UV-blue Light Research Articles

Facile solution-precipitation assisted synthesis and luminescence property of greenish-yellow emitting Ca6Ba(PO4)4O:Eu2+ phosphor

Greenish-yellow emitting microcrystalline Ca6Ba(PO4)4O:Eu2+ phosphor was successfully prepared by a solution-precipitation assisted high temperature reaction method. Phase structure, morphology and/or luminescence properties of the precursor and the as-prepared phosphors were characterized. The phase-pure Ca6Ba(PO4)4O:Eu2+ phosphors were obtained with smooth grain surface and particle size of 2–8μm. Ca6Ba(PO4)4O:Eu2+ exhibits bright greenish-yellow color emission with its maximum at 540nm upon UV-blue light excitation. The maximum position of the broad emission band is independent on the calcination temperature. The emission intensity increases with increasing calcination temperature due to improved crystallinity. Besides, the presence of two Eu2+ emission centers in the Ca6Ba(PO4)4O crystal lattice was confirmed and the coordination effects are considered concerning the roles of isolated O atoms and those from the PO4 tetrahedra.

Low-Temperature Preparation of Ag-Doped ZnO Nanowire Arrays, DFT Study, and Application to Light-Emitting Diode.

Doping ZnO nanowires (NWs) by group IB elements is an important challenge for integrating nanostructures into functional devices with better and tuned performances. The growth of Ag-doped ZnO NWs by electrodeposition at 90 °C using a chloride bath and molecular oxygen precursor is reported. Ag acts as an electrocatalyst for the deposition and influences the nucleation and growth of the structures. The silver atomic concentration in the wires is controlled by the additive concentration in the deposition bath and a content up to 3.7 atomic % is reported. XRD analysis shows that the integration of silver enlarges the lattice parameters of ZnO. The optical measurements also show that the direct optical bandgap of ZnO is reduced by silver doping. The bandgap shift and lattice expansion are explained by first principle calculations using the density functional theory (DFT) on the silver impurity integration as an interstitial (Ag(i)) and as a substitute of zinc atom (Ag(Zn)) in the crystal lattice. They notably indicate that Ag(Zn) doping forms an impurity band because of Ag 4d and O 2p orbital interactions, shifting the Fermi level toward the valence band. At least, Ag-doped ZnO vertically aligned nanowire arrays have been epitaxially grown on GaN(001) substrate. The heterostructure has been inserted in a light emitting device. UV-blue light emission has been achieved with a low emission threshold of 5 V and a tunable red-shifted emission spectrum related to the bandgap reduction induced by silver doping of the ZnO emitter material.

Brilliant IR Reflecting Yellow Colorants in Rare Earth Double Molybdate Substituted BiVO4 Solid Solutions for Energy Saving Applications

Brilliant IR reflecting yellow colorants are developed in rare earth double molybdate substituted BiVO4 solid solutions. Li0.10RE0.10Bi0.8Mo0.2V0.8O4 (RE = La, Pr, Sm, Gd, Tb, Dy, Y, Yb and Lu) pigments are prepared by a conventional solid-state reaction route and their optical, structural and morphological properties are analyzed. X-ray diffraction analysis confirms the tetragonal scheelite phase formation in the series. These pigments have a strong optical absorption in the UV-blue light wavelength region. CIE LAB color analysis shows that different hues of yellow shades are obtained in these solid solutions. The color characteristics are comparable to commercial BiVO4 pigment. Incorporation of double rare earth molybdates of La, Gd, Tb, Y and Lu into BiVO4 results in nontoxic IR reflecting cool pigments. The applicability of the developed pigment was tested on a concrete cement surface as well as on a metal panel. These pigments are composed of less toxic elements that make them favorable for energy sa...

Ba3Si6O12N2:Eu2+ green-emitting phosphor for white light emitting diodes: Luminescent properties optimization and crystal structure analysis

The Eu2+-doped Ba3Si6O12N2 green phosphor was synthesized by high temperature solid state method (twice sintered). It could be efficiently excited by UV–blue light (280–500nm) and showed a single intense broadband emission (470–625nm). The influence of sintering times on emission spectra of prepared Ba3Si6O12N2:0.2Eu2+ was discussed. It was a useful way to improve the luminescent property of phosphors materials by twice sintered. In addition, extending soaking time was also an effective approach to improve the luminescent property of phosphors materials in conventional solid-state reaction method. The effect of the crystal structure of Ba3Si6O12N2 and the concentration of the doped-Eu2+ in Ba3Si6O12N2:Eu2+ on the photoluminescence (PL) were also investigated. The phosphors have concentration quenching effect at x=0.15 and a systematic red-shift in emission wavelength with the increase of Eu2+ concentration. The result reveals that Ba3Si6O12N2:Eu2+ is a potential green-emitting phosphor for white LEDs.

Optimization and temperature-dependent photoluminescence properties of yellow–orange emitting Sr1.99−x−yCaxMy(Si1−yZy)O4: 0.01Eu2+ (M = Y3+, K+, Z = Al3+, P5+) phosphors for white light-emitting diodes

The yellow–orange phosphors Sr1.99−x−yCaxMySi1−yZyO4: 0.01Eu2+ (M=Y3+, K+, Z=Al3+, P5+, 0⩽x⩽0.9, 0⩽y⩽0.01) were synthesized by the solid state reaction. X-ray diffraction and photoluminescence spectra were utilized to characterize the samples. The results indicate that the phosphors can be efficiently excited by the UV–blue light and show a broad band emission from about 425 to 700nm. Ca2+ plays an important role in the red-shift of the emission band in Sr1.99−xCaxSiO4: 0.01Eu2+. When the Ca2+ concentration x=0.7, the emission peak under the excitation of 450nm reaches a maximum at about 600nm, which implies that the samples Sr1.99−xCaxSiO4: 0.01Eu2+ could serve as a red phosphor for the blue LEDs. The trace doping of Al3+ and P5+ with Y3+ and K+ as charge compensation significantly enhances the emission intensities of Sr1.29Ca0.7SiO4: 0.01Eu2+. In addition, thermal properties of typical samples are also carefully investigated.

Identification of skin lesions through aminolaevulinic acid-mediated photodynamic detection

Non-melanoma skin cancer is the most common cancer lesion worldwide. In Brazil, it represents 95% of all skin cancer lesions, and 25% of all tumor types. Early diagnosis allows treatment at initial stages of the disease, improving patient's prognosis. Thus, it is of great importance the development of techniques to aid diagnosis, such as marked fluorescence, which we propose here for early detection of skin cancer lesions. In this study, we use a photosensitive substance, aminolaevulinic acid (ALA), as biomarkers, and analyze its in situ fluorescence response to light excitation. The use of ALA as a biomarker precursor is interesting because it shows selectivity for protoporphyrin IX production/concentration in abnormal cells. Protoporphyrin IX shows high fluorescence yield when excited with UV-blue light. In this study, ALA solutions (at 5% and 10% concentrations) were applied to malignant (basal cell carcinoma) and potentially malignant skin lesions (actinic and seborrheic keratoses), aiming to investigate our ability in detecting and distinguishing them by using this technique. At regular time intervals (15, 30, 45 and 60min), fluorescence images were collected with a prototype system for widefield fluorescence imaging. ALA has provided a marked fluorescence that allowed significant discrimination of normal and tumor. Potentially malignant and benign lesions were all well-identified by their autofluorescence; photodynamic detection did not improve diagnostics. This technique also provided a better delineation of the lesion margins, which is very important for an effective treatment of malignant, potentially malignant and benign skin lesions.

Luminescence properties of Ba3Si6O9N4:Eu2+ green-emitting phosphors for white LEDs

A green-emitting phosphor, Eu2+-activated Ba3Si6O9N4 phosphor, was synthesized by a conventional solid state reaction method. X-ray diffraction patterns showed that the synthesized phosphor sintered at 1300°C for 6h was a Ba3Si6O9N4 pure phase. It could be efficiently excited by UV–blue light (280–500nm) and showed a single intense broad emission band (470–625nm). Suitable excitation range makes it match well with the emission of near-UV or blue LEDs. Concentration quenching of the doped-Eu2+ ions occurred at x=0.15, and the critical distance is calculated to be about 1.807nm by theory of energy transfer. The result indicates that Ba3Si6O9N4:Eu2+ is a promising green-emitting phosphor for white LEDs.

Enhanced luminescence of Ba3Si6O9N4:Eu2+ phosphors by codoping with Ce3+, Mn2+, and Dy3+ ions

A novel phosphor Ba3Si6O9N4 doped with Eu and M (M=Ce3+, Mn2+ and Dy3+) has been synthesized by a solid state reaction at 1350°C for 6h under 90%N2/10%H2 atmosphere. It could be efficiently excited by UV–blue light (280–500nm) and showed a single intense broadband emission (470–625nm). Suitable excitation range make it match well with the emission of near-UV LEDs or blue LEDs. It was found that the luminescence intensity of the Ba3Si6O9N4:Eu2+ phosphors can be efficiently enhanced by codoping with M. The addition of M in Ba3Si6O9N4:Eu2+ remarkably enhances the luminescent intensity by the factor of 198%, 166% and 188% for Ce3+, Mn2+ and Dy3+, respectively. The Ba3Si6O9N4:Eu2+ phosphor has potential application as a phosphor for white light-emitting diodes.

Synthesis of a White-Light-Emitting ZnSe:Mn Nanocrystal via Thermal Decomposition Reaction of Organometallic Precursors

Low-dimensional nanosized semiconductor materials, such as quantum dots, have attracted considerable interest in the past decade. Due to their size-dependent physical and optical properties, these nanosized semiconductor materials offer various technological applications in photoelectronic devices. Among the II-VI semiconductor materials, zinc selenide (ZnSe) is of special interest due to its intense UV blue light emission at 460 nm wavelength with a band gap of 2.7 eV, which has not been observed in other well-known semiconductor materials, such as CdS and CdSe. In addition, it has been reported that when the surface of ZnSe is passivated by another semiconductor nanocrystal layer such as ZnS, a ZnSe/ZnS core shell quantum dot can be formed, and the quantum yield of the ZnSe/ZnS quantum dot is much higher (about 20 times) than that of bare ZnSe nanocrystallite. The preparation method of ZnSe or ZnSe/ZnS quantum dot often includes a thermal decomposition reaction of organometallic precursors in a hot coordinating organic solvent such as trioctylphosphineoxide (TOPO), leading to a hydrophobic surface on the resulting nanocrystal. Previously, in this lab, water-dispersible ZnSe and ZnSe/ZnS nanocrystals were also prepared by exchanging the hydrophobic nanocrystal surface with polar organic ligands such as mercaptoacetic acid (MAA) and ethylenediaminetetraacetic acid (EDTA) molecules. Manganese-ion doped ZnSe nanocrystals have been prepared in various media. In most cases, emission wavelengths of the ZnSe:Mn nanocrystals were far shifted from that of the undoped ZnSe nanocrystal. They usually emit orangecolored lights (580-600 nm) due to the dopant Mn ions. In this paper we report on the synthesis of Mn ion-doped ZnSe nanocrystal via thermal decomposition reaction from organometallic precursors, and unexpected white light emission from the prepared ZnSe:Mn nanocrystal. Figure 1 presents an HR-TEM image of ZnSe:Mn nanocrystal. In the picture, the measured and calculated average particle size was 3.5 nm. In addition, the appearance of distinct lattice planes in the fringe image with an approximate spacing of 3.4 A suggests that all the solid samples were made of single crystals rather than poly-crystalline aggregate mixtures. An energy dispersive X-ray spectroscopy diagram (EDXS, in Fig. 2) was also obtained to confirm the elemental compositions of the ZnSe:Mn nanocrystal in the solid state. The obtained doping concentration of manganese(II) ions in the ZnSe:Mn nanocrystal was 2.3 atomic %. To determine the doping concentration of Mn ions more precisely, Inductively Coupled Plasma-Atomic Emission Spectrometry (ICPAES) analysis was performed. Three trials of the sample measurements revealed that the average elemental proportion of the Mn ions relative to ZnSe parent crystal was Figure 1. HR-TEM image of ZnSe:Mn nanocrystal, the scale bar represents 5 nm.

Origin of visible photoluminescence from arrays of vertically arranged Si-nanopillars decorated with Si-nanocrystals

Arrays of vertically aligned Si-nanopillars, with average diameters of 100 nm and 5 μm length, have been prepared by wet chemical etching of crystalline silicon in a special manner. Samples with smooth- and porous-walled nanopillars have been studied. In the case of the latter, Si-nanocrystals, passivated with SiOx, decorating the surface of the nanopillars are identified by the means of TEM and FTIR. When excited by UV–blue light, the porous-walled Si-nanopillars are found to have a strong broad visible emission band around 1.8 eV with a nearly perfect Gaussian shape, μs luminescence lifetimes, minor emission polarization and a non-monotonic temperature dependence of luminescence. The Si-nanocrystal surface is found to be responsible for the luminescence. The red-shift of the emission maximum and the luminescence quenching induced by oxidation in UV-ozone confirm this assumption. A model of luminescence involving UV photon absorption by Si-nanocrystals with subsequent exciton radiative recombination on defect sites in SiOx covering Si-nanocrystals has been proposed. Possible applications of the nanopillar arrays are discussed.

Photoluminescence and light reabsorption in SiC quantum dots embedded in binary-polyelectrolyte solid matrix

We report photoluminescence (PL) and light reabsorption in the SiC quantum dots (QDs) embedded in the binary poly(allylamine hydrochloride)-sodium poly(styrene sulfonate) polyelectrolytes solid matrix. The emission maximum wavelength can be tuned over a wide blue-violet spectral region indicating a PL origin of quantum confinement. The emission maximum exhibits a red shift with increasing concentration of the QDs in the polyelectrolytes matrix. The analysis shows that this shift stems from reabsorption of PL of smaller SiC QDs by larger ones in the matrix. We find that deposition of Ag nanoparticles on the surface of the solid matrix can dramatically reduce light reabsorption owing to surface plasmon-induced concentration of incident light. Additionally, the PL intensity was enhanced by a factor of 1.4. Our results open the possibility of the SiC QDs-based solid blue-UV light emitters for applications in full-solid-state lighting and display.

UV-blue photoluminescence from close-packed SiC nanocrystal film

We observed stable photoluminescence from close-packed cubic SiC nanocrystals that are self-assembled into thin solid film. The peak wavelength shifts from blue to near UV with increasing excitation energy and follows well the quantum-confinement effect. The photoluminescence excitation spectrum indicates a 3.47 eV bandgap corresponding to a particle size of 2.3 nm. The nanocrystal film shows triple-exponential photoluminescence decay with lifetimes of 2.3, 8.5, and 36.9 ns. The results open the possibility of the solid state UV-blue light emitting by use of the SiC nanocrystals in photonics and photonics/electronics integration.

Green Eu 2+-doped Ba 3Si 6O 12N 2 phosphor for white light-emitting diodes: Synthesis, characterization and theoretical simulation

The Eu 2+-doped Ba 3Si 6O 12N 2 green phosphor (Eu x Ba 3− x Si 6O 12N 2) was synthesized by a conventional solid state reaction method. It could be efficiently excited by UV-blue light (250–470 nm) and shows a single intense broadband emission (480–580 nm). The phosphor has a concentration quenching effect at x=0.20 and a systematic red-shift in emission wavelength with increasing Eu 2+ concentration. High quantum efficiency and suitable excitation range make it match well with the emission of near-UV LEDs or blue LEDs. First-principles calculations indicate that Ba 3Si 6O 12N 2:Eu 2+ phosphor exhibits a direct band gap, and low band energy dispersion, leading to a high luminescence intensity. The origin of the experimental absorption peaks is clearly identified based on the analysis of the density of states (DOS) and absorption spectra. The photoluminescence properties are related to the transition between 4f levels of Eu and 5d levels of both Eu and Ba atoms. The 5d energy level of Ba plays an important role in the photoluminescence of Ba 3Si 6O 12N 2:Eu 2+ phosphor. The high quantum efficiency and long-wavelength excitation are mainly attributed to the existence of Ba atoms. Our results give a new explanation of photoluminescence properties and could direct future designation of novel phosphors for white light LED.

Atomic Force Microscopy Study of Nano-Physiological Response of Ladybird Beetles to Photostimuli

BackgroundInsects are of interest not only as the most numerous and diverse group of animals but also as highly efficient bio-machines varying greatly in size. They are the main human competitors for crop, can transmit various diseases, etc. However, little study of insects with modern nanotechnology tools has been done.Methodology/Principal FindingsHere we applied an atomic force microscopy (AFM) method to study stimulation of ladybird beetles with light. This method allows for measuring of the internal physiological responses of insects by recording surface oscillations in different parts of the insect at sub-nanometer amplitude level and sub-millisecond time. Specifically, we studied the sensitivity of ladybird beetles to light of different wavelengths. We demonstrated previously unknown blindness of ladybird beetles to emerald color (∼500nm) light, while being able to see UV-blue and green light. Furthermore, we showed how one could study the speed of the beetle adaptation to repetitive flashing light and its relaxation back to the initial stage.ConclusionsThe results show the potential of the method in studying insects. We see this research as a part of what might be a new emerging area of “nanophysiology” of insects.

Synthesis, growth mechanism, photoluminescence and field emission properties of metal–semiconductor Zn–ZnO core–shell microcactuses

Metal–semiconductor Zn–ZnO core–shell microcactuses have been synthesized on Si substrate by simple thermal evaporation and condensation route using NH 3 as carrier gas at 600 °C under ambient pressure. Microcactuses with average size of 65–75 μm are composed of hollow microspheres with high density single crystalline ZnO rods. The structure, composition and morphology of the product were characterized by X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS), scanning electron microscope (SEM), transmission electron microscopy (TEM) and selected area electron diffraction (SAED). A vapor–liquid–solid (VLS) based growth mechanism was proposed for the formation of Zn–ZnO core–shell microcactuses. Room temperature photoluminescence (PL) investigations revealed a strong and broad blue emission band at 441 nm associated with a weak ultraviolet (UV) peak at 374 nm. This blue emission (BE) is different from usually reported green/yellow-green emission from Zn–ZnO or ZnO structures. The field emission (FE) measurements exhibited moderate values of turn-on and threshold fields compared with reported large field emissions for other materials. These studies indicate the promise of Zn–ZnO core–shell microcactuses for the applications in UV-blue light display and field emission microelectronic devices.

Nanoparticle Self-Lighting Photodynamic Therapy for Cancer Treatment

Photodynamic therapy (PDT) has been designated as a "promising new modality in the treatment of cancer" since the early 1980s. Light must be delivered in order to activate photodynamic therapy. Most photosensitizers have strong absorption in the ultraviolet (UV)-blue range, therefore, UV-blue light is needed for their activation. Unfortunately, UV-blue light has minimal penetration into tissue and its application for in vivo activation is a problem. To solve the problem and enhance the PDT treatment for deep cancers, we introduce new PDT systems in which the light is generated by afterglow nanoparticles with attached photosensitizers. When the nanoparticle-photosensitizer conjugates are targeted to tumor, the light from afterglow nanoparticles will activate the photosensitizers for photodynamic therapy. Therefore, no external light is required for treatment. More importantly, it can be used to treat deep tumor such as breast cancer because the light source is attached to the photosensitizers and are delivered to the tumor cells all together. This new modality is refereed as Nanoparticle Self-Lighting Photodynamic Therapy (NSLPDT).

The epitaxial growth of ZnO nanowires for optical devices by a modified thermal evaporation method

The epitaxial growth of ZnO nanowires over ZnO thin film deposited on silicon substrates was carried out using a modified thermal evaporation method. The precursor, which consisted of 10–30 wt.% zinc nitrate loaded over activated carbon, was prepared specifically for this study. The loading amount of zinc nitrate was varied to control the length and diameter of the ZnO nanowires. X-ray diffraction patterns confirmed that the ZnO nanowires grown on the silicon substrates were composed of typical single-crystalline ZnO. The single-crystal ZnO nanowires synthesized in this study were also studied by photoluminescence spectroscopy, and emitted intense blue UV light at around 380 nm.

Characteristics of Dielectrophoretically Aligned UV-Blue GaN Nanowire LEDs

This is a report on the characteristics of UV-blue light emitting diodes (LEDs) containing homojunction gallium nitride (GaN) nanowires (NWs). These LEDs were prepared by the dielectrophoresis assisted assembly deposition (DAAD) method. The incorporation of an additional silicon dioxide (SiO2) and a Au capping metal layer was found to improve the electrical and optical properties of the DAAD-prepared GaN NW LEDs. These LEDs exhibited a parasitic series resistance of 120-180 komega with a sharp turn-on forward voltage of 3.4-4.0 V and had as low as approximately approximately 7 x 10(-7) A of leakage current for a reverse bias of -10 V. Typical electroluminescence (EL) spectra, observed from these LEDs under a forward bias, had a broad ultraviolet (UV)-blue emission with a wavelength of 388-422 nm. These LEDs could be seen with the naked eye. We concluded that the high-brightness EL spectra resulted from the enhancement of the carrier injection due to the size effect of the n-GaN nanowires on the p-GaN substrate.

Sintering Effects of ZnO Nanopowders Synthesized by Solution–Combustion Method

ZnO nanopowders with an average grain size of 30nm were prepared by a solution combustion method with various sintering temperatures (100-1000o C). The optical properties of the ZnO nanopowders were investigated in the temperature range of 14-150K in air. Based on the results of XRD, Photoluminescence, and excitation spectra, the ZnO powders showed wurtzite single phase with UV-blue light emitting. Deep level defects such as oxygen vacancies and Zn interstitials were not observed from the ZnO powders sintered up to 700 o C. However, these defects were observed as the sintering temperature was increased up to 900 o C. This seems to be due to the generation of oxygen vacancies and zinc interstitials. Furthermore, the blue light intensity was doubled when the synthesized ZnO powders were sintered at 700 o C. This might be very useful for high efficiency photocatalysts and the blue light emitting phosphors of displays such as field emission displays and plasma display panels.

Second-harmonic generation of 405-nm light using periodically poled KTiOPO4 pumped by external-cavity laser diode with double grating feedback

A frequency-doubled laser diode system for generation of blue–UV light is described. The system is based on an external-cavity high-power laser diode with double feedback from the zeroth and the first orders of a diffraction grating. Light at 405 nm is generated in a single-pass configuration using periodically poled KTiOPO4. We show that the double grating feedback improves the second harmonic conversion efficiency by several orders of magnitude as compared to the freely running laser. The conversion efficiency may be improved further such that higher second-harmonic powers may be generated.