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CdSe cores with rod (an aspect ratio of 1.8, d-5 nm) and spherical (an aspect ratio of 1, d-5 nm) morphologies were fabricated by two kinds of organic approaches through adjusting growth processes. Because of large difference of size and morphology, two kinds of cores revealed different absorption spectra. However, these cores exhibited almost same photoluminescence (PL) spectra with a red-emitting PL peak of around 625 nm. This is ascribed that they have a similar size in diameter. A graded Cd(x)Zn1-xS shell of larger band gap was grown around CdSe rods and spheres using oleic acid as a capping agent. Based on the growth kinetics of CdS and ZnS, interfacial segregation was created to preferentially deposit CdS near the core, providing relaxation of the strain at the core/shell interface. For spherical CdSe cores, the homogeneous deposition of the Cd(x)Zn1-xS shell created spherical core/shell nanocrystals (NCs) with a size of 7.1 nm in diameter. In the case of using CdSe cores with rod morphology, the anisotropic aggregation behaviors of CdS monomers on CdSe rods led to the size (approximately 10 nm in diameter) of spherical CdSe/Cd(x)Zn1-xS core/shell NCs with a small difference to the length of the CdSe rod (approximately 8.9 nm). The resulting spherical core/shell NCs created by the rod and spherical cores exhibited almost same PL peak wavelength (652 and 653 nm for using rod and spherical cores, respectively), high PL efficiency up to 50%, and narrow PL spectra (36 and 28 nm of full with at half maximum of PL spectra for the core/shell NCs with CdSe spheres and rods, respectively). These core/shell NCs provide an opportunity for the study of the evolution of PL properties as the shape of semiconductor NCs.

ABSTRACT In this study, a series of LaNbTiO6:RE3+ (RE = Tb, Dy, Ho) down-converting phosphors were synthesized using a modified sol-gel combustion method, and their photoluminescence (PL) properties were investigated as a function of activator concentration and annealing temperature. The resultant particles were characterized using X-ray diffraction, transmission electron microscopy, scanning electron microscopy, UV/Vis diffuse reflectance spectroscopy and PL spectra. The highly crystalline LaNbTiO6:RE3+ (RE = Tb, Dy, Ho) phosphors with an average size of 200-300 nm obtained at 1100°C have an orthorhombic aeschynite-type structure and exhibit the highest luminescent intensity in our study range. The emission spectra of LaNbTiO6:RE3+ (RE = Tb, Dy, Ho) phosphors under excitations at UV/blue sources are mainly composed of characteristic peaks arising from the f-f transitions of RE3+, including 489 nm (5D4 → 7F6) and 545 nm (5D4 → 7F5) for Tb3+, 476 and 482 nm (4F9/2 → 6H15/2) and 571 nm (4F9/2 → 6H13/2) for Dy3+, and 545 nm (5F4 + 5S2 → 5I8) for Ho3+, respectively. The luminescent mechanisms were further investigated. It can be expected that these phosphors are of intense interest and potential importance for many optical applications. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

CdTe0.5Se0.5/Cd0.5Zn0.5S core/shell quantum dots (QDs) with a tunable photoluminescence (PL) range from yellow to dark red (up to a PL peak wavelength of 683 nm) were fabricated using various reaction systems. The core/shell QDs created in the reaction solution of trioctylamine (TOA) and oleic acid (OA) at 300 °C exhibited narrow PL spectra and a related low PL efficiency (38%). In contrast, the core/shell QDs prepared in the solution of 1-octadecene (ODE) and hexadecylamine (HDA) at 200 °C revealed a high PL efficiency (70%) and broad PL spectra. This phenomenon is ascribed that the precursor of Cd, reaction temperature, solvents, and ligands affected the formation process of the shell. The slow growth rate of the shell in the solution of ODE and HDA made QDs with a high PL efficiency. Metal acetate salts without reaction with HDA led to the core/shell QDs with a broad size distribution. [ABSTRACT FROM AUTHOR]

Abstract: A sol–gel approach including partially removing capping agents, depositing SiO2 monomers, and growing a SiO2 shell was developed to generate a bio-compatible functionalization on CdTe quantum dots (QDs). The QDs retained their high photoluminescence (PL) efficiency after coating with a SiO2 shell (22.5%) by controlling the surface state of the QDs to decrease PL degradation during a sol–gel preparation. Furthermore, the CdTe QDs with a SiO2 shell were conjugated with IgG using 3-sulfo-N-hydroxysuccinimide or streptavidin–maleimide as linkers. The biotin–streptavidin linker resulted in a high PL efficiency retained (only ∼23% lower than the initial value of the QDs), which is crucial for bio-applications. [Copyright &y& Elsevier]

Abstract: Eu3+ doped yttrium zirconate ((Y1−x Eu x )2Zr2O7) nanocrystals were synthesized by a simple sol–gel combustion method, and characterized by X-ray diffractometry (XRD), transmission electron microscopy (TEM), UV–vis absorption and photoluminescence (PL) spectroscopy. Photoluminescence spectra of (Y1−x Eu x )2Zr2O7 (x =0.005–0.15) show multi-peaks corresponding to the f–f transitions 5 D 0–7 F J (J =1, 2, 3, 4 and 5) of Eu3+. Both the 5 D 0–7 F 1 magnetic dipole transition and the 5 D 0–7 F 2 electric dipole transition are intense and the 5 D 0–7 F 2 emissions split into several peaks depending on the doping concentration. The fine structure of the PL spectra is related to host lattice and the local situation around Eu3+. [Copyright &y& Elsevier]

Abstract: A series of rare-earth zirconate RE2Zr2O7 nanocrystals (RE=La, Nd, Eu and Y) were prepared by a simple combustion method. These compounds possess either a pyrochlore structure (P-RE2Zr2O7) or a defect fluorite structure (F-RE2Zr2O7), which depends on the ionic radius of RE3+. The photoluminescence (PL) property of the as-prepared RE2Zr2O7 nanocrystals was studied, and the observed emissions in the UV and visible range were attributed to different transition mechanisms for RE2Zr2O7 with different RE ion. A PL mechanism has been proposed, associated with the transition between the valence band and a mid-gap state related to oxygen vacancies. Divalent Pb ions were introduced into RE2Zr2O7 nanocrystals and the luminescence of the Pb2+-doped samples was also recorded for comparison. The PL property of RE2Zr2O7 was found to be intimately related to their intrinsic defect structure, and PL was thought as a new method to estimate the degree of disorder in the A2B2O7 structure (from pyrochlore structure to defect fluorite structure). [Copyright &y& Elsevier]

CdSe/Cd x Zn 1-x S core-shell quantum dots capped with oleic acid have been encapsulated into SiO 2 nanospheres by a modified reverse microemulsion method. As an effective approach to convert quantum dots with nonpolar capping agent into hydrophilic and biocompatible ones, silica coating technology is limited by the inevitable luminescence degradation during the silication process. Cd x Zn 1-x S shell involved to protect CdSe core quantum dots from luminescence quenching was found to be quite helpful to restrain the luminescence degradation during the silica coating process. The luminescent intensity has been highly enhanced by controlling the thickness of Cd x Zn 1-x S shells. Luminescence quenching has also been observed when the as-prepared silica coated quantum dots were transferred from the reaction solution into different solvent. According to the time-resolved luminescence and stability examination, the micro channels in the SiO 2 shells should be responsible for the degradation. Polyethylene glycol has thus been introduced to block the channel, resulting in a product with much higher emission efficiency, which performed well as a fluorescent labeling probe for MCF-7 cells. • The Cd x Zn 1-x S shell plays a significant role in keeping PLQY during SiO 2 coating process. • The micro channels in the SiO 2 shells are responsible for the solvent-related PL quenching. • PEG modified CdSe/Cd x Zn 1-x S@SiO 2 nanospheres applied as a fluorescent labelling probe for MCF-7 cells. [ABSTRACT FROM AUTHOR]

Abstract: Eu3+-doped SrZrO3 nanocrystals with a size of about 10nm were synthesized by a simple sol–gel combustion method, and characterized by X-ray diffraction, transmission electron microscopy and photoluminescence spectroscopy. The nanocrystalline intend to assemble to a porous morphology. Both intrinsic defects related and activator luminescence were observed. The red emission of Eu3+ is intense and the spectra show a minor difference with different excitation wavelengths. [Copyright &y& Elsevier]

Abstract: Strontium zirconate (SrZrO3) nanocrystals with an average size of 19nm were prepared by a simple sol–gel combustion method. The combustion reaction was induced just at 300°C. Under conventional UV excitation, the SrZrO3 nanocrystals showed a strong violet emission at 400nm. The number of luminescent zirconates is small, especially of those with visible emission. The novel luminescence was tentatively attributed to the existence of defect levels. Further study was carried out corresponding the size dependence of the luminescence property. [Copyright &y& Elsevier]

The polyvinylpyrrolidone (PVP) hybrid luminescent micro-/nanofibers doped with the novel hybrid SiO 2 -coated CdTe nanocrystals (HS-CdTe NCs) have been fabricated for the first time via the electrospinning technique. The morphologies and photoluminescence (PL) emissions of HS-CdTe/PVP micro-/nanofibers prepared by doping the HS-CdTe NCs with the different PL peak wavelength (571, 616, and 643 nm) in PVP fibers were investigated by optical and PL microscope. The results revealed that all the HS-CdTe/PVP hybrid fibers showed an ultralong length for several hundreds of micrometers and a relatively uniform diameter of 1000 ∼ 1200 nm. The hybrid fibers displayed a wavelength-tunable PL emission, determining by the PL of doped HS-CdTe NCs. Moreover, similar to the original PL properties of HS-CdTe NCs before the electrospinning, the HS-CdTe/PVP fibers also showed a series of superior PL properties, such as narrow and symmetry PL spectrum, high, and uniform brightness. For comparison purpose, we also prepared three CdTe/PVP hybrid fibers by doping the 553 nm, 600 nm, and 633 nm PL-emitting CdTe NCs respectively in PVP electrospinning fibers. The characterization results showed that, the obtained three CdTe/PVP hybrid fibers had a basically satisfactory micro-/nanofiber morphology with a long length and relatively uniform diameter, but all the fibers exhibited very weak PL emissions. The enormous contrast in PL properties between HS-CdTe/PVP and CdTe/PVP fibers should mainly be ascribed to the different connection modes of ligands with the NCs and the passivation effect of inert hybrid silica shell on HS-CdTe. It is hopeful that the high luminescent HS-CdTe/PVP micro-/nanofibers with the tunable PL peak wavelength would be a good candidate in the optical sensor, light-emitting devices (LEDs), nanometer-scale waveguides, and the other related photonic materials. [ABSTRACT FROM AUTHOR]

Abstract: Undoped and Eu3+-activated Bi3TiNbO9 (BTNO) nanophosphors have been successfully synthesized by sol–gel combustion method. The effects of thermal annealing on the phase structure and crystallinity, morphology and UV–vis absorption of BTNO particles were investigated. Photoluminescence (PL) properties show that a broad blue emission was detected for BTNO nanoparticles, and the characteristic Eu3+ ion 5D0 → 7F J (J =1, 2, 3, 4) transitions were observed for the doped samples. Further investigation illuminates that the Eu3+ ions substituted for Bi3+ ions at A site in the pseudo-perovskite layers. It can be confirmed from high bright fluorescence image and short decay time that the novel orange-red phosphor has the potential applications in luminescence devices. [Copyright &y& Elsevier]

Abstract: Nb2O5 nanorods have been prepared using water/ethanol media. The samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), UV–visible absorption and photoluminescence spectroscopy. The as-prepared Nb2O5 nanorods appeared to be single pseudohexagonal (TT-Nb2O5) phase. From the photoluminescence spectrum, two emission bands at 407 and 496nm, respectively, were observed. The origin of the luminescence was discussed in detail. [Copyright &y& Elsevier]

Abstract: A novel red luminescent material Li0.9Y0.9Zr0.1O2 doped with trivalent europium ions and dysprosium ions was synthesized by solution–combustion method. X-ray diffractometry, transmission electron microscopy and optical spectroscopy were used to valuate the crystallinity, the morphological characterization and the optical properties of the products. The results showed that combustion at 800°C was enough to obtain highly crystalline and phase-pure samples. Photoluminescence spectra of Li0.9Y(0.9−x−y)Zr0.1O2:Eu x 3+,Dy y 3+ samples indicated the dominant red emissions (613nm) at a single-wavelength ultraviolet excitation (395nm) due to 5D0 → 7F2 transition. The relation between the luminescence intensity and dopant concentration was also discussed. [Copyright &y& Elsevier]

Abstract: Three-dimensional reticular-structured luminescence SrAl2O4:Eu,Dy powders were prepared by refluxing- and sonication-combustion synthesis without using any surfactant for the first time and were characterized using X-ray diffraction, transmission electron microscopy, scanning electron microscopy. All the samples have a very porous, open and spongelike morphology with fractal properties. The excitation and emission spectra of the products have been measured by Edinburgh FLS920 at room temperature. The new formation-mechanism of the three-dimensional reticular-structure was proposed in this article. [Copyright &y& Elsevier]

Abstract: Pure and Mn-doped SrNb2O6 nanoparticles have been prepared by sol–gel combustion method using citric acid as fuel and complexing agent and nitrates as oxidants at a relatively low temperature compared to solid-state reaction method. X-ray diffraction (XRD) patterns of the pure SrNb2O6 samples show that the SrNb2O6 nanoparticles exhibited orthorhombic phase. Photoluminescence (PL) properties of all the undoped and Mn-doped samples were studied in detail. For the pure SrNb2O6 samples, a strong blue emission band centered at 442nm and two weak emission bands centered at 524nm and 626nm, respectively, can be observed. For the Mn-doped SrNb2O6 samples, no emission from Mn2+ was observed while the blue emission intensity of SrNb2O6 varied with the Mn-doping concentration. This novel PL characteristic of the doped samples was explained. [Copyright &y& Elsevier]

Abstract: Pure and Dy3+-doped NiNb2O6 nanoparticles have been prepared by a sol–gel combustion method using citric acid as fuel and complexing agent and nitrates as oxidants at a relatively low temperature compared to solid-state reaction method. The photoluminescence properties of these NiNb2O6 nanoparticles were studied in detail. For the pure NiNb2O6 nanoparticles, a blue emission band centered at 445nm is observed. For NiNb2O6:Dy3+ nanoparticles, no characteristic luminescence of Dy3+ can be observed while the host blue emission enhances. It is suggested that energy transfer from Dy3+ to niobate groups maybe occurs. [Copyright &y& Elsevier]

Abstract: Eu2+, R3+ co-doped alkaline earth aluminates MAl2O4: Eu2+, R3+ (M=Sr, Ba and Ca; R=Dy, Nd and La) nanoparticles with high brightness and long afterglow have been prepared by solution-combustion synthesis at 600°C without a post-annealing process for the first time. The morphologies and the phase structures of the products have been characterized by transmission electron microscopy and X-ray diffraction. The excitation and emission spectra of the products have been measured by an Edinburgh FLS920 spectrometer at room temperature. The characteristic luminescence of the as-prepared sample has been evaluated, and the reason why the wavelength changed from yellow-green to blue-green and then to blue-purple in visible range when the composition changed from SrAl2O4: Eu2+, Dy3+ to BaAl2O4: Eu2+, Nd3+ and then to CaAl2O4: Eu2+, La3+ has been explained. Furthermore, a new persistent luminescence mechanism was proposed in this article. [Copyright &y& Elsevier]