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).     

Persistent luminescence of SrAl2O4: Eu,Dy, Cr phosphors in the tissue transparency window

We report on the persistent luminescence of SrAl₂O₄: Eu²⁺, Cr³⁺ phosphor centered at 760 nm. The phosphor was prepared by sol-gel-combustion method. Persistent luminescence from Cr³⁺ lasted for hundreds of seconds, comparable to the long afterglow from Eu²⁺ ions in the visible region based on the continuous energy transfer from Eu²⁺ ions to Cr³⁺ ions. The introduction of Dy³⁺ ions into the phosphor further prolonged the afterglow time of Eu²⁺ and Cr³⁺ ions through the depth control of the charge traps. The optimum doping concentrations for Eu²⁺, Cr³⁺ and Dy³⁺ were 1%, 2% and 1.5%, respectively.     

White-emitting phosphors Ca6La2Na2(PO4)6F2:Dy and luminescence enhancement through Ce → Dy energy transfer

Ce³⁺ and Dy³⁺ activated fluoro-apatite Ca₆La₂Na₂(PO₄)₆F₂ with chemical formulas Ca₆La_2−xLn_xNa₂(PO₄)₆F₂ (Ln = Ce³⁺, Dy³⁺) were prepared by a solid state reaction technique at high temperature. The vacuum-ultraviolet (VUV) and ultraviolet (UV) spectroscopic properties are investigated. The results indicate that Ce³⁺ ions show the lowest 5d excitation band at ∼305 nm and a broad emission band centered at ∼345 nm. Dy³⁺ ions exhibit intense absorption at VUV and UV range. White-emitting under 172 nm excitation is obtained based on two dominant emissions from Dy³⁺ ions centered at 480 and 577 nm. In addition, the energy transfer from Ce³⁺ to Dy³⁺ in the co-doped samples are observed and discussed.     

Self-activated afterglow luminescence of un-doped Ca2ZrSi4O12 material and explorations of new afterglow phosphors in a rare earth element-doped Ca2ZrSi4O12 system

Un-doped Ca₂ZrSi₄O₁₂ material is prepared using a solid state reaction and it emits intense green afterglow luminescence peaking at 490 nm. The afterglow luminescence can be recorded for about 4800 s (0.32 mcd m⁻²). The thermoluminescence revealed that at least four types of traps existed in the Ca₂ZrSi₄O₁₂ material and the depths of these traps were calculated. The contributions of these traps on the afterglow luminescence were also investigated in detail. Accordingly, a possible afterglow mechanism of Ca₂ZrSi₄O₁₂ was proposed. Moreover, Ca₂ZrSi₄O₁₂ was also doped by rare earth or metal ions for developmental purpose and we arrived at some useful conclusions according to the experimental results.     

Near-ultraviolet excitable Ca4Y6(SiO4)6O: Ce,Tb white phosphors for light-emitting diodes

The present investigation aims to demonstrate the potentiality of Tb³⁺ and Ce³⁺ co-doped Ca₄Y₆(SiO₄)₆O phosphors. By incorporation of Ce³⁺ into Ca₄Y₆(SiO₄)₆O: Tb³⁺, the excitation band was extended from short-ultraviolet to near-ultraviolet region. The energy transfer from Ce³⁺ to Tb³⁺ in Ca₄Y₆(SiO₄)₆O host was investigated and demonstrated to be a resonant type via a dipole–dipole mechanism with the critical distance of 10.2 Å. When excited by 352 nm, Ca₄Y₆(SiO₄)₆O: Ce³⁺, Tb³⁺ exhibited a brighter and broader violet-blue emission (421 nm) from the Ce³⁺ and an intense green emission (542 nm) from the Tb³⁺. Combining the two emissions whose intensities were adjusted by changing the doping levels of the co-activator, an optimized white light with chromaticity coordinates of (0.278, 0.353) is generated in Ca₄Y₆(SiO₄)₆O: 2% Ce³⁺, 8% Tb³⁺, and this phosphor could be potentially used in near-ultraviolet light-emitting diodes.     

Engineering of luminescence from Gd2O3:Eu nanophosphors by pulsed laser deposition

Nanostructured Gd₂O₃:Eu³⁺ thin films were prepared by pulsed laser ablation technique. The dependence of structural, morphological and optical properties of these films on photoluminescence was systematically studied by varying the annealing temperature, Eu³⁺ incorporation concentration and laser fluence. The intensity of the XRD peak from (2 2 2) crystal plane was found to increase with annealing temperature in the range 973–1173 K. Films annealed at 1173 K show a preferential growth along (2 2 2) crystal plane of the cubic Gd₂O₃ and enhanced photoluminescence at 612 nm. XRD and Micro-Raman spectra and lattice strain investigations suggest that Eu³⁺ incorporation introduce a strong lattice distortion in Gd₂O₃ matrix. Morphological investigations using atomic force microscopy indicate a strong influence of the annealing process on the surface roughness and particle size. This kind of transparent thin film phosphors may promise for applications in flat-panel displays and X-ray imaging systems.     

Low-temperature synthesis,phonon and luminescence properties of Eu doped Y3Al5O12 (YAG) nanopowders

This contribution presents two simple and cost-effective routes for the low-temperature and large-scale production of pure and Eu-doped Y₃Al₅O₁₂ (yttrium aluminum garnet YAG) nanopowders. The proposed methodologies combine a mechanically assisted metathesis reaction or coprecipitation from solution followed by crystallization of the obtained precursors from molten sodium nitrate/nitrite. Both procedures allow obtaining pure and/or doped YAG nanopowders at remarkably low temperatures, i.e. already at 350 °C although firing at 500 °C is needed in order to get single phase and fully crystalline materials. As-obtained samples were characterized by XRD, TEM, Raman, IR and luminescence methods. These methods showed that the mean crystallite size is near 23–31 and 51 nm, when crystallization is performed from the amorphous precursor obtained by a mechanically assisted metathesis reaction and coprecipitation, respectively. Raman and IR spectra indicated better crystallinity of the powders prepared at 500 °C. The emission study showed that the intensity ratio between hypersensitive ⁵D₀ → ⁷F₂ and magnetic-dipole ⁵D₀ → ⁷F₁ transitions of Eu³⁺ is significantly larger than expected for well-crystallized YAG. Origin of this behavior is discussed.     

Influence of additional Eu coactivator on the luminescence properties of Tb3Al5O12:Ce, Eu

The luminescence properties of doubly activated terbium aluminium garnet samples were investigated in the present study. Commercial Tb₃Al₅O₁₂:Ce³⁺ (TAG:Ce) shows the typical Ce³⁺ ion luminescence of the allowed Ce³⁺ d–f transition. Eu³⁺ co-doping, however, reveals interesting results. In TAG:Ce, Eu, both Ce³⁺ and Eu³⁺ luminescence was measured at different Ce and Eu activator concentrations. The Ce³⁺ ion can be used as a sensitizer in the TAG lattice that transfers its energy directly or via the Tb sublattice to the activator Eu³⁺. The energy-level diagram was proposed to explain the luminescence mechanism. Application of TAG:Ce, Eu with improved chromaticity coordinates CIE (Commission Internationale de l’Eclairage) and color rendering index (CRI) in light emitting diodes (LEDs) is demonstrated.     

Infrared emission properties of RE (RE = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, and Dy) and Mn co-doped Co0.6Zn0.4Fe2O4 ferrites

The RE (RE = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, and Dy) and Mn ions co-doped Co-Zn ferrites were prepared by solid-state reaction method. X-ray diffraction, infrared spectra, X-ray photoelectron spectroscopy, Mössbauer spectroscopy and infrared emission measurement (IRE-2) were employed to investigate the effect of the substitution RE³⁺ and Mn ions for Fe³⁺ ones on the spinel structure, the chemical homogeneity, and the infrared emission properties of the Co-Zn ferrites. The substitution leads to non-monotonous change of the lattice parameters and infrared emissivity properties, which is mainly attributed to the partial cation exchange among the spinel structure of Co-Zn ferrites. The infrared emission properties of Co-Zn ferrites seem to be greatly influenced by the co-doped of RE³⁺ and Mn ions—maxima values were 0.96-0.97, found for LaF, NdF and GdF, respectively.     

Electron–vibrational interaction in 5d state of Ce ion in (LiMg/Li2Na/Li3)BF6 phosphors

The electron–vibrational interaction (EVI) parameters such as Huang–Rhys factor, effective phonon energy and zero phonon line position were estimated using data from our recent reported work, on photoluminescence in rare earth doped complex hexafluorides phosphors LiMgBF₆, Li₂NaBF₆ and Li₃BF₆ Validity of results were established by modeling the emission line which was found to be in good agreement with experimental photoluminescence spectra.     

Preparation and studies of Eu and Tb co-doped Gd2O3 and Y2O3 sol-gel scintillating films

Eu³⁺ (2.5 at.%) and Tb³⁺ (0.005-0.01 at.%) co-doped gadolinium and yttrium oxide (Gd₂O₃ and Y₂O₃) powders and films have been prepared using the sol-gel process. High density and optical quality thin films were prepared with the dip-coating technique. Gadolinium (III) 2,4-pentadionate and yttrium (III) 2,4-pentadionate were used as precursors, and europium and terbium in their nitrate forms were used as doping agents. Chemical and structural analyses (infrared spectroscopy, X-ray diffraction and high-resolution transmission electron microscopy) were conducted on both sol-gel precursor powders and dip-coated films. The morphology of thin films heat-treated at 700 °C was studied by means of atomic force microscopy. It was shown that the highly dense and very smooth films had a root mean roughness (RMS) of 2 nm ± 0.2 (A = 0.0075 Tb³⁺) and 24 nm ± 3.0 (B = 0.01 Tb³⁺). After treatment at 700 °C, the crystallized films were in the cubic phase and presented a polycrystalline structure made up of randomly oriented crystallites with grain sizes varying from 20 to 60 nm. The X-ray induced emission spectra of Eu³⁺- and Tb³⁺-doped Gd₂O₃ and Y₂O₃ powders showed that Tb³⁺ contents of 0.005, 0.0075 and 0.01 at.% affected their optical properties. Lower Tb³⁺ concentrations (down to 0.005 at.%) in both systems enhanced the light yield.     

Preparation and characterization of rare earth orthoborates, LnBO3 (Ln = Tb, La, Pr, Nd, Sm, Eu, Gd, Dy, Y) and LaBO3:Gd, Tb, Eu by metathesis reaction: ESR of LaBO3:Gd and luminescence of LaBO3:Tb, Eu

Lanthanide orthoborates of composition LnBO₃ (Ln = Tb, La, Pr, Nd, Sm, Eu, Gd, Dy, Y) and LaBO₃:Gd, Tb, Eu have been prepared by metathesis reaction. This method provides a convenient route for the synthesis of orthoborates and its solid solutions at low temperatures. Powder X-ray diffraction and FT-IR spectroscopy were used to characterize these borates. Rare earth borates, (LnBO₃) are isomorphous with different forms of CaCO₃ depending on the radius of rare earth ion. LaBO₃, LaBO₃:Gd, Tb, Eu, PrBO₃, NdBO₃ crystallized in aragonite structure, SmBO₃ crystallized in H-form and TbBO₃, EuBO₃, GdBO₃, DyBO₃, YBO₃ crystallized in vaterite structure. The structural analysis of TbBO₃ was carried out. The morphology of these borates was obtained from Scanning electron microscopy. Spin-Hamiltonian parameters for Gd³⁺ are deduced from room temperature electron spin resonance spectrum of LaBO₃:Gd. The luminescence of LaBO₃:Tb, Eu gave characteristics peaks corresponding to Tb³⁺, Eu³⁺ respectively.     

Multifunctional γ-Fe2O3@Ca3(PO4)2@YPO4:Tb,Ce nanocomposites as a potential drug carrier

Multifunctional γ-Fe₂O₃@Ca₃(PO₄)₂@YPO₄:Tb³⁺,Ce³⁺ nanocomposites were synthesized using an easy direct-precipitation method. The nanocomposites had a monodispersed spherical morphology with a narrow size distribution, and dispersed well in water. The nanocomposites showed the characteristic emission peaks of Ce³⁺ (5d–4f) and Tb³⁺ (⁵D₄–⁷F₃ to ⁵D₄–⁷F₆). Magnetism measurements revealed that the samples were nearly superparamagnetic. The multifunctional nanocomposites were used for in vitro drug delivery tests under ambient conditions, and we discuss the influence of different media on the release of cisplatin (cis-diamminedichloroplatinum). We assessed the loading and release performance for cisplatin by means of UV–visible spectrophotometry. Our findings will provide guidance for engineering similar multifunctional nanocomposites for use in future drug delivery applications.     

Enhanced luminescence of UV irradiated Zn(1−x)NixS nanoparticles

PVP-capped Zn_(1−x)Ni_xS (x = 0.001, 0.005, 0.01, 0.03, 0.05 and 0.1) nanoparticles have been synthesized using chemical precipitation route, in aqueous media, at room temperature. The synthesized nanoparticles have been irradiated by UV light for 24 h so as to study the effect on their structural and optical properties. The nanoparticles have been characterized through XRD and HRTEM to study the crystal structure and size. Characterization was also carried out through FTIR spectroscopy to reveal the presence of PVP and the effect of UV irradiation on the surface chemistry of the synthesized nanoparticles. The optical properties have been studied through UV–vis absorption spectroscopy and room temperature photoluminescence. There has been an enhancement in the intensity of the green emission centered at 547 nm, with increase in Ni concentration up to 0.5 at.% and a decrease in the intensity, observed for higher concentrations of Ni. However, the I(green)/I(blue) intensity ratio increases continuously with the increase in Ni concentration and also on prolonged UV irradiation of the samples.     

Luminescent characteristics of LiSrBO3:M (M = Eu, Sm, Tb, Ce, Dy) phosphor for white light-emitting diode

LiSrBO₃:M (M = Eu³⁺, Sm³⁺, Tb³⁺, Ce³⁺, Dy³⁺) phosphors which have been developed for white light-emitting diodes (LEDs) were synthesized by a normal solid-state reaction. The emission and excitation spectra indicate that these phosphors can be effectively excited by near-ultraviolet light-emitting diodes (UVLED), and exhibit satisfactory red, green and blue performances, respectively, nicely fitting in with the widely applied UV chip. Under the condition of doping charge compensation Li⁺, Na⁺ and K⁺, the luminescence intensities of these phosphors were increased.     

Synthesis, physical and optical properties, and electronic structure of the rare-earth oxysulfides Ln2O2S (Ln=Sm, Eu)

The compounds Ln₂O₂S (Ln=Sm, Eu) were prepared from the respective oxides by partial sulfurization under flowing CS₂/Ar/O₂ atmosphere. The main feature of the structure is the packing of S²⁻ and O²⁻ anions with Ln³⁺ located in the center of a capped octahedron. Electrical conductivity measurements on pressed pellets showed that both phases are highly resistive with conductivities lower than 10⁻⁸ S cm⁻¹ at room temperature. The optical bandgaps were assessed at 4.2 and 4.4 eV for Sm₂O₂S and Eu₂O₂S, respectively. Electronic structure calculations were performed by means of extended Hückel tight-binding method. The insulating properties are in good agreement with the results predicted by theoretical calculations.     

Thermally stable luminescence and energy transfer in Ce, Mn doped Sr2Mg(BO3)2 phosphor

Sr₂Mg(BO₃)₂:Ce³⁺,Li⁺ and Sr₂Mg(BO₃)₂:Ce³⁺,Li⁺,Mn²⁺ phosphors have been synthesized by conventional solid state reaction technology at 900 °C for 12 h in reducing atmosphere. The phase purity, photoluminescence (PL) properties, thermal stability, energy transfer and luminescent decay curves have been investigated. Sr₂Mg(BO₃)₂:Ce³⁺,Li⁺,Mn²⁺ phosphors show blue and deep-red¹ emission bands. The deep-red emission band is attributed to the energy transfer from Ce³⁺ to Mn²⁺. The fluorescence lifetimes of Ce³⁺ in co-doped sample are shorter than that in single doped one, which confirms that the energy transfer takes place. The phosphors have weak thermal quenching. The luminescence properties of Sr₂Mg(BO₃)₂:Ce³⁺,Li⁺,Mn²⁺ make the phosphor a new bicolor emitting material.     

Spectral analysis of RE (RE = Sm, Dy, and Tm): P2O5–Al2O3–Na2O glasses

Phosphate glasses in the compositions of 70P₂O₅–15Al₂O₃–14Na₂O–1RE³⁺ (RE = Sm, Dy, and Tm) (mol%) were prepared by melt-quenching technique and characterized optically. The differential thermal analysis (DTA) profile of the host glass was carried out to confirm its thermal stability. For all the glasses absorption, photoluminescence and decay measurements have also been carried out. These glasses have shown strong emission and absorption bands in visible and near-infrared (NIR) region. From the measured absorption spectra, Judd–Ofelt (J–O) intensity parameters (Ω₂, Ω₄ and Ω₆) have been calculated for all the studied ions. For Sm³⁺ doped glass, four emission bands centered at 562 nm (⁴G_5/2 → ⁶H_5/2), 598 nm (⁴G_5/2 → ⁶H_7/2), 644 nm (⁴G_5/2 → ⁶H_9/2), and 704 nm (⁴G_5/2 → ⁶H_11/2) have been observed with 402 nm (⁶H_5/2 → ⁴F_7/2) excitation wavelength. Of them, 598 nm (⁴G_5/2 → ⁶H_7/2) has shown a bright orange emission. With regard to Dy³⁺ doped glass, a blue emission band centered at 486 nm (⁴F_9/2 → ⁶H_15/2) and a bright yellow emission at 575 nm (⁴F_9/2 → ⁶H_13/2) have been observed, apart from 662 nm (⁴F_9/2 → ⁶H_11/2) emission transition with an excitation at 388 nm (⁶H_15/2 → ⁴I_13/2,⁴F_7/2) wavelength. Emission bands of 650 nm (¹G₄ → ³F₄) and 785 nm (¹G₄ → ³H₅) transitions for the Tm³⁺ doped glass, with an excitation wavelength at 466 nm (³H₆ → ¹G₄), have also been observed. The stimulated emission cross-sections of all the emission bands of RE³⁺ glasses (RE = Sm, Dy, and Tm) have been computed based on their measured full-width at half maximum (FWHM, Δλ) and measured lifetimes (τ_m).     

Photoluminescence properties of emission-tunable Ca9Y(PO4)7: Tm,Dy phosphor for white light emitting diodes

A white-emitting Ca₉Y(PO₄)₇: Tm³⁺, Dy³⁺ phosphor has been successfully prepared by conventional high-temperature solid-state reaction. X-ray diffraction (XRD) and fluorescence spectrophotometer were used to characterize the as-synthesized phosphors. The excitation and emission spectra show that all the Tm³⁺ and Dy³⁺ co-doped Ca₉Y(PO₄)₇ samples can be effectively excited by UV light and then emit blue and yellow light simultaneously. Furthermore, the emission and color coordinate of as-obtained samples pumped by 365 nm are able to be adjusted around white light by varying the doping concentrations of Tm³⁺ and Dy³⁺. So, the as-fabricated single-composition Ca₉Y(PO₄)₇: Tm³⁺, Dy³⁺ phosphor will have a promising application in the area of white light emitting diodes.     

Synthesis and photoluminescence of nano-Y2O3:Eu phosphors

We report nano-Y₂O₃:Eu³⁺ phosphors with particle size of about 50 nm and relatively high photoluminescence (PL) intensity which is close to the standard for application. The influences of the dope amount, the surfactant and the precipitation pH on the PL intensity, the particle size and the dispersion have been studied. It has been found that 4% is the best Eu³⁺ molar concentration to get the highest PL intensity for both nano- and micro-Y₂O₃:Eu³⁺. The addition of butanol as a surfactant inhibits the grain growth and the agglomeration of particles efficiently by reducing the oxygen bridge bonds. As the pH rises, the PL intensity and the particle size increase due to the formation of oxygen bridge bonds.