UV LED Excitation Research Articles

Rare-Earth-Ion (RE3+)-Doped Aluminum and Lanthanum Borates for Mobile-Phone-Interrogated Luminescent Markers

In this paper, we present the synthesis and luminescent spectra of rare-earth (RE)-doped aluminum and lanthanum borates intended to serve as narrow excitation–emission band fluorescent markers. We perform a detailed 3D excitation–emission matrix (EEM) analysis of their spectra, compare the measurements from both standard and mobile phone spectrometers, and outline the basic differences and advantages of each method. While smartphones have a different and non-uniform spectral response compared to standard spectrometers, it is shown that they offer a number of advantages such as contactless interrogation, efficient suppression of the UV excitation light, and simultaneous spectral analysis of spatially arranged arrays of fluorescent markers. The basic emission peaks have been observed and their corresponding electronic transitions identified. The obtained results show that the rare-earth-doped La and Al borates feature excitation–emission bandwidths as low 15 nm/12 nm, which makes them particularly appropriate for use as luminescent markers with UV LED excitation and smartphone interrogation.

Compact Fluorescence Spectrometer with Built-In In-Line Calibration: Application to Detect Dissolved Organic Matter in Water.

Fluorescence spectrometer (FS) is widely used for component analysis because each fluorescing material has its own characteristic spectrum. However, the spectral calibration is complicated and bulky. Herein, an in-line spectral calibration sheet (ISCS) was proposed in which a narrow band-pass filter and a linear variable filter (LVF) were integrated on a metal plate. By moving the ISCS, the transmitted excitation light power (TEP) as well as fluorescence spectrum can be seamlessly scanned, and the TEP can be used for in-line spectral calibration. A compact FS apparatus based on UV-LED excitation, metal capillary (MC) and ISCS was fabricated (i.e., ISCS-FS), and the ISCS-FS apparatus was applied to detect sodium humate in water. By employing TEP calibration, both the primary inner filter effect (PIFE) and the drift in the optical power of UV-LED can be simultaneously compensated. The linear correlation coefficient of signal concentration was improved from 0.89 to 0.998, and the relative standard deviation (RSD) of replicated detection was improved from 3 to 0.7%. A detection limit of concentration (DLC) of 1.3 μg/L was realized, which is 15-fold lower than that of a commercial FS apparatus (20 μg/L). The DLC is even comparable with that (0.5-4 μg/L) of commercial total organic carbon (TOC) analyzers, which are bulky and expensive. The linear correlation between the measurement results of ISCS-FS and commercial TOC analyzers can reach a good value of 0.94.

Separation of overlapping fingerprints by principal component analysis and multivariate curve resolution-alternating least squares analysis of hyperspectral imaging data.

Overlapping fingerprints are often found at crime scenes, but only individual fingerprints separated from each other are admissible as evidence in court. Fingerprint components differ slightly among individuals, and thus their fluorescence spectra also differ from each other. Therefore, the separation of overlapping fingerprints using the difference of the fluorescence spectrum was performed with a hyperspectral imager. Hyperspectral data (HSD) of overlapping fingerprints were recorded under UV LED excitation. Principal component analysis (PCA) and multivariate curve resolution-alternating least squares (MCR-ALS) were applied to the HSD to determine the optimal method for obtaining high-contrast images of individual fingerprints. The results suggested that MCR-ALS combined with PCA-based initialization is capable of separating overlapping fingerprints into individual fingerprints. In this study, a method for separating overlapping fingerprints without initial parameters was proposed.

A Bio-Fluorometric Acetone Gas Imaging System for the Dynamic Analysis of Lipid Metabolism in Human Breath

We constructed an imaging system to measure the concentration of acetone gas by acetone reduction using secondary alcohol dehydrogenase (S-ADH). Reduced nicotinamide adenine dinucleotide (NADH) was used as an electron donor, and acetone was imaged by fluorescence detection of the decrease in the autofluorescence of NADH. In this system, S-ADH–immobilized membranes wetted with buffer solution containing NADH were placed in a dark box, and UV-LED excitation sheets and a high-sensitivity camera were installed on both sides of the optical axis to enable loading of acetone gas. A hydrophilic polytetrafluoroethylene (H-PTFE) membrane with low autofluorescence was used as a substrate, and honeycomb-like through-hole structures were fabricated using a CO2 laser device. After loading the enzyme membrane with acetone gas standards, a decrease in fluorescence intensity was observed in accordance with the concentration of acetone gas. The degree of decrease in fluorescence intensity was calculated using image analysis software; it was possible to quantify acetone gas at concentrations of 50–2000 ppb, a range that includes the exhaled breath concentration of acetone in healthy subjects. We applied this imaging system to measure the acetone gas in the air exhaled by a healthy individual during fasting.

Quantitative Assessment of Age-dependent Changes in Porphyrins from Fluorescence Images of Ultraviolet Photography by Image Processing

BackgroundSkin is the first line of defense against harmful external environmental factors. Skin flora living on the skin surface impact skin health and skin disease. Bacteria, form part of the unique and complex skin micro-ecological system. For example, Propionibacterium acnes (P. acnes) is a member of the anaerobic organisms and is involved in the induction of skin acne. It produces porphyrins that absorb ultraviolet light and emit red fluorescence in response. As a result, fluorescence surveillance of the skin can be important in both the diagnosis of skin acne and the evaluation of therapeutic effects. Many different measurement methods for single skin biophysical properties have been reported.. This study focused on the age-dependent changes in porphyrins for normal skin, and developed a novel algorithm to evaluate porphyrins using the fluorescence images by image processing quantitatively. Materials and methodsAn extraction algorithm was proposed for the segmentation of porphyrin fluorescence images in OpenCV. The algorithm consisted primarily of preprocessing, conversion from RGB color space to HSV color space, and classification of fluorescence. There are 3595 healthy Japanese aged 16–85 years enrolled in the study and fluorescence images were acquired from their cheek sites under 375 nm UV-LED excitation. Age-related fluorescence variation was conducted applying the algorithm implemented. ResultsA new extraction algorithm has been proposed with fluorescence image input and three indexes output, including the number of fluorescence, area of fluorescence, and mean intensity of fluorescence. Proposed algorithm was verified by three parameters, the accuracy, sensitivity, and precision, which refer to the ability of algorithm to detect the number of fluorescence correctly and repeatedly. The verification results were 71%, 72%, and 88% respectively, taking a validly fundamental step for skin health record and analysis. Furthermore, large-scale fluorescence image segmentation results revealed that similar trends were coming out for all three indexes in cheek as people get older. All the fluorescence number, area and mean intensity arrived at the highest at 30 years old and fell off since then. ConclusionThe number, area, and fluorescence intensity of porphyrins can be extracted well from fluorescence images with the proposed algorithm in the study, which has the potential to aid in thediagnosis of skin acne and predict skin conditions as an assisted tool. It is implicated that fluorescence status is influenced by age, which rises to the peak around 30 years old for normal cheek's skin.

Thermal Performance of GaN/Si HEMTs Using Near-Bandgap Thermoreflectance Imaging

Superlattice (SL) structures have been used to reduce the stress in the GaN epilayer of high-electron-mobility transistors (HEMTs). This has led to an improvement in their properties such as the breakdown voltage. The increase in thermal resistance associated with these structures, however, causes elevated device temperatures which may outweigh the benefits of this approach. To verify this, the thermal performance of SL structures on HEMTs must, thus, be accurately characterized. Transient thermoreflectance imaging (TTI) is an optical technique that can map the temperature distribution across a surface. For materials, such as gold, TTI shows a high spatial and temporal resolution. Consequently, the technique has been primarily used to monitor the gate metal temperature distribution in HEMTs. The origin of the localized heating in HEMTs, however, is known to be in the active GaN layer and, thus, accurate thermal characterization of the channel is necessary. Using a UV LED excitation source with a wavelength near the bandgap of GaN, TTI of GaN channels in HEMTs is presented and verified by comparing the gate metal temperature. To ensure a strong thermoreflectance signal from the GaN surface, the importance of using an excitation wavelength near the bandgap of the GaN channel is highlighted. The effect of the bandgap on the magnitude and the linearity of the thermoreflectance coefficient is presented and discussed. Overall, the improvements to TTI discussed in this article make the technique an accurate method to measure the temperature distribution in GaN HEMT SL structures.

Luminescent characteristics of Tm3 +/Tb3 +/Eu3 + tri-doped phosphate transparent glass ceramics for white LEDs

Tm3+/Tb3+/Eu3+ tri-doped transparent glass ceramics (GCs) are obtained via melt-quenching technique and subsequent heating of glass with composition of 20Na2O-42ZnO-28P2O5-9B2O3-1Sb2O3 (mol%). XRD and TEM results demonstrate that orthorhombic NaZnPO4 nanocrystals (NCs) are precipitated among the glass matrix. Under 362nm excitation, the color tones of GCs change from light blue (0.3134, 0.3477) to warm white (0.3886, 0.3373) by altering concentration of Eu3+. The energy transfer of Tm3+→Eu3+ and Tb3+→Eu3+ is confirmed by photoluminescence spectra and fluorescence decay curves. The results indicate that the as-prepared Tm3+/Tb3+/Eu3+ co-doped GCs is a potential matrix material for white light-emitting diodes under UV-LED excitation.

High-sensitivity detection of cardiac troponin I with UV LED excitation for use in point-of-care immunoassay.

High-sensitivity cardiac troponin assay development enables determination of biological variation in healthy populations, more accurate interpretation of clinical results and points towards earlier diagnosis and rule-out of acute myocardial infarction. In this paper, we report on preliminary tests of an immunoassay analyzer employing an optimized LED excitation to measure on a standard troponin I and a novel research high-sensitivity troponin I assay. The limit of detection is improved by factor of 5 for standard troponin I and by factor of 3 for a research high-sensitivity troponin I assay, compared to the flash lamp excitation. The obtained limit of detection was 0.22 ng/L measured on plasma with the research high-sensitivity troponin I assay and 1.9 ng/L measured on tris-saline-azide buffer containing bovine serum albumin with the standard troponin I assay. We discuss the optimization of time-resolved detection of lanthanide fluorescence based on the time constants of the system and analyze the background and noise sources in a heterogeneous fluoroimmunoassay. We determine the limiting factors and their impact on the measurement performance. The suggested model can be generally applied to fluoroimmunoassays employing the dry-cup concept.

Enhancing the white light emission of SrAl2O4:Ce3+ phosphors by codoping with Li+ ions

The structural, morphological and luminescent properties of SrAl2O4:Ce3+(SAO:Ce) phosphors doped with Ce3+ concentrations from 0.5at% up to 7at% and synthesized by combustion synthesis are reported. The morphology of the particles changes from coalesced grains (with average size of 121nm) for a cerium concentration of 0.5at% to needle-like shape when the cerium concentration is above 1% (with an average length of 1–2µm). XRD patterns also show a change in the crystalline structure from monoclinic to hexagonal when the Li ion is introduced to improve the luminescent properties. The sample doped with 0.5at% of Ce3+ presents the highest white luminescence. When this sample was codoped with 0.2at% of Li+, there was an increase of 100% in the white light emission. The luminance values of the samples with and without Li+, under UV-LED excitation (365nm commercial Star LED) were 1630cd/m2 and 3760cd/m2, respectively. That is, the luminance enhancement achieved by lithium co-doping was 130%. Thus, our results indicate that Li codoped SrAl2O4:Ce3+ phosphors could be useful for applications in displays and solid state lighting.

White light emission from novel host-sensitized single-phase Y2WO6: Ln3+ (Ln3+=Eu3+, Dy3+) phosphors

A series of Eu3+- or Dy3+-doped and Eu3+/Dy3+ co-doped Y2WO6 in pure phase was synthesized via high-temperature solid-state reaction. X-ray diffraction, diffuse reflection spectra, photoluminescence excitation and emission spectra, the CIE chromaticity coordinates and temperature-dependent emission spectra were exploited to investigate the phosphors. Upon UV excitation at 310nm, efficient energy transfer from the host Y2WO6 to dopant ions in Eu3+ or Dy3+ single-doped samples was demonstrated and those phosphors were suitable for the UV LED excitation. The intense red emission was observed in Y2WO6: Eu3+, and blue and yellow ones were observed in Y2WO6: Dy3+. Concentration quenching in Y2WO6: Dy3+ phosphors could be attributed to the electric dipole-dipole interaction. In Eu3+/Dy3+ co-doped Y2WO6 phosphors energy transfer process only took place from the host to Eu3+/Dy3+ ions and warm white-light emission can be obtained by adjusting the dopant concentrations. The temperature-dependent luminescence indicated Eu3+/Dy3+ co-doped Y2WO6 was thermally stable. Our overall results suggested that Y2WO6: Ln3+ (Ln3+=Eu3+, Dy3+) as warm white-light emitting host-sensitized phosphor might be potentially applied in WLEDs.

Practical implementation, characterization and applications of a multi-colour time-gated luminescence microscope.

Time-gated luminescence microscopy using long-lifetime molecular probes can effectively eliminate autofluorescence to enable high contrast imaging. Here we investigate a new strategy of time-gated imaging for simultaneous visualisation of multiple species of microorganisms stained with long-lived complexes under low-background conditions. This is realized by imaging two pathogenic organisms (Giardia lamblia stained with a red europium probe and Cryptosporidium parvum with a green terbium probe) at UV wavelengths (320–400 nm) through synchronization of a flash lamp with high repetition rate (1 kHz) to a robust time-gating detection unit. This approach provides four times enhancement in signal-to-background ratio over non-time-gated imaging, while the average signal intensity also increases six-fold compared with that under UV LED excitation. The high sensitivity is further confirmed by imaging the single europium-doped Y2O2S nanocrystals (150 nm). We report technical details regarding the time-gating detection unit and demonstrate its compatibility with commercial epi-fluorescence microscopes, providing a valuable and convenient addition to standard laboratory equipment.

Crystallographic and Luminescent Characteristics of New Blue Phosphor (Sr,Ba)Al2Si3O4N4:Eu2+

Recently, nitrides and oxynitrides have received a great deal of attention as phosphor materials for white LED (WLED) lighting application, since these are thermally and mechanically stable owing to a strong lattice consisting of point-shared and/or edge-shared (Si,Al)(N,O)4tetrahedral network. In this paper, new oxynitride-based phosphor materials (Sr,Ba)Al2Si3O4N4:Eu2+ are proposed as the WLED phosphor for near-UV LED excitation. The crystal structure of SrAl2Si3O4N4 is monoclinic system and belongs to space group P21 (No.4) [1]. By using the single phase crystal samples, lattice parameters have been accurately determined as a = 7.2516(5) Å, b = 9.3434(5) Å, c = 10.8761(5) Å, β = 104.489(1)°, V = 713.45(7) Å3 [1]. The substructure in this crystal consists of (Si,Al)(N,O)4 tetrahedra and Sr2+ ions occupy the channel formed from its tetrahedrons. The crystallographic and luminescent characteristics are investigated for the (Sr,Ba)Al2Si3O4N4:Eu2+samples having different Ba content. The (Sr1-xBax)Al2Si3O4N4:Eu2+ phosphor samples were synthesized at 1400 ~ 1700 ¢ªC in N2 at atmospheric pressure for a few hours. SrCO3, BaCO3, Al2O3, Si3N4 and Eu2O3 were used as source materials. The Ba content x was varied from 0 to 1. In all xrange, almost the single crystal phase of the solid solution compound was obtained. Figure 1 shows the photoluminescence (PL) and PL excitation spectra of the SrAl2Si3O4N4:Eu2+ and Bal2Si3O4N4:Eu2+ [2]. The measurements were performed at room temperature under near UV excitation at 405 nm. Both samples show a broad blue luminescence attributed to the 4f65d to 4f7 internal transition in Eu2+ centers. The peak wavelength is 473 nm for the SrAl2Si3O4N4:Eu2+. The wavelength shifts to 465 nm by replacing Sr with Ba. The PL excitation bands lie in UV and near-UV region below 450 nm for both samples. The result indicates that (Sr,Ba)Al2Si3O4N4:Eu2+phosphors are a promising blue phosphor for WLED for near UV-LED excitation. Figure 2 shows dependences of the internal quantum efficiency (I.Q.E.) on the Ba content x. The I.Q.E. drastically increases with increasing x and reaches 0.90 at x = 0.5. The thermal quenching characteristics were investigated. In Fig. 2, the relative PL intensity measured at 200°C to that at 30°C (I200/I30) is shown. The relative intensity increases with increasing xas well as I.Q.E.. From the accurate determination of crystal structure analysis in these samples, it was found that the lattice structure changes from monoclinic to orthorhombic at around x of 0.25. Since the lattice symmetry of orthorhombic crystal is higher than that of monoclinic one, it is considered that the inherent lattice distortion is relaxed by the crystal phase transition, resulting in improvement of luminescent characteristics such as I.Q.E. and thermal quenching. In oxy-nitride materials, MSi2O2N2:Eu2+ (M = Ca, Sr, Ba) phosphor and have been investigated in detail on luminescent characteristics [3,4]. In the reference [3], it is reported that the efficiency of SrSi2O2N2:Eu2+ and BaSi2O2N2:Eu2+ is 91% and 76%, respectively. The crystal structure of Sr0.5Ba0.5Si2O2N2:Eu2+ was determined as triclinic with the space group P1(No.1) [5]. Additionally, the crystal structure of Ba(Si,Al)5(N,O)8 with space group A21ma(No.36) has been reported by W. B. Park et al.. [2] However, the systematic investigation regarding the relations between the space group and luminescent efficiency and thermal quenching characteristics have not been discussed yet. At the meeting, we will discuss the relation with considering the lattice distortion and/or defects, which may strongly affect the I.Q.E. and thermal quenching.

Synthesis and luminescence properties of a novel phosphor Ca2−x/2Si1−xPxO4:Eu2+ for near UV-excited white-light-emitting diodes

A novel green-emitting phosphor, Eu2+-doped Ca2−x/2Si1−xPxO4 (0.25≤x≤0.30), was prepared through a conventional solid- state reaction. X-ray diffraction (XRD), photoluminescence (PL) and decay studies were employed to characterize the sample, which was assigned to P63mc space group in the hexagonal system. The effect of P-doping on the α-Ca2SiO4 was studied and P2O5 broken down by the raw material of (NH4)2HPO4 played an important role in stabilizing α-Ca2SiO4 which can only be stable at high temperature. The XRD patterns of the Ca2−x/2Si1−xPxO4 host were found pure and optimized when the mole fraction of P2O5 was 14.5%. The diffuse reflectance spectra of the Ca1.855Si0.71P0.29O4 and Ca1.845Si0.71P0.29O4:0.01Eu2+ covered the spectral region of 230–400 nm, implying that the phosphor was suitable for UV or near-UV LED excitation. The phosphor could be effectively excited in the near UV region with the maximum at 372 nm. The emission spectrum of the Ca1.845Si0.71P0.29O4:0.01Eu2+ phosphor showed an asymmetrical single intensive band centered at 513 nm, which corresponded to the 4f65d1→4f7 transition of Eu2+. Eu2+ ions might occupy two types of Ca2+ sites in the Ca1.855Si0.71P0.29O4 lattice and form two corresponding emission centers, which led to the asymmetrical emission of Eu2+ in Ca1.855Si0.71P0.29O4. The effects of Eu2+-doped concentration in Ca1.855−xSi0.71P0.29O4:xEu2+ on the PL were also discussed, the optimum doping concentration of Eu2+ was 1 mol.% and the critical distance of the energy transfer was also calculated by the concentration-quenching method. The non-radiative energy transfer between Eu2+ seemed to be caused by the multipole-multipole interaction. The fluorescence lifetime of Eu2+ was found to be 0.55711 μs. The results suggested that these phosphors might be promising candidates used for near UV light excited white LEDs.

Color tunable green–yellow–orange–red Er3+/Eu3+-codoped PbGeO3:PbF2:CdF2 glass phosphor for application in white-LED technology

Color tunable wide gamut light covering the greenish, yellow–green, yellow, orange, and reddish tone chromaticity region in Er3+/Eu3+-codoped lead–cadmium–germanate PbGeO3:PbF2:CdF2 glass phosphor is presented. The phosphors were synthesized, and their light emission properties examined under UV and blue LED excitation. Luminescence emission around 525, 550, 590, 610, and 660nm was obtained and analyzed as a function of Eu/Er concentration, excitation wavelength, and glass host composition. The color tunability was actually obtained via proper combination of Er3+ and Eu3+ active ions concentration. The combination of the emission tone with blue LEDs in the region of 400–460nm, yielded a mixture of light with color in the white-light region presenting a color correlated temperature in the range of 2000–4000K. Results indicate that the color-tunable fluorolead germanate erbium/europium co-doped glass phosphor herein reported is a promising novel contender for application in LED-based solid-state illumination technology

Luminescence properties and energy transfer mechanism of Ce3+/Mn2+ co-doped transparent glass-ceramics containing β-Zn2SiO4 nano-crystals for white light emission

A series of Ce3+/Mn2+ doped transparent glass-ceramics containing β-Zn2SiO4 nano-crystals were prepared by heat-treatment on the as-made glasses and their photoluminescence (PL) properties were investigated. Emission spectra of the glass-ceramics show a blue broad band peaking at 430nm and a yellow band peaking at about 575nm, originate from the allowed 5d→4f transition of Ce3+ ion and the 4T1g(4G)→6A1g(6S) transition of Mn2+ ion, respectively. Energy transfer from Ce3+ to Mn2+ via a dipole–quadrupole mechanism was confirmed by the luminescence spectra, decay time data, and the calculation of energy transfer efficiency of the glass-ceramics. The critical distance (RC) of energy transfer was calculated to be 8.32Ǻ. The varied emission color of Ce3+/Mn2+ doped transparent glass-ceramics from blue to white and eventually to yellow can be achieved by tuning the relative ratio of the Ce3+ to Mn2+ ions based on the principle of energy transfer. Based on the results in this study, Ce3+/Mn2+ doped transparent glass-ceramics can be used as a potential matrix material for White LED under UV–LED excitation.

Luminescence properties of Na3YSi3O9:M3+ (M = Sm, Tb, Tm) glass ceramics

The transparent Na3YSi3O9:M3+ (M=Sm, Tb, Tm) glass ceramics were prepared by high temperature melting with a heat-treatment at 750°C. X-ray diffraction, transmission electron microscopy, and photoluminescence spectroscopy were used to investigate their structure and optical properties. The M3+ ions were introduced as luminescence centers into the Na3YSi3O9 glass ceramics. Under ultraviolet (UV) excitation, the Na3YSi3O9:Sm3+, Na3YSi3O9:Tb3+, and Na3YSi3O9:Tm3+ glass ceramics exhibited the characteristic transitions of Sm3+ (4G5/2→6HJ, J=5/2 and 7/2), Tb3+ (5D4→7FJ, J=6, 5 and 4), and Tm3+ (1D2→3F4), respectively. The color tones of Na3YSi3O9:Sm3+, Tb3+, Tm3+ glass ceramic changed from cool white (0.2589, 0.3119) to warm white (0.3231, 0.4491) by adjusting the excitation wavelength. The results indicated that the Na3YSi3O9:M3+ (M=Sm, Tb, Tm) glass ceramic is a potential matrix material for white light-emitting diodes (LEDs) under UV-LED excitation.

The Fluorescence Image of Portable System Enhanced by Asynchronous Trigger UV-LED Excitation

Fluorescence is widely used to detect the biochemical effect and some substance containing certain dye. In general, the formation of fluorescent reaction is that an organism or dye, excited by UV light, emits a specific frequency of light; the light is usually a visible or near infrared light. Practically, the fluorescence of object can be excited by continued UV light, but the contrast and sharpness of fluorescence image decrease readily with stray light from the surrounding. In this study, we connect a trigger LED light module to a portable camera system and to perform the fluorescence inspection. When the fluorescent object is excited by asynchronous trigger UV-LED light, the extra intensity of fluorescence can be obtained. In the experiment of security organic dye (BL-ORT), the relative intensity of fluorescence acquired by 30 fps CCD can be increased by more than 11 %. In addition, when the fluorescent dye (chlorine e6) is injected into the tail vein of nude mouse, if its tail excited by the 375nm asynchronous trigger and continuous UV-LED are processed, the average relative intensity is 56.5 % and 49 %, respectively. Therefore, an added relative fluorescence of 15.3 % can be obtained from asynchronous triggering method. Furthermore, the ratio of extra intensity increases with the increase of frame rate of camera.

Color Locating of Ce<sup>3+</sup> and Eu<sup>2+</sup> Doped Calcium Magnesium Chlorosilicate UV-LED Phosphors

Color coordinates (0.1573, 0.0528) and (0.1542, 0.4663) have been identified in Ce3+and Eu2+singly doped calcium magnesium chlorosilicate (CMSC) phosphors, which present the purplish-blue and green lights under ultraviolet (UV) radiation, respectively. In Ce3+/Eu2+co-doped CMSC phosphors, with sensitizing the green emission of Eu2+, Ce3+co-doping changed the luminescence color from green to bluish-green, presenting a preferable mixed effect from two primary colors. Potential mixture of red phosphors will provide the possibility in achieving the ideal white fluorescence under UV-LED excitation.

Spray pyrolysis synthesis of MAl 2O 4:Eu 2+ (M=Ba, Sr) phosphor for UV LED excitation

The UV excited green emitting Eu 2+-activated BaAl 2O 4 and SrAl 2O 4 phosphors were prepared by ultrasonic spray pyrolysis at low temperature. The morphologies of phosphors were spherical and ∼1 μm size with non-aggregation. The BaAl 2O 4:Eu 2+ and SrAl 2O 4:Eu 2+ were efficiently excited under UV range from 320 to 370 nm, and exhibited broad band emission at about 500 and 520 nm, respectively, corresponding to the 5d–4f transition of Eu 2+. The detailed properties of crystal structure and luminescence behaviors were discussed by measurements of X-ray diffraction and photoluminescence. Phosphor conversion LEDs were fabricated by combining GaN-based 380 nm emitting UV LED as an optical pumping source with the prepared phosphors. The BaAl 2O 4:Eu 2+ phosphor LEDs showed the CIE coordinate of (0.171, 0.432) in bluish-green emission, and SrAl 2O 4:Eu 2+ phosphor LEDs showed that of (0.224, 0.518) in green emission.

Detection of synaptic glutamate release in cerebellar cortex using covalent immobilized enzyme assay and UV-LED excitation system

Detection of synaptic glutamate release in cerebellar cortex using covalent immobilized enzyme assay and UV-LED excitation system