Highly symmetric lattice environment induced orange-red emitting of Eu3+ in a novel tungstate phosphor with broad-band ultraviolet excitation.

In this work, we reported the synthesis and characteristic luminescence of an orange-red emitting phosphor NaBa10Y5W4O30: Eu3+ for ultra-violet white light emitting diodes. The phase compound, crystalline structure and morphology are analyzed. The results indicate that a heavy doping of Eu3+ (x = 50%) is realized in NaBa10Y5-5xW4O30: xEu3+ without any impurity phase. Moreover, the optical band gap is analyzed by diffuse reflectance spectroscopy and further confirmed by density function theory (DFT). Meanwhile, the as-synthesized NaBa10Y5W4O30: Eu3+ phosphor can be efficiently pumped by strong broad-band excitation around 315 nm due to the charge transfer transition from [WO6]6- groups to Eu3+. Owing to the highly symmetric lattice environment of Eu3+ in YO6 sites, a strong orange-red emission at 596 nm with color purity of 95.34% is obtained, corresponding to the 5D0→7F1 magnetic dipole transition of Eu3+ ions. The critical concentration is obtained to be x = 15%, and the quenching mechanism is discussed to be dipole-dipole interaction. Furthermore, the temperature dependent emission behavior are analyzed, and the thermal quenching mechanism are explained by the variable temperature decay curve and configuration coordination diagram. Finally, an orange-red light emitting diode lamp is fabricated based on NaBa10Y5W4O30: 15%Eu3+ phosphor and 315 nm semiconductor chip. In summary, the results indicate that NaBa10Y5W4O30: Eu3+ phosphor has the potential to be an orange-red phosphor for white light emitting diodes.

A metal-to-metal charge transfer induced green-yellow phosphor CsAlGe2O6:Bi3+ for full-spectrum LED devices.

With the development of solid-state lighting, full-spectrum lighting has gradually received extensive attention. Until now, Bi3+-doped narrow-band blue phosphors have been widely reported, but broadband green-yellow Bi3+-doped luminescent materials generated by metal-to-metal charge transfer have been rarely reported. In this study, a Bi3+ ion doped germanate luminescent material CsAlGe2O6:x%Bi3+ (1 ≤ x ≤ 11) is synthesized by a high-temperature sintering method. The phosphor can generate a broad green-yellow band peaking at 535 nm with a full width at half maximum of 165 nm under ultraviolet radiation. Through the analysis of the coordination environment, photoluminescence spectra and decay curves, the broadband emission spectra of Bi3+ ions are proved to be generated by the metal-to-metal charge transfer state and the 3P1 → 1S0 transition. By using theoretical research, luminescence kinetics, and Gaussian fitting, the luminescence mechanism of Bi3+ is examined. Meanwhile, the high quantum efficiency and superior thermal stability prove that the phosphor can be used as an efficient luminescent material in the field of full-spectrum LED devices.

Tunable luminescence and efficient energy transfer investigation of a borosilicate phosphor KBSi2O6: Bi3+, Eu3+ with hypersensitive thermal quenching.

Energy transfer between Bi3+ and Eu3+ has undergone substantial research but Bi3+ and Eu3+ co-doped luminescent materials with high energy transfer efficiency for temperature sensing are rarely investigated until now. Herein, Eu3+ and Bi3+ co-doped KBSi2O6 phosphors were successfully synthesized by solid-state reaction method. The phase purity structure as well as the element distribution were carefully investigated through X-ray diffraction structural refinement and energy dispersive spectrometer analysis. The characteristic luminescence property and luminescence kinetics of KBSi2O6: Bi3+, Eu3+ were investigated. By the large spectra overlap between the emission spectrum of Bi3+ and excitation spectrum of Eu3+, the energy transfer from Bi3+ to Eu3+ can be inferred. The corresponding decrease of the emission intensity and decay time of Bi3+ in KBSi2O6: Bi3+, Eu3+ provided direct evidence for the effective energy transfer from Bi3+ to Eu3+. The interaction and energy transfer mechanism between Bi3+ and Eu3+ ions were also studied. By increasing the Eu3+ concentration in KBSi2O6: Bi3+, Eu3+, the color-tunable emission from blue to red can be realized. KBSi2O6: Bi3+, Eu3+ shows hypersensitive thermal quenching behavior and the maximum absolute sensitivity (Sa) and relative sensitivity (Sr) are determined to be 1.87 %K-1 and 2.895 %K-1, respectively. All of the above results imply that KBSi2O6: Bi3+, Eu3+ phosphor can be a color-tunable phosphor for optical temperature sensing.

Controllable luminescence and efficient energy transfer investigation of a novel white light emission phosphor Ca19Na2Mg(PO4)14: Dy3+, Tm3+ with high thermal stability.

White light emission phosphors are widely researched for application in lighting and display fields. However, the poor thermal stability is a real problem for the known single-phased white phosphors, which limits their further application. In this paper, Ca19Na2Mg(PO4)14: xDy3+, yTm3+ (CNMP, 0 ≤ x ≤ 0.06, y = 0, 0.01) phosphors with adjustable emission and good thermal stability are synthesized. The X-ray diffraction and X-ray energy dispersive spectrometer measurement distinctly confirm the successful synthesis of CNMP: xDy3+, yTm3+ (CNMP, 0 ≤ x ≤ 0.06, y = 0, 0.01). The photoluminescence results reveal that CNMP: Dy3+ shows characteristic excitation peaks in the range of 350-450 nm, and mainly exhibits strong yellow emission around 575 nm ascribed to the 4F9/2-6H13/2 transitions of Dy3+. To compensate the deficiency of blue light emission of CNMP: Dy3+, the trivalent Tm3+ ion is co-doped owing to its characteristic blue emission at 450 nm due to its 1D2-3F4 transitions. Therefore, the emission of CNMP: Dy3+, Tm3+ can be tuned from blue light region with CIE coordinates of (0.1649, 0.0387) to white light region with CIE coordinates of (0.3001, 0.3003) and finally move to yellow light region with CIE coordinates of (0.3732, 0.4493) through adjusting the doping ratio of Dy3+/Tm3+. The energy transfer efficiency and the energy transfer mechanism from Tm3+ to Dy3+ are further investigated. Moreover, CNMP: Dy3+, Tm3+ exhibites a high thermal stability and the emission intensity still keeps 84% of the initial intensity of Dy3+ at 230 °C. These outstanding properties show that Ca19Na2Mg(PO4)14: Dy3+, Tm3+ have great advantages and potentiality for applying in solid state lighting.

Thermally robust and valence-variation-induced white-light emission of a novel stannate phosphor Sr3Al10SnO20:Dy3+: crystal structure, luminescence property, and mechanism investigation.

The development of novel white-light-emission phosphors is of great importance for applications in lighting and display fields. Trivalent Dy3+ is widely used as a potential luminescence center for white-light emission. However, Dy3+-doped phosphors often suffer a poor yellow to blue ratio due to the deficiency of its 4F9/2 → 6H15/2 transition, low luminescence efficiency, and unsatisfactory thermal stability. The importance of the present research work is that we have achieved a tunable white light in a single phased stannate phosphor Sr3Al10SnO20:Dy3+ with robust thermal stability. The crystal structure, phase purity, and chemical composition were investigated via X-ray diffraction Rietveld structure refinement, scanning electron microscopy, and energy dispersive spectrometry. The luminescence spectra indicated that Sr3Al10SnO20:Dy3+ not only exhibited characteristic 4F9/2 → 6HJ/2 (J=11, 13, and 15) inherent transition emissions of Dy3+, but also showed an abnormal blue band emission, which was identified through X-ray photoelectric spectroscopy as the T1 → S0 transitions of Sn2+, resulting from the valence variation of Sn4+. The efficient energy transfer from Sn2+ to Dy3+ was also confirmed and the transfer efficiency was calculated. Owing to the valence-variation-induced emission of Sn2+, a tunable white light could be realized from a cool to warm white light region, with Commission Internationale de l'Eclairage coordinates and a correlative color temperature varying from (0.277, 0.333) and 8634 K to (0.353, 0.404) and 4913 K, respectively. The luminescent and defects formation mechanism as well as the luminescence kinetics were further investigated. Moreover, Sr3Al10SnO20:Dy3+ had a high quantum efficiency (∼34.6%) and a super-stable thermal stability behavior (82.5% at 240 °C of the initial integral emission intensity at 30 °C) with a large activation energy (ΔE ∼ 0.1654 eV). Finally, a charge-compensation test was performed to further verify the effect of defects on the luminescence property and the related mechanism was discussed. The current work provides a novel method to achieve tunable white-light emission in Dy3+ single-doped phosphors and the related mechanism is effectual for other rare earths for potential applications in lighting and display fields.

Highly Eu3+ ions doped novel red emission solid solution phosphors Ca18Li3(Bi,Eu)(PO4)14: structure design, characteristic luminescence and abnormal thermal quenching behavior investigation.

To research and develop potential phosphors for ultraviolet-based white light emitting diodes, a novel red emission phosphate phosphor Ca18Li3Bi1-xEux(PO4)14 was synthesized and investigated in the full range of 0 ≤x≤ 1. The phase purity and crystal structure of the solid solution phosphors were investigated in detail by employing X-ray diffractometer structure refinement, scanning electron microscopy and energy dispersive spectrometry. The crystal structure information was confirmed and the structure as well as the doping concentration dependent characteristic photoluminescence properties were discussed in detail. The results indicated that high Eu3+ doping content x could be realized in Ca18Li3Bi1-xEux(PO4)14 solid solutions even when x = 1. The luminescence performance revealed that Ca18Li3Bi1-xEux(PO4)14 phosphors could emit intense red emission under 394 nm excitation with excellent CIE chromaticity coordinates and high color purity. The concentration dependent emission decay behavior at room temperature and the temperature dependent decay behavior were studied to investigate the luminescent dynamics. The abnormal thermal quenching behavior was investigated via the temperature dependent emission. The related mechanism was discussed through thermoluminescence analysis, charge compensation contrast test and the cooling emission curve measurement, and the thermal activation energy was studied. The above results indicated that the Ca18Li3Bi1-xEux(PO4)14 could be a promising red-emitting phosphor for white light emitting diodes.

Structure- and temperature-sensitive photoluminescence in a novel phosphate red phosphor RbZnPO4:Eu(3.).

A novel phosphate RbZnPO4 has been developed for the first time and the characteristic crystal structure of RbZnPO4 has been investigated in detail, based on the Fourier transform infrared reflection spectra and the structure refinement of X-ray diffraction data. After doping with Eu(3+),RbZnPO4:Eu(3+) shows distinctive deep red emission with dominating peaks at 596 and 701 nm. To provide a reasonable explanation for the relationship between photoluminescence and structure, the photoluminescence property has been discussed by analyzing the particular local ligand environment and site occupation of Eu(3+) in RbZnPO4. More interestingly, temperature-sensitive emission behavior was found in RbZnPO4:Eu(3+). Through the synthetical analysis of the configurational coordinate diagram, the charge compensation experiment and the CASTEP band structure calculation, a complex underlying mechanism is proposed to explain the abnormal temperature-sensitive emission behavior in RbZnPO4:Eu(3+). The mechanism could be helpful for better understanding the thermal quenching process of Eu(3+) in RbZnPO4 and also as a reference in some other temperature-sensitive phosphors.

A blue-emitting Sc silicate phosphor for ultraviolet excited light-emitting diodes.

A blue-emitting phosphor BaSc2Si3O10:Eu(2+) was synthesized using the conventional solid-state reaction. The crystallographic occupancy of Eu(2+) in the BaSc2Si3O10 matrix was studied based on the Rietveld refinement results and the photoluminescence properties. BaSc2Si3O10 exhibits blue emission ascribed to (3)T2-(1)A1 and (3)T1-(1)A1 charge transfer of SiO4(4-) excited by 360 nm. All the phosphors of BaSc2Si3O10:Eu(2+) exhibit strong broad absorption bands in the near ultraviolet range, and give abnormal blue emission upon 330 nm excitation. The abnormal phenomenon was explored in detail through many pieces of experimental evidence. The concentration of Eu(2+) is optimized to be 3 mol% according to emission intensity and the quenching mechanism is verified to be a quadrupole-quadrupole interaction. The CIE coordinates of BaSc2Si3O10:0.03Eu(2+) are calculated to be (0.15, 0.05) and BaSc2Si3O10:0.03Eu(2+) shows similar thermal stability to commercial BaMgAl10O17:Eu(2+).

Size/morphology induced tunable luminescence in upconversion crystals: ultra-strong single-band emission and underlying mechanisms.

In this work, we present a two-step method to controllably synthesize novel and highly efficient upconversion materials, Lu5O4F7:Er(3+),Yb(3+) nano/micro-crystals, and investigate their size/morphology induced tunable upconversion properties. In addition to the common phenomenon aroused by a surface quenching effect, direct experimental evidence for the regulation of phonon modes is obtained in nanoparticles. The findings in this work advance the existing mechanisms for the general explanation of size/morphology induced upconversion features. Because of the adjustment of phonon energy and density as well as the surface quenching effect, the biocompatible Lu5O4F7:Er(3+),Yb(3+) nanoparticles exhibit an ultra-strong single-band red upconversion, rendering them promising for biomedical applications.

Photoluminescence of nanosized GdAl3(BO3)4:Sm3+, Eu3+ phosphor under UV excitation.

GdAl3(BO3)4:Eu3+, Sm3+ nanophosphors were successfully prepared by a sol-gel process. The nanoparticles have been characterized by X-ray diffraction, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques, and fluorescence measurements. The results show that the samples are composed of nanoparticles 40-60 nm in width. Under 406 nm excitation, the predominant emission peak of the GdAl3(BO3)4:Sm3+ nanoparticles is located at 599 nm, which is due to the 4G5/2-6H7/2 transition of Sm3+; Eu3+ activated GdAl3(BO3)4 shows intense red emission at 613 nm in the emission spectrum under 393 nm excitation, belonging to the 5D0-7F2 transition of Eu3+; For the Eu3+/Sm3+ co-doped sample, the most intensive emission at 613 nm under 393 nm excitation has been enhanced about 54% over that of the Eu3+ single-doped sample, due to an energy transfer from Sm3+ to Eu3+.

Differences in photoluminescence properties and thermal degradation between nanoparticle and bulk particle BaMgAl10O17:Eu2+ phosphors under UV?VUV irradiation.

BaMgAl10O17:Eu2+ (BAM) phosphors used for plasma display panels and three-band fluorescence lamps are exposed to an oxidizing environment at about 500 degrees C, which is currently unavoidable in actual applications. We investigated the mechanism of the luminance degradation of BAM caused by annealing at 500 degrees C based on the difference in luminance degradation of bulk particle and nanoparticle samples under various excitation source irradiations. When the samples were excited by the different light sources, more than 30% degradation of luminance occurred under 147 nm while less than 10% degradation occurred under 254 nm both for nanoparticle and bulk particle samples. In addition, the luminescence degradation of nanophosphors shows a different tendency compared to the bulk phosphors. With a model based on the particle size and excitation light penetration depth, we demonstrate that the degradation is still mainly ascribed to the oxidized of divalent Eu. The differences in luminescence properties between nanophosphors and bulk phosphors are also illustrated by this model. As a result, the potential industrial applications of nanophosphors are evaluated.

The luminous and magnetic properties of Tb3+-doped four angle star-like NaGd(WO4)2.

Four angle star-like double tungstates NaGd(WO4)2 have been prepared hydrothermally with cetyl trimethyl ammonium bromide (CTAB) as the chelating agent and ethanol as the mixing solvent. Monodisperse micron-sized four angle star-like NaGd(WO4)2 were fabricated for the first time. The samples were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), and vibrating sample magnetrometer (VSM) techniques. This work emphasizes the luminescence properties of Tb(3+)-doped NaGd(WO4)2 under ultraviolet (UV) and vacuum ultraviolet (VUV) excitation and the magnetic properties. The results demonstrate the phosphors are expected to have potential applications in weak lighting systems and magnetic resonance imaging.

Preparation and drug-delivery properties of hollow YVO4:Ln3+ and mesoporous YVO4:Ln3+@nSiO2@mSiO2 (Ln = Eu, Yb, Er, and Ho).

In this paper, size-controlled morphologies of (Y, Gd)VO4 and (Y, Gd)VO4:Ln3+ (Ln = Eu, Yb, Er, and Ho) were obtained via a facile hydrothermal route, and their properties for drug delivery and photoluminescence were investigated. Monodisperse ellipsoid-like hollow (Y, Gd)VO4 were designed by employing (Y, Gd)(OH)CO3 colloidal spheres as a sacrificial template and NH4VO3 as a vanadium source, and the formation mechanism could be interpreted by the Kirkendall effect. The control of particle size for hollow (Y, Gd)VO4 was realized, facilitating their practical application. Mesoporous core-shell structured (Y, Gd)VO4:Ln3+@nSiO2@mSiO2 were designed to improve the properties for drug release. Typically, red emission of YVO4:Eu3+ predominated under 465 nm excitation; the upconversion spectra of YVO4:Yb3+, Er3+ and YVO4:Yb3+, Ho3+ revealed green and red color upon 980 nm excitation, respectively. The biocompatibility and drug release evaluations indicate the potential biological applications of the samples.

A facile one-step solvothermal synthesis of graphene/rod-shaped TiO2 nanocomposite and its improved photocatalytic activity.

Graphene sheets were obtained through solvothermal reduction of colloidal dispersion of graphene oxide in benzyl alcohol. The graphene/rod-shaped TiO(2) nanocomposite was synthesized by this novel and facile solvothermal method. During the solvothermal reaction, both the reduction of graphene oxide and the growth of rod-shaped TiO(2) nanocrystals as well as its deposition on graphene occur simultaneously. The photocatalytic activity of graphene/rod-shaped TiO(2) and graphene/spherical TiO(2) nanocomposites was compared. In the photocatalytic degradation of methyl orange (MO), the graphene/rod-shaped TiO(2) nanocomposite with the optimized graphene content of 0.48 wt% shows good stability and exhibits a significant enhancement of photocatalytic activity compared to the bare commercial TiO(2) (P25) and graphene/spherical TiO(2) nanocomposite with the same graphene content. Photocurrent experiments were performed, which demonstrate that the photocurrent of the graphene/rod-shaped TiO(2) nanocomposite electrode is about 1.2 times as high as that of the graphene/spherical TiO(2) nanocomposite electrode. The photocatalytic mechanism of graphene/rod-shaped TiO(2) nanocomposite was also discussed on the basis of the experimental results. This work is anticipated to open a possibility in the integration of graphene and TiO(2) with various morphologies for obtaining high-performance photocatalysts in addressing environmental protection issues.