Luminescent and structural properties of Yb-doped Al2O3 nanopowders

In this work, we discuss structural and luminescent properties of Al₂O₃ nanopowders doped with Yb³⁺ ions prepared by a novel method, in which organic compounds were used as a solvent and lanthanide organic derivatives, served as a rare-earth ion source. The set of samples differing in activator concentrations and particle sizes was carefully studied by means of structural and optical characterization methods. In particular, the high resolution electron and transmission microscopy has been deployed together with X-ray diffraction technique to determine fundamental structural properties of nanopowders. The optical characterization was focused mainly on basic excitation and emission features and their sensitiveness on dopant concentration and the average nanoparticle size.     

Eu3+ concentration effect on luminescence properties of YAG:Eu3+ nanoparticles

Nanocrystalline Eu³⁺-doped YAG powders were prepared by modified Pechini method. The structural properties were investigated with XRD, SEM and Raman spectroscopy. XRD pattern indicated that the phase-pure YAG:Eu³⁺ crystallites were obtained without the formation of any other phases. Raman spectrum revealed good homogeneity and crystallinity of synthesized nanopowders. The luminescent properties were studied by measurement of excitation and emission spectra, quantum yields and decay curves. The effect of Eu³⁺ concentration on ⁵D₀ level lifetime was studied. The processes resulting in the relaxation of excited state (⁵D₀ level) were discussed and the probabilities of radiative and nonradiative processes were calculated using the model of f–f transition intensities. It was found that the observed shortening of ⁵D₀ level lifetime with Eu concentration is caused by increase of nonradiative process probability.     

Properties of Gd2O3:Eu, Tb nanopowders obtained by sol-gel process

A significant practical application for nanostructured materials is X-ray medical imagery, because it is necessary to use dense materials in order to enable absorption of high energy photons. An important requirement of these materials is UV-vis range emission produced by X-ray excitation, which can be influenced by the particle size. Europium doped gadolinium oxide is a well known red phosphor. Moreover, nanophosphors of Gd₂O₃ codoped with Tb³⁺, Eu³⁺ increase their light yield by energy transfer between Tb³⁺ and Eu³⁺. In this study, Gd₂O₃ nanopowders codoped with Eu³⁺ and Tb³⁺ (2.5 at.% Eu³⁺, and 0.005 and 0.01 at.% Tb³⁺) were obtained via a sol-gel process using gadolinium pentanedionate as precursor and europium and terbium nitrates as doping sources. In this paper, we report the influence of annealing temperature on the structure, morphology and luminescent properties of Gd₂O₃:Eu³⁺, Tb³⁺ by means of TGA, XRD, TEM and X-ray emission measurements.     

Color tunable luminescence from LaAlO<Subscript>3</Subscript>:Bi<Superscript>3+</Superscript>, Ho<Superscript>3+</Superscript> doped phosphors for field emission displays

Bi³⁺-activated LaAlO₃:Ho³⁺ Phosphor, was prepared by Polyol method, and its photoluminescent properties were investigated under (UV) light excitation. Luminescence studies indicated that optimum concentration of Bi³⁺ and Ho³⁺ in LaAlO₃ was found to be 1 and 1.5 at.%. The luminescent intensity of Ho³⁺ emission lines was remarkably enhanced on exciting with 272 nm, which suggested that efficient energy transfer from Bi³⁺ ions to Ho³⁺ ions takes place. There is significant energy overlap between the emission band of Bi³⁺ ions and the excitation band of Ho³⁺ ions.The ET efficiency has been calculated and found to be 69%. The critical ET distance has been calculated by the concentration–quenching method. The enhanced intensity and tuned luminous color of LaAlO₃: Bi³⁺/Ho³⁺ phosphors from blue to cyan provides a promising material for field emission display devices.     

A novel green emitting phosphor Ca2GeO4:Tb3+

A novel green emitting phosphor, Tb³⁺-doped Ca₂GeO₄ was prepared for the first time by a solid-state reaction. The phosphor showed prominent luminescence in green due to the magnetic dipole transition of ⁵D₄ → ⁷F₅. Structural characterization of the luminescent material was carried out with X-ray powder diffraction (XRD) analysis and field emission scanning electron microscopy (FE-SEM). Luminescence properties were analyzed by measuring the excitation and photoluminescence spectra. Photoluminescence measurements indicated that the phosphor exhibited bright green emission at about 541 and 550 nm under UV excitation. In addition, Al³⁺ or Li⁺ co-doping enhances the green emission from Ca₂GeO₄:Tb³⁺ by about 18 and 4 times, respectively, under UV excitation. The excellent luminescence properties make it a possible candidate for flat panel display application.     

Intrinsic and Ce-related luminescence of YAG and YAG:Ce single crystals, single crystalline films and nanopowders

A comparative analysis of the luminescent properties of YAG and YAG:Ce nanopowders (NP) in comparison with single crystalline film (SCF) and single crystal (SC) analogues was performed under excitation by a pulsed synchrotron and X-ray radiation. It was shown that the natural defects concentration in NP was between the SC with a large (0.18–0.19 at.%) concentration of Y_Al antisite defects (AD) and SCF of these garnets where Y_Al AD were completely absent. At the same time, Ce³⁺ doped YAG NP showed luminescent properties close to those of YAG:Ce SCF.     

Synthesis and luminescent characterization of YAl<Subscript>3</Subscript>(BO<Subscript>3</Subscript>)<Subscript>4</Subscript>:Tb<Superscript>3+</Superscript> phosphors

YAl₃(BO₃)₄:Tb³⁺ phosphors were fabricated by the sol–gel method. The phosphor showed prominent luminescence in green due to the magnetic dipole transition of ⁵D₄–⁷F₅. Structural characterization of the luminescent material was carried out with X-ray powder diffraction (XRD) analysis. Luminescence properties were analyzed by measuring the excitation and photoluminescence spectra. Photoluminescence measurements indicated that the phosphor exhibited bright green emission at about 541 nm under UV excitation. It is shown that the 11% of doping concentration of Tb³⁺ ions in YAl₃(BO₃)₄:Tb³⁺ phosphors is optimum.     

Structural and photoluminescent properties of Al2O3: Cr3+ nanoparticles via solution combustion synthesis method

In the present work, we have discussed the structural and photoluminescent properties of Al₂O₃ nanoparticles doped with Cr³⁺ ion prepared through solution combustion synthesis (SCS) technique. SCS is a well-known method for the production of different metal oxides and composite materials such as metal matrix composites and for producing this need an extra reduction step. The set of samples differing in activator concentration were studied carefully by means of structural and optical characterization methods. In particular, the transmission electron microscopy (TEM) has been deployed together with X-ray diffraction (XRD) technique to determine fundamental structural properties of nanoparticles. XRD results showed that pure α-Al₂O₃ single phase was obtained and TEM result indicates that nanoparticles are spherical in shape. The selected area electron diffraction (SAED) and Energy dispersive analysis by X-rays (EDAX) analysis suggested the crystallinity and chemical composition of the Cr³⁺ doped Al₂O₃. The change in crystal structure parameters was obtained by Rietveld refinement method. The optical characterization focused mainly on the basic excitation and emission features and their sensitivity to the dopant concentrations. The excitation spectrum of Cr³⁺-doped Al₂O₃ nanopowders consist of two bands peaking at 406 nm and 570 nm and the emission spectrum consist of two bands peaking at 694 nm and 670 nm.     

Luminescent properties of YAl3(BO3)4:Eu3+ phosphors

YAL₃(BO₃)₄:Eu³⁺ phosphors were fabricated by the sol-gel method. The structure properties were measured by x-ray diffraction (XRD) and infrared spectra (IR). Doping concentration of Eu³⁺ ions in YAL₃(BO₃)₄:Eu³⁺ phosphors of 0, 1, 3, 4, and 5 mol% were studied. The excitation spectra and emission spectra of YAL₃(BO₃)₄:Eu³⁺ phosphors were examined by fluorescent divide spectroscopy (FDS). The luminescent properties of YAL₃(BO₃)₄:Eu³⁺ phosphors are discussion. The optimal doping concentration of Eu³⁺ ions in YAL₃(BO₃)₄:Eu³⁺ phosphors was found to be approximately 3 mol%.     

Luminescence and structural properties of Y(Ta,Nb)O4:Eu3+,Tb3+ phosphors

Yttrium tantalate (YTaO₄), yttrium niobium-tantalate (YTaNbO₄) and yttrium niobate (YNbO₄) doubly doped by Eu³⁺ and Tb³⁺, were investigated using X-ray diffraction and X-ray excitation luminescence in order to study their structural and luminescent properties. By means of X-ray diffraction, the crystallographic data for YTaO₄ and YNbO₄ with double activation by Eu³⁺ and Tb³⁺ were first calculated. Under X-ray excitation luminescence, the rare earth emission centers contribute to the overall luminescence. Due to their various luminescence chromaticities, the proposed rare earth activated phosphors are promising materials for optoelectronics as well as for X-ray intensifying screens for medical diagnosis providing the broad variation of visible photoluminescence from blue to red.     

Luminescent properties of Na3YSi3O9 doped with Eu under UV-VUV excitation

The luminescent properties of Na₃Y_1−xSi₃O₉:xEu³⁺ (0.05 ≦ x ≦ 0.80) powder crystals were investigated in UV-VUV region. The Eu³⁺-O²⁻ charge transfer band (CTB) was observed to be located at around 233 nm and the environmental parameter (h_e) was estimated to be about 0.730. The excitation spectrum monitoring the 613 nm red emission from Eu³⁺ ions reveals the host absorption band (HAB) to be around 145 nm. The calculated Commission Internationale de l’Eclairage (CIE) chromaticity coordinates indicate the emission by 233 nm rather than by 147 nm excitation has the better color purity and the possible mechanisms have been proposed. The Eu³⁺-emission showed high quenching concentration due to the isolated YO₆ octahedra in the host and the small h_e for the Eu³⁺ ions and the optimum concentration was determined to be as high as x = 0.65 and 0.30 with 233 and 147 nm excitation, respectively.     

Efficiency enhancement by aluminum addition to CaTiO3:Pr phosphor thin films

The mechanism of enhancement of the red emission efficiency from CaTiO₃:Pr³⁺ thin film by Al addition has been investigated. Al-ions have been attracting interest as a sensitizer to improve the luminescent efficiency of phosphors. Also, influence of Al-doping on the crystallization, surface morphology and luminescent properties of CaTiO₃:Pr³⁺ thin films have been discussed. CaTiO₃:Pr³⁺ and Al-doped CaTiO₃:Pr³⁺ films were grown using pulsed laser deposition technique on Al₂O₃ (0001) substrates under different substrate temperatures and oxygen pressures. The crystalline phase and surface morphology of the films were very dependent on the oxygen pressure and substrate temperature and they affected the luminescent brightness of the films. The crystalline structure and microstructure of these films have been characterized by X-ray diffraction and electron microscopy and their luminescent properties have been evaluated at room temperature using a luminescence spectrometer and excitation by a broadband incoherent ultraviolet light source with a dominant excitation wavelength of 325 nm. In particular, the incorporation of Al³⁺ ions into CaTiO₃ lattice could induce a remarkable increase of photoluminescence. The enhancement of luminescence for Al-doped films may result not only from the improved crystallinity but also from the reduced internal reflections caused by rougher surfaces. Also, the luminescent intensity and surface roughness of the films exhibited similar behavior as a function of oxygen pressure.     

A novel green emitting phosphor SrAl2B2O7:Tb3+

SrAl₂B₂O₇:Tb³⁺ phosphors were fabricated by the sol–gel method. The phosphor showed prominent luminescence in green due to the ⁵D₄–⁷F₅ transition of Tb³⁺_. Structural characterization of the luminescent material was carried out with X-ray powder diffraction (XRD) analysis. Luminescence properties were analyzed by measuring the excitation and photoluminescence spectra. Photoluminescence measurements indicated that the phosphor exhibited bright green emission at about 541 nm under UV excitation. It is shown that the 11% of doping concentration of Tb³⁺ ions in SrAl₂B₂O₇:Tb³⁺ phosphors is optimum.     

Preparation and blue–white luminescence properties of Bi3+-doped Ba5SiO4Cl6

The Ba₅SiO₄Cl₆:Bi³⁺ phosphor was synthesized by high-temperature solid-state reaction and its luminescence property was investigated. The results showed that the Bi³⁺-doped Ba₅SiO₄Cl₆ phosphors exhibited an intense blue–white light emission located at 480 nm and a broad excitation band from 230 to 340 nm. The Bi³⁺-doped Ba₅SiO₄Cl₆ phosphors can be efficiently excited by the incident light of 220–340 nm, and the emission properties of the Bi³⁺-doped Ba₅SiO₄Cl₆ samples are strongly dependent on the excitation wavelength. The emission color tunability can be obtained by changing the excitation wavelength. The visible region emission characteristics of Ba₅SiO₄Cl₆:Bi³⁺ indicates that it can potentially be used as a new efficient blue–white luminescent material.     

Preparation and luminescent properties of Eu3+-doped zinc sulfide nanocrystals

The preparation and luminescent properties of Eu³⁺-doped zinc sulfide nanocrystal were investigated. The best reactive conditions were determined, such as the concentration of reactants, the kinds and amount of the surfactants, the reaction temperature and reaction time, the pH, the flowing speed and pressure of reactive gases. The crystal structure of the nanocrystal powders was tested by X-ray diffraction (XRD). The emission and excitation spectra of ZnS:Eu were characterized by fluorescent divide spectroscopy (FDS). The luminescent sites and their strength as a function of doping Eu³⁺ ions are discussed.     

Preparation,structural and spectroscopic studies of (YxLu1−x)2O3:Eu3+ nanopowders

Lutetium and yttrium oxides are promising scintillating materials suitable for use in medical planar X-ray imaging and mammography. In this paper the procedure for preparation of europium doped mixed lutetium–yttrium oxide nanopowders using polymer complex solution synthesis method is presented. Detailed information on nanopowder phase, morphology and crystallinity are obtained using X-ray powder diffraction, SEM and TEM while optical properties are investigated by photoluminescence and radioluminescence measurements. Constituting nanoparticles are 20–40 nm in size, and have excellent structural ordering in cubic bixbyite-type. Unit cell parameter, ionic coordinates, crystal coherence size and microstrain are determined from Rietveld analysis. All powders show strong Eu³⁺-characteristic red emission, with an average ⁵D₀ emission lifetime of 1.5 ms. Radioluminescence efficiency is about 15% of the commercial micron-sized Gd₂O₂S:Eu³⁺ powder while negligible level of afterglow is found.     

Luminescent properties of Al2O3:Tb3+ powders embedded in polyethylene terephthalate films

The luminescent properties of Al₂O₃:Tb³⁺ powders embedded in polyethylene terephthalate (PET) films have been studied. Luminescent Al₂O₃:Tb³⁺ polycrystalline powders were synthesized by a simple evaporation method. The powder embedded films were obtained by the spray pyrolysis technique. The photoluminescence and cathodoluminescence emission spectra from these samples show, in both cases, luminescence peaks associated with transitions within the electronic energy levels of Tb³⁺ ions. The dominant peak is at 544 nm corresponding to the ⁵D₄ to ⁷F₅ transition. In the case of the powder embedded films, the CIE coordinates depend on the excitation wavelength because there is a blue emission contribution from the PET host. UV–Vis% transmission measurements on these films show that they are transparent (∼80% and 95% T).     

Co-precipitation synthesis of ZnAl2O4: Cr3+ phosphor for better light penetration in pc-LED

Cr doped ZnAl₂O₄ spinel samples were prepared by the traditional solid state reaction and co-precipitation synthetic route, and the results suggest that the co-precipitation method has some superiority in contrast to the solid state reaction method. XRD, FT-IR, and XPS spectra confirmed that the well-crystallized spinel cubic phase of ZnAl₂O₄: Cr³⁺ samples were successfully formed. The morphology of the samples was investigated by FE-SEM and FE-TEM, and the results show that the samples by the co-precipitation route can generate a smaller size of particles compared to the solid state reaction. Photoluminescence excitation spectra monitored at 686 nm are comprised of two broad excitation bands near 530 nm and 395 nm, and the emission spectra show emissions ranging from 640 to 780 nm, due to the ²E?→?⁴A₂ spin-forbidden transition of Cr³⁺ ions in spinel lattices. The optimized concentration monitored at 686 nm is 1%, while at 693 nm is 3.5%. Compared with the samples by solid state reaction method, the samples by co-precipitation method show preferable luminescent properties, such as the higher photoluminescence intensity and higher quantum efficiency. Several phosphor-converted LEDs were to investigate the applicability of the prepared samples. The results confirm that the phosphor has potential applications in plant growth and supplementing the red region in white-LEDs and the phosphors prepared by co-precipitation are more suitable to be used in phosphor-converted LED devices due to their preferable luminescent properties.

     

Study on the emission properties of Sr2MgSi2O7:Eu,Dy for luminous fiber application

Rare earth long afterglow phosphors Sr₂MgSi₂O₇:Eu²⁺,Dy³⁺ was synthesized by a modified solid-state reaction using H₃BO₃ as auxiliary reagents. In order to promote the emission properties of Sr₂MgSi₂O₇:Eu²⁺,Dy³⁺, samples of Sr₂MgSi₂O₇:Eu²⁺,Dy³⁺ were prepared and the effect of manufacturing elements including the concentration of H₃BO₃ and environmental factor of calcining temperature, concentration of Eu²⁺ and Dy³⁺ ions, external environmental factors of applications such as fiber-forming polymer as well as the addition of Ca²⁺ ion on its emission property were investigated through evaluating their emission spectra. The results showed that the molar ratio of the Eu²⁺ ions and Dy³⁺ ions, the amount of doping H₃BO₃, calcining temperature and fiber-forming polymer had little effect on the position of the emission peak and the shape in the luminescence, but greatly influenced the emission intensity of luminescent materials. The effect of Ca²⁺ ion doping was further studied. Ca²⁺ influenced not only the intensity but also the wavelength of emission and spectra of the emission peak shifted to longer wavelength as the concentration of Ca²⁺ increased.     

Enhanced red-emitting phosphor Na<Subscript>2</Subscript>Ca<Subscript>3</Subscript>Si<Subscript>2</Subscript>O<Subscript>8</Subscript>:Eu<Superscript>3+</Superscript> by charge compensation

A series of novel red-emitting Na₂Ca_3???x Si₂O₈:xEu³⁺ phosphors were synthesized by solid state reactions. The phosphors can strongly absorb 395 nm light, and show red emission with a good color purity. The excitation and emission spectra properties of Na₂Ca₃Si₂O₈:Eu³⁺ were characterized. Na₂Ca₃Si₂O₈:Eu³⁺ with self-compensated and alkali metal ions charge compensated approaches (2Ca²⁺→Eu³⁺ + M⁺, M?=?Li⁺, Na⁺, K⁺) have investigated, which found that the red emission of luminescent intensity can be greatly enhanced, and shows superior luminescent property to the commercial Y₂0₃S:Eu³⁺. The present work implies that the efficient charge compensated phosphors are promising candidates as red-emitting phosphor for w-LEDs.