time of the excited states. This work demonstrates a simple strategy to develop optical materials with simultaneous luminescence and has improved the photocatalysis in bismuth oxychlorides featuring strong polarization and rigid phonons.

Luminescence properties of the Cr3+-doped LiGaW2O8 crystals are investigated by laser excitation spectroscopy. The powder samples for various Cr3+ concentration were prepared by high-temperature solid state reaction. The temperature behaviors of the emission intensity and the decay time of the self-activated LiGaW2O8 host are discussed. The emission spectra and decay times of LiGa1-xW2O8:xCr3+ are measured under UV excitation in the temperature range 10–300 K. The luminescence quenching of LiGaW2O8:Cr3+ as functions of temperature and Cr3+-concentration is explained by structural and spectral characteristics.

Ce3+, Tb3+ and Ce3+-Tb3+ activated Ba3Y2(B2O5)3 phosphors were synthesized by a sol-gel pyrolysis method. The synthesized phosphors were investigated using X-ray diffraction (XRD) analysis, photoluminescence emission and excitation spectra and luminescence decay curves. In the Ce3+ activated Ba3Y2(B2O5)3 samples, two different Ce3+ centers (marked as Ce(1) and Ce(2)) could exist. The Ba3Y2(B2O5)3:Tb3+ phosphor shows some emission peaks at ∼350–650 nm among which the green emission peak at 540 nm is the strongest. For the Ba3Y2(B2O5)3:Ce3+, Tb3+ co-doped phosphor, the existence of energy transfer process from Ce3+ center to Tb3+ center is confirmed and the interaction mechanism between Ce3+ and Tb3+ in Ba3Y2(B2O5)3:Ce3+,Tb3+ system is dipole-dipole interaction based on Inokuti–Hirayama (I H) model.

Cs-doped α-Bi2O3 was synthesized via a facile hydrothermal reaction. The phase formations of the samples were investigated via X-ray powder diffraction (XRD) patterns and structural refinements. The samples present well-crystalized microplates with smooth surfaces and a thickness about 300 nm. The experiments revealed that the undoped and Cs-doped α-Bi2O3 microplates could crystallized in a pure monoclinic phase. The band gap of α-Bi2O3 could be reduced via the Cs-doping in the lattices. The photocatalytic activity on photo-degradation of methylene blue (MB) was significantly improved with the Cs-doping. The effective photocatalysis was discussed on the improved visible-light response, the enhanced dispersion in the valence band composed of hybrid orbitals of Bi6s, O2p and Cs3d, and the lowered electron–hole recombination.

Gd8V2O17 was prepared via the facile solid-state reaction. The optical absorption, temperature-dependent luminescence, and decay lifetimes were investigated. Gd8V2O17 has a direct allowed electronic transition with band gap energy of 3.18 eV. Under the excitation of UV light, the phosphor shows the typical self-activated luminescence from the charge transfer (CT) transitions in VO43− groups. The emission intensity has a nearly constant value from 10 to 150 K, while it increases above 150 K. And the emission has an abnormal blue-shift with the increase of temperature from 10 to 300 K, so the luminescence color varies from green to blue. Over the whole temperature ranges, the maximum emission wavelength showed a linear dependence on temperature; consequently, the temperature-dependent properties have a potential advantage in luminescence thermometry. The luminescence mechanism was discussed on the proposed two VO4 emission centers and the energy transfer between them.

Photoluminescence properties of CaS:Cu+, CaS:Mn2+ and CaS:Cu+, Mn2+ rare-earth -free phosphors prepared by a carbon-thermal reduction method were investigated. The emission spectrum of Cu+-doped CaS consists of two overlapped bands peaking at 415 nm (attributed to isolated Cu+ activator) and 475 nm (attributed to aggregated Cu+ center). The influence of Cu+ doping concentration on the emission spectrum is discussed. The emission spectrum of Mn2+-doped CaS exhibits a band emission peaking at 568 nm under 250 nm excitation. The emission spectra of the doubly activated CaS:Cu+, Mn2+ phosphors consist of Cu+ and Mn2+ emissions simultaneously, and their shapes depend strongly on the Mn2+ concentration. Based on the emission and excitation spectra of the CaS:0.15 mol%Cu+, xMn2+ phosphors, the energy transfer from Cu+ to Mn2+ takes place. The emitting colors of the doubly activated phosphors can also be tuned. In particular, the emitting color of CaS:0.15 mol% Cu+, 0.6 mol % Mn2+ sample is close to white light.

In the present study, BiNb5O14 and BiNb5O14/Nb2O5 heterojunction were prepared with co-precipitation synthesis. The crystal structure was studied via XRD patterns and Rietveld refinements, which has a typical tetragonal tungsten bronze (TTB)-type structure. The samples crystallized in micorods with a length of 1–4 µm and a diameter about 1 µm. As an indirect transition semiconductor, BiNb5O14 has a band energy of 2.81 eV with the valence-band formed by hybridized O-2p and Bi-6s, and the conduction band formed by Nb(6d) orbitals. The photocatalysis abilities of BiNb5O14 and BiNb5O14/Nb2O5 heterojunctions were evaluated via the photo-degradation of dye solutions. The photocatalytic activities were significantly improved via coupling BiNb5O14 with Nb2O5. In the photocatalysis reactions, •OH was the main reactive species, and the immigration rate of light-created charge-carriers was greatly improved via the heterojunction structure. The luminescence and decay lifetime were measured to discuss the photocatalysis mechanism.

Molybdenum and vanadium mixed oxides of Mo6V9O40 and Mo6V8.5Te0.5O40 were synthesized by the modified sol-gel method. The phase formation and structure were investigated through X-ray powder diffraction (XRD) patterns. The optical absorption measurements show that the sample has an efficient light response covering the region UV-visible to near IR wavelength. The two Mo-V mixed oxides of Mo6V9O40 and Mo6V8.5Te0.5O40 show an indirect forbidden transition with band energies of 1.67 eV and 1.64 eV, respectively. The multivalent cations (V and Mo ions) were confirmed via X-ray photoelectron spectroscopy (XPS) measurements. The effective photocatalysis of the samples was conducted via the photodegradation of RhB under visible-light irradiation (λ≥420 nm). The conductivity properties and lifetime of charge carriers were characterized via impedance spectra and luminescence decay curves respectively. It was suggested that intrinsic redox couples in these Mo-V mixed oxides lead to intervalence transfer between V5+/4+ and Mo6+/5+ couples, which can improve photocatalysis. This work offers a potential alternative material with rich intrinsic redox couples and defects toward high-performance photocatalyst.

Optical thermometry based on the adjacent thermally coupled levels of rare earth ions has been widely studied in the high temperature range, and shows unobvious effect at low temperature range. In this work, we propose a new method to achieve optical thermometry in 10˜300 K range through manipulating the energy transfer from WO66− to Ho3+. A comprehensive five-level rate-equation model is developed to establish the relation between lifetime ratios and temperature. It is found that the lifetime ratios of 540 nm (Ho3+) and 471 nm (WO66−) emissions are dependent on the phonon energy of Y2WO6 host and temperature. The values of sensor sensitivity reach the maximum 2.1% K−1 at 211 K in 30%Ho3+ doped Y2WO6, which is higher than the maximum of the reported phosphors at low temperature. It overcomes the shortcoming of unobvious thermal population of thermally coupled levels in low temperature range through traditional Boltzmann distributing method.

We present an optical pressure sensor KMgF3:Eu2+ suitable for experiments in diamond anvil cell (DAC), which we have calibrated against the ruby reference sensor at pressures ranging from atmospheric up to 30 GPa (300 kbar), at room temperature. The emission spectra of KMgF3:Eu2+ consist of one prominent emission line related to the 6P7/2 → 8S7/2 electronic transition (zero phonon line) accompanied by weak phonon sidebands. The energy of emission at atmospheric pressure was determined to be 27846 ± 7 cm−1. The edge of the excitation spectrum lies at wavelength around 325 nm (30800 cm−1) making it suitable to excite with He-Cd laser (325 nm). The sensor exhibits linear pressure shift of rate equal to −0.815 ± 0.007 cm−1/kbar at pressures up to 300 kbar. The pressure shift of the emission is totally reversible and the pressure sensor is suitable for multi cycle pressure experiments. The sensor's exceptional feature is that excitation and emission spectra lie in near UV, which makes it very convenient to use in high pressure optical measurements in visible and IR region with no interference from the sensor's luminescence.

Luminescence properties of sodalite Zn4B6O13:Mn2+ are investigated by optical and laser excitation spectroscopy in the temperature range 10 – 300 K. The samples of Zn4B6O13:Mn2+ are prepared in the carbon reducing atmosphere. The green emission at 540 nm are observed in Zn4B6O13:Mn2+ for various Mn2+ concentration. Optimum Mn2+ concentration and critical distances between Mn2+ ions in Zn4B6O13 are obtained by the luminescence intensity as functions of Mn2+ concentration. The decays of Mn2+ emission depend strongly on Mn2+ concentration due to the energy transfer and energy diffusion in Zn4B6O13:Mn2+. The fine structures consisting of the intense zero phonon line (ZPL) and weak vibrational sidebands are observed at low temperature. The relevant mechanism of excitation bands, ZPL, vibrational sidebands and the bandwidth as functions of temperature are interpreted in detail by energy level diagram of the 3d5 transition metal ions and configuration coordinated diagram. The high thermal stability of the Zn4B6O13:Mn2+ phosphor are observed in the temperature range 10–300 K.

Ce3+, Tb3+ co-doped T-phase orthosilicate Ba1.2Ca0.8SiO4 phosphors were prepared by means of solid state reactions. The synthesized samples were investigated using XRD and PL emission and excitation spectra. The emission spectra for Ce3+ doped Ba1.2Ca0.8SiO4 phosphors show broad bands in the 320–550 nm spectral region. The excitation spectra exhibit several absorption peaks in the range of 250–400 nm. Both the emission and excitation spectra are dependent on the excitation or monitoring wavelengths. We attribute these results to Ce3+ ions occupying two different crystallographic sites (i.e., Ce I and Ce II). The Ce3+, Tb3+ co-doped Ba1.2Ca0.8SiO4 phosphors show Tb3+-related line emissions in the 475–600 nm spectral region and Ce3+-related band emissions in the 350–525 nm spectral region when the 4f → 5d transition of Ce3+ is excited (λex = 345 nm), indicating that energy transfer from Ce3+ to Tb3+ takes place. Moreover, the emission intensity of 5D4 → 7F5 transition for Ba1.00Ce0.02Tb0.08Li0.10Ca0.8SiO4 is 30 times stronger than that of Ba1.04Tb0.08Li0.08Ca0.8SiO4 sample under 345-nm UV excitation.

Pure and V-doped NiTiO3 (NiTiO3:V) nanorods were synthesized via electrospinning synthesis using sol–gel precursors, followed by sintering the samples at 600 °C. And the subsequent Ag-loaded NiTiO3:V nanorods were prepared by the chemical precipitation method (Ag/NiTiO3:V). The phase formations were studied via X-ray powder diffraction (XRD) measurements. The Rietveld refinements were conducted to investigate the structural characteristics. The surface property of the nanorods was measured via morphologies and X-ray photon spectrascope (XPS) measurements. The absorption spectra of products indicate sufficient optical response in visible wavelength region. The indirect allowed band gap (2.18 eV) of NiTiO3 originates from the characteristic charge-transfer (CT) transitions of O2− → Ti4+ (UV region) and Ni2+ → Ti4+ (visible light region). While Ag/NiTiO3:V composites have a smaller band energy of 2.09 eV. The photocatalytic activities were investigated by photo-degradation of Rhodamine B (RhB) dye solutions under visible-light irradiation. The Ag/NiTiO3:V nanorods were efficient for the photo-degradation of RhB dye solutions. EIS measurements were used to analyze the charge-carrier migration at the interfaces. The improved photocatalysis of Ag/NiTiO3:V is ascribed to the narrowed band energy and enhanced efficiencies of the charge separations due to the Ag-coupling and V-doping in NiTiO3 lattices.

The Y2WO6:Yb3+/Er3+ crystals were synthesized by the hydrothermal method. The needle-shaped morphology is controllably formed and a number of crystals aggregate as spheres by adding the surfactant of sodium dodecylbenzenesulfonate (SDBS) into the reaction system. The crystal structure, morphology and upconversion luminescence properties of the Y2WO6:Yb3+/Er3+ crystals are conducted on the basis of X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), FTIR and emission spectra. The different emission intensity ratio of the red and green bands is observed for the Y2WO6:Yb3+/Er3+ precursors under different heat treatments. The different intensity ratio are illustrated according to the upconversion mechanism.

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 7–300 K. 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 (

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 4f65d→4f7(8S7/2) transition, together with a sharp line at 360 nm corresponding to the forbidden 4f7(6P7/2)→4f7(8S7/2) 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.

Nano-sized V2O5 has been widely investigated as photocatalysis due to good chemical stability and smaller band gap than TiO2. However, it suffers some disadvantages such as narrow optical absorption, easy recombination of photo-generated charges. In this work, CsV3O8 was prepared by a facile hydrothermal synthesis without help of any additive inorganic chemicals. The samples developed into well-crystalized microplates with the length and width of about 1 and 3 µm, respectively. Phase formation and structure were investigated by XRD structure refinement. CsV3O8 has an unusual V–O framework consisting of VO6 octahedra, which constructs V2O5-like layer-structure. The samples were characterized with SEM, TEM, EDS and optical absorption. CsV3O8 has an indirect allowed electronic transition with band energy 2.18 eV. Efficient photo-degradation of Rhodamine B (RhB) solutions in presence of CsV3O8 was confirmed. The result suggests that vanadate semiconductor CsV3O8 is a potential candidate for photocatalytic application under visible-light irradiation.

Transition metal oxide semiconductors have been reported to be potential for light-energy conversion and storage-related applications because of the unique structures and properties. This work reports a transition metal oxide Nb2WO8 synthesized by the sol-gel synthesis. The crystal structure, optical band nature, intrinsic luminescence, and photocatalytic properties were investigated. Nb2WO8 is a typical indirect allowed semiconductor and the band transition energy is 3.58 eV. The top of the valence band (EVB) and the minimum of the conduction band (ECB) are +2.88 eV and −0.7 eV, respectively. Nb2WO8 presents an intrinsic emission at 300 K with the maximum wavelength at 510 nm and the lifetime was 1.96 μs. The introduction of the impurity ions Li+ into the lattices of Nb2WO8 resulted in the improved luminescence efficiency. Meanwhile, compared with the undoped sample, the luminescence thermal stability of Nb2WO8:Li was also enhanced. The decay lifetime of Nb2WO8:Li was prolonged to 2.41 μs. The slow decay time could delay the recombination of the photo-produced holes and electrons after light excitation. This improves photocatalytic performances by delaying the charge-separation. Therefore, the photodegradation of RhB by Nb2WO8:Li is much more efficient than that by the reference sample of Nb2WO8 under visible light irradiation. Li+ doping is an effective way to modify the optical properties of Nb2WO8 semiconductor.

Two-dimensional bismuth layered oxyhalogenides have excellent photoelectric applications for energy conversion and storage due to its unique crystal structures, narrow band gaps. In this work, we reported an indirect semiconductor NaBi3O4Cl1.5Br0.5 prepared via sol–gel synthesis with the subsequent solid-state reaction. This is a typical bismuth layered framework characterized by [Bi2O2]2+ slab intercalated with [Cl/Br]− layers. There are distinct influences of rare ions (La3+, Gd3+, Eu3+) doping on the optical properties of NaBi3O4Cl1.5Br0.5. La3+ and Gd3+ doping slightly narrowed the band gap (several nanometers) of NaBi3O4Cl1.5Br0.5, while the band energy was greatly decreased from 2.37 eV to 2.18 eV via the Eu3+ doping in the lattice. As far as photochemical properties are concerned, La3+/Gd3+ doping didn’t show an obvious contribution, while, Eu3+-doping gave an improvement to photodegradation. A comparison with DFT calculations revealed that Eu-4f could bring about the isolated energy band intersecting the forbidden band of NaBi3O4Cl1.5Br0.5, which was suggested to enhance photodegradation and delay the recombination of light-generated electrons and holes. Eu3+-doped NaBi3O4Cl1.5Br0.5 is favorable for photocatalysis, but is not favorable for photoluminescence application. This bismuth layered semiconductor can be expected to have possible applications in developing advanced energy conversion or energy storage materials such as photocatalyst, optoelectronics, and batteries.

A Mn4+ doped Na2WO2F4 phosphor was synthesized through a two-step wet chemical method. The relationship between crystal structure and luminescence properties is discussed and unusual strong intense zero phonon lines (ZPLs) have been found in a distorted octahedral environment. The power dependent luminescence spectra exhibit the existence of down conversion luminescence intensity saturation under a high pumping power limit. The fluorescence intensity ratios of anti-Stokes bands to the ZPL and Stokes bands reveal an obvious temperature dependent relationship based on thermal de-population from the low states to the upper states of an intrinsic Mn4+ 2Eg → 4A2g transition. The temperature dependent emission intensity of Mn4+ is investigated by changing the excitation power, and an optical temperature sensitivity as high as 0.00658 K−1 is achieved at 193 K with the intensity ratio of anti-Stokes bands to the ZPL under 488 nm excitation by a Xenon lamp. This work presents a new method to realize optical thermometry at low temperature by controlling the intensity ratio of the anti-Stokes bands to the ZPL.

Yb3+ (0.5–30 mol %) activated Y4CdMo3O16 phosphors have been prepared by the traditional solid-state reaction method. The phase formation was investigated by the XRD structural refinements. The surface properties of the powder phosphors were verified by SEM, TEM and EDS measurements. The optical properties were evaluated by the reflectance spectra, photoluminescence excitation and emission spectra, decay curves (lifetimes), and the absolute quantum efficiency (QE). Under the excitation of UV light, Yb3+-activated Y4CdMo3O16 shows the efficient near-infrared (NIR) emission bands (900–1100 nm), which is ascribed to the 2F5/2 → 2F7/2 transitions of Yb3+ ions. The NIR emission intensity shows a dependence on Yb3+ contents, which has an optimal doping of 25 mol %. The energy transfer (ET) from MoO4 to Yb3+ ions in the lattices was discussed. The NIR emission around 1000 nm just corresponds to the optical response of Si-based solar cells. Consequently, the efficiency could be enhanced by arranging luminescent layers mixed with Y4CdMo3O16:Yb3+ phosphors and transparent matrix in the front surface of Si solar cells.

Cation disorder in the phosphor lattice could be one of the effective approaches to modify the luminescence efficiency. In this work, cation substitutions of (Mo6+ → V5+) and (Na+ → Mg2+) were conducted in the self-activated NaMg2V3O10. All the samples of Na1+xMg2−xV3−xMoxO10 (x = 0, 0.01, 0.05, 0.1, 0.2, 0.3) were prepared via solid-state reaction. The morphological properties were measured via SEM and EDS analyses. Structural Rietveld refinement was performed to investigate the microstructure in the lattices. The cation substitution brings about structural disorder in the phosphor, which exerts great modifications in the luminescence properties. NaMg2V3O10 presents an intrinsic indirect transition with a band gap of 3.22 eV. The incorporation of Mo6+ and Na+ in the lattices moves the optical absorption to a longer wavelength bringing about a narrower band gap. The luminescence intensity, thermal stability and corresponding lifetime were modified by the cation disorder in the self-activated phosphor.

The dysprosium ions-doped zinc oxyflluorotellurite glasses of three different compositions have been synthesized and analyzed their vibrational, thermal, optical and white light emission properties. The differential thermal analysis curves, Fourier Transform Infrared, absorption, emission and excitation spectra and lifetimes from the luminescent level (4F9/2) have been measured and analyzed. Absorption spectra have been characterized in the frame of Judd-Ofelt model to determine essential radiative properties namely, transition probabilities, calculated lifetimes and branching ratios of the 4F9/2 luminescent level. Photoluminescence spectra of the glasses are measured by exciting with 388 nm broad band and 355 nm laser. The glasses emit intense white luminescence with 388 nm broad band excitation. The CIE chromaticity color coordinates of one of the glass are nearer to the equal energy point. Decay time profiles of the 4F9/2 state are non-exponential for three glasses under study where their effective lifetimes have been evaluated. Quantum efficiencies of the glasses vary from 30 to 62% with change in ZnF2 content.

Silver-containing niobate AgNb7O18 nanoparticles were prepared via sol-gel polymerized complex synthesis. The sample was given a good XRD Rietveld refinement in a typical perovskite-like structure. The detailed surface properties of AgNb7O18 nanoparticles were tested by SEM, EDS, TEM, nitrogen adsorption-desorption isotherms and XPS measurements. AgNb7O18 is characterized via a direct transition and the band energy is 2.76 eV. The hybridization between O 2p and Ag 3d states in valence band contributes to the narrowed band gap. The first principles electronic structure elucidation supports the narrow band gap of AgNb7O18. The sample shows an efficient degradation of methylene blue dye (MB) solutions. The trapping tests were performed to elucidate the real active species in the photocatalytic reactions. The results indicate that the superoxide radical is the main active species in the photocatalytic system, and the photocatalyst also shows a good stability and durability.

In this work, the new calcium-magnesium-silicate Ca5MgSi3O12 ceramic was made via traditional solid-state reaction. The bioactivities were investigated by immerging the as-made ceramics in simulated body fluid (SBF) for different time at body temperature (37 °C). Then the samples were taken to measure X-ray powder diffraction (XRD), Scanning electron microscopy (SEM), X-ray energy-dispersive spectra (EDS), and Fourier transform infrared spectroscopy (FT-IR) measurements. The bone-like hydroxyapatite nanoparticles formation was observed on the ceramic surfaces after the immersion in SBF solutions. Ca5MgSi3O12 ceramics possess the Young’s modulus and the bending strength and of 96.3 ± 1.2 GPa and 98.7 ± 2.3 MPa, respectively. The data suggest that Ca5MgSi3O12 ceramics can quickly induce HA new layers after soaking in SBF. Ca5MgSi3O12 ceramics are potential to be used as biomaterials for bone-tissue repair. The cell adherence and proliferation experiments are conducted confirming the reliability of the ceramics as a potential candidate.

The novel luminescent polymer-rare earth complexes, denoted as (PFSi-IPDI)-Tb(Ⅲ)-Phen, have been successfully synthesized and can be made into flexible films. Amino-modified fluorine silicone oil-isophorone diisocyanate (PFSi-IPDI) was used as the host macromolecular ligand, and 1, 10-Phenanthroline (Phen) as the secondary small-molecular co-ligand. The luminescent lanthanide complexes were characterized by fourier transform infrared (FITR), scanning electron microscope (SEM), thermogravimetric analysis (TGA). The luminescent properties were investigated through photoluminescence excitation (PLE) and emission (PL) spectroscopy. FTIR analysis verifies the successful preparation and integration of PFSi-IPDI to Tb3+. The comparatively uniform morphological structure can be observed in the images of SEM. The polymer-rare earth complexes display the typical luminescence emission peaks under the excitation wavelength of 330 nm. From the decay curve, the short lifetime (about 0.89 ms) is observed for (PFSi-IPDI)-Tb(Ⅲ)-Phen (0.6 mol/L). Moreover, these luminescent polymer-rare earth complexes possess superior thermal stability (T5 > 195 °C). All the interesting results suggest the potential application of the luminescent polymer-rare earth complexes in green-emitting luminescent materials under high temperature.

This work improved the optical absorption and photocatalytic ability of four-layered Aurivillius Bi5Ti3FeO15 through microstructural modification via partial substitution of Ti4+ with Fe3+. Bi5Ti3−xFe1+xO15 (x = 0–0.6) photocatalysts were prepared through sol-gel citrate-complexation synthesis. The sample crystallized into plate-like nanoparticles with [001] facets. Phase formation and crystal structure were confirmed via X-ray powder diffraction (XRD) Rietveld refinements. Bi5Ti3−xFe1+xO15 (x = 0–0.6) maintained its structural characteristic, i.e., a perovskite unit of (Bi3Ti3−xFe1+xO13)2– sandwiched by two (Bi2O2)2+ layers along c axis. The samples were investigated via scanning electron microscope (SEM), transmission electron microscope (TEM), energy-dispersive X-ray spectroscopy (EDX), and specific surface area analyses. The band gap showed characteristic transitions from the valence band (VB) of (O2p+Fet2 g+Bi6s) to the conduction band (CB) of (Ti-3d+Fe-eg). With increasing substitution of Ti4+ with Fe3+, the sample greatly red shifted its absorption edges. The d–d transitions in FeO6 greatly contribute to the narrow band-gap. Aurivillius is a potential photocatalyst and demonstrated photodegradation of Rhodamine B (RhB) under visible light irradiation (λ > 420 nm). Such photocatalytic activities were attributed to the special structural layer and the catalytic mediators of multivalent Ti4+/3+ and Fe3+/2+ ions in the perovskite slabs as confirmed by XPS measurements. Results suggested that substitution of Ti4+ with Fe3+ in an Aurivillius phase was an efficient method to modify the bandwidth and structure of Aurivillius phase. This phenomenon can be used as a strategy to improve the photochemical properties of Ti/Fe-containing Aurivillius phases.

Ag-containing niobate AgNb13O33 has been prepared by the sol–gel polymerized complex method. The structure was investigated via a good XRD Rietveld refinement in a typical perovskite-like framework. The morphological properties of the AgNb13O33 nanoparticles were tested via transmission electron microscopy (TEM), scanning electron microscope (SEM), and energy dispersive spectra (EDS) measurements. AgNb13O33 is a typical direct allowed semiconductor with band energy of 2.81 eV, which is much narrower than 3.4 eV of Nb2O5. This silver niobate can harvest both UV and near UV light, which is benefited from the (O-2p/Ag-4d) hybridization in the valence band. The photocatalytic abilities of AgNb13O33 nanoparticles were reported. The sample presents more efficient photocatalytic effects on photo-degradation of methylene blue (MB) dye solutions than that of Nb2O5. The photocatalytic mechanism was discussed on band energy levels, trapping experiments, photoluminescence and the decay lifetime.

Ilmenite FeTiO3 nanoparticles were prepared by electrospinning synthesis using the sol–gel precursors, followed by the sintering at 650 °C. The pure crystalline phase was verified by X-ray powder diffraction (XRD) measurements together with Rietveld refinements. The surface properties of the nanoparticles were studied by TEM, SEM, BET and XPS measurements. The optical absorption of FeTiO3 nanoparticles is in the visible wavelength region. The indirect allowed band gap (2.6 eV) of FeTiO3 shows the characteristic charge-transfer (CT) transitions of O-2p→(Ti/Fe)-3d in visible light wavelength region. The photochemical properties were investigated by the methylene blue (MB) degradation under the irradiation of visible-light. FeTiO3 nanoparticles were efficient in the photo-degradation of MB dye solutions. The photocatalysis activities and mechanisms were discussed on the crystal structure characteristics such as multivalent elements of Ti3+, Fe3+/Fe2+ redox couples. The magnetic properties of FeTiO3 nanoparticles were measured, which permit this photocatalyst to be recycled after the photocatalytic reactions.

A new ferrotitanate semiconductor NaFeTi 3 O 8 was developed by sol−gel citrate complexation synthesis. The sample preferentially developed into nanorods. The nanorods showed good XRD Rietveld refinements in the isostructure with Na 0.2 TiO 2 . The structure retains the two-dimensional layers of (Fe/Ti)O 6 octahedra and one-dimension channels in the structure. SEM, TEM, EDS, and specific surface area analysis were employed to characterize the samples. Results showed that the optical absorption of NaFeTi 3 O 8 nanorods is in the visible wavelength region. The direct allowed bandgap (2.12 eV) shows the characteristic charge-transfer transitions of O 2p/Fe 3d→(Ti/Fe) 3d. The d–d allowed transitions in the FeO 6 octahedron presented considerable contributions to the narrow bandgap. NaFeTi 3 O 8 exhibited potential as a photocatalyst for RhB photodegradation under visible light excitation ( λ > 420 nm). Photocatalytic activities are discussed in relation to the structural properties.

Eu 3+ -doped NaGd(WO 4 ) 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(WO 4 ) 2 :Eu 3+ phosphors. The results show that the Eu 3+ -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(WO 4 ) 2 . The well-crystallized sheet-like NaGd(WO 4 ) 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 NaGd 1-x Eu x (WO 4 ) 2 (0 ≤ x ≤ 1) are investigated. It is found that the charge transfer band of Eu 3+ shifts to lower energy and broadens with increasing the Eu 3+ -concentration.

Ni-doped Cu2(OH)3Cl microcrystals were prepared by a facile hydrothermal synthesis without the help of any additive inorganic or organic reagent. The micro-particles were investigated by X-ray powder diffraction (XRD) with Rietveld refinement, scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV–vis optical absorption, and X-ray photoelectron spectroscopy (XPS) etc. Ni-doping could well stabilize the Cu2(OH)3Cl paratacamite phase at ambient temperature. The band structure and energy positions of Ni-doped Cu2(OH)3Cl microparticles were investigated. The band gap of Cu2(OH)3Cl could be greatly decreased by Ni-doping. The conduction band bottom of Ni-doped Cu2(OH)3Cl is lower and possesses greater dispersion than that of pure Cu2(OH)3Cl. The photocatalytic activity of Ni-doped Cu2(OH)3Cl micro-particles was evaluated by the photodegradation of Rhodamine B (RhB) dye under visible-light irradiation. The Ni-doping increases the photocatalytic activity of Cu2(OH)3Cl. The photocatalytic activity was discussed on the base of the structural and electronic characteristics. Keywords: Photocatalyst, Optical properties, Semiconductors, Band structure, Copper oxide

In 2 Si 2 O 7 is a known indium-based scintillator with fast ultraviolet photoluminescence. Unfortunately the emission only can be detected below 200 K. the poor thermal stability limits its application at room temperature. In this work, the luminescence improvement of In 2 Si 2 O 7 was realized by F − -ions doping in the lattices. The ceramic phosphors were via typical solid-state reaction method. The pure crystalline phase with thortveirite-type structure was confirmed by X-ray diffraction (XRD) Rietveld refinements. The photoluminescence (PL) emission and excitation spectra together with the luminescence thermal stability were tested. The fluorescence decay curves CIE emission Stokes shifts were measured. The ceramic samples could present blue luminescence with maximum wavelength at about 340 nm under the excitation of UV light or high energy X-ray irradiation. The pure sample only presents luminescence below 200 K, however, the F-doping can be greatly enhance the luminescence thermal stability. The F-doped In 2 Si 2 O 7 could present emission signals with fast decay lifetime of 850 ns at room temperature. The luminescence transitions from the In 3+ -O 2− charge transfer (CT) were discussed on the structure properties.

Pure and V 5+ -doped Bi 6 Mo 2 O 15 (3Bi 2 O 3 ·2MoO 3 ) photocatalysts were synthesized through electrospinning, followed by low-temperature heat treatment. The samples developed into nanoparticles with an average size of approximately 50 nm. The crystalline phases were verified via X-ray powder diffraction measurements (XRD). The surface properties of the photocatalysts were studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) analyses. The UV–vis spectra showed that V doping in Bi 6 Mo 2 O 15 shifted the optical absorption from the UV region to the visible-light wavelength region. The energy of the band gap of Bi 6 Mo 2 O 15 was reduced by V doping in the lattices. The photocatalytic activities of the pure and V-doped Bi 6 Mo 2 O 15 were tested through photodegradation of rhodamine B (RhB) dye solutions under visible light irradiation. Results showed that 20 mol% V-doped Bi 6 Mo 2 O 15 achieved efficient photocatalytic ability. RhB could be degraded by V-doped Bi 6 Mo 2 O 15 in 2 h. The photocatalytic activities and mechanisms were discussed according to the characteristics of the crystal structure and the results of EIS and XPS measurements.

A2NiWO6 (A = Ca, Sr) double perovskite semiconductors were prepared via the sol–gel method. The crystal phases were confirmed via X-ray powder diffraction (XRD) measurements together with Rietveld refinements. The morphological and chemical properties of the samples were investigated by the scanning electron microscope (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), and the specific surface area measurements. The optical absorptions and the band structures of the two double perovskites were discussed based on the on the experimental results and theoretical calculation. The d–d allowed transitions in Ni2+–O octahedra have great contributions to the narrow band-gap. The Ni2+-containing tungstate perovskites were potential photocatalysts, which are efficient for its photodegradation for methylene blue (MB) under the irradiation of visible light (λ> 420 nm). The photocatalytic activities were attributed to the special structure properties and multivalent Ni and W ions in the perovskite lattices.

Pure and V 5+ -doped Bi 4 Ti 3 O 12 (BTO) photocatalysts were prepared by sol–gel routine and subsequent hydrothermal synthesis. The samples were developed into the platelike microparticles with the exposed (001) facets. The crystalline phases were verified via the XRD measurement. The surface characteristics of the photocatalysts were studied by TEM, SEM, BET, EDX and XPS measurements. The UV–vis optical absorption spectra showed that the V-doped photocatalysts exhibit an obvious red shift in the visible light absorption band compared with the pure BTO. Rhodamine B (RhB) dye solution was used as the model organic pollutants to verify the influence of V-doping on the photocatalytic activity. The 10 mol % V-doped BTO showed efficient photocatalytic ability. The photocatalytic activities and mechanisms were discussed on the crystal structure characteristics and the measurements such as EES and XPS results.