Luminescent Particles Research Articles

GROWTH AND CHARACTERIZATION OF CdS AND CdS:Ag LUMINESCENT QUANTUM DOTS DISPERSED IN SOLUTION

A fast-chemically capping method in aqueous solution was developed to synthesize CdS and CdS : Ag luminescent nanoparticles and particles with sizes between 2–4 nm. The achieving of well-dispersed and narrow-sized particles in colloidal solution and also, high stability of them using mercaptoethanol (ME) as a capping agent was established. Quantum confinement effect was observed in UV-vis absorption as well as in PL spectra. PL spectroscopy also showed green emission and Ag dopants caused a faster energy transfer between CdS inter-bands. XRD patterns exhibited that both cubic and hexagonal phases exist in solutions. Ultimately, TEM images captured from QDs displayed the shapes of nanoclusters which are almost spherical.

Sparkle lamp ingestion: a rare cause of death

A 51-year-old man was brought to the emergency department after he had drunk 200 mL of fluid from a decorative sparkle lamp. His calcium level was 4.99 mmol/L with a blood gas pH of 7.21. His calcium levels were corrected and his acidosis improved, but his stay in the intensive care department was complicated on day 10 by upper gastrointestinal hemorrhage because of caustic erosions in his stomach. Ten days after admission, he had an emergency right hemicolectomy during which residual luminescent particles were found to have eroded through his cecal mucosa. He eventually died 15 days after admission because of disseminated intravascular coagulopathy and refractory septic shock. This case demonstrates the potential for fatal toxicity associated with ingestion of a common household item.

Synthesis of YAG:Ce/TiO 2 nanocomposite films

Our work is devoted to the development of YAG:Ce 3+ phosphor nanoparticle-based converter layer for white LEDs. To avoid losses due to scattering effects, the strategy is to control separately the down-conversion and the extraction of light instead of using micron-sized luminescent particles acting simultaneously as both converter and scatterer. YAG:Ce nanoparticles were synthesized by a glycothermal method in autoclave at low temperature (300 °C). Y 3Al 5O 12 garnet phase with a crystallite size of 25 nm was obtained, as verified by X-ray diffraction and electron microscopy. The quantum yield of nanoparticles is 55%. The colloidal nanoparticles are finally incorporated into a sol–gel matrix of TiO 2. The small difference in refractive index between particles and matrix and the nanosize of the particles contribute to the transparency of the converter films. The surface of these layers can be periodically patterned by soft nano-imprint lithography. The diffraction due to the obtained photonic crystal at the surface may offer the opportunity to compensate the absence of scattering to extract the converted light.

Magnetic luminescent porous silicon microparticles for localized delivery of molecular drug payloads.

Magnetic manipulation, fluorescent tracking, and localized delivery of a drug payload to cancer cells in vitro is demonstrated, using nanostructured porous silicon microparticles as a carrier. The multifunctional microparticles are prepared by electrochemical porosification of a silicon wafer in a hydrofluoric acid-containing electrolyte, followed by removal and fracture of the porous layer into particles using ultrasound. The intrinsically luminescent particles are loaded with superparamagnetic iron oxide nanoparticles and the anti-cancer drug doxorubicin. The drug-containing particles are delivered to human cervical cancer (HeLa) cells in vitro, under the guidance of a magnetic field. The high concentration of particles in the proximity of the magnetic field results in a high concentration of drug being released in that region of the Petri dish, and localized cell death is confirmed by cellular viability assay (Calcein AM).

Stability improvement of moisture sensitive CaS:Eu 2+ micro-particles by coating with sol–gel alumina

Here we report on the usage of alumina coating for the protection of moisture sensitive CaS:Eu 2+ micro-particles. Alumina sol was prepared using a water-free sol–gel technique and single crystal CaS:Eu 2+ luminescent micro-particles were synthesized via solvothermal way. After deposition of the particles on a substrate, they were coated with an alumina layer and heat treated at 500 °C for 30 min. In addition to in situ measurements of accelerated ageing of the luminescent particles, photoluminescence (PL) spectra of coated and uncoated particles were compared. Coated particles showed a broad band PL emission with a maximum at 650 nm identical to that of uncoated particles. Coating with an alumina layer drastically increased the resistivity of the luminescent material against moisture.

Radiation effects in atomic cryogenic solids

Radiation effects and relaxation processes in atomic solids are discussed with the example of solid Xe preliminarily irradiated by an electron beam. The study was performed employing concurrently the combination of current and optical “activation spectroscopy” methods. Three relaxation processes were monitored simultaneously upon controlled warming-up of pre-irradiated solids: thermally stimulated exoelectron emission (TSEE), thermally stimulated luminescence (TSL) in the VUV range and the total desorption yield by pressure measuring above the sample. Anomalous strong low-temperature “post-desorption” (ALTpD) of own atoms from pre-irradiated Xe solids was observed for the first time. The data obtained demonstrated a clear correlation between the yields of exoelectrons, photons of recombination luminescence and neutral particles pointing to the common origin of the phenomena. It was shown that the key primary process of the relaxation cascade including the ALTpD is a thermally stimulated electron detrapping, promoting electrons into the conduction band. Subsequent branching of the relaxation paths results in the relaxation emissions observed. An accumulation of charges of both signs as well as excess electrons under exposure to an electron beam was found.

Combined two-dimensional velocity and temperature measurements using a high-speed camera and luminescent particles

This paper proposes a combined method for two-dimensional temperature and velocity measurements using temperature sensitive particles (TSParticles), a pulsed ultraviolet (UV) laser and a single high-speed camera. TSParticles were synthesized using ion-exchange particles and Eu(TTA) luminescent dye. The size and material of the particles for synthesizing TSParticles are selectable. TSParticles respond to temperature changes in a flow and can also serve as tracers for the velocity field. TSParticles were seeded into a heated water flow in a complex-shaped channel constructed of MEXFLON resin, which has a refractive index exactly equal to that of water. Particle images of flow beyond the structure can be recorded without any distortion. The TSParticles were excited by the UV pulsed laser and the luminescence from the TSParticles were recorded at 40,000 frames per second as sequential images for a lifetime-based temperature analysis. Another advantage of our approach is that high time-resolved PIV can be carried out without a high-frequency laser. The recorded images were also used for the particle image velocimetry (PIV) calculation.

Semiconductor quantum dots as fluorescent probes for in vitro and in vivo bio-molecular and cellular imaging.

Over the years, biological imaging has seen many advances, allowing scientists to unfold many of the mysteries surrounding biological processes. The ideal imaging resolution would be in nanometres, as most biological processes occur at this scale. Nanotechnology has made this possible with functionalised nanoparticles that can bind to specific targets and trace processes at the cellular and molecular level. Quantum dots (QDs) or semiconductor nanocrystals are luminescent particles that have the potential to be the next generation fluorophores. This paper is an overview of the basics of QDs and their role as fluorescent probes for various biological imaging applications. Their potential clinical applications and the limitations that need to be overcome have also been discussed.

Microencapsulation of Moisture-Sensitive CaS : Eu2 + Particles with Aluminum Oxide

Single-crystal, submicrometer-sized CaS:Eu luminescent particles were synthesized via a solvothermal route, and these moisture-sensitive particles were coated with aluminum oxide using atomic layer deposition (ALD). Photoluminescence (PL) spectra of coated and uncoated particles were compared. They both showed a broad-band PL emission with a maximum of 650 nm. Microencapsulation by aluminum oxide layers did not have a pronounced effect on the intensity of the emission. In situ luminescence measurements during the accelerated aging (, 80% relative humidity) of coated and uncoated CaS:Eu particles were performed. While the uncoated phosphor was largely degraded within 30 h of aging, it was observed that a 20 nm thick aluminum oxide coating dramatically increased the resistance of the luminescent material against moisture, showing the conformity of the coating by the ALD process. Upon degradation, was formed, leading to emission as observed in cathodoluminescence. Finally, the use of these coated particles as a wavelength conversion material in light-emitting diodes was evaluated.

Characterization of Fluorescence in Heat-Treated Silver-Exchanged Zeolites

Thermal treatment of Ag(+)-exchanged zeolites yields discrete highly photostable luminescent clusters without formation of metallic nanoparticles. Different types of emitters with characteristic luminescence colors are observed, depending on the nature of the cocation, the amount of exchanged silver, and the host topology. The dominant emission bands in LTA samples are situated around 550 and 690 nm for the samples with, respectively, low and high silver content, while in FAU-type materials only a broad band around 550 nm is observed, regardless of the degree of exchange. Analysis of the fluorescent properties in combination with ESR spectroscopy suggests that a Ag(6)(+) cluster with doublet electronic ground state is associated with the appearance of the 690-nm emitter, having a decay of a few hundred microseconds. Tentatively, the nanosecond-decaying 550-nm emitter is assigned to the Ag(3)(+) cluster. This new class of photostable luminescent particles with tunable emission colors offers interesting perspectives for various applications such as biocompatible labels for intracellular imaging.

Development of ZnO:Ga as an ultra-fast scintillator

We report on several methods for synthesizing the ultra-fast scintillator ZnO(Ga), and measurements of the resulting products. This material has characteristics that make it an excellent alpha detector for tagging the time and direction of individual neutrons produced by t–d and d–d neutron generators (associated particle imaging). The intensity and decay time are strongly dependent on the method used for dopant incorporation. We compare samples made by diffusion of Ga metal to samples made by solid-state reaction between ZnO and Ga 2O 3 followed by reduction in hydrogen. The latter is much more successful and has a pure, strong near-band-edge fluorescence and an ultra-fast decay time of the X-ray-excited luminescence. The luminescence increases dramatically as the temperature is reduced to 10 K. We also present results of an alternate low-temperature synthesis that produces luminescent particles with a more uniform size distribution. We examine possible mechanisms for the bright near-band-edge scintillation and favor the explanation that it is due to the recombination of Ga 3+ donor electrons with ionization holes trapped on H + ion acceptors.

Photoluminescent Nanofibers for Solid-State Lighting Applications

AbstractPhotoluminescent nanofibers (PLN) can be formed by combining electrospun polymeric nanofibers and luminescent particles such as quantum dots (QD). The physical properties of PLNs are dependent upon many different nanoscale parameters associated with the nanofiber, the luminescent particles, and their interactions. By understanding and manipulating these properties, the performance of the resulting optical structure can be tailored for desired end-use applications. For example, the quantum efficiency of quantum dots in the PLN structure depends upon multiple parameters including quantum dot chemistry, the method of forming the PLN nanocomposites, and preventing agglomeration of the quantum dot particles. This is especially important in solution-based electrospinning environments where some common solvents may have a detrimental effect on the performance of the PLN. With the proper control of these parameters, high quantum efficiencies can be readily obtained for PLNs. Achieving high quantum efficiencies is critical in applications such as solid-state lighting where PLNs can be an effective secondary conversion material for producing white light. Methods of optimizing the performance of PLNs through nanoscale manipulation of the nanofiber are discussed along with guidelines for tailoring the performance of nanofibers and quantum dots for application-specific requirements.

A luminescent solar concentrator with 7.1% power conversion efficiency

AbstractThe Luminescent Solar Concentrator (LSC) consists of a transparent polymer plate, containing luminescent particles. Solar cells are connected to one or more edges of the polymer plate. Incident light is absorbed by the luminescent particles and re‐emitted. Part of the light emitted by the luminescent particles is guided towards the solar cells by total internal reflection. Since the edge area is smaller than the receiving one, this allows for concentration of sunlight without the need for solar tracking. External Quantum Efficiency (EQE) and current–voltage (I –V) measurements were performed on LSC devices with multicrystalline silicon (mc‐Si) or GaAs cells attached to the sides. The best result was obtained for an LSC with four GaAs cells. The power conversion efficiency of this device, as measured at European Solar Test Installation laboratories, was 7.1% (geometrical concentration of a factor 2.5). With one GaAs cell attached to one edge only, the power efficiency was still as high as 4.6% (geometrical concentration of a factor 10). To our knowledge these efficiencies are among the highest reported for the LSC. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Preparation of luminescing nanocrystal and its application to electrospinning

In this study, quantum dots (QDs) having the photophysical properties of brightness, photostability and narrow emission were synthesized. The electrospinning has been introduced to be a simple technique for generating ultrathin fibers. Herein, we have synthesized QDs and electrospun polyvinylacetate (PVAc) nanofibers having these strongly luminescing QDs particles. The size and morphology of QDs were recorded with transmission electron microscopy (TEM). The structural nanofiber webs have been discussed by scanning electron microscopy (SEM). And fluorescence properties of strongly luminescing QDs nanofibers were also discussed.

Synthesis and lectin-binding activity of luminescent silica particles peripherally functionalized with lactose

A novel O-protected lactose (Galβ1→4Glcβ1–) derivative bearing trimethoxysilyl group at the aglycon was developed as a silane coupling agent. Reaction of the coupling agent with tris(2,2′-bipyridine)ruthenium (II) dichloride (Rubpy) doped silica particle gave a Rubpy-doped silica particle peripherally functionalized with O-protected lactose derivative. De-O-protection of the particle with aqueous ammonia provided lactose-coating Rubpy-doped silica particles, combining luminophor encapsulated in silica matrix and carbohydrate having lectin-recognition ability. Specific adhesion of fluorescein isothiocyanate-labeled peanut agglutinin (FITC-PNA) to the lactose-coating Rubpy-doped silica particles was confirmed by fluorescence microscopic analysis.

Preparation and characterization of magnetic luminescent nanocomposite particles

A new kind of magnetic luminescent nanocomposite (MLNC) particles was prepared by a combination process of sol–gel and electrostatic self-assembly techniques. In this process, superparamagnetic Fe 3O 4 nanoparticles were coated with silica, forming SiO 2/Fe 3O 4 core-shell structure particles. A surface-active agent, 3-aminopropyltrimethoxysilane was then used to terminate the silica surface of these particles with amino groups. Finally, thioglycolic acid (TGA)-capped CdSe Quantum Dots (QDs) were attached onto the surface of SiO 2/Fe 3O 4 particles by electrostatic self-assembly. X-ray diffraction (XRD), transmission electron microscopy (TEM), microelectrophoresis, UV–vis absorption and emission spectroscopy and magnetometry were applied to characterize the nanocomposite particles. The particles exhibited favorable superparamagnetic and photoluminescenct (PL) properties. With increasing the thickness of silica shell, more dense CdSe QDs were attached on the SiO 2/Fe 3O 4 nanoparticles and the PL intensity increased.

Fabrication of nanocomposite particles with superparamagnetic and luminescent functionalities

A new kind of superparamagnetic luminescent nanocomposite particles has been synthesized using a modified Stöber method combined with an electrostatic assembly process. Fe 3O 4 superparamagnetic nanoparticles were coated with uniform silica shell, and then 3-aminopropyltrimethoxysilane was used to terminate the silica surface with amino groups. Finally, negatively charged CdSe quantum dots (QDs) were assembled onto the surface of the amino-terminated SiO 2/Fe 3O 4 nanoparticles through electrostatic interactions. X-ray diffraction (XRD), transmission electron microscopy (TEM), microelectrophoresis, UV–vis absorption and emission spectroscopy and magnetometry were applied to characterize the nanocomposite particles. Dense CdSe QDs were immobilized on the silica surface. The thickness of silica shell was about 35 nm and the particle size of the final products was about 100 nm. The particles exhibited favorable superparamagnetic and photoluminescent properties.

Influence of Molten Salt on Luminescent Intensity and Particle Size of Y 2 O 3 :Eu 3+ Phosphor

The Y-Eu oxalate precursor was prepared with a homogeneous precipitation method. And the additives, Na 2CO 3, S, NaCl or their combination, were introduced into the precursor to prepare Y 2O 3:Eu 3+ red phosphors at 1000 ~ 1300 °C for 2 h. The effect of molten salts on particle size and luminescent intensity was studied. The experimental results showed that the complex molten salt (Na 2CO 3 + S + NaCl) was conductive to enhance the luminescent intensity of Y 2O 3:Eu 3+. The emission intensity of the phosphor prepared with these additives at 1300 °C was about 45% higher than that of the one prepared without molten salt, and about 11% higher than that of the corresponding commercial phosphor. Meanwhile, the particle size of Y 2O 3:Eu 3+ phosphor was controlled effectively with the molten salt.

White luminescence from silica glass containing red/green/blue luminescent nanocrystalline silicon particles

Silica glasses containing blue/green/red luminescent nanocrystalline silicon (nc-Si) particles that consist of monolayer and/or three-layer structures were fabricated by a radio-frequency sputtering technique and postannealing treatment. These silica glasses showed very broad luminescence spectra with a peak at 460 nm (blue light), 550 nm (green light), and 800 nm (red light). When these samples were irradiated by using a xenon lamp with an optical bandpass filter of 313 nm, the luminescence colors from these silica glasses were a white light. The white luminescence of the sample with the three-layer structure exhibited the high luminance value of 1.5 cd/m2. This value was ascribed to the adjustment of sizes and densities of blue/green/red luminescent nc-Si particles, and the lowering of densities of Pb centers (nonradiative recombination centers) at the nc-Si particle/silica glass interface layer.

In situ synthesis of photoluminescent films of PVC, doped with Ce 3+ ion

In this paper we report on the in situ synthesis of photo luminescent and patterned polyvinyl chloride (PVC) films, doped with cerium chloride. The precursor of the doping agent is the Tris(2-4 pentanedionate)cerium(III) 3H 2O, Ce(acac) 3, which absorbs UV and visible light. The PVC is both the photochemical source of chloride ion and the rigid matrix where the CeCl 3 luminescent particles are dispersed. The PVC films containing cerium complex in the concentration range 0–3% w/w did not exhibit luminescence over 320 nm. After irradiation at 254 nm, the films of pure PVC exhibited luminescence emission with a maximum at about 420 nm, by excitation at 300 nm, due to the presence of polyenes, likely formed by PVC photodehydrochlorination. In PVC films, containing cerium complex, the HCl photoproduct underwent substitution of acac −, with the formation of CeCl 3 and Hacac, detected by XPS and FTIR, respectively. Thus, these films exhibited the luminescence emissions of the cerium chloride at about 360 nm and that of the polyenes at 420 nm, that was evidenced well by excitation at 260 and 300 nm, respectively. The film luminescence appeared after an induction period which was a function of the Ce(acac) 3 percentage and which was different for the two emitting species, as resulted by deconvolution of the luminescence band. The film irradiation by using a mask resulted in direct photopatterning. The luminescence emission occurred exclusively from directly irradiated zones. Thus no reaction occurred for the migration of reactive species. The FTIR analysis of the films, before and after sufficient irradiation to obtain luminescence, did not evidence significant changes in the chemical structure of the polymer and in the surface properties. Thus, this method can be used to provide PVC with luminescence without damaging side effect.