Nano-sized Phosphors Research Articles

Synthesis, characterization, and temperature-dependent luminescence of Tb3+-activated and self-activated Sr10(PO4)6Cl2 phosphors

In this work, a series of new nanosized phosphors based on strontium chlorapatite (Sr10(PO4)6Cl2, abbreviated as SrClAp) with varying terbium concentration were synthesized using a modified microwave-hydrothermal method. This study meticulously investigated the impact of Tb3+ concentration and annealing temperature on factors such as crystal purity, particle morphology, photoluminescence, chromatic properties, and the mechanism of thermal quenching.The synthesized phosphors underwent characterization using X-Ray Diffraction (XRD) and scanning electron microscopy (SEM) to verify their crystal structure purity and examine their morphology. Upon near-ultraviolet (NUV) excitation at the 378 nm line, the obtained nanosized powders emitted green light arising from the characteristic 5D4→7FJ (J = 6, 5, 4, 3) transitions of Tb3+ ions. Notably, a broad host-related emission was discernible at 80 K, with its intensity diminishing as the temperature increased. The mechanism governing this host-related emission and the process of its thermal quenching have been proposed. Moreover, a comprehensive exploration of the influence of ambient temperature on the emission of Tb3+-doped SrClAp was undertaken.

Preparation, microstructures and luminescence properties of transparent red-emitting Eu2Ca0.6(MoO4)3.6 suspension

Eu2Ca1−x(MoO4)4−x (x = 0, 0.20, 0.40, 0.60, 0.80, 1), non-concentration quenching phosphors with 100% of Eu3+ activator ion, were synthesized. Nano-sized phosphors were synthesized via a solvothermal reaction by using non-polar Ca-oleate, Eu-oleate and TOA–MoO4 complexes as surfactant complexes prepared through a phase-transfer method in a water-toluene bilayer system. Among the Eu2Ca1−x(MoO4)4−x, Eu2Ca0.6(MoO4)3.6 showed the strongest red emission at 615 nm due to the 5D0 → 7F2 transition of the Eu3+ ions. The mean size of the Eu2Ca0.6(MoO4)3.6 is ∼5 nm, which is sufficiently small to avoid light-scattering behavior. Thus, the Eu2Ca0.6(MoO4)3.6 nanophosphor can be used as a red-emitting material in transparent displays.

Hydrothermal synthesis and characterization of nano-sized phosphors based on rare-earth activated yttrium compounds for photodynamic therapy

Hydrothermal synthesis and characterization of nano-sized phosphors based on rare-earth activated yttrium compounds for photodynamic therapy

Quantum dots: experience and prospects of application in analytical systems

The article is of a review nature, in which the dynamics of publication activity is analyzed and the possibilities of using quantum dots to solve various analytical problems are evaluated. The attention is paid to both traditional and relatively rare areas of analytical application of these nanostructures. A brief review of the types, advantages and disadvantages of synthesis methods, the influence of external factors on the band gap and luminescence intensity of inorganic nanosized phosphors, quantum dots of different nature, is presented. The areas of application and the main tasks solved with the use of quantum dots are systematized. Their analytical characteristics, operational properties and ways of regulating them are discussed. An effective way to control the analytical properties of the systems based on quantum dots is a directional change of the affinity for components by varying the nature of the stabilizing or modifying shell. Semiconductor colloidal quantum dots coated with a larger bandgap shell were selected for analytical use as the most commonly used systems due to their good photostability and fluorescence quantum yield. The advantages and disadvantages of other types of shells, as well as ways of modifying them, are shown. Solutions for organic analysis and medical diagnostics are considered. Systems of quantum dots used as biosensors with various guiding agents are considered, and their properties, advantages and disadvantages compared. Little studied issues and solutions in the direction of using quantum dots for developing sensor systems and their use for non-invasive analysis of living systems based on the results of detection of volatile organic compounds are identified.

The Influence of Defects on the Luminescence of Trivalent Terbium in Nanocrystalline Yttrium Orthovanadate.

Terbium-doped YVO4 has been considered a nonluminescent solid since the first classic studies on rare-earth-doped phosphors in the 1960s. However, we demonstrate that defect engineering of YVO4:Tb3+ nanoparticles overcomes the metal-metal charge transfer (MMCT) process which is responsible for the quenching of the Tb3+ luminescence. Tetragonal (Y1-xTbx)VO4 nanoparticles obtained by colloidal precipitation showed expanded unit cells, high defect densities, and intimately mixed carbonates and hydroxides, which contribute to a shift of the MMCT states to higher energies. Consequently, we demonstrate unambiguously for the first time that Tb3+ luminescence can be excited by VO43- → Tb3+ energy transfer and by direct population of the 5D4 state in YVO4. We also discuss how thermal treatment removes these effects and shifts the quenching MMCT state to lower energies, thus highlighting the major consequences of defect density and microstructure in nanosized phosphors. Therefore, our findings ultimately show nanostructured YVO4:Tb3+ can be reclassified as a UV-excitable luminescent material.

Structural, morphological and photoluminescence characterizations of Sm3+ doped Y2O3 nano-sized phosphors synthesized by ultrasound assisted sol-gel method

Nanosized 1 at% Sm3+ doped Y2O3 powders were prepared by an ultrasound assisted sol-gel method. Y2O3:Sm3+ powders crystallize in Y2O3 pure cubic phase and XRD analysis shows that the as-used agitation protocol affects strongly the crystallite's shape and mean size. The recorded emission spectra under λem=600nm exhibit two absorption bands; the first one is assigned to O2− → Sm3+ charge transfer state (CTS) with a maximum absorption at 223 nm, and the second is due to intra-configurational transition 4f5-4f5 of Sm3+ with a maximum absorption at 407 nm. The 223 and 407 nm transitions are attributed to characteristics intra-configurational transitions of Sm3+. All emission spectra are dominated by reddish/orange luminescence located at 606 nm and assigned to 4G5/2 → 6H7/2 transition. It is found that the photoluminescence intensity of samples obtained under excitation at 407 nm is 60 times smaller than that obtained under 223 nm excitation. Decay time measurements of the 4G5/2 → 6H7/2 luminescence transition indicate that decay time of nano-sized powder is significantly shorter than bulk material one.

An efficient synthesis of trivalent erbium activated BaYZn3AlO7 nano-sized phosphors for illumination purpose

Nanocrystalline BaY1−xErxZn3AlO7 (x = 0.01–0.05) phosphors are derived via solution combustion synthesis. Williamson-Hall plot evaluated crystallite size (86.12 nm) and micro strain (0.00143) of the optimized sample. TEM study validates the fabricated particles size in nano-range. Under excitation upon near ultraviolet source (381 nm), emissive peaks are identified at 527 nm (2H11/2→4I15/2) and 566 nm (4S3/2→4I15/2). CIE color coordinates proved emanation in the yellowish-green section. The energy band gap, refractive index and CCT values for optimum nanosample are found to be 4.66 eV, 1.77 and 5416 K respectively. All results indicate that BaY1−xErxZn3AlO7 nanophosphors possess ample applications in WLEDs.

Synthesis of rare-earth nanosized phosphors using microwave processing

Nanomaterials find permanently extending applications in various areas of life. In particular, nanosized phosphors can be used as pharmaceutical carriers capable of emitting ultraviolet or visible light that activates a photosensitizer, thus significantly expanding the possibilities of photodynamic therapy in the treatment of oncological, bacterial and viral diseases. The conditions required for the use of nanosized phosphors in medicine include their fine dispersion and effective luminescence in the red region of visible light spectrum upon stimulation by X-ray radiation of the range accepted for medical applications, particularly for diagnostic and therapeutic purposes in many diseases. The aim of this work was to study the effect of microwave treatment of Y2O3:Eu phosphors prepared by hydrothermal synthesis in ethylene glycol at 230 °C for 6 hours, involving the decomposition of mixed acetate. In order to reduce the aggregation and growth of the resulting particles, Aerosil A300 with average particle size 7 nm was added to the reaction mixture in the course of hydrothermal synthesis in the ratio 1:1 relating to the obtained phosphor. The microwave treatment was carried out at 800 °C for 5 minutes. The developed method provided Y2O3:Eu phosphor samples featuring with increased luminescence intensity in the region 610…700 nm compared to similar phosphors earlier prepared using the rapid thermal annealing (RTA) procedure.

Low Temperature Synthesis of Halide Phosphors Using Novel Water-Assisted Solid-State Reaction Method

In recent years, nano-phosphor materials have attracted much attention due to their significant potential for high-performance micro-LED displays and solid state lighting devices. In addition, nano-phosphors are considered to be promising candidates for spectral-converters to enhance the energy-conversion efficiency of silicon solar cells. Synthesis of nano-phosphors can be categorized in two ways namely, chemical and physical methods. Various methods such as the sol-gel, hydro-thermal, or the polymerized complex methods are usually used to synthesize nano-phosphor materials. However, these methods require expensive and special experimental equipment, raw materials, or solvents.In this study, we synthesized nano-sized halide phosphors using a novel water-assisted solid-state reaction (WASSR) method. This novel soft chemical synthesis method is very simple and can synthesize nano-particle materials just by storing or mixing raw materials added a small amount (typically 10wt%) of water in a reactor at low temperature below 500 K. Typical particle sizes (under 100 nm) of the samples prepared by the WASSR method were smaller than that (2 - 10 micrometer size) of the sample prepared by the conventional solid-state reaction method.For example, a stoichiometric mixture of CsCl, CaCl2 and EuCl3 hydrate was mixed for the WASSR synthesis of CsCaCl3:Eu2+ phosphor. Then, a small amount (2 wt%) of water was added to the mixture and mixed using mortar for 1 min to synthesize a single phase of CsCaCl3:Eu3+. For the reduction of Eu3+ ion, 6 wt % of hydrazine monohydrate was added to the CsCaCl3:Eu3+ and heated in the closed reactor for 12 h at 493 K. The XRD pattern of the products are in good agreement with that of single phase CsCaCl3. The SEM image and the photoluminescence spectra of CsCaCl3:Eu2+ is shown in Figure. CsCa0.09Eu0.01Cl3 shows strong blue emission under the excitation of UV light. Our proposed low cost and low-temperature synthesis technique are promising for an industrial application for phosphor materials synthesis processing.AcknowledgmentThis research was financially supported by the Ministry of Trade, Industry and Energy(MOTIE) and Korea Institute for Advancement of Technology(KIAT) through the International Cooperative R&D program (P0006844_Development of color conversion nanocrystal luminescence materials for next generation display).

Synthesis of Y<sub>2</sub>O<sub>3</sub>: Eu Nanosized Phosphor Using Hydrothermal Technique and Rapid Thermal Annealing (RTA)

The application of special nanomaterials is promising for the development of new methods for the diagnostics and treatment of cancer. Photodynamic therapy (PDT) is a well-known and recognized method of cancer treatment. This type of therapy is less carcinogenic and mutagenic compared to radiation and chemotherapy, since the applied photosensitizers do not bind to DNA of the cells. However, currently this technique is only applicable to skin cancer, while its extension to the treatment of abdominal tumors requires the creation of pharmacological drugs for PDT, which along with a photosensitizer include a colloidal solution of nanosized luminescent phosphor emitting visible light with the required wavelength under the influence of infrared, X-ray or γ-radiation, which easily penetrates the body tissues. Since photosensitizers are already available as commercial products, the most important goal is the development of nanosized phosphors providing the required radiation convertion. In this study, the effects of hydrothermal synthesis, duration and the conditions of rapid thermal annealing (RTA) on Y2O3:Eu phosphor particle size were studied. The hydrothermal synthesis technique was carried out in two ways: chloride (precipitation from a chloride solution using NaOH and NH4OH precipitators) and acetate (decomposition of mixed acetate either without a dispersant at 230° C for 24 hours, or using PEG-200 and PEG-2000 as dispersants at 230 °C for 12 hours). The rapid thermal annealing was performed either at 600 °C for 20 minutes, or at 800 °C for 5 minutes. The developed synthetic approaches afforded Y2O3:Eu nanosized phosphor samples with the particle size not exceeding 200 nm.

Flexible nanophosphor films doped with Mie resonators for enhanced out-coupling of the emission.

Herein, we present a general method to prepare self-standing flexible photoluminescent coatings of controlled opacity for integration into light-emitting diodes (LEDs) employing cost-effective solution-processing methods. From colloidal suspensions of nano-sized phosphors, we fabricate light-emitting transparent films that can be doped with spherical scatterers, which act as Mie resonators that trigger a controlled photoluminescence enhancement, evidenced by the reduction of the guided light along the layer. This results in an enhanced emission compared to that extracted from a bare phosphor layer. We show not only that emission is visible under ultraviolet-LED illumination for both rigid and flexible versions of the coatings, but we also prove the feasibility of the integration of these flexible conversion layers into such devices. We believe these results can contribute to develop more efficient and cost-effective illumination sources by providing efficient and easy-to-handle conversion layers susceptible to excitation by LEDs emitting at wavelengths in the near UV region.

Temperature-dependence of efficient up-conversion luminescence in NaY(WO4)2 nanophosphor doped with Er3+ for cryogenic temperature sensor

The fluorescence-based temperature sensor using temperature-dependent fluorescence properties is a great candidate to replace traditional temperature-measurement detector like thermocouple, because the latter is inaccessible to conquer some special circumstances such as a corrosive environment. In this study, the nano-sized Er3+ doped NaY(WO4)2 phosphors were synthesized by solvothermal method. The origins of three emission peaks located at 527 nm, 549 nm and 665 nm were identified. The 2H11/2 → 4I15/2 (green emission 1) and 4S3/2 → 4I15/2 (green emission 2) transitions of the Er3+ ion possessed a temperature dependent behavior over the range of 300–30 K and it was proposed for temperature sensing (optical thermometry) using the fluorescence intensity ratio (FIR) method. The FIR value of nano-sized phosphors decreased with the decrease of temperature, and the experimental data were well fitted with a theoretical function. A large energy difference (1048.5) was obtained from the fitting curve, which indicate that the sensitivity of nano-sized NaY(WO4)2: Er is higher than that of micro-sized one prepared by high temperature solid state reaction. Particularly, at temperatures below 150 K, the sensitivity of nano-sized UC phosphors was enhanced obviously. The results suggested that this nano-sized phosphor could be a splendid option for next generation luminescence-based temperature sensing devices in cryogenic region.

Photoluminescence properties of YAG:Ce3+,Pr3+ nano-sized phosphors synthesized by a modified co-precipitation method

Monophasic Ce3+ and Pr3+ co-doped yttrium aluminum garnet (YAG:Ce3+,Pr3+) nanoparticles with good dispersity and uniform grain sizes in the range of 50–80 nm were prepared by a two-step route, which consisted of a modified co-precipitation preparation of mixed metal hydroxide hydrate intermediates at low temperature of about 40 °C and a subsequent calcination conversion of the synthesized intermediates to crystalline nanoparticle products at about 1000 °C. The influences of both the lanthanide ion (Ce3+ and Pr3+) doping concentration and different doping (Ce3+/Pr3+) ratio on the photoluminescence intensity were systematically investigated. The synthesized (Ce0.6Pr0.4)0.04Y2.96Al5O12 nanoparticles were near spherical nanoclusters with good dispersity and uniform sizes in the range of 50–80 nm for about 85% of the particles. The strongest photoluminescence intensity was observed for the (Ce0.6Pr0.4)0.04Y2.96Al5O12 nanoparticle products.

Size controllable synthesis and multicolor fluorescence of SiO2:Ln3+(Ln=Eu, Tb) spherical nanoparticles

A series of size controllable Tb3+ and/or Eu3+ activated nano-sized silica phosphors have been successfully synthesized through a facile sol-gel method. The structure, morphology, compositions, and luminescence properties of as-prepared samples were well investigated using X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive spectrometer (EDS), X-ray photoelectron spectroscopy (XPS), Brunauer-Emmett-Teller (BET) and photoluminescence spectroscopy (PL). The results showed that all as-prepared samples were spherical nanoparticles but the sizes reduced gradually with the temperature increased from 25°C to 65°C, which was contrary to the BET surfaces as well as the luminescence intensity. Under ultraviolet excitation, the SiO2:Ln3+(Ln=Eu, Tb) spherical nanoparticles showed characteristic red and green emissions corresponding to f-f transition of Eu3+ and Tb3+, respectively. Moreover, the luminescence emissions of samples can be tuned from green to yellow, orange and red by co-doping the Tb3+ and Eu3+ ions in different concentration ratio into the SiO2 host due to the efficient dipole–dipole energy transfer mechanism from Tb3+ to Eu3+ under 377nm excitation. These results show that as-prepared phosphors may find potential applications in color display fields.

(Invited) Fabrication and Characterization of Transparent Fluorescence Nanocomposite Film Containing Inorganic Phosphor Nanoparticles

Nano-sized inorganic phosphors possess good photostability and thermal stability as compared with organic dyes and metal complexes. They exhibit high transparency due to low light scattering intensity in the visible region. A transparent fluorescence film of phosphor nanoparticles with a function of conversion from near UV light to visible light are therefore suitable candidates for applications to spectral down-shifters in white LEDs and photovoltaic devices. To fabricate the transparent nanocomposite film, the phosphor nanoparticles must be well-dispersed without their aggregation because light scattering intensity is proportional to the sixth power of a particle diameter according to Rayleigh’s theory. Nanoparticles aggregate easily in a solution due to their high surface energy. To solve this problem, we use electrostatic repulsion between charged nanoparticle surfaces. In this presentation, we discuss fabrication and characterization of transparent fluorescence nanocomposite films containing phosphor nanoparticles in a matrix.

Improvement of Quantum Efficiency of the Nanosized Phosphors Using a Flux

Micron-sized phosphors have been widely researched for a near UV-LED by the mean of the convenient solid-state method. The phosphors with micron-sized tend to show good quantum efficiency oriented from their large crystallite size, but present high light-scattering and decrease packing density on the LED device, causing low resolution. Therefore, integration of the phosphors for a near-UV LED package has particles size requirements in order to overcome the issue from bulk size phosphors. The scatter effect in visible and UV radiation region will be negligible when the radii of phosphors particles are less than ~400 nm. However, phosphors with nano-size particles have poor quantum efficiency comparing to phosphors with micron sized particles. In this work, flux effect on quantum efficiency is studied in nano-sized phosphors. Blue colored CaMgSi2O6:Eu2+ phosphors were synthesized by a co-precipitation method and NH4F, NH4Cl, or H3BO3 was added as a flux. Flux is typically used in the solid-state reaction to help diffusion of atoms in the bulk materials, not nano-sized materials. The crystallite size is increased from ~20 nm to ~40 nm, but particles size is unchanged (~ 50 nm) with the addition of a flux in the materials, confirmed by X-ray diffraction, Dynamic Light Scattering analysis, and Scanning Electron Microscopy. The emission wavelength of CaMgSi2O6:Eu2+ is 458 nm under 350 nm as an excitation wavelength. The intensity of emission wavelength is about twice increased when 5wt% NH4F is added as a flux in the phosphors materials comparing to the phosphors without a flux, indicating the improvement of quantum efficiency. This study shows the potential of flux that could improve quantum efficiency in the nano-sized phosphors. This work is supported by the National Science Foundation, Ceramics Program Grant (DMR-1411192).

RF 열플라즈마를 이용한 Y2O3:Eu3+적색 나노 형광체 분말 합성

is an excellent red-emitting phosphor, which has been widely used for display devices due to highly luminescent property and chemical stability. In this study, red phosphors were prepared using the solid state reaction and RF thermal plasma synthesis. The particle size of phosphors obtained by the solid state reaction varied from 10 to , and 30~100 nanometer sized particles were obtained from a liquid form of raw material through RF thermal plasma synthesis without an additional heat treatment. Photoluminescence measurements of the obtained particles showed a red emission peak at 611 nm (). PL intensity of red nano phosphors prepared by RF thermal plasma synthesis was comparable to that of red phosphors prepared by the solid state reaction, indicating that nano-sized red phosphors could be successfully synthesized using one-step process of RF thermal plasma.

Blue upconversion of Tm3+ using Yb3+ as energy transfer bridge under 1532 nm excitation in Er3+, Yb3+, Tm3+ tri-doped CaMoO4

Nano-sized CaMoO4 phosphors tri-doped with Er3+, Yb3+ and Tm3+ ions were successfully synthesized by sol-gel method. Intense blue emission from Tm3+ ions was observed upon excitation of 1532 nm infrared light in Er-Yb-Tm system, while this blue upconversion could not be achieved with the absence of Yb3+ ions in Er-Tm co-doped sample. In order to understand this upconversion process, the upconversion spectra in these samples were investigated, and the possible mechanism was proposed based on experimental results. It showed that two different energy transfer from Er3+ to Tm3+ existed simultaneously in Er-Yb-Tm system, the one-step direct energy transfer from Er3+ to Tm3+, and the two-step Er3+→Yb3+→Tm3+ energy transfer. In particular, the 1G4 state of Tm3+ could only be populated from the 3H4 state by cross-relaxation with an excited Yb3+ ion, producing blue emission of Tm3+. In this upconversion process, Yb3+ ions acted as an energy transfer bridge between Er3+ and Tm3+, which also meant that the upconversion of other rare-earth ions under the excitation of 1532 nm was possible with the presence of Er3+ and Yb3+.

Concentration Quenching and Energy Transfer in Tm3+ and Dy3+ Single- and Double-Doped Nano-Sized GdVO4 Phosphors.

In this paper, Tm3+ and Dy3+ single- and double-doped nano-sized GdVO4 phosphors were prepared via a co-precipitation reaction. X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and photoluminescence (PL) were utilized to characterize the as-prepared samples. The XRD and FE-SEM results reveal that the samples are single phase and that the average size is about 30 nm, respectively. Under 280 nm ultraviolet excitation, Dy3+ and Tm3+ single-doped nano-sized GdVO4 phosphors show the characteristic emissions of Dy3+ (4F9/2 --> 6H15/2 and 4F9/2 -*6H13/2 transitions) and Tm3+ (1G4 --> 3H6 transition), respectively. All the luminescence results from efficient energy transfer from the GdVO4 host to the doped Dy3+ and Tm3+ ions. Moreover, the interaction types for Dy3+ and Tm3+ ions in nano-sized GdVO4 host are confirmed as exchange and electrical dipole-dipole interaction by theoretical calculation. In Tm3+ and Dy3+ co-doped nanosized GdVO4 phosphors, the luminescence intensities of Dy3+ ions increase with increasing Tm3+ ion doping concentration, which suggests that energy transfer from Tm3+ to Dy3+ ions occurs. The responding luminescence mechanisms have been proposed in this paper. Finally, in order to evaluate the luminescence of Tm3+ and Dy3+ co-doped nano-sized GdVO4 phosphors, the color coordinates were calculated.

Stability of luminescence in LaPO4, LaPO4 :RE(3+) (RE = Dy, Eu) nanophosphors.

The property of high refractive index, low solubility in water as well as stability to high temperature variation of lanthanum phosphate (LaPO4 ) proved it was the most effective candidate for the production of display lamps, and plasma display panel devices and sensors. The morphological and nanostructural characteristics play a key role in the working efficiency of the luminescent material. These properties can be controlled by the synthesis method, which we have adopted in this paper. We have prepared LaPO4 nanoparticles at a relatively low temperature (110 ºC) in polyethylene glycol medium by using a wet chemical one-step synthesis. The phase composition and structural properties of the sample have been characterized by X-ray diffraction, Fourier transform infrared, transmission electron microscopy and the luminescent property by photoluminescence and thermoluminescence. The samples were well crystallized and the average crystallite size of 15 nm has been calculated for pure LaPO4 using the Debye-Scherrer equation. The result from heat-treated samples shows the phase combination and morphological structure of the powder depend on the annealing temperature. The heat treatment changes the structure of LaPO4 from cuboid rods to fine grains at about 600 °C. The emission spectrum of LaPO4 shows the broad emission band at 368 nm and shoulder at 465 nm with emission of blue color when monitored at an excitation wavelength at 256 nm. The stability of phosphor has been studied with respect to humidity, temperature, doping, doping concentration, γ-ray exposures, etc. The prepared nanosized phosphors were thermally stable and may be a promising blue phosphor for lighting technology as well as radiation dosimetry.