Luminescent materials derived from the surface-modification of Ln3+-doped zeolite L with a silylated terpyridine

Herein we report luminescent materials of Ln³⁺ (Ln = Eu or Tb) doped disc shaped zeolite L crystals (Eu³⁺/ZLD, Tb³⁺/ZLD) modified with a silylated terpyridine (Terpy-Si). The modified crystals show bright red emission and green emission under UV-light irradiation due to the energy transfer from the Terpy-Si to the Eu³⁺ and Tb³⁺ ions. The obtained materials were characterized with FT-IR, SEM, XRD and elemental analysis. Luminescence spectroscopy was used to study the luminescence properties of the modified Eu³⁺(Tb³⁺)/ZLD crystals. The formation of europium(III) and terbium(III) Terpy-Si silicon complexes and energy transfer from Terpy-Si to Eu³⁺ ions and Tb³⁺ have been confirmed by luminescence spectroscopy.     

Luminescence properties of the single-phase white light emitting phosphors Li0.04Ca0.93−xSiO3:Eu0.01,Bi0.02,Tbx

The single-phase white light emitting Li_0.04Ca_0.93?xSiO₃:Eu_0.01,Bi_0.02,Tb_x (x?=?0.01–0.05) phosphors were successfully synthesized using the sol–gel method. The phase structure, morphology and photoluminescence properties (PL) of phosphors were characterized by X-Ray Diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), photoluminescence (PL) and absorption spectra. The results show that the Li_0.04Ca_0.93?xSiO₃:Eu_0.01,Bi_0.02,Tb_x phosphors only consist of β-CaSiO₃ phase. The diffraction peak of (320) plane shows right-shift caused by Tb³⁺ ions doped into the β-CaSiO₃ host. The Li_0.04Ca_0.93?xSiO₃:Eu_0.01,Bi_0.02,Tb_x phosphors exhibit bright white emitting light on the excitation of 228 nm and the luminescence intensity increases with increase of Tb³⁺ ions until the concentration of Tb³⁺ ions is x?=?0.03. Then the luminescence intensity gradually decreases owing to concentration quenching behavior of Tb³⁺ ions. The emission color of phosphors would move from the white light region towards green direction with the increase of concentrations of Tb³⁺ ions. The color correlated temperature (CCT) values decrease from 8964 to 6118 K with the increase in concentration of Tb³⁺. Li_0.04Ca_0.9SiO₃:Eu_0.01,Bi_0.02,Tb_0.03 phosphor has higher band gap energy E_g (5.43 eV) than that of Li_0.04Ca_0.93SiO₃:Eu_0.01,Bi_0.02 phosphor. The addition of Tb³⁺ ions improve the thermal stability of phosphors with the thermal activation energy of 0.28 eV. The experimental result confirms that Tb³⁺ ions show the transfer energy behavior from Tb³⁺ to Eu³⁺ ions in the Li_0.04Ca_0.93?xSiO₃:Eu_0.01,Bi_0.02,Tb_x phosphors.

     

Layered rare-earth hydroxide and oxide nanoplates of the Y/Tb/Eu system: phase-controlled processing,structure characterization and color-tunable photoluminescence via selective excitation and efficient energy transfer

Abstract

Well-crystallized (Y_0.97?xTb_0.03Eu_x)₂(OH)₅NO₃·nH₂O (x = 0–0.03) layered rare-earth hydroxide (LRH) nanoflakes of a pure high-hydration phase have been produced by autoclaving from the nitrate/NH₄OH reaction system under the optimized conditions of 100 °C and pH ～7.0. The flakes were then converted into (Y_0.97?xTb_0.03Eu_x)₂O₃ phosphor nanoplates with color-tunable photoluminescence. Detailed structural characterizations confirmed that LRH solid solutions contained NO₃^? anions intercalated between the layers. Characteristic Tb³⁺ and Eu³⁺ emissions were detected in the ternary LRHs by selectively exciting the two types of activators, and the energy transfer from Tb³⁺ to Eu³⁺ was observed. Annealing the LRHs at 1100 °C produced cubic-lattice (Y_0.97?xTb_0.03Eu_x)₂O₃ solid-solution nanoplates with exposed 222 facets. Multicolor, intensity-adjustable luminescence was attained by varying the excitation wavelength from ～249 nm (the charge transfer excitation band of Eu³⁺) to 278 nm (the 4f⁸–4f⁷5d¹ transition of Tb³⁺). Unitizing the efficient Tb³⁺ to Eu³⁺ energy transfer, the emission color of (Y_0.97?xTb_0.03Eu_x)₂O₃ was tuned from approximately green to yellowish-orange by varying the Eu³⁺/Tb³⁺ ratio. At the optimal Eu³⁺ content of x = 0.01, the efficiency of energy transfer was ～91% and the transfer mechanism was suggested to be electric multipole interactions. The phosphor nanoplates developed in this work may be incorporated in luminescent films and find various lighting and display applications.     

Preparation and luminescence properties of sol-gel hybrid materials incorporated with europium complexes

Microporous silica gel has been prepared by the sol-gel method utilizing the hydrolysis and polycondensation of tetraethylorthosilicate (TEOS). The gel has been doped with the luminescent ternary europium complex Eu(TTA)₃·phen: where HTTA = 1-(2-thenoyl)-3,3,3-trifluoracetone and phen = 1,10-phenanthroline. By contrast to the weak f-f electron absorption bands of Eu³⁺, the complex organic ligand exhibits intense near ultraviolet absorption. Energy transfer from the ligand to Eu³⁺ enables the production of efficient, sharp visible luminescence from this material. Utilizing the polymerization of methyl methacrylate or ethyl methacrylate, the inorganic/polymer hybrid materials containing Eu(TTA)₃·phen have also been obtained. SEM micrographs show uniformly dispersed particles in the nanometre range. The characteristic luminescence spectral features of europium ions are present in the emission spectra of the hybrid material doped with Eu(TTA)₃·phen.     

Luminescence Spectra of Poly(methylmethacrylate)/ZnS:Eu(III),Tb(III) Composites

Colloidal zinc sulfide solutions have been prepared by reacting zinc trifluoroacetate and thioacetamide in methyl methacrylate as a reaction medium, and europium and terbium salts have been added to the solution. Using methyl methacrylate block polymerization, we have synthesized PMMA/ZnS, PMMA/ZnS:Eu(III), PMMA/ZnS:Tb(III), and PMMA/ZnS:Eu(III),Tb(III) composites. The luminescence of the composites is due to charge recombination at energy levels of structural defects and impurities in ZnS and also to ⁵D₀ → ⁷F _j and ⁵D₄ → ⁷F _j electronic transitions of the Eu³⁺ and Tb³⁺ ions. It depends on the composition and structure of the composites, excitation wavelength, and other factors. The mutual effects of the ZnS and the Eu³⁺ and Tb³⁺ ions show up as changes in the position and relative intensity of luminescence bands in the spectra of the composites.     

Strong luminescence and efficient energy transfer in Eu3+/Tb3+-codoped ZnO nanocrystals

Single crystalline Eu³⁺/Tb³⁺-codoped ZnO nanocrystals have been synthesized by using a simple co-precipitation method. Successful doping is realized so that strong green and red luminescence can be efficiently excited by ultraviolet and near ultraviolet radiation, demonstrating an efficient energy transfer from ZnO host to rare earth ions. The energy transfer from the ZnO host to Tb³⁺ in ZnO: Tb³⁺ samples and ZnO host to Eu³⁺ in the ZnO: Eu³⁺ samples under UV excitation are investigated. It is found that the red ⁵D₀ → ⁷F₂ emission of Eu³⁺ ions decreases with increasing temperature but the green ⁵D₄ → ⁷F₅ emission of Tb³⁺ ions increases with increasing temperature, implying a different energy transfer processes in the two samples. Moreover, energy transfer from Tb³⁺ ions to Eu³⁺ ions in ZnO nanocrystals is also observed by analyzing luminescence spectra and the decay curves. By adjusting the doping concentration, the Eu³⁺/Tb³⁺-codoped ZnO phosphors emit green and red luminescence with chromaticity coordinates near white light region, high color purity and high intensity, indicating that they are promising light-conversion materials and have potential in field emission display devices and liquid crystal display backlights.     

Luminescence of SrGdGa3O7:RE(RE = Eu, Tb) phosphors and energy transfer from Gd to RE

Eu³⁺- and Tb³⁺-activated SrGdGa₃O₇ phosphors were synthesized by the solid-state reaction and their luminescence properties were investigated. Sr(Gd_1 − xEu_x)Ga₃O₇ and Sr(Gd_1 − xTb_x)Ga₃O₇ formed continuous solid solution in the range of x = 0-1.0. Unactivated SrGdGa₃O₇ exhibited a typical characteristic excitation and emission of Gd ion. The SrGdGa₃O₇:xEu³⁺ and SrGdGa₃O₇:xTb³⁺ phosphors also showed the well-known Eu³⁺ and Tb³⁺ excitation and emission. The energy transfer from Gd³⁺ to Eu³⁺ and Tb³⁺ were verified by photoluminescence spectra. The dependence of photoluminescence intensity on Eu³⁺ and Tb³⁺ concentration were also studied in detail and the photoluminescence (PL) intensity of SrGdGa₃O₇:Eu and SrGdGa₃O₇:Tb were compared with commercial phosphors, Y₂O₃:Eu and LaPO₄:Ce,Tb. The luminescence decay measurements showed that the lifetimes of Eu³⁺ and Tb³⁺ were in the range of microsecond. The energy transfer from Gd³⁺ to Tb³⁺ was also observed in decay curve.     

Structure and photoluminescence property of complexes of aromatic carboxylic acid-functionalized polysulfone with Eu(Ⅲ) and Tb(Ⅲ)

With chloromethylated polysulfone as starting substance, naphthoic acid (NA) and benzoic acid (BA) were bonded onto the side chains of polysulfone (PSF) via polymer reactions, obtaining two kinds of aromatic carboxyl acid-functionalized polysulfone, PSFNA and PSFBA. Subsequently, the luminescent binary and ternary polymer-rare earth complexes of Eu(Ⅲ) and Tb(Ⅲ) were prepared through coordination reactions, respectively, with PSFNA and PSFBA as macromolecule ligands and with 1,10-phenanthroline (Phen) and 4,4′-bipyridine (Bipy) as small-molecule co-ligands. This work focuses on investigating the relationship between structure and photoluminescence property of these complexes. The experimental results indicate that the macromolecule ligands PSFNA and PSFBA can strongly sensitize the fluorescence emissions of Eu³⁺ ion or Tb³⁺ ion, and the sensitization effect is strongly dependent on the structure of the ligands and the property of the central ions. The fluorescence emission of the binary complex PSF–(NA)₃–Eu(Ⅲ) is stronger than that PSF–(BA)₃–Eu(Ⅲ), suggesting the bonded ligand NA has stronger sensitization action for Eu³⁺ ion than ligand BA; The binary complex PSF–(BA)₃–Tb(Ⅲ) emit very strong characteristic fluorescence of Tb³⁺ ion, displaying that ligand BA can strongly sensitize Tb³⁺ ion, whereas PSF–(NA)₃–Tb(Ⅲ) does not emit the characteristic fluorescence of Tb³⁺ ion, showing that the bonded ligand NA does not sensitize Tb³⁺ ion. The fluorescence intensity of the ternary complexes is stronger than that of the binary complexes in the same series. The solid films of these complexes also emit the strong characteristic fluorescence of Eu³⁺ ion or Tb³⁺ ion.     

Luminescent properties of single-phase Ba<Subscript>2</Subscript>P<Subscript>2</Subscript>O<Subscript>7</Subscript>:Tb<Superscript>3+</Superscript>, R (R = Eu<Superscript>2+</Superscript>, Ce<Superscript>3+</Superscript>) phosphors for white LED

The Ba₂P₂O₇:Tb³⁺, R (R?=?Eu²⁺, Ce³⁺) phosphors were synthesized by use of a co-precipitation method. Crystal phase, excitation and emission spectra of sample phosphors are analyzed by means of XRD and FL, respectively. The emission spectra of Ba₂P₂O₇:Ce³⁺, Tb³⁺ phosphors exhibit four linear peaks attributed to the ⁵D₄?→?⁷F_J (J?=?6–3) transition of Tb³⁺ while four broad emission bands are observed in the emission spectra of Ba₂P₂O₇:Eu²⁺, Tb³⁺ phosphors. The effects of Eu²⁺ concentration on the luminescent properties of Ba₂P₂O₇:Tb³⁺, R (R?=?Eu²⁺, Ce³⁺) are studied. Ce³⁺ affects the luminescent properties of Ba₂P₂O₇:Ce³⁺, Tb³⁺ phosphors just as the sensitizer. However, Eu²⁺ is considered both as the sensitizer and the activator in Ba₂P₂O₇:Eu²⁺, Tb³⁺ phosphors. The chromaticity coordinates of Eu²⁺ and Tb³⁺ co-doped phosphors gather around the white light field with the CCT approximate to 5000 K, indicating that the luminescent property of Ba₂P₂O₇:Eu²⁺, Tb³⁺ phosphors may approach to a desired level needed for white LED application.     

Structural and photophysical properties of lanthanide complexes with N-(diphenylphosphoryl)-4-methylbenzenesulfonamide

Lanthanide complexes with N-(diphenylphosphoryl)-4-methylbenzenesulfonamide (HPMSP) as new sensitizers of visible luminescence were obtained. The series of stable lanthanide complexes Na[Ln(PMSP)₄], where Ln = Eu³⁺, Gd³⁺, Tb³⁺ were characterized by X-ray diffraction, IR, absorption, emission, and excitation spectra at 295 and 77 K as well as luminescence decay times and intrinsic emission quantum yields. The Tb complex, exhibiting relatively efficient ligand-to-metal energy transfer and strong metal-centred emission, is a promising candidate for effective UV-to-visible energy converters. Temperature dependent quenching of sensitized ⁵D₀ europium emission and presence of ⁵D₁ emission are discussed.     

Electrospinning fabrication of color-tunable flexible composite nanofibers containing lanthanide ions

A novel color-tunable PVP/[Tb(BA)₃phen+Eu(BA)₃phen] luminescent composite nanofibers had been fabricated by single axial electrospinning. The morphology and elements components of the as-prepared nanofibers were characterized by field emission scanning electron microscopy and energy dispersive spectroscopy. The luminescent properties were systematically investigated by photoluminescence spectroscopy. The obtained nanofibers had excellent fibrous morphology and smooth surface, and the average diameter was about 200 nm. The novel luminescent composite nanofibers exhibited the green, orange and red fluorescence emission peaks at 490, 545, 592 and 616 nm, which were ascribed to the ⁵D₄ → ⁷F₆ (490 nm) and ⁵D₄ → ⁷F₅ (545 nm) energy transitions of Tb³⁺ ions, and the ⁵D₀ → ⁷F₁ (592 nm), ⁵D₀ → ⁷F₂ (616 nm) transitions of Eu³⁺ ions, respectively. The emitting color of the luminescent composite nanofibers could be tuned by adjusting the mass ratio of terbium complexes and europium complexes in a wide color range of red-yellow-green under the excitation of 274-nm single-wavelength ultraviolet light. The color-tunable luminescent composite nanofibers have potential applications in the fields of display panels, lasers and bioimaging.     

Controllable hydrothermal synthesis and morphology evolution of Zn4B6O13:Tb/Eu phosphors with tunable luminescent properties

A series of Tb, Eu single or co-doped Zn₄B₆O₁₃ phosphors with tetrahedral morphology were synthesized by facile hydrothermal method. The influences of reaction temperature and the pH value of the reaction system on the structures and compositions of product were also investigated, in which four kinds of zinc borates with different structures and compositions (Zn₄B₂O₇·H₂O, Zn₄B₆O₁₃, Zn(H₂O)B₂O₄·0.12H₂O, and H(Zn₆O₂(BO₃)₃)) were obtained. A possible growth mechanism of tetrahedral morphology of Zn₄B₆O₁₃ has been proposed according to reaction time. The obtained samples were characterized by XRD, EDS, SEM, TEM, XPS, BET, DR, PL and QY. XPS results indicate that Eu²⁺ and Tb⁴⁺ are present in Tb/Eu co-doped Zn₄B₆O₁₃, which might be generated from charge transfer between Tb³⁺ and Eu³⁺. The PL results shows that Eu³⁺, Tb³⁺ ion single-doped Zn₄B₆O₁₃ microstructure exhibit orange and green emission under ultraviolet excitation, respectively. Compared to Eu³⁺ and Tb³⁺ single doped Zn₄B₆O₁₃ phosphors, the Eu/Tb co-doped Zn₄B₆O₁₃ phosphors showed stronger blue emission of Eu²⁺. These results imply that the tetrahedral morphology of Eu³⁺, Tb³⁺ ion single-doped and Eu^2+/3+/Tb^3+/4+ co-doped Zn₄B₆O₁₃ phosphors have the promise application for nano/micro-optical functional devices.     

In situ synthesis and luminescence characteristics of complexes of europium(III) with 4,6-diacetylresorcinol

The complexes of europium(III) with 4,6-diacetylresorcinol (H₂DAR) and a co-ligand (phen, bpy or 2,2′-bipyridine N,N′-dioxide (2,2′-bpyO₂)) were in situ synthesized in silica matrix via a two-step gel process. The formation of complexes in silica gel was confirmed by the luminescence excitation spectra. The silica gels that contain in situ synthesized europium complexes exhibit the characteristic emission bands of the Eu(III). The results show that there are two ways to enhance the emission intensity of the Eu(III): (i) synthesize the complex in silica matrix and (ii) synthesize the complex with a co-ligand, which coordinates with Eu(III) in the composite system and can efficiently transfer the energy from 4,6-diacetylresorcinol to the Eu(III). The order of the luminescence intensities of the complexes is: Eu₂(DAR)₃(phen)₂-(sol–gel) > Eu₂(DAR)₃(2,2′-bpyO₂)₂-(sol–gel) > Eu₂(DAR)₃ (bpy)₂-(sol–gel) > Eu₂(DAR)₃-(sol–gel) > pure Eu₂(DAR)₃·4H₂O.     

NaScMo<Subscript>2</Subscript>O<Subscript>8</Subscript>:RE<Superscript>3+</Superscript> (RE = Tb,Eu, Tb/Eu,Yb/Er,Yb/Ho) phosphors: hydrothermal synthesis,energy transfer and multicolor tunable luminescence

NaScMo₂O₈:RE³⁺ (RE = Tb, Eu, Tb/Eu, Yb/Er, Yb/Ho) phosphors were successfully synthesized by surfactant-free hydrothermal method and post-calcination treatment. The energy transfer (ET) of MoO₄ ^2? → Tb³⁺ → Eu³⁺ was proved by photoluminescence spectra and decay features. Multicolor emissions (green → yellow → red) were obtained by adjusting the ratio of Tb³⁺/Eu³⁺ upon excitation into the MoO₄ ^2? at 292 nm. The ET of Tb³⁺ → Eu³⁺ was demonstrated to be a resonant type via a dipole–dipole mechanism, and the crystal distance (R _c) was calculated by the quenching concentration method. Under 980 nm excitation, the emission of NaScMo₂O₈:RE³⁺ (RE = Yb/Er, Yb/Ho) showed strong green (Yb³⁺/Er³⁺: ⁴S_3/2, ²H_11/2 → ⁴I_15/2; Yb³⁺/Ho³⁺: ⁵S₂ → ⁵I₈) luminescence, respectively. Moreover, the doping concentration of the Yb³⁺ has been optimized under a fixed concentration of Er³⁺ and Ho³⁺, respectively. The NaScMo₂O₈:RE³⁺ phosphors have potential applications for color displays and light-emitting devices due to a variety of luminous colors.     

Molten salt synthesis,characterization, and luminescence of SrWO4, SrWO4:Tb3+ and SrWO4:Eu3+ powders

SrWO₄, SrWO₄:Tb³⁺, and SrWO₄:Eu³⁺ powders were synthesized by a method of molten salt. XRD patterns showed that the synthesized powders have a pure tetragonal scheelite structure without the presence of deleterious phases. Scanning electron microscopy images show that powders are in the range of 20–35 nm. The emission spectrum of SrWO₄ shows the emission peak in the blue spectral region. The excitation spectra of SrWO₄:Tb³⁺ and SrWO₄:Eu³⁺ show the energy transfer from WO₄ ^2? group to Tb³⁺ and Eu³⁺ ions with a high efficiency. The emission spectrum of SrWO₄:Tb³⁺ shows the green emission at 545 nm corresponding to the ⁵D₄ → ⁷F₅ transition of Tb³⁺. The emission spectrum of SrWO₄:Eu³⁺ shows the red emission located at 612 nm corresponding to the ⁵D₀ → ⁷F₂ transition of Eu³⁺. The asymmetry ratio of SrWO₄:Eu³⁺ is found to be 5.54, which indicates that the Eu³⁺ ions are located in a lower symmetric site.     

Photo- and thermoluminescence of BaGa2S4:Eu2+ and BaGa2S4:Eu2+,Ce3+ crystals

Data are presented on the photo- and thermoluminescence of polycrystalline BaGa₂S₄:Eu²⁺ and BaGa₂S₄:Eu²⁺, Ce³⁺ at temperatures from 77 to 300 K. The broad photoluminescence band at 505 nm in BaGa₂S₄:Eu²⁺ is shown to be due to the 4f ⁶5d → 4f ⁷ transition. The broad emission bands at 460 and 510 nm in BaGa₂S₄:Ce³⁺ arise from the 5D (² D _3/2) → 4f ²(² F _5/2) and 5D (² D _3/2) → 4f ²(² F _7/2) transitions. Codoping of BaGa₂S₄ with Eu²⁺ and Ce³⁺ increases the luminescence efficiency owing to energy transfer from Ce³⁺ to Eu²⁺. The thermoluminescence data were used to evaluate the energies of the traps involved: 0.26, 0.31, 0.42, 0.57, and 0.64 eV in BaGa₂S₄:Eu²⁺ and 0.28, 0.32, 0.54, 0.61, and 0.65 eV in BaGa₂S₄:Eu²⁺, Ce³⁺. Original Russian Text ? A.N. Georgobiani, B.G. Tagiev, S.A. Abushov, O.B. Tagiev, Zheng Xu, Suling Zhao, 2008, published in Neorganicheskie Materialy, 2008, Vol. 44, No. 2, pp. 151–155.     

Luminescent properties of nanoparticles LaSrAl<Subscript>3</Subscript>O<Subscript>7</Subscript>:RE<Superscript>3+</Superscript> (RE = Eu,Tb) via the citrate sol–gel method

Phosphors of nanoparticles LaSrAl₃O₇:RE³⁺ (RE = Eu, Tb) have been prepared by a sol–gel method. The structure and luminescent properties of LaSrAl₃O₇:Eu³⁺ and LaSrAl₃O₇:Tb³⁺ phosphors were characterized by X-Ray diffraction (XRD) and atomic force microscopy (AFM), photoluminescence excitation and emission spectra were utilized. From XRD patterns, it is indicated that the phosphor LaSrAl₃O₇ forms without impurity phase at 900 °C. From AFM images, it is shown that the crystal size of the phosphors are about 60–80 nm. Upon excitation with ultraviolet (UV) irradiation, it is shown that there is a strong emission at around 617 nm corresponding to the forced electric dipole ⁵D₀–⁷F₂ transition of Eu³⁺, and at around 543 nm corresponding to the ⁵D₄–⁷F₅ transition of Tb³⁺. The dependence of photoluminescence intensity on Eu³⁺ (or Tb³⁺) concentration and annealing temperature were also studied in detail.     

Synthesis and photoluminescence properties of the Eu(III)-containing silica nanoparticles via a mechanochemical solid-state reaction between SiO2 and EuCl3·6H2O

In this study, Eu³⁺-containing amorphous silica nanoparticles and Eu compounds were successfully synthesized via a mechanochemical solid-state reaction between silica nanoparticles and EuCl₃·6H₂O. This reaction was induced by a grinding process, and the states of Eu³⁺ in the silica/europium composites were investigated. The silica/europium composites exhibited orange–red color luminescence owing to the ⁵D₀–⁷F₀, ⁵D₀–⁷F₁, and ⁵D₀–⁷F₂ transitions, which indicated the presence of Eu³⁺ in the silica framework and the newly formed Eu compounds such as EuOCl and Eu(OH)₂Cl. The mechanochemical reaction because of the grinding process effectively induced an interaction between the silica surface and europium chloride; subsequently, Eu(OH)₂Cl was formed in the silica/europium composites. Additionally, the Eu(OH)₂Cl in the silica/europium composite exhibited a higher thermal stability than that of simple Eu(OH)₂Cl, indicating that the mechanochemical reaction mediated the formation of Eu(OH)₂Cl and new chemical bonding between the newly formed Eu(OH)₂Cl and the silica surface, providing improved thermal stability to Eu(OH)₂Cl. Thus, we successfully prepared silica nanoparticles containing not only Eu(III) in the silica framework but also Eu compounds that exhibit unique chemical bonding during a mechanochemical reaction.     

Tunable color emitting of CaAl2Si2O8: Eu,Tb phosphors for light emitting diodes based on energy transfer

A series of single-phased CaAl₂Si₂O₈: Eu, Tb phosphors have been synthesized at 1400 °C via a solid state reaction. The emission bands of Eu²⁺ and Eu³⁺ were observed in the air-sintered CaAl₂Si₂O₈: Eu phosphor due to the self-reduction effect. Tb³⁺ ions that typically generated green emission were added in CaAl₂Si₂O₈: Eu phosphor for contributing for a wider-range tunable emission. Energy transfer from Eu²⁺ to Tb³⁺ and the modulation of valence distribution of Eu²⁺/Eu³⁺ that contributes to the tunable color emitting were elucidated. More importantly, a white emission can be obtained by controlling the codoped contents of Li⁺ as well as suppressing the self-reduction degree of Eu. The white light emitting with the color coordinate (0.326, 0.261) was obtained, which indicates that CaAl₂Si₂O₈: Eu, Tb is a promising tunable color phosphor for application in ultraviolet light emitting diodes (UV-LEDs).     

Photoluminescence investigation of rare-earth activated GdCa3(GaO)3(BO3)4 phosphors under UV excitation

A borate compound was adopted as a new host material of Eu³⁺ and Tb³⁺ activators to fabricate efficient luminescence materials. The phosphor compositions, Gd_1−xEu_xCa₃(GaO)₃(BO₃)₄ and Gd_1−xTb_xCa₃(GaO)₃(BO₃)₄, were synthesized by conventional solid-state reactions. The crystalline phases of the resulting powders were identified using an X-ray diffraction system. Their photoluminescence properties were investigated under long-wavelength UV excitation. The Eu³⁺-doped and Tb³⁺-doped GdCa₃(GaO)₃(BO₃)₄ phosphors efficiently emitted red and green light, respectively. The temperature dependency of emission intensity was measured in a range from room temperature to 150 °C. The emission intensities of the red and green phosphors at 150 °C are 87% and 91% of those at room temperature, respectively. In addition, the decay times of both the red and green phosphors are shorter than 3 ms.