Direct white-light from core-shell-like sphere with Sr3Mg-Si2O8: Eu2+, Mn2+ coated on Sr2SiO4:Eu2+

A method of color mixture for white light is presented with Sr3MgSi2O8:Eu2+, Mn2+ shell coated on Sr2SiO4:Eu2+ core by spray pyrolysis procedure. Upon near ultraviolet (NUV) excitation, a 550 nm band emission of Eu2+ from core host combines with the simultaneous emissions of Eu2+ at 457 nm and Mn2+ at 683 nm based on energy transfer in the shell lattice to generate warm white light with color rendering index (CRI) of 91. With such a core-shell-like structure, the re-absorption of blue light from shell layer can be effectively suppressed, and the chemical stability of the phosphor is verified experimentally to be superior to that of the Sr2SiO4:Eu2+. This new proposed phosphor provides great potential in the color mixture of blending-free phosphor converted white NUV light emitting diode (LED) devices.     

Multi-Mode Optical Manometry Based on Li4SrCa(SiO4)2:Eu2+ Phosphors

Optical manometry is a highly promising method for measuring pressure. However, its wider application is limited by the lower sensitivity and influenced by environmental factors. Herein, multi-mode optical pressure sensors based on Eu²⁺-doped Li₄SrCa(SiO₄)₂ phosphors suitable for a variety of complex pressure-measuring environments are designed. The phosphors contain two separate luminescence centers at 443 nm (Eu_Sr) and 584 nm (Eu_Ca), respectively. In the lower pressure range, the emission peak undergoes a massive redshift of 5.19 nm GPa⁻¹ of Eu_Ca, which is 14× better than commercially available ruby sensors. In order to improve the pressure response range and the accuracy of pressure measurement, for the first time, a new approach in the pressure readout method in which single Eu²⁺ ions doping based on fluorescence intensity ratio (FIR) pressure measurement is realized in designed materials. Meanwhile, the measured full width at half maximum (FWHM) as an indicator of pressure sensor performance also reveals that the sensing performance is d FWHM/d P ≈ 1.23 nm GPa⁻¹ and d FWHM/d P ≈ 0.84 nm GPa⁻¹ for Eu_Sr and Eu_Ca positions, respectively. Additionally, the structural stability of the phosphor is confirmed by in situ Raman spectrum. The above results indicate that the Li₄SrCa(SiO₄)₂:0.04Eu²⁺ phosphor is a good candidate for multi-mode optical pressure sensors.     

Photoluminescence properties of YVO4:Eu3+,Ba2+ nanoparticles prepared by an ion exchange method

YVO₄:Ba²⁺ nanoparticles with a Ba²⁺ doping concentration x=0%, 1%, 3%, 5%, 7% and 9% were synthesized by a solvothermal method and then they were codoped with Eu³⁺ ions by an ion exchange method to form the YVO₄:Eu³⁺,Ba²⁺ nanoparticles. It was found that the photoluminescence intensity of the as-prepared YVO₄:Eu³⁺,Ba²⁺ nanoparticles steadily increased with x until x=7%, and then decreased for higher x. Thermal annealing resulted in considerable enhancement in their photoluminescence, and higher annealing temperature led to stronger photoluminescence enhancement. The emission intensity of the YVO₄:Eu³⁺,Ba²⁺ (x=7%) nanoparticles annealed at 500 °C was about 205% stronger than the sample without Ba²⁺ doping. Thermal annealing of the ion-exchanged YVO₄:Eu³⁺,Ba²⁺ nanoparticles at 500 °C and 700 °C resulted in photoluminescence enhancement of about 14 times and 27 times, respectively. The asymmetric ratio of Eu³⁺ in the ion-exchanged YVO₄:Eu³⁺,Ba²⁺ nanoparticles was found to increase after annealing.     

Application research of CdS: Eu3+ quantum dots-sensitized TiO2 nanotube solar cells

Trivalent Eu³⁺-doped CdS quantum dot (CdS: Eu³⁺ QD)-sensitized TiO₂ nanotube arrays (TNTAs) solar cells are prepared by using the direct adsorption method. The influences of sensitization time, sensitization temperature, and Eu³⁺ ion concentrations are investigated systematically. The photo-current of the CdS: Eu³⁺ QDs/TiO₂ nanotubes appear at the main absorption region of 320–480 nm, and the maximum incident photon to the current conversion efficiency (IPCE) value is 21% at 430 nm when the sensitization condition is 4% doping Eu³⁺ concentration, 60 °C sensitization temperature, 8 h sensitization time. Compared with the un-doped CdS QD-sensitized TNTAs, the conversion efficiency and IPCE of CdS: Eu³⁺ QDs/TNTAs are two times and three times than that of un-doped CdS QDs sensitized TNTAs. This scenario exhibits the potential applications of rare earth elements in QD-sensitized solar cells.     

Effect of europium doping levels on photoluminescence and thermoluminescence of strontium yttrium oxide phosphor

The present paper deals with the effect of europium (Eu³⁺) doping concentration (0.1–2.5 mol%) on photoluminescence (PL) and thermoluminescence (TL) of strontium yttrium oxide (SrY₂O₄) phosphor. The sample was prepared by the modified solid state reaction method, which is the most suitable method for large-scale production. The prepared phosphor sample was characterized by using X-ray Diffraction (XRD), field emission gun scanning electron microscopy, fourier transform infrared spectroscopy, high resolution transmission electron microscopy, photoluminescence, thermoluminescence and commission internationale de I׳Eclairage techniques. The PL emission was observed in the range of 410–630 nm for the SrY₂O₄ phosphor doped with Eu³⁺. Excitation spectrum was found at 254 and 325 nm, sharp peaks were found around 593, 615 and 625 nm with high intensity. From the XRD data, using Scherrer׳s formula, calculated average crystallite size of Eu³⁺ doped SrY₂O₄ phosphor is around 32 nm. Thermoluminescence study was carried out for the phosphor with UV and gamma irradiation. The TL response of SrY₂O₄:Eu³⁺ phosphor for two different radiations was compared and studied in detail. The present phosphor can act as a single host for white light emission in display devices. The detailed process and possible mechanisms for PL and TL are studied and discussed. For the variable concentration of Eu³⁺ on PL studies the PL intensity increases with increasing the concentration of dopant and the concentration quenching found after 2 mol% of Eu³⁺ the optimized concentration was 2 mol%, which is suitable for the display device application. In TL glow curve the optimized concentration was 1 mol% for the UV irradiated sample and 0.2 mol% of Eu³⁺ for the gamma irradiated sample and beta irradiated sample for 10 Gy dose. The kinetic parameters were calculated by the computerized glow curve deconvolution (CGCD) technique.     

Fabrication and study of properties of the PLA/Sr2MgSi2O7:Eu2+, Dy3+ long-persistent luminescence composite thin films

In this paper, Sr₂MgSi₂O₇:Eu²⁺,Dy³⁺ (SMS) particles were first synthesized by sol–gel method and then modified with 3-aminopropyltriethoxysilane (APS) to improve their dispersibility and compatibility in the polylactic acid (PLA) matrix. The structure of pure SMS particles was analyzed by XRD and XPS. The properties of SMS particles before and after modification were characterized by FT-IR and SEM. PLA/SMS composite films containing 15 wt% of SMS particles were prepared by spin coating on silicon wafer. Their morphology and luminescence properties were examined. It was found that the composite films can be excited by a broad band from 330 nm to 425 nm with the highest excitation intensity at 360 nm. The fluorescent and phosphorescent emission bands of the composite films and SMS particles all have a major emission peak at 468 nm. Decay curves of the composite films have a similar tendency with that of the pure SMS particles, except for the lower intensity.     

Bioinspired Design of SrAl2O4:Eu2+ Phosphor

A phosphor based on Sr_0.97Al₂O₄:Eu_0.03 with a biomorphous morphology is manufactured via vacuum assisted infiltration of wood tissue (Pinus sylvestris) with a precursor nitrate solution. The nitrate solution penetrates homogeneously into the uniform arrangement of rectangular shaped tracheidal cells of the wood tissue. According to scanning electron microscopy, the original wood cell walls are completely transformed retaining the original wood structure. The major crystalline phase is monoclinic SrAl₂O₄, detected by X‐ray diffraction and confirmed by Rietveld refinement. Energy‐dispersive X‐ray analysis proves the homogeneous conversion of the original wood cell wall into Sr_0.97Al₂O₄:Eu_0.03 struts. The optical properties of the resulting phosphor material are determined by photoluminescence and cathode‐luminescence spectroscopy in scanning electron microscopy. The biotemplated Sr_0.97Al₂O₄:Eu_0.03 shows a characteristic green emission at 530 nm (2.34 eV). Shaping biomorphous SrAl₂O₄:Eu²⁺ phosphor with a microstructure pseudomorphous to the bioorganic template anatomy offers a novel approach for designing micropatterned phosphor materials.     

Sb2(SxSe1−x)3 sensitized solar cells prepared by solution deposition methods

Solid state semiconductor sensitized solar cells are a very active research subject in emerging photovoltaic technologies. In this work, heterojunctions of antimony sulfide-selenide (Sb₂(S_xSe_1−x)₃) solid solution as the absorbing material and cadmium sulfide coated titanium dioxide (TiO₂/CdS) as the electron conductor have been developed with solution deposition methods such as spin-coating, successive ionic layer adsorption and reaction (SILAR), and chemical bath deposition. In particular, CdS has been deposited on mesoporous TiO₂ layers by SILAR deposition, followed by the chemical deposition of Sb₂(S_xSe_1−x)₃. It was found that by increasing the number of CdS SILAR deposition, both the open circuit voltage V_oc and the short circuit current density J_sc of the Sb₂(S_xSe_1−x)₃ sensitized solar cells had been increased from 153 to 434 mV and 0.77–9.73 mA/cm², respectively. This improvement was attributed to the fact that the presence of the CdS on TiO₂ surface reduces the formation of undesired Sb₂O₃ and promotes a better nucleation of the Sb₂(S_xSe_1−x)₃ during the chemical bath deposition. The best result was obtained for the solar cell with 30 cycles of CdS which produced a V_oc of 434 mV, a J_sc of 9.73 mA/cm², and a power conversion efficiency of 1.69% under AM1.5 G solar radiation.     

Shape controlled synthesis and formation mechanism of Y2(C2O4)3 and Eu3+–Y2O3 phases via hydrothermal microemulsion

The flat or truncated flat cube Y₂O₃ precursor powders were synthesized in a reverse microemulsion and hydrothermal. Hexadecyl Trimethyl Ammonium Bromide (CTAB) and Organophosphate (OP) were used as the mixed surfactants, n-pentanol was used as assistant, and cyclohexane was used as oil phase. Y(NO₃)₃ and Na₂C₂O₄ solution were used as the water-phrase and starting materials. The resulting products were characterized by X-ray powder diffraction (XRD), field emission scanning electron microscopy (FESEM), d thermogravimetric – differential scanning calorimetry (TG–DSC), and photoluminescence spectroscopy (PL). The results show that the monoclinic rod-like Y₂(C₂O₄)₃ have been obtained via hydrothermal microemulsion and the sizes of the particles were diameters of 100 nm and lengths up to about 1–2 μm. The precursor calcined products were doped with Eu³⁺, and the prepared phosphors showed well-defined red luminescence due to radiative transitions from ⁵D₀ to ⁷F_J (J=1, 2) levels of Eu³⁺ ions. Furthermore, We reported Eu³⁺–Y₂O₃ phases represented a new class of optically active materials.     

Photoluminescence properties of novel white phosphor of Dy3+-doped LaBSiO5 glass

A single-phased white emitting phosphor LaBSiO₅:Dy³⁺ was successfully synthesized via a solid state reaction. The X-ray diffraction results confirmed that the doped Dy³⁺ ions did not change the lattice structure. Several strong excitation peaks of LaBSiO₅:Dy³⁺ were found around 300–450 nm. Under excitation of 350 nm, the LaBSiO₅:Dy³⁺ exhibited white emission by combining the two emission peaks at 478 and 574 nm corresponding to the typical ⁴F_9/2→⁶H_15/2 and ⁴F_9/2→⁶H_13/2 transitions. The optimal substitution proportions of Dy³⁺ for La³⁺ was determined to be 1 mol% and the critical distance of Dy³⁺ was 25.9628 Å. Moreover, the CIE chromaticity coordinates of LaBSiO₅:Dy³⁺ phosphor was (0.3116, 0.3474) which is close to the ideal white light coordinates (0.333, 0.333), indicating that the phosphor has a potential application as a single component ultraviolet-convertible white light emitting phosphor.     

Oxide-free Sb2S3 sensitized solar cells fabricated by spin and heat-treatment of Sb(III)(thioacetamide)2Cl3

Pure Sb₂S₃ without oxide impurities was formed by thermal decomposition of Sb(thioacetamide: TA)₂Cl₃ precursor. From the analysis of thermal properties of Sb(TA)₂Cl₃, we developed a spin-coating and heat-treatment process to form pure Sb₂S₃ thin-films with controllable thickness due to the formation of insoluble Sb₂S₃ by heat-treatment. Through the spin-coating and heat-treatment process, we could fabricate oxide-free Sb₂S₃ planar type sensitized solar cell with 8.12 mA/cm² of short circuit current density (J_sc), 0.616 V of open circuit voltage (V_oc), 45.9% of fill factor (F.F), and overall power conversion efficiency (η) of 2.3% at 1 sun condition.     

Edge termination strategies for a 4 kV 4H–SiC thyristor

Thyristors able to block 4 kV have been fabricated and characterised. The experimental forward current is 1.3 A @ V_AK = 10 V for a 9 mA gate current during 550 ns. The device active area is 2.3 mm². The devices and their edge terminations have been designed using numerical simulations. Two different edge terminations have been envisaged (mesa and a combination of mesa and JTE). A SiO₂ passivation layer also improves the forward blocking voltage depending on the sign and the magnitude of the effective charge density in the oxide. The mesa protection is not enough to allowing the thyristor to block 5 kV, due to the low etching rate in SiC. Thus, a mesa/JTE protection has been used. The influence of the etching depth, the JTE dose and length on the forward blocking voltage of the thyristor has been studied in details. Simulation results have allowed designing the devices, not far from the optimal structure. The best results of the forward blocking voltage are 4 kV for the mesa protected thyristor, while the mesa/JTE combination yields 3.6 kV. Furthermore, experimental results confirm the simulations concerning the influence of the oxide thickness on the forward blocking voltage. The better results for the mesa protected thyristor are due to a lower interface SiC/SiO₂ charge density provided by the different oxidation processes (at different foundries).In addition, the comparison between experiments and simulations allows estimate the effective charge density of the SiO₂ layer in 10¹²–5 × 10¹² cm⁻² range for the two fabricated thyristors. The improvement in the forward blocking voltage must pass through an improvement of the passivation layer. Passivation still remains a technological key step to obtain SiC high-voltage devices.     

Improved performance of nanoporous TiO2 film in dye-sensitized solar cells via ZrCl4 and TiCl4 surface co-modifications

In this study, nanoporous TiO₂ films were modified by a dip-coating process using a mixture aqueous solution of ZrCl₄ and TiCl₄ followed by calcination to prepare a photoanode for dye-sensitized solar cells. Compared with the control film modified with 0.04 mol L⁻¹ TiCl₄, the power conversion efficiency of the TiO₂ film modified with a mixed solution of 0.05 mol L⁻¹ ZrCl₄ and 0.04 mol L⁻¹ TiCl₄, was 18.67% higher because of the improved short circuit current (J_sc) and open circuit voltage (V_oc). The improvement in J_sc was due to the suppression of charge recombination, which was demonstrated by a series of measurements, including electrochemical impedance spectroscopy, monochromatic incident photon-to-electron conversion efficiency spectroscopy, and the open-circuit voltage decay technique. The Mott-Schottky measurement results indicated that the negative shift of a flat band led to the increased V_oc.     

Energy transfer of Ce3+ → Eu2+ in the CaGa2S4 compound

Photoluminescence of CaGa₂S₄:Eu²⁺, CaGa₂S₄:Ce³⁺, and CaGa₂S₄:(Eu²⁺, Ce³⁺) is shown to be caused by intracenter transitions of Eu²⁺ and Ce³⁺ ions. It is ascertained that an energy transfer with an efficiency of 0.43 takes place from Ce³⁺ to Eu²⁺.     

Efficient solution processed D1-A-D2-A-D1 small molecules bulk heterojunction solar cells based on alkoxy triphenylamine and benzo[1,2-b:4,5-b′]thiophene units

Two molecules denoted as VC96 and VC97 have been synthesized for efficient (η = 6.13% @ 100 mW/cm² sun-simulated light) small molecule solution processed organic solar cells. These molecules have been designed with the D₁-A-D₂-A-D₁ structure bearing different central donor unit, same benzothiadiazole (BT) as π-acceptor and end capping triphenylamine. Moreover, the optical and electrochemical properties (both experimental and theoretical) of these molecules have been systematically investigated. The solar cells prepared from VC96:PC₇₁BM and VC97:PC₇₁BM (1:2) processed from CF (chloroform) exhibit a PCE (power conversion efficiency) of η = 4.06% (J_sc = 8.36 mA/cm², V_oc = 0.90 V and FF = 0.54) and η = 3.12% (J_sc = 6.78 mA/cm², V_oc = 0.92 V and FF = 0.50), respectively. The higher PCE of the device with VC96 as compared to VC97 is demonstrated to be due to the higher hole mobility and broader IPCE spectra. The devices based on VC96:PC₇₁BM and VC97:PC₇₁BM processed with solvent additive (3 v% DIO, 1,8-diiodooctane) showed PCE of η = 5.44% and η = 4.72%, respectively. The PCE device of optimized VC96:PC₇₁BM processed with DIO/CF (thermal annealed) has been improved up to 6.13% (J_sc = 10.72 mA/cm², V_oc = 0.88 V and FF = 0.61). The device optimization results from the improvement of the balanced charge transport and better nanoscale morphology induced by the solvent additive plus the thermal annealing.     

Fluorosilicate and fluorophosphate superfluorescent multicore optical fibers co-doped with Nd3+/Yb3+

In the paper spectroscopic properties of two fluorosilicate and fluorophosphate glass systems co-doped with Nd³⁺/Yb³⁺ ions are investigated. As a result of optical excitation at the wavelength of 808 nm strong and wide emission in the 1 μm region corresponding to the superposition of optical transitions ⁴F_3/2 → ⁴I_11/2 (Nd³⁺) and ²F_5/2 → ²F_7/2 (Yb³⁺) can be observed. The optimization of Nd³⁺ → Yb³⁺ energy transfer in both glasses allows to manufacture multicore optical fibers with narrowing and red-shifting of amplified spontaneous emission (ASE) at 1.1 μm.     

Preparation and luminescent properties of novel red phosphors for white-light emitting diodes (W-LEDs) application

A series of Eu³⁺–Gd³⁺ co-doped solid solution of Ca_0.54Sr_{0.46–1.5x–1.5z}Eu_zGd_x (MoO₄)_y (WO₄)_1−y (x=0.01–0.20, y=0–1.0, z=0.01–0.30) have been prepared by solid-state reactions. It is found that appropriate amount of Mo⁶⁺ or W⁶⁺, Eu³⁺ and Gd³⁺concentrations can enhance the luminescent intensity and improve crystal structure. These phosphors can be effectively excited by ultraviolet light at 394 nm and blue light at 465 nm (f–f transition) and emits red light (616 nm) with line spectrum. The wavelengths at 394 and 465 nm are nicely fitted in with the widely applied output wavelengths of ultraviolet or blue LED chips.     

The effect of different lattice sites substitution on photoluminescence characteristics of Eu2+/Ce3+ doped M5(ZO4)3X

The empirical formula of Van Uitert is applied to calculating the emission wavelengths of haloapatite and silicon apatite phosphors doped with Eu²⁺/Ce³⁺. The relationship between emission wavelengths and occupied lattice sites of Eu²⁺/Ce³⁺ is discussed in haloapatite crystal. For phosphors of haloapatite and silicon apatite doped with Eu²⁺, the emission bands of the long-wave region are interpreted reasonably. Phosphors Sr₅(PO₄)₂SiO₄ doped with Eu²⁺/Ce³⁺ are synthesized by high temperature solid state reaction under two different atmospheres, the spectral characteristics of Eu²⁺/Ce³⁺ occupying different lattice sites are studied. The luminescent materials Sr₅(PO₄)₂SiO₄ doped with Eu²⁺/Ce³⁺ are promising blue-green phosphors for application in white-LEDs.     

Stepwise co-sensitization as a useful tool for enhancement of power conversion efficiency of dye-sensitized solar cells: The case of an unsymmetrical porphyrin dyad and a metal-free organic dye

A tertiary arylamine compound (DC), which contains a terminal cyano-acetic group in one of its aryl groups, and an unsymmetrical porphyrin dyad of the type Zn[Porph]-L-H₂[Porph] (ZnP-H₂P), where Zn[Porph] and H₂[Porph] are metallated and free-base porphyrin units, respectively, and L is a bridging triazine group functionalized with a glycine moiety, and were synthesized and used for the fabrication of co-sensitized dye-sensitized solar cells (DSSCs). The photophysical and electronic properties of the two compounds revealed spectral absorption features and frontier orbital energy levels that are appropriate for use in DSSCs. Following a stepwise co-sensitization procedure, by immersing the TiO₂ electrode in separate solutions of the dyes in different sequence, two co-sensitized solar cells were obtained: devices C (ZnP-H₂P/DC) and D (DC/ZnP-H₂P).The two solar cells were found to exhibit power conversion efficiencies (PCEs) of 6.16% and 4.80%, respectively. The higher PCE value of device C, which is also higher than that of the individually sensitized devices based on the ZnP-H₂P and DC dyes, is attributed to enhanced photovoltaic parameters, i.e. short circuit current (J_sc = 11.72 mA/cm²), open circuit voltage (V_oc = 0.72 V), fill factor (FF = 0.73), as it is revealed by photovoltaic measurements (J–V curves) and by incident photon to current conversion efficiency (IPCE) spectra of the devices, and to a higher total dye loading. The overall performance of device C was further improved up to 7.68% (with J_sc = 13.45 mA/cm², V_oc = 0.76 V, and FF = 0.75), when a formic acid treated TiO₂ ZnP-H₂P co-sensitized photoanode was employed (device E). The increased PCE value of device E has been attributed to an enhanced J_sc value (=13.45 mA/cm²), which resulted from an increased dye loading, and an enhanced V_oc value (=0.76 V), attributed to an upward shift and increased of electron density in the TiO₂ CB. Furthermore, dark current and electrochemical impedance spectra (EIS) of device E revealed an enhanced electron transport rate in the formic acid treated TiO₂ photoanode, suppressed electron recombination at the photoanode/dye/electrolyte interface, as well as shorter electron transport time (τ_d), and longer electron lifetime (τ_e).     

A novel white-bluish emitting phosphor of (Ba0.49Sr0.49)2-B2P2O10:0.02Eu2+ for white LEDs

A novel white-bluish emitting phosphor of (Ba0.49Sr0.49)2B2P2O10:0.02Eu2+ is synthesized by the solid state reaction. (Ba0.49Sr0.49)2B2P2O10:0.02Eu2+ can be effectively excited by 370 nm ultraviolet (UV) light, and exhibits two emission bands at 430 nm and 522 nm which are attributed to the d-f transitions of the Eu2+ ions in two different cation sites in the host lattices. And the chromaticity coordinate of (Ba0.49Sr0.49)2B2P2O10:0.02Eu2+ phosphor is (0.29, 0.25).