Synthesis of monodisperse spherical core-shell SiO2-SrAl2Si2O8: Eu2+ phosphors by hydrothermal homogeneous precipitation method

Nanocrystalline SrAl₂Si₂O₈ :Eu²⁺ phosphor layers were coated on nonaggregated, monodisperse and spherical SiO₂ particles using a hydrothermal homogeneous precipitation. After annealing at 1100 °C, core-shell SiO₂@SrAl₂Si₂O₈ :Eu²⁺ particles were obtained. They were characterized with x-ray diffraction (XRD), scanning electron microscopy, transmission electron microscopy and photoluminescence techniques. XRD analysis confirmed the formation of SiO₂ @SrAl₂Si₂O₈ :Eu²⁺ particles; it indicated that the SrAl₂Si₂O₈ :Eu²⁺ shells on SiO₂ particles consisted of hexagonal crystallites. The core-shell phosphors obtained are well-dispersed submicron spherical particles with a narrow size distribution. The thickness of the coated layer is approximately 20–40 nm. Under ultraviolet excitation (361 nm), the particles emit blue light at about 440 nm due to the Eu²⁺ ions in their shells.     

Synthesis of ultrafine spherical YAG:Eu phosphors by MOCVD

Ultrafine Europium-doped yttrium aluminum garnet (YAG:Eu³⁺) phosphor powders, with uniform diameters of about 1 μm, have been prepared by metallorganic chemical vapor deposition (MOCVD). The metal-organic precursors have been characterized by thermogravimetry-differential scanning calorimeter (TG-DSC). The phosphor powders have been identified by X-ray diffraction (XRD), scanning electron microscope (SEM) and photoluminescence measurements. It shows that the YAG:Eu³⁺ particles annealed at 1473 K for 3 h are nonaggregated and spherical, the diameter of particles is in the range of 1-2 μm. Phase-pure YAG which is of spherical shaped particles have been obtained and observed good luminescence property. Three major emission peaks were observed at 589, 594, and 607 nm.     

Preparation of SrAl2O4: Eu, Dy nanometer phosphors by detonation method

SrAl₂O₄: Eu²⁺, Dy³⁺ nanometer phosphors were synthesized by detonation method. The particle morphology and optical properties of detonation soot that was heated at different temperatures (600–1100 °C) had been studied systematically by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Results indicated SrAl₂O₄: Eu²⁺, Dy³⁺ nanometer powders in monoclinic system (a = 8.442, b = 8.822, c = 5.160, β = 93.415) can be synthesized by detonation method, when detonation soot was heated at 600–800 °C. The particle size of SrAl₂O₄: Eu²⁺, Dy³⁺ is 35 ± 15 nm. Compared with the solid-state reaction and sol-gel method, synthesis temperature of the detonation method is lower about 500 and 200 °C respectively. After being excited under UN lights, detonation soot and that heated at 600–1100 °C can emit a green light.     

Nanorods of white light emitting Sr2SiO4:Eu2+: microemulsion-based synthesis,EPR, photoluminescence,and thermoluminescence studies

White light emitting Sr₂SiO₄:Eu²⁺ nanoparticles were prepared using reverse micellar route using Tergitol as a surfactant. The systems were characterised by X-ray diffraction, scanning electron microscopy (SEM), photoluminescence, thermoluminescence (TL), and electron paramagnetic resonance (EPR) spectroscopy. SEM shows the formation of silicate nanorods. Two emission bands of bluish-green at 490 nm (S(I)) and of orange-red at 605 nm (S(II)) were observed. The two emission bands are assigned to the 4f–5d transition of Eu²⁺ ions in two different cation sites in α′-Sr₂SiO₄ orthorhombic lattices. Gamma-irradiated Sr₂SiO₄:Eu showed the presence of three TL glow peaks at 437, 487 K and weak peak at 540 K; however, no glow was observed in the undoped sample. Reduction of Eu³⁺ to Eu²⁺ is confirmed by EPR spectroscopy.     

Effects of Zn doping on the structural and luminescent properties of Sr4Si3O8Cl4:Eu phosphors

Sr₄Si₃O₈Cl₄: Eu²⁺ phosphors were synthesized by the solid-reaction at high temperature. The emission intensity reaches a maximum at 0.08 mol% of Eu²⁺ concentration. The present paper mainly focused on the effects of Zn²⁺ on the crystallization behavior and photoluminescence (PL) properties of Sr₄Si₃O₈Cl₄:0.08Eu²⁺. Results suggested that no new phase is introduced by co-doping with a small amount of Zn²⁺ ions, but when co-doped with excessive amount of Zn²⁺ ions, Sr₂ZnSi₂O₇ appears. We find that the co-doping of a small amount of Zn²⁺ could remarkably improve the PL intensity of Sr₄Si₃O₈Cl₄:0.08Eu²⁺. When x = 0.05, the intensity of Sr₄Si₃O₈Cl₄:0.08Eu²⁺,xZn²⁺ was increased up to 2.3 times that of pure Sr₄Si₃O₈Cl₄:0.08Eu²⁺, which could be attributed to the flux effect of Zn²⁺ ions, and the Zn²⁺ doping reduces the opportunities of the energy transfer between Eu²⁺.     

Luminescence and energy transfer of Mn co-doped SrSi2O2N2:Eu green-emitting phosphors

Eu²⁺ and Mn²⁺ co-doped SrSi₂O₂N₂ green-phosphors, with promising luminescent properties (examined by their powder diffuse reflection, photoluminescence excitation and emission spectra) suitable for UV converted white LEDs, were produced by high temperature solid-state reaction method. The produced materials exhibited intense broad absorption bands at 220–500 nm and a broad emission band centered at ca. 530 nm, attributed to 4f–5d transitions of Eu²⁺. The emission intensity of Eu²⁺ ions was greatly enhanced by introducing Mn²⁺ ions into SrSi₂O₂N₂:Eu²⁺ due to the energy transfer from Mn²⁺ to Eu²⁺. The energy transfer probability from Mn²⁺ to Eu²⁺ depends strongly on the Mn²⁺ concentration, which is maximized at a Mn²⁺ concentration of 3 mol%. It drastically decreases for higher concentrations. The results indicated that SrSi₂O₂N₂:Eu²⁺, Mn²⁺ is a promising green-emitting phosphor for white-light emitting diodes with near-UV LED chips.     

Synthesis of high efficient nanosized Y(V,P)O4:Eu red phosphors by a new technique

A new synthesis technique (liquid-phase precursor method) has been employed to synthesize nanosized Y(V,P)O₄:Eu³⁺ red phosphor particles of size 10-35 nm. X-ray diffraction analysis confirmed the synthesis of single phase Y(V,P)O₄:Eu³⁺ nanoparticles with tetragonal structure. The surface treatment with the KOH ionic solution at room temperature enhanced the grain growth (40-70 nm) of the nanoparticles. The possible grain growth mechanism is explained on the basis of formation of more OH⁻ groups in the solid solution after KOH introduction. The photoluminescence spectra obtained from the nanophosphors showed strong red luminescence due to ⁵D₀ → ⁷F_2,4 forced electric dipole transition. The luminescence intensity of the KOH-treated nanophosphors is comparable (about 70%) with the commercial sample.     

Synthesis and photoluminescence properties of new NaAlSiO4:Eu phosphors for near-UV white LED applications

A new NaAlSiO₄:0.1Eu²⁺ phosphors were synthesized at different temperatures using a liquid phase precursor (LPP) technique. The XRD patterns indicate the presence of hexagonal nepheline phase for all the samples. The synthesized phosphors can be excited efficiently in the broad near-UV region. The PL emission spectra showed a broad emission peak at around 551 nm corresponding to 5d → 4f transition of Eu²⁺ ions. The synthesized phosphors showed better thermal stability when compared with the standard YAG:Ce³⁺ phosphor.     

Photoluminescence properties of Y2O3:Tb and YBO3:Tb green phosphors synthesized by hydrothermal method

In this work, two Tb³⁺ activated green phosphors: Y₂O₃:Tb³⁺ and YBO₃:Tb³⁺ were prepared by hydrothermal method. Photoluminescence properties of both phosphors were studied in details. Both phosphors exhibit similar luminescent characteristics symbolized by the dominant green emission at 545 nm. Concentration quenching occurs at the Tb³⁺ concentration of 1.60 atomic% and 2.57 atomic% for Y₂O₃:Tb³⁺ and YBO₃:Tb³⁺, respectively. Luminescence decay properties were characterized to better understand the mechanism of concentration quenching. Based on the calculation, the concentration quenching in both phosphors was caused by the dipole–dipole interaction between Tb³⁺ ions.     

Synthesis and luminescent properties of SrAl2O4:Eu green-emitting phosphor for white LEDs

SrAl₂O₄:Eu²⁺ phosphor was prepared by a solid-state reaction in CO-reductive atmosphere. X-ray powder diffraction (XRD) analysis confirmed the formation of SrAl₂O₄:Eu²⁺. Field-emission scanning electron-microscopy (FE-SEM) observation indicated that the microstructure of the phosphor consisted of irregular fine grains with an average size of about 7–8 μm. Photoluminescence measurements showed that the phosphor can be efficiently excited by UV–visible light from 350 to 430 nm, and exhibited bright green emission peaked at about 516 nm. Bright green LEDs were fabricated by incorporating the phosphor with an InGaN-based UV chip. All the characteristics indicated that SrAl₂O₄:Eu²⁺ is a good candidate phosphor applied in white LEDs.     

Influence of excitation wavelengths on luminescent properties of Sr3Al2O6:Eu, Dy phosphors prepared by sol-gel-combustion processing

Eu²⁺ and Dy³⁺ ion co-doped Sr₃Al₂O₆ red-emitting long afterglow phosphor was synthesized by sol-gel-combustion methods using Sr(NO₃)₂, Al(NO₃)₃·9H₂O, Eu₂O₃, Dy₂O₃, H₃BO₃ and C₆H₈O₇·H₂O as raw materials. The crystalline structure of the phosphors were characterized by X-ray diffraction, luminescent properties of phosphors were analyzed by fluorescence spectrophotometer. The effect of excitation wavelengths on the luminescent properties of Sr₃Al₂O₆:Eu²⁺, Dy³⁺ phosphors was discussed. The emission peak of Sr₃Al₂O₆:Eu²⁺, Dy³⁺ phosphor lays at 516 nm under the excitation of 360 nm, and at 612 nm under the excitation of 468 nm. The results reveal that the Sr₃Al₂O₆:Eu²⁺, Dy³⁺ phosphor will emit a yellow-green light upon UV illumination, and a bright red light upon visible light illumination. The emission mechanism was discussed according to the effect of nephelauxetic and crystal field on the 4f⁶5d¹ → 4f⁷ transition of the Eu²⁺ ions in Sr₃Al₂O₆. The afterglow time of (Sr_0.94Eu_0.03Dy_0.03)₃ Al₂O₆ phosphors lasts for over 600s after the excited source was cut off.     

Sr3.5Mg0.5Si3O8Cl4: Eu bluish-green-emitting phosphor for NUV-based LED

Sr₄Si₃O₈Cl₄:Eu²⁺ and Sr_3.5Mg_0.5Si₃O₈Cl₄:Eu²⁺ phosphors were prepared by a conventional solid state reaction (SS). Excited by 370 nm near-ultraviolet light, the phosphors show an efficient bluish-green wide-band emission centering at 484 nm, which originates from the 4f5d¹ → 4f⁷ transition of Eu²⁺ ion. The excitation spectra of the phosphors are a broad band extending from 250 nm to 400 nm. Mg²⁺-codoping greatly enhances the bluish-green emission of the phosphors. An LED was fabricated by coating the Sr_3.5Mg_0.5Si₃O₈Cl₄:0.08Eu²⁺ phosphor onto an ~ 370 nm-emitting InGaN chip. The LED exhibits bright bluish-green emission under a forward bias of 20 mA. The results indicate that Sr_3.5Mg_0.5Si₃O₈Cl₄:0.08Eu²⁺ is a candidate as a bluish-green component for fabrication of NUV-based white LEDs.     

Assembly of Fe3O4 nanoparticles on SiO2 monodisperse spheres

The assembly of superparamagnetic Fe₃O₄ nanoparticles on submicroscopic SiO₂ spheres have been prepared by an in situ reaction using different molar ratios of Fe³⁺/Fe²⁺ (50–200%). It has been observed that morphology of the assembly and properties of these hybrid materials composed of SiO₂ as core and Fe₃O₄ nanoparticles as shell depend on the molar ratio of Fe³⁺/Fe²⁺.     

Surface modification of the (Y,Gd)BO3:Eu phosphor by dual-coating of oxide nano-particles

The surface of (Y,Gd)BO₃:Eu³⁺ phosphor, red-emitting source in the plasma display panel (PDP), was dual-coated with SiO₂ and Al₂O₃ nano-particles. The surface modification of the phosphor was performed by a modified sol-gel method using the colloidal alumina and silica as surface coating precursors. We observed the oxide nano-particles on the surface of the single coated and the dual-coated phosphors and it was found that the luminance intensity was increased in the photoluminescence (PL) by a suppression of the nonradiative recombination via surface defects. The experimental results suggest that the surface modification of phosphors with nano-particles of the oxides leads to an increase in the luminance intensity of phosphors in the PDP (plasma display panel) and the gas discharge lamps.     

M2Si5N8:Eu-based (M = Ca, Sr) red-emitting phosphors fabricated by nitrate reduction process

M₂Si₅N₈:Eu²⁺-based (M = Ca, Sr) red-emitting phosphors were fabricated at relatively low temperature (1200 °C) and atmospheric pressure using a simple solid-state reaction process. Several processing parameters were systematically investigated to optimize the phosphors structural characterization and photoluminescence performance, including the amount of europium and the properties of the precursor and activated materials. The as-prepared M₂Si₅N₈:Eu²⁺-based (M = Ca, Sr) phosphors were orange in color and emitted intensively in the red region of 580-670 nm under 465 nm excitation. This simple fabrication technique can be readily used for the optimization of phosphor microstructures and high-performance red-emitting phosphors since it eliminates many air-sensitive precursors.     

CaSc2O4:Eu: A tunable full-color emitting phosphor for white light emitting diodes

We report an intense full-color emission originating from ⁵D_0,1,2,3 to ⁷F_0,1,2,3,4 transitions of Eu³⁺ in CaSc₂O₄ upon 395 nm excitation. The emission spectra vary with increasing Eu³⁺ concentration, demonstrating tunable color coordinates from white to red region in the CIE chromaticity diagram. Considering the relaxation from ⁵D_J to ⁵D_J−1 through cross energy transfer, the Eu³⁺ concentration dependent emission spectra are well simulated based on the analysis of steady state rate equations and the measured lifetimes of the ⁵D_J levels. It is suggested that CaSc₂O₄:Eu³⁺ could be a potential single-phased full-color emitting phosphor for near-ultraviolet InGaN chip pumped white light emitting diodes.     

Influence of calcination temperature on luminescent properties of Sr3Al2O6:Eu, Dy phosphors prepared by sol–gel-combustion processing

The detailed preparation process of Eu²⁺ and Dy³⁺ ion co-doped Sr₃Al₂O₆ phosphor powders with red long afterglow by sol–gel-combustion method in the reducing atmosphere is reported. X-ray diffraction, scanning electron microscopy and photoluminescence spectroscopy are used to investigate the effects of synthesis temperature on the crystal characteristics, morphology and luminescent properties of the as-synthesized Sr₃Al₂O₆:Eu²⁺, Dy³⁺ phosphors. The results reveal that Sr₃Al₂O₆ crystallizes completely when the combustion ash is sintered at 1200 °C. The excitation and the emission spectra indicate that the excitation broad-band lies chiefly in visible range and the phosphor powders emit strong light at 618 nm under the excitation of 472 nm. The light intensity and the light-lasting time of Sr₃Al₂O₆:Eu²⁺, Dy³⁺ phosphors are increased when increasing the calcination temperatures from 1050 to 1200 °C. The afterglow of Sr₃Al₂O₆:Eu²⁺, Dy³⁺ phosphors sintered at 1200 °C lasts for over 600 s when the excited source is cut off. The red emission mechanism is discussed according to the effect of nephelauxetic and crystal field on the 4f⁶5d¹ → 4f⁷ transition of the Eu²⁺ ions.     

Electro-deposition of Y2O3:Eu thin film phosphor and its luminescent properties

Y₂O₃:Eu³⁺ red-emitting thin film phosphor was prepared by a two-step process: the cathodical deposition of thin film of yttrium hydroxide and europium hydroxide followed by an annealing process to achieve Eu³⁺ doped Y₂O₃ film. It is found that the atomic content of Eu³⁺ can be well controlled by simply adjusting the volume ratio of Y(NO₃)₃ to Eu(NO₃)₃ solutions. Dependence of the photoluminescence intensity on the atomic content of Eu³⁺ in Y₂O₃ was also studied. The best photoluminescence performance of Y₂O₃:Eu³⁺ thin film phosphor was achieved as atomic content of Eu³⁺ equal to 1.85 at.%.     

Shift in room-temperature photoluminescence of low-fluence Si+-implanted SiO2 films subjected to rapid thermal annealing

Abstract

We experimentally demonstrate the effect of the rapid thermal annealing (RTA) in nitrogen flow on photoluminescence (PL) of SiO₂ films implanted by different doses of Si⁺ ions. Room-temperature PL from 400-nm-thick SiO₂ films implanted to a dose of 3×10¹⁶ cm^?2 shifted from 2.1 to 1.7 eV upon increasing RTA temperature (950–1150 °C) and duration (5–20 s). The reported approach of implanting silicon into SiO₂ films followed by RTA may be effective for tuning Si-based photonic devices.     

Greatly improved photoluminescence properties of the electrodeposited Y2O3:Eu thin film phosphors by the addition of Na and K ions

In this work, Y₂O₃:Eu³⁺ thin film phosphors were prepared by electro-deposition method. The effect of Na⁺ and K⁺ ions on the photoluminescence properties of Y₂O₃:Eu³⁺ thin film phosphor was studied in details. It was found that the addition of Na⁺ and K⁺ ions could improve the photoluminescence intensity by 3 to 4 times. The highly improved photoluminescence intensity may be caused by different factors. The improved crystallinity and the increased optical volume caused by the flux effect of Na⁺ and K⁺ ions could be the major reasons for the enhanced photoluminescence intensity. It was also found that the average lifetime of Y₂O₃:Eu³⁺ thin film phosphors could be adjusted by the molar amount of Na⁺ and K⁺ ions.