Synthesis and luminescent properties of Eu2+ doped nitrogen-rich Ca-α-SiAlON phosphor for white light-emitting diodes

Yellow/orange-emitting nitrogen-rich Ca_0.9Si₉Al₃(O,N)₁₆: Eu²⁺ phosphors were successfully prepared by solid-state reaction synthesis. The fluorescence excitation spectra of all of the nitrogen-rich Ca_0.9Si₉Al₃(O,N)₁₆: Eu²⁺ phosphor powders displayed two broad bands centered at about 300 nm and 400–475 nm. The first peak was assigned to the absorption of the host lattice and the second to the 4f⁷ → 4f⁶5d¹ absorption of the Eu²⁺ ions, its means enhanced 4f⁷ → 4f⁶5d excitation of Eu²⁺ ion. The absorption peak intensity increased upon increasing the Eu²⁺ doping amount, but only up to a Eu²⁺ concentration ratio of 0.15. The emission spectra of the prepared Ca_0.9Si₉Al₃(O,N)₁₆: Eu²⁺ phosphors all exhibited a single broad band in the 500–700 nm region, maximum emission peak observed at 591 nm. The room temperature decay times were observed τ₁ = 1.27 μs and τ₂ = 9.90 μs.     

Crystal, electronic structures and photoluminescence properties of rare-earth doped LiSi2N3

The crystal and electronic structures, and luminescence properties of Eu²⁺, Ce³⁺ and Tb³⁺ activated LiSi₂N₃ are reported. LiSi₂N₃ is an insulator with an indirect band gap of about 5.0 eV (experimental value ∼6.4 eV) and the Li 2s, 2p states are positioned on the top of the valence band close to the Fermi level and the bottom of the conduction band. The solubility of Eu²⁺ is significantly higher than Ce³⁺ and Tb³⁺ in LiSi₂N₃ which may be strongly related to the valence difference between Li⁺ and rare-earth ions. LiSi₂N₃:Eu²⁺ shows yellow emission at about 580 nm due to the 4f⁶5d¹→4f⁷ transition of Eu²⁺. Double substitution is found to be the effective ways to improve the luminescence efficiency of LiSi₂N₃:Eu²⁺, especially for the partial replacement of (LiSi)⁵⁺ with (CaAl)⁵⁺, which gives red emission at 620 nm, showing highly promising applications in white LEDs. LiSi₂N₃:Ce³⁺ emits blue light at about 450 nm arising from the 5d¹→4f¹5d⁰ transition of Ce³⁺ upon excitation at 320 nm. LiSi₂N₃:Tb³⁺ gives strong green line emission with a maximum peak at about 542 nm attributed to the ⁵D₄→⁷F_J (J=3-6) transition of Tb³⁺, which is caused by highly efficient energy transfer from the LiSi₂N₃ host to the Tb³⁺ ions.     

Preparation and luminescence properties of green-light-emitting afterglow phosphor Ca8Mg(SiO4)4Cl2:Eu2+

Green-light-emitting long-lasting phosphorescence phosphor, Eu²⁺ activated calcium magnesium chlorosilicate Ca₈Mg(SiO₄)₄Cl₂, has been prepared by a modified solid-state reaction method using Ca₂SiO₄:Eu²⁺ as a precursor. Its properties have been discussed and analyzed utilizing XRD, photoluminescence, excited-state decay curve and long-lasting phosphorescence decay curve. Upon UV light excitation, the emission spectrum of Ca₈Mg(SiO₄)₄Cl₂:Eu²⁺ phosphor is composed of two separate bands centered at 425 nm and 505 nm, respectively. Furthermore, after irradiation by a 320-nm UV light for 3 min, the 2% Eu²⁺-doped Ca₈Mg(SiO₄)₄Cl₂ phosphor emits intense green-light-emitting afterglow from the 4f⁶5d¹→4f⁷ transition of Eu²⁺, and its afterglow can be seen with the naked eye in the dark clearly for more than 3 h after removal of the excitation source. The disappearance of the high-energy 425 nm band in the afterglow emission spectrum is explained by its different crystallographic sites. The afterglow decay curve of the Eu²⁺-doped Ca₈Mg(SiO₄)₄Cl₂ phosphor contains a fast decay component and another slow decay one. The possible mechanism of this long-lasting phosphorescence phosphor is also discussed based on the experimental results.     

Darstellung,Kristallstruktur, Schwingungsspektren und Normalkoordinatenanalyse von (Ph4P)2[OsN(N3)5] und 15N‐NMR‐Verschiebungen von Nitridoosmaten(VI,VIII)

Synthesis, Crystal Structure, Vibrational Spectra, and Normal Coordinate Analysis of (Ph₄P)₂[OsN(N₃)₅] and ¹⁵N NMR Chemical Shifts of Nitridoosmates(VI, VIII) The treatment of (Ph₄P)[OsNCl₄] with NaN₃ yields (Ph₄P)₂[OsN(N₃)₅], which crystal structure has been determined by single crystal X‐ray diffraction analysis (monoclinic, space group P 2₁/a, a = 20.484(6), b = 11.168(1), c = 20.666(4) Å, β = 97.35(3)°, Z = 4). The IR and Raman vibrations were assigned by a normal coordinate analysis based on the molecular parameters of the X‐ray determination. The valence force constants are f_d(Os≡N) = 8.52, f_d(Os–N^α) = 1.99, f_d(N^α–N^β) = 12.42, f_d(N^β–N^γ) = 12.73 and for the azido ligand in trans‐position to the nitrido group f_d(Os–N^{α ·} ) = 1.84, f_d(N^{α ·} –N^{β ·} ) = 11.91, f_d(N^{β ·} –N^{γ ·} ) = 12.18 mdyn/Å. The ¹⁵N NMR spectra of various nitridoosmates reveal the chemical shifts δ(¹⁵N) for K[OsO₃¹⁵N] = 387.6, K₂[Os¹⁵NCl₅] = 446.7, (Ph₄P)[Os¹⁵NCl₄] = 352.9, [(n‐C₆H₁₃)₄N]₂[Os¹⁵N(N₃)₅] = 307.3 and for [(n‐Pr)₄N]₂[Os¹⁵N(¹⁵NCO)₅] = 483,7 (Os≡N), –417,7 (OsNCO_eq) und –392,8 ppm (OsNCO_ax).     

Thermoluminescence and photoluminescence study on 150 MeV proton beam irradiated K2Ca2(SO4)3:Eu phosphor

This paper investigates the thermoluminescent response of K₂Ca₂(SO₄)₃:Eu prepared by solid state diffusion method, to 150 MeV proton beams. The structural confirmation of the sample was done using the XRD technique revealing the polycrystalline nature and the formation of the compound. Samples in the form of pellets were irradiated by 150 MeV proton clinical beams with dose range of 0.1 Gy–300 Gy. Thermoluminescence glow curves of the irradiated samples were recorded and studied. It has been found that the phosphor shows a characteristic single peak at around 420 K. The TL response is linear in the range up to 200 Gy and then becomes supralinear for higher doses. Photoluminescence spectra of the sample have also been studied and reported. When the material was excited at 320 nm, single emission bands were observed at 436 nm, which can be assigned to the transitions between the lowest band of the 4f⁶5d configuration and the ground state ⁸S_7/2 of the 4f⁷ configuration of Eu²⁺ ion, confirming the incorporation of the impurity in the prepared sample. The excitation spectra of these samples at emission wavelength of 436 nm show a major band at 320 nm. The linear TL response of K₂Ca₂(SO₄)₃:Eu and low fading with good reusability, makes it a potential candidate to be used as a dosimeter for detecting the doses of proton beams for specific applications.     

CdS nanospheres hybridized with graphitic C3N4 for effective photocatalytic hydrogen generation under visible light irradiation

Graphitic carbon nitride (g‐C₃N₄)‐based photocatalysts have received considerable attention in the field of photocatalysis, especially for photocatalytic H₂ evolution. However, the intrinsic disadvantages of g‐C₃N₄ seriously limit its practical application. Herein, CdS nanospheres with an average diameter of 135 nm prepared using a solvothermal method were used as co‐catalysts to form CdS/g‐C₃N₄ composites (CSCN) to enhance the photocatalytic activity. Various techniques were employed to characterize the structure, composition and optical properties of the as‐prepared samples. It was found that the CdS nanospheres were relatively uniformly dispersed on the surface of g‐C₃N₄. Moreover, the photocatalytic H₂ generation activity of the samples was evaluated using lactic acid as sacrificial reagent in water under visible light irradiation. When the amount of CdS nanospheres loaded in the hybridized composites was 5 wt%, the optimal H₂ evolution rate reached 924 μmol g^?1 h^?1, which was approximately 1.4 times higher than that (680 μmol g^?1 h^?1) of Pt/g‐C₃N₄ (3 wt%). Based on the results of analysis, a possible mechanism for the photocatalytic activity of CSCN is proposed tentatively.     

Kinetic study of the oxidation reaction of 4-methylphenyl radical

A kinetic study of the reaction of the 4-methylphenyl radical (4-C₆H₄CH₃) with the oxygen molecule was conducted using experimental and theoretical approaches. The absorption spectrum for the λ = 266 nm photolysis of the 4-C₆H₄CH₃X (X = Cl, Br)/N₂/O₂ mixture was measured in the wavelength range of λ = 503-512 nm using N₂ as the buffer gas at a total pressure of 40 Torr using a cavity ring-down spectroscopy apparatus coupled with a pulsed laser photolysis system. Based on the absorbance of the product of the 4-C₆H₄CH₃ + O₂ reaction at λ = 504 nm, the reaction rate coefficient for the 4-C₆H₄CH₃ + O₂ reaction was determined to be k = (1.21 ± 0.10) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹ and k = (1.18 ± 0.21) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹ using 4-C₆H₄CH₃Cl and 4-C₆H₄CH₃Br, respectively, as the radical precursor. And there was no pressure dependence in the total pressure range of 10-90 Torr varying partial pressure of N₂ buffer gas at T = 296 ± 5 K. The geometries, vibration frequencies, and potential energy surfaces of the reactants, major products, and transition states in the 4-C₆H₄CH₃ + O₂ reaction were determined using the CBS-QB3 method. The k value at the high-pressure limit was calculated to be 1.26 × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹ using the variational transition-state theory. The calculated value of k was consistent with the experimental value, which indicated that the 4-C₆H₄CH₃ + O₂ reaction reaches the high-pressure limit at 10 Torr. Therefore, the oxidation of the 4-C₆H₄CH₃ radical is almost 10 times faster than that of the benzyl radical, which has the same chemical formula, at the high-pressure limit.     

Ruthenium piano-stool complexes containing mono- or bidentate pyrrolidinylalkylphosphines and their reactions with small molecules

Ruthenium piano-stool complexes incorporating the new bidentate aminoalkylphosphine ligand 1,2-bis(dipyrrolidin-1-ylphosphino)ethane (dpyrpe, I) or its monodentate counterpart bis(pyrrolidin-1-yl)methylphosphine (pyr₂PMe, II) have been prepared, [(C₅R₅)RuCl(PP)] (R = Me and PP = dpyrpe, 1; R = Me and PP = (pyr₂PMe)₂, 2; R = H and PP = dpyrpe, 3). Complexes 2 and 3 have been characterized by X-ray crystallography. Complexes 1 and 2 react with NaBAr₄^f in the presence of ligand L to yield [Cp^∗Ru(L)(dpyrpe-κ²P)][BAr^f₄] (L = MeCN, 4a; CO, 4b; N₂, 4c) and [Cp^∗Ru(L)(pyr₂PMe)₂][BAr₄^f] (L = MeCN, 5a; CO, 5b; N₂, 5c). Complex 4a was crystallographically characterized. The CO complexes 4b and 5b were examined using IR spectroscopy in an attempt to establish the electron-donating capabilities of I and II. Complex 1 oxidatively adds H₂ in the presence of NaBAr₄^f to yield the Ru(IV) dihydride [Cp^∗RuH₂(dpyrpe-κ²P)][BAr₄^f], 7.     

Synthesis and characterization of Pr<Superscript>3+</Superscript>-doped glass scintillators prepared by the sol–gel method

Transparent and crack-free Pr-doped silica glass scintillators were successfully synthesized using the sol–gel method. A peak found at 301 nm in the photoluminescence spectrum was ascribed to a radiative transition of the Pr³⁺ emission center. The associated excitation peak was located at 276 nm. The energy of the excitation peak (4.50 eV) was significantly lower than the energy gap (5.83 eV) of the ¹S₀ to ³H₄ f–f transition. Therefore, the f–f transition was excluded as the origin, and the transition was attributed to 5d–4f. In the absorption spectrum, several bands of the f–f transition were observed. Fourier transform infrared spectroscopy was employed to understand the microstructural features and OH group concentration in the Pr³⁺-doped silica glass. It was revealed that a Si–O network had been successfully formed, and that the OH group concentration decreased with increasing thermal treatment temperature reaching a saturation value for temperatures higher than 750 °C. The absence of praseodymium oxide nanocrystalline clusters was confirmed by transmission electron microscopy (TEM), even in the sample with the highest Pr ion concentration. Scintillation properties of the Pr³⁺-doped silica glass were also characterized. The scintillation decay time constants were estimated to be approximately 1.3 and 14 ns, which supports the assignment of the luminescence to the 5d–4f transition. The scintillation light yield of the Pr³⁺-doped silica glass was estimated to be approximately 130 photons/MeV.     

Microwave synthesis of bis(tetrazolato)-Pd complexes with PPh3 and water-soluble 1,3,5-triaza-7-phosphaadamantane (PTA). The first example of C-CN bond cleavage of propionitrile by a Pd Centre

[2 + 3] Cycloaddition reactions of the di(azido)-Pd^II complex trans-[Pd(N₃)₂(PPh₃)₂] (1) with an organonitrile RCN (2), under heating for 12 h, give the bis(tetrazolato) complexes trans-[Pd(N₄CR)₂(PPh₃)₂] (3) [R = Me (3a), Ph (3b), 4-ClC₆H₄ (3c), 4-FC₆H₄ (3d), 2-NC₅H₄ (3e), 3-NC₅H₄ (3f), 4-NC₅H₄ (3g)]. The reaction of trans-[Pd(N₃)₂(PPh₃)₂] (1) with propionitrile (2h) also affords, apart from trans-[Pd(N₄CEt)₂(PPh₃)₂] (3h), the unexpected mixed cyano-tetrazolato complex trans-[Pd(CN)(N₄CEt)(PPh₃)₂] (3h′) which is derived from the reaction of the bis(tetrazolato) 3h with propionitrile, with concomitant formation of 5-ethyl-1H-tetrazole, via a suggested unusual oxidative addition of the nitrile to Pd^II. The [2 + 3] cycloadditions of [Pd(N₃)₂(PTA)₂] (4) (PTA = 1,3,5-triaza-7-phosphaadamantane) with RCN (2), under heating for 12 h, give the bis(tetrazolato) complexes trans-[Pd(N₄CR)₂(PTA)₂] (5) [R = Ph (5a), 2-NC₅H₄ (5b), 3-NC₅H₄ (5c), 4-NC₅H₄ (5d)]. All these reactions are greatly accelerated by microwave irradiation (1 h, 125 °C, 300 W). Taking advantage of the hydro-solubility of PTA, a simple liberation of 5-phenyl-1H-tetrazole from the coordination sphere of trans-[Pd(N₄CPh)₂(PTA)₂] (5a) was achieved. The complexes were characterized by IR, ¹H, ¹³C{¹H} and ³¹P{¹H} NMR spectroscopies, ESI⁺-MS, elemental analyses and, for 3b, also by X-ray structure analysis. Weak agostic interactions between the CH groups of the triphenylphosphines and the palladium(II) centre were found.     

A relativistic DFT study of magnetic exchange coupling in ketimide bimetallic uranium(IV) complexes

Magnetic exchange couplings in bis(ketimide) binuclear U^IV/U^IV complexes [Cp′₂UCl]₂(μ-ketimide) diuranium(IV) and [(C₅H₅)₂(Cl)An]₂(μ-ketimide) (Cp′ = C₅Me₄Et; ketimide = N=CMe-(C₆H₄)-MeC=N) have been investigated computationally using relativistic density functional theory (DFT) combined with the broken symmetry (BS) approach. Using the B3LYP hybrid functional, the BS ground state of these U^IV/U^IV 5f ²–5f ² complexes has been found of lower energy than the high spin (HS) quintet state, indicating an antiferromagnetic character (estimated coupling constant |J| < 5 cm⁻¹) which has not yet been evidenced unambiguously experimentally. On the contrary, the BP86 GGA functional overestimates greatly the antiferromagnetic character of the complexes (|J| > 100 cm⁻¹). As recently reported for para-bis(imido) [(C₅H₅)₃U]₂(μ-imido) uranium(V) complex, spin polarization is mainly responsible for the antiferromagnetic coupling through the π-network orbital pathway within the bis(ketimide) bridge. Furthermore, spin polarization is exalted by the combined roles of the 5f metal orbitals and of the π-conjugated ketimide bridging ligand which permit electronic communication between the two uranium atoms albeit separated by a distance of the order of 10 ?. The MO analysis clarifies which MOs contribute to the antiferromagnetic coupling in the binuclear complexes under consideration and brings to light the 5f orbitals driving contribution.     

Engineering oxygen into ultrathin graphitic carbon nitride: synergistic improvement of electron reduction and charge carrier dynamics for efficient photocatalysis

The fast separation rate of photogenerated carriers and the high utilization of sunlight are still a major challenge that restricts the practical application of carbon nitride (g-C₃N₄) materials in the field of photocatalytic hydrogen (H₂) evolution. Here, ultrathin oxygen (O) engineered g-C₃N₄ (named UOCN) was successfully obtained by a facial gaseous template sacrificial agent-induced bottom-up strategy. The synergy of O doping and exfoliating bulk into an ultrathin structure is reported to simultaneously achieve high-efficiency separation of photogenerated carriers, enhance the utilization of sunlight, and improve the reduction ability of electrons to promote photocatalytic H₂ evolution of UOCN. As a proof of concept, UOCN affords enhanced photocatalytic H₂ evolution (93.78 μmol h^?1) under visible light illumination, which was significantly better than that of bulk carbon nitride (named CN) with the value of 9.23 μmol h^?1. Furthermore, the H₂ evolution rate of UOCN at a longer wavelength (λ = 450 nm) was up to 3.92 μmol h^?1 due to its extended light absorption range. This work presents a practicable strategy of coupling O dopants with ultrathin structures about g-C₃N₄ to achieve efficient photocatalytic H₂ evolution. This integrated engineering strategy can develop a unique example for the rational design of innovative photocatalysts for energy innovation.     

VUV spectroscopic properties of rare-earth (RE3+ = Sm3+, Eu3+, Tb3+, Dy3+) -activated layered borate Ba6Gd9B79O138

Vacuum ultraviolet (VUV) spectroscopic properties of rare-earth RE³⁺- activated (RE³⁺ = Sm³⁺, Eu³⁺, Tb³⁺ and Dy³⁺) Ba₆Gd₉B₇₉O₁₃₈ borates (BGBO) are investigated. The strong absorption bands in the VUV range of un-doped and RE³⁺-activated BGBO were observed. The band range from 140 to 200 nm with a peak at about 173 nm results from the host lattice absorption. For Sm³⁺-activated BGBO, the charge transfer transition from O^2- to Sm³⁺ was observed at 202 nm. In addition, it exhibits bright red emission originating from the Sm³⁺ f-f transitions of ⁴G_5/2 → ⁶H_J (J = 5/2, 7/2 and 9/2). The O^2--Eu³⁺ charge transfer (CT) at 249 nm is observed in the excitation spectrum for Eu³⁺-doped BGBO. For Tb³⁺-activated BGBO, the broad bands around 208 and 230 nm are due to the spin-allowed and spin-forbidden f-d transitions of Tb³⁺, respectively. In addition, the absence of the f-d transitions of Sm³⁺ and Dy³⁺ in the excitation spectra probably due to the photo-ionization effect. It is demonstrated that there are energy transfers from the BGBO host lattice to the luminescent activators depending on the activators.     

Pyrolytic synthesis and Eu→Eu reduction process of blue-emitting perovskite-type BaLiF3:Eu thin films

Perovskite-type barium lithium fluoride (BaLiF₃) was synthesized by pyrolysis of metal trifluoroacetates. The reaction temperature necessary for producing a single-phase material was found to be 600°C, which was lower than that for a conventional solid-state reaction or a melting method. Eu-doped BaLiF₃ was also prepared and characterized to examine the suitability of trifluoroacetates for precursors in synthesizing homogeneous complex metal fluoride materials. It was demonstrated that trivalent Eu³⁺, which was used as acetate for a starting material, was reduced to divalent Eu²⁺ in the pyrolysis process of BaLiF₃, as indicated by a broad blue emission due to an allowed 4f⁶5d→4f⁷ transition at 408 nm with a ultraviolet excitation at 254 nm. The concentration quenching of the blue emission occurred at 5 at% of Eu in BaLiF₃, indicating that Eu was homogeneously dispersed in the BaLiF₃ host lattice. Mechanisms of the formation and reduction process of BaLiF₃ were discussed based on pertinent chemical reactions.     

Synthesis, structure, and properties of a binuclear Fe(III) complex with N-(1-propanol)-N,N-bis(3-tert-butyl-5-methyl-2-hydroxybenxyl)amine

Mannich reaction of 2-Amino propanol, 2-tert-butyl-4-methylphenol, and formaldehyde in the ratio of 1:2:2 provides a new compound, N-(1-propanol)-N,N-bis(3-tert-butyl-5-methyl-2-hydroxybenxyl)amine (H₃L), which has been characterized by X-ray crystallography and elemental analysis. In the presence of Et₃N, the reaction of H₃L and FeCl₃·6H₂O gives a dinuclear Fe(III) complex [Fe₂L₂] 1, which has been characterized by X-ray crystallography, magnetic measurement, and cyclic voltammetry. The value of μ_eff at room temperature (5.97 μ_B) is much less than the expected spin-only value (8.37 μ_B) of two high spin (hs) Fe³⁺ (S = 5/2) ions [μ = g[∑ZS(S + 1)]^1/2], indicating there are strong coupling interactions between Fe³⁺ ions. The magnetic behavior of 1 denotes the occurrence of intramolecular antiferromagnetic interactions (J = −13.35 cm⁻¹ ). CV of 1 reveals two reversible waves at 0.433 and 1.227 V versus AgCl/Ag, which can be ascribed to the successive redox coupling of Fe^IIFe^II/Fe^IIIFe^II and Fe^IIIFe^II/Fe^IIIFe^III, respectively.     

Co-precipitation synthesis,humidity sensing and photoluminescence properties of nanocrystalline Co2+ substituted zinc(II)molybdate (Zn1–xCoxMoO4; x = 0, 0.3, 0.5, 0.7, 1)

Zinc-cobalt molybdate composites (Zn_1–xCo_xMoO₄; x = 0, 0.3, 0.5, 0.7, 1) were synthesised by a simple co-precipitation method and characterised by thermogravimetric/differential thermal analysis (TG/DTA), Fourier transform-infrared (FT-IR), Fourier transform Raman (FT-Raman) spectroscopy, X-ray diffraction spectroscopy (XRD), scanning electron microscopy (SEM/EDAX) and transmission electron microscopy (TEM). The surface area was calculated by BET analysis in the adsorption/desorption isotherm. The humidity sensing properties of zinc-cobalt molybdates were tested by dc electrical measurements at different relative humidity environments (RH = 5–98%). The electrical resistance of the composites linearly decreases and the maximum sensitivity of 3672 ± 110 was observed for the Zn_0.3Co_0.7MoO₄ (ZnCM-4) composite towards humidity, which is calculated by the relation S_f = R_5%/R_98%, where the response time is 200 s and the recovery time is 100 s. Photoluminescence (PL) measurement at the room temperature of ZnM-1 composite exhibited a blue emission peak at 475 nm (λ_em) when excited at a wavelength (λ_ex) of 430 nm. During Co²⁺ substitution in Zn²⁺ matrix, a green and red emission peak was observed when excited at a wavelength (λ_ex) of 520 nm.     

Surface chemical bonding states and ferroelectricity of Ce-doped BiFeO<Subscript>3</Subscript> thin films prepared by sol–gel process

Bi_1−x Ce _x FeO₃ (x = 0, 0.05, 0.1, 0.15 and 0.20) (BCFO) thin films were deposited on Pt/TiN/Si₃N₄/Si substrates by sol–gel technique. Crystal structures, surface chemical compositions and bonding states of BCFO films were investigated by X-ray diffraction and X-ray photoelectron spectroscopy (XPS), respectively. Compared to BiFeO₃ (BFO) counterparts, the fitted XPS narrow-scan spectra of Bi 4f_7/2, Bi 4f_5/2, Fe 2p_3/2, Fe 2p_1/2 and O 1s peaks for Bi_0.8Ce_0.2FeO₃ film shift towards higher binding energy regions by amounts of 0.33, 0.29, 0.43, 0.58 and 0.49 eV, respectively. Dielectric constants and loss tangents of the BCFO (x = 0, 0.1 and 0.2) film capacitors are 159, 131, 116, 0.048, 0.041 and 0.035 at 1 MHz, respectively. Bi_0.8Ce_0.2FeO₃ film has a higher remnant polarization (P _r = 2.04 μC/cm²) than that of the BFO (P _r = 1.08 μC/cm²) at 388 kV/cm. Leakage current density of the Bi_0.8Ce_0.2FeO₃ capacitor is 1.47 × 10⁻⁴ A/cm² at 388 kV/cm, which is about two orders of magnitude lower than that of the BFO counterpart. Furthermore, Ce cations are feasibly substituted for Bi³⁺ in the Bi_0.8Ce_0.2FeO₃ matrix, possibly resulting in the enhanced ferroelectric properties for the decreased grain sizes and the reduced oxygen vacancies.     

Precipitation polymerization of <Emphasis Type="Italic">N-tert</Emphasis>-butylacrylamide in water producing monodisperse polymer particles

The precipitation polymerizations of N-tert-butylacrylamide (NtBAM) in water are demonstrated; for example, the polymerization with potassium peroxodisulfate using a 15 g L⁻¹ (118 mmol L⁻¹) concentration of NtBAM in the feed ([NtBAM]₀) was performed at 70 °C for 12 h, quantitatively producing poly(N-tert-butylacrylamide) particles with a number-average diameter (d _n) of 203 nm and a coefficient of variation (C _v) of 4.7%. The particle sizes were controlled in the d _ns range between 75 and 494 nm by changing the monomer feeds or adding an electrolyte such as NaCl. The solid contents in the resulting aqueous latex solutions ranged from 0.1 to 1.5%, whereas it increased to 4.8% by applying a “shot-growth” technique. The polymerization in water under a somewhat unique condition is described, which was started from a heterogeneous system due to the presence of significantly large amounts of monomers ([NtBAM]₀ = 50 g L⁻¹). This also provided monodisperse latexes with the d _n of 370 nm in 96% yield, in which the solid content reached 4.9%.     

Luminescent properties and energy transfer process of Sm3+-Eu3+ co-doped MY2(MoO4)4 (M=Ca,Sr and Ba) red-emitting phosphors

MY₂(MoO₄)₄:Sm³⁺ and MY₂(MoO₄)₄:xSm³⁺,yEu³⁺ (M=Ca, Sr and Ba) phosphors were successfully prepared using solid-state reaction route, and their luminescent properties and energy transfer process from Sm³⁺ to Eu³⁺ were systematically investigated. The results indicate that MY₂(MoO₄)₄:Sm³⁺ phosphors can be effectively excited by 407 nm near UV light originating from the ⁶H_5/2 → ⁴F_7/2 transition of Sm³⁺, and exhibit a satisfactory red emission at 646 nm attributed to the ⁴G_5/2 → ⁶H_9/2 transition of Sm³⁺, in which the emission intensity of SrY₂(MoO₄)₄:Sm³⁺ is the strongest among the MY₂(MoO₄)₄:Sm³⁺ (M=Ca, Sr and Ba) phosphors. For Eu³⁺ co-doped MY₂(MoO₄)₄:Sm³⁺ samples, with increasing Eu³⁺ doping content, the main emission peaks of Sm³⁺ (approximately 646 nm) are decreased, but the emission peaks and intensity of Eu³⁺ are increased while the maximum intensity of luminescence at the Eu³⁺ concentration 0.9. The introduction of Eu³⁺ in the MY₂(MoO₄)₄:Sm³⁺ phosphors can remarkably generate a strong emission line at 616 nm, originating from the ⁵D₀→⁷F₂ transition of Eu³⁺ and Sm³⁺ (⁴G_5/2) → Eu³⁺ (⁵D₀) effective energy transfer process. The energy transfer mechanism from Sm³⁺ to Eu³⁺ was discussed in detail.     

Tunable luminescence and energy transfer process between Tb3+ and Eu3+ in GYAG:Bi3+, Tb3+, Eu3+ phosphors

A series of Eu³⁺ ions co-doped (Gd_0.9Y_0.1)₃Al₅O₁₂:Bi³⁺, Tb³⁺ (GYAG) phosphors have been synthesized by means of solvothermal reaction method. The XRD pattern of GYAG phosphor sintered at 1500 °C confirms their garnet phase. The luminescence properties of these phosphors have been explored by analyzing their excitation and emission spectra along with their decay curves. The excitation spectra of the GYAG:Bi³⁺, Tb³⁺, Eu³⁺ phosphors consists of broad bands in the shorter wavelength region due to 4f⁸ → 4f⁷5d¹ transition of Tb³⁺ ions overlapped with 6s² → 6s¹6p¹ (¹S₀ → ³P₁) transition of Bi³⁺ ions and the charge transfer band of Eu³⁺–O^2?. The present phosphors exhibit green and red colors due to ⁵D₄ → ⁷F₅ transition of Tb³⁺ ions and ⁵D₀ → ⁷F₁ transition of Eu³⁺ ions, respectively. The emission was shifted from green to red color by co-doping with Eu³⁺ ions, which indicate that the energy transfer probability from Tb³⁺ to Eu³⁺ ions are dependent strongly on the concentration of Eu³⁺ ions.