Light-emitting Diode Excitation Research Articles

Fluorescence Microscopy with Deep UV, Near UV, and Visible Excitation for In Situ Detection of Microorganisms.

We report a simple, inexpensive design of a fluorescence microscope with light-emitting diode (LED) excitation for detection of labeled and unlabeled microorganisms in mineral substrates. The use of deep UV (DUV) excitation with visible emission requires no specialized optics or slides and can be implemented easily and inexpensively using an oblique illumination geometry. DUV excitation (<280 nm) is preferable to near UV (365 nm) for avoidance of mineral autofluorescence. When excited with DUV, unpigmented bacteria show two emission peaks: one in the near UV ∼320 nm, corresponding to proteins, and another peak in the blue to green range, corresponding to flavins and/or reduced nicotinamide adenine dinucleotide (NADH). Many commonly used dyes also show secondary excitation peaks in the DUV, with identical emission spectra and quantum yields as their primary peak. However, DUV fails to excite key biosignature molecules, especially chlorophyll in cyanobacteria. Visible excitation (violet to blue) also results in less mineral autofluorescence than near UV, and most autofluorescence in the minerals seen here is green, so that red dyes and red autofluorescence of chlorophyll and porphyrins are readily distinguished. The pairing of DUV and near UV or visible excitation, with emission across the visible, represents the most thorough approach to detection of labeled and unlabeled bacteria in soil and rock.

Metal-enhanced fluorescence biosensor integrated in capillary flow-driven microfluidic cartridge for highly sensitive immunoassays

Point-of-care testing (POCT) for low-concentration protein biomarkers remains challenging due to limitations in biosensor sensitivity and platform integration. This study addresses this gap by presenting a novel approach that integrates a metal-enhanced fluorescence (MEF) biosensor within a capillary flow-driven microfluidic cartridge (CFMC) for the ultrasensitive detection of the Parkinson's disease biomarker, aminoacyl-tRNA synthetase complex interacting multi-functional protein 2 (AIMP-2). Crucial point to this approach is the orientation-controlled immobilization of capture antibody on a nanodimple-structured MEF substrate within the CFMC. This strategy significantly enhances fluorescence signals without quenching, enabling accurate quantification of low-concentration AIMP-2 using a simple digital fluorescence microscope with a light-emitting diode excitation source and a digital camera. The resulting platform exhibits exceptional sensitivity, achieving a limit of detection in the pg/mL range for AIMP-2 in human serum. Additionally, the CFMC design incorporates a capillary-driven passive sample transport mechanism, eliminating the need for external pumps and further simplifying the detection process. Overall, this work demonstrates the successful integration of MEF biosensing with capillary microfluidics for point-of-care applications.

High-Gain of NdIII Complex Doped Optical Waveguide Amplifiers at 1.06 and 1.31µm Wavelengths Based on Intramolecular Energy Transfer Mechanism.

Chelate phosphine oxide ligand (9,9-dimethyl-9H-xanthene-4,5-diyl) bis (diphenylphosphineoxide) (XPO) is prepared as a neutral ligand to synthesize complex Nd (TTA)3 (XPO) (TTA = 2-thenoyltrifluoroacetone). An appropriate energy gap between the XPO and TTA ligands, which can support two additional energy transfer routines from the first excited triplet state (T1 ) energy level of the XPO to that of the TTA, improves energy transfer in the Nd complex. Based on intramolecular energy transfer mechanism, optical gains at 1.06 and 1.31µm are demonstrated in Nd (TTA)3 (XPO)-doped polymer waveguides with the excitation of low-power light-emitting diodes (LEDs) instead of semiconductor lasers as pump sources. Using the vertical top-pumping mode of a 365nm LED, relative gains of 22.5 and 8.4dBcm-1 are obtained at 1.06 and 1.31µm, respectively, in a 0.2 cm long embedded waveguide with a cross-section of 8×5µm2 . The active core layer is Nd (TTA)3 (XPO)-doped SU-8 polymer. Moreover, relative gains are achieved in evanescent-field waveguide with a cross-section of 6×4µm2 . The 21.0 and 5.6dBcm-1 relative gains are achieved at 1.06 and 1.31µm, respectively, with a net gain of 13.8±0.3dBcm-1 obtained at 1.06µm in a 0.9 cm long SU-8 waveguide with Nd (TTA)3 (XPO)-doped polymethylmethacrylate as upper cladding.

Optical Amplification at 637 and 1067 nm Based on Organic Molecule AQ(PhDPA)2 and NdIII Complex Codoped Polymer Waveguides.

Based on the molecular energy transfer mechanism, relative gains at 1067 and 637nm wavelengths are achieved in thermally activated delayed fluorescence molecule AQ(PhDPA)2 and Nd complex with chelating phosphine oxide as ligands codoped polymer waveguides, with the excitation of low-power UV light-emitting diodes (LEDs) instead of traditional semiconductor lasers as pump sources. For AQ(PhDPA)2 -Nd(DBTTA)3 (DBFDPO) (DBTTA = dibenzotetrathienoacene, DBFDPO = 4,6-bis (diphenylphosphoryl) dibenzofuran) -codoped polymethylmethacrylate (PMMA), and AQ(PhDPA)2 -Nd(DBTTA)3 (FDPO) (FDPO = 9,9-bis (diphenylphosphorylphenyl) fluorene)-codoped PMMA polymers with a mass ratio of 1:4 respectively, when they are spin-coated as upper claddings, the relative gains of 2.2 and 1.8dB cm-1 at 1067nm are obtained in evanescent-field waveguides with cross-section of 4 × 8µm2 under excitation of 300mW 405nm LED, and the gains of 3.9 and 4.9dB cm-1 at 637nm are achieved with pumping of 530mW 450nm LED respectively. By growing a 100nm-thick aluminum reflector with the waveguides, the optical gain at 1067 and 637nm can be enhanced to 3.5 and 6.1dB cm-1 , corresponding to AQ(PhDPA)2 -Nd(DBTTA)3 (DBFDPO) and AQ(PhDPA)2 -Nd(DBTTA)3 (FDPO)-codoped PMMA polymers, respectively.

High-precision tumor resection down to few-cell level guided by NIR-IIb molecular fluorescence imaging

In vivo fluorescence/luminescence imaging in the near-infrared-IIb (NIR-IIb, 1,500 to 1,700 nm) window under <1,000 nm excitation can afford subcentimeter imaging depth without any tissue autofluorescence, promising high-precision intraoperative navigation in the clinic. Here, we developed a compact imager for concurrent visible photographic and NIR-II (1,000 to 3,000 nm) fluorescence imaging for preclinical image-guided surgery. Biocompatible erbium-based rare-earth nanoparticles (ErNPs) with bright down-conversion luminescence in the NIR-IIb window were conjugated to TRC105 antibody for molecular imaging of CD105 angiogenesis markers in 4T1 murine breast tumors. Under a ∼940 ± 38 nm light-emitting diode (LED) excitation, NIR-IIb imaging of 1,500- to 1,700-nm emission afforded noninvasive tumor–to–normal tissue (T/NT) signal ratios of ∼40 before surgery and an ultrahigh intraoperative tumor-to-muscle (T/M) ratio of ∼300, resolving tumor margin unambiguously without interfering background signal from surrounding healthy tissues. High-resolution imaging resolved small numbers of residual cancer cells during surgery, allowing thorough and nonexcessive tumor removal at the few-cell level. NIR-IIb molecular imaging afforded 10-times-higher and 100-times-higher T/NT and T/M ratios, respectively, than imaging with IRDye800CW-TRC105 in the ∼900- to 1,300-nm range. The vastly improved resolution of tumor margin and diminished background open a paradigm of molecular imaging-guided surgery.

Self‐Referenced Temperature Imaging with Dual Light Emitting Diode Excitation and Single‐Band Emission of AVO4:Eu3+ (A=Y, La, Lu, Gd) Nanophosphors

Luminescence thermometers exhibiting ratiometric response in their emission spectrum are widely investigated but to obtain two‐dimensional measurements, either the emission spectrum must be slowly scanned over the area of interest or the emission decomposed using two separate detector arrays with spectral filters. Here, the authors propose to exploit instead an excitation‐spectrum based ratiometric response. In AVO4 (A = Lu, Y, Gd, La) nanocrystals doped with Eu3+, the 1 E(1 T 1)→ 1 B 2(1 T 2) absorption band is thermally enhanced with respect to the 1 A 2(1 T 1)→ 1 B 2(1 T 2) of the V5+ ion. When observing the Eu3+ emission as a result of (VO4)3− to Eu3+ charge transfer, the ratio of intensities recorded upon two different excitation wavelengths is temperature dependent. This response is exploited for transient 2‐dimensional temperature imaging using two ultraviolet light emitting diodes (LEDs) for excitation, which are subsequently pulsed, while recording the emission on a single camera. As a demonstration, a YVO4:Eu3+ coated metal plate is subjected to localised heating by a flame. Thanks to the efficient excitation and signal collection, an accuracy of 0.6 °C and a precision of 1.5 °C are achieved at a resolution of 160 μm and a repetition rate of 2.5 Hz, all with peak LED powers below 1 mW and a single low‐frame‐rate camera.

Photoconductance Determination of Carrier Capture Cross Sections of Slow Traps in Silicon Through Variable Pulse Filling

The capture cross sections are a key metric to characterize carrier traps in semiconductors. In this article, photoconductance measurements are used to estimate the capture cross sections of traps that are induced by thermal donors in Czochralski-grown silicon wafers. Here, we use a pulse-filling technique with light-emitting diode excitation to measure the capture rate. The measured capture rates are shown to be similar to the values that were measured previously by deep-level transient spectroscopy. Our method allows the contactless measurements of the capture cross sections. The minority carrier cross sections for the two distinct trap states that are studied here are of the order of 10−18 cm2 and the majority carrier cross sections are orders of magnitude smaller. Therefore, it is concluded that the slow traps that are originating from the thermal donors are dominated by the minority carrier trapping.

Multi-channel fiber optical spectrometer for high-throughput characterization of photoluminescence properties.

High-throughput experiment can significantly accelerate the materials research efficiency. Thanks to national efforts, the Materials Genome Initiative further promotes the development of high-throughput experimental technology. A multi-channel fiber optical spectrometer has been designed and developed by us for high-throughput characterization of photoluminescence (PL) properties. It can quickly and automatically detect the PL spectrum, Commission International de l'Eclairage chromaticity, and PL intensity over time for luminescent materials under a given condition. The multi-channel fiber optical spectrometer synergistically combines a sample library holder, multiple modular excitation sources, multiple spectrometers, and Coral software, so it can measure and analyze multiple samples simultaneously. The number of channels in the multi-channel fiber optical spectrometer can be added or subtracted as required. Various modular light-emitting diode or laser diode excitation sources with the wavelength from 370 nm to 980 nm and corresponding filters can be provided according to the measurement need of different luminescent materials. The monitoring wavelength of the currently used fiber optical spectrometer is from 300 nm to 1000 nm. For example, the PL spectral measurement of 54 samples in a {6 × 9} array is completed in only about 30 min by using a representative triple-channel fiber optical spectrometer. The designed multi-channel fiber optical spectrometer facility not only makes PL measurements faster and more intuitive but is also easy to popularize for wide users.

Light-Emitting Diode Excitation for Upconversion Microscopy: A Quantitative Assessment

Lanthanide-based upconversion nanoparticles (UCNPs) generally require high power laser excitation. Here, we report wide-field upconversion microscopy at single-nanoparticle sensitivity using incoherent excitation of a 970 nm light-emitting diode (LED). We show that due to its broad emission spectrum, LED excitation is about 3 times less effective for UCNPs and generates high background compared to laser illumination. To counter this, we use time-gated luminescence detection to eliminate the residual background from the LED source, so that individual UCNPs with high sensitizer (Yb3+) doping and inert shell protection become clearly identified under LED excitation at 1.18 W cm-2, as confirmed by correlated electron microscopy images. Hydrophilic UCNPs are obtained by polysaccharide coating via a facile ligand exchange protocol to demonstrate imaging of cellular uptake using LED excitation. These results suggest a viable approach to bypassing the limitations associated with high-power lasers when applying UCNPs and upconversion microscopy to life science research.

Narrow-Band SrMgAl10O17:Eu2+, Mn2+ Green Phosphors for Wide-Color-Gamut Backlight for LCD Displays.

The strength of the photoluminescence excitation (PLE) spectrum of SrMgAl10O17:Eu2+, Mn2+ (SAM:Eu2+, Mn2+) phosphor increased at deep blue (∼430 nm) and red-shifted from violet to deep blue with increasing concentrations of both Eu2+ ions Mn2+ ions. Eu2+–Mn2+ energy transfer between Eu2+ ions in Sr–O layer and Mn2+ ions at Al–O tetrahedral sites was maximized, and the photoluminescence (PL) intensity of the narrow-band Mn2+ emission was improved by optimizing the concentrations of Eu2+ and Mn2+ ions. The PL emission spectrum of the (Sr0.6Eu0.4)(Mg0.4Mn0.6)Al10O17 (SAM:Eu2+, Mn2+) phosphor peaks was optimized at 518 nm at a full width at half-maximum (FWHM) of 26 nm under light-emitting diode (LED) excitation at 432 nm LED. The color gamut area of a color-filtered RGB triangle of down-converted white LEDs (DC-WLEDs) incorporated with optimum SAM:Eu2+, Mn2+ green and K2SiF6:Mn4+ (KSF:Mn4+) red phosphors is enlarged by 114% relative to that of the NTSC standard system in the CIE 1931 color space. The luminous efficacy of our DC-WLED was measured and found to be ∼92 lm/W at 20 mA. Increased energy transfers between dual activators and red-shifted band-edge and enhanced intensity of PLE spectrum indicate the possibility of developing dual-activated narrow-band green phosphors for wide-color gamut in an LCD backlighting system.

A far‐red‐emitting (Gd,Y)3(Ga,Al)5O12:Mn2+ ceramic phosphor with enhanced thermal stability for plant cultivation

AbstractAs for plants, far‐red (FR) light with wavelength from 700 nm to 740 nm is critical for processes of photosynthesis and photomorphogenesis. Light‐controlled development depends on light to control cell differentiation, structural and functional changes, and finally converge into the formation of tissues and organs. Phosphor converted FR emission under LED excitation is a cost‐effective and high‐efficient way to provide artificial FR light source. With the aim to develop an efficient FR phosphor that can promote the plant growth, a series of gadolinium yttrium gallium garnet (GYGAG) transparent ceramic phosphors co‐doped with Mn2+ and Si4+ have been fabricated via chemical co‐precipitation method, followed sintered in O2 and hot isostatic pressing in this work. Under UV excitation, the phosphor exhibited two bright and broadband red emission spectra due to Mn2+: 4T1 → 6A1 spin‐forbidden transition, and one of which located in the right FR region. And then, Ce3+ ions were co‐doped as the activator to enhance the absorption at blue light region and the emission of Mn2+. It turns out that the emission band of GYGAG transparent ceramic phosphors matches well with the absorption band of phytochrome PFR, which means they are promising to be applied in plant cultivation light‐emitting diodes (LEDs) for modulating plant growth. Besides, the thermal stability of this material was investigated systematically, and an energy transferring model involves defects was also proposed to explain the phenomenon of abnormal temperature quenching.

Plasmonic hot electron transfer-induced multicolor MoO3-x-based chromogenic system for visual and colorimetric determination of silver(I).

A plasmonic hot electron transfer-induced multicolor chromogenic system is described for label-free visual colorimetric determination of silver(I). The chromogenic system consists of plasmonic MoO3-x nanosheets with oxygen vacancies and Ag(I). Under white light-emitting diode (LED) excitation, energetic hot hole-electron pairs are formed on the surface of the blue MoO3-x nanosheets. The resulting hot electrons are transferred to Ag(I) upon which it becomes reduced. This results in the generation of yellow silver nanoparticles. Simultaneously, the hot holes lead to the oxidation of the MoO3-x nanosheets to yield colorless MoO3 nanosheets. Similarly, energetic hot hole-electron pairs can also be generated on the surface of AgNPs under white LED irradiation, which contributes to the reduction of Ag(I) and the oxidation of MoO3-x. Overall, a colorful transition from blue to green and finally to yellow can be observed. This multicolor chromogenic system was applied to the colorimetric determination of Ag(I) in the 33-200μM concentration range and a 0.66μM limit of detection, at analytical wavelengths of 430 and 760nm. The method also is amenable to semi-quantitative visual determination of Ag(I). Graphical abstractSchematic representation of plasmonic hot electron transfer-induced multicolor MoO3-x-based chromogenic system for visual and colorimetric determination of silver(I).

Ultrasound assisted synthesis of CaF2 :Eu3+ phosphor nanoparticles.

In this work, the optical and structural properties of ultrasonically prepared CaF2 :Eu3+ nanoparticles have been reported. Ultrasonically prepared CaF2 :Eu3+ phosphor shows orange, red emission bands at 591nm and 612nm, respectively, when it is excited by 394 light-emitting diode (LED) excitation wavelengths. Further phosphor materials are well characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and transmission electron microscopy (TEM) techniques to confirm the phase purity, metal oxygen (MO) bonding and crystallites size of the materials. Here synthesized materials show a tube-like structure under 100nm resolution and 0.1mol% is the best doping value of the europium ion (Eu3+ ) in calcium fluoride (CaF2 ) that shows highest intensity when prepared with an ultrasound assisted method.

Triplet-Triplet Annihilation Upconversion in Broadly Absorbing Layered Film Systems for Sub-Bandgap Photocatalysis.

Upconversion (UC) of sub-bandgap photons extends the effective light absorption range of photovoltaic and photocatalytic devices, allowing them to reach higher conversion efficiencies. Recent advances in polymer host materials make it possible to translate triplet-triplet annihilation (TTA)-UC, the UC mechanism most suitable for this purpose, to solid films that can be integrated into devices. The promise of these films is currently limited by the narrow light absorption of TTA-UC sensitizer chromophores, but incorporating multiple sensitizers into layered film systems presents a promising strategy for producing UC materials with broadened light absorption. This strategy is hereinapplied for photocatalytic air purification, demonstrating its use in a real-world application for the first time. We superimpose optimized red-to-blue and green-to-blue UC films within dual-layer systems and develop a new photocatalyst compatible with their fluorescence emission. By integrating the dual-layer UC film systems withfilms of this photocatalyst, we produce the first devices that use TTA-UC to harness both red and green sub-bandgap photons for hydroxyl radical generation and photocatalytic degradation of gaseous acetaldehyde, a model volatile organic compound (VOC). Under white light-emitting diode excitation, the dual-layer film systems' broadened light absorption enhances their devices' photocatalytic degradation efficiency, enabling them to degrade twice as much acetaldehyde as their single-sensitizer counterparts. We show that as a result of the different absorption profiles of the two sensitizers, the film order significantly impacts UC fluorescence and VOC degradation. By probing the influence of the excitation light source, excitation geometry, and chromophore spectral overlap on the film systems' UC performance, we propose a framework for the design of multilayer TTA-UC film systems suitable for integration with a variety of photovoltaic and photocatalytic devices.

Application of LED-based thermographic phosphorescent technique to diesel combustion chamber walls in a pre-burn-type optical constant-volume vessel

This study presents a method for direct measurement of wall surface temperature realising two-dimensional, thermographic phosphorescence imaging. The experiments were performed in a constant-volume combustion chamber (CVCC) wherein the ambient gas and fuel injection conditions closely mimic those found in a typical diesel engine. The new method successfully made use of a high-power light emitting diode (LED) system and intensified charge-coupled device (ICCD) camera—which offers practical advantages such as much lower cost and reduced safety concerns in comparison to laser-based phosphorescence diagnostics. Previous studies have successfully demonstrated measurement strategies using LEDs (Atakan et al., Exp Measur Strat. https://doi.org/10.1088/0957-0233/20/7/075304 , 2009; Salem et al., Exp Fluids 49:797–807, 2010); however, most have implemented a lifetime-based approach. Aizawa and Kosaka (Int J Fuels Lubr 1:549–558, 2008) demonstrated the applicability of the absolute intensity method as a viable alternative, using a laser source for excitation. This paper combines Aizawa and Kosaka’s intensity-ratio methodology with LED excitation, and implements the technique to a diesel flame/wall interaction case in a pre-burn-type optical CVCC. Europium-doped lanthanum oxysulphide (La2O2S:Eu) was selected as a suitable phosphor material due to its high temperature sensitivity at this engine relevant condition. The present study first investigates how phosphorescence signals are influenced by the coating thickness. The thickness of the phosphor-binder layer was measured by a scanning electron microscope (SEM) in the 11.9–19.0 µm range. The optimal layer thickness was chosen as 14.3 µm, the thinnest possible layer capable of achieving the highest emission signal, as thicker coatings are more prone to thermal gradients—especially at a transient flame/wall interaction condition. Calibration images were obtained in the 294–523 K range with ± 2 K uncertainty in an electric furnace, thereby allowing two-dimensional temperature measurements in the CVCC application. The results obtained for various timings after the start of fuel injection, namely before and after the flame impingement on the wall, indicate effective wall temperature measurements with low spatial (pixel-by-pixel) and shot-to-shot variations of < 7.5 K (95% confidence).

Highly stable and tunable white luminescence from Ag-Eu3+ co-doped fluoroborate glass phosphors combined with violet LED.

Ag-Eu3+ co-doped fluoroborate glass phosphors doped with various Eu3+-concentrations were prepared by a melt-quenching technique. The luminescent properties of these glass phosphors were characterized by excitation and emission spectra. Broad excitation and emission bands located, respectively, at 300-450 nm and 390-700 nm originating from silver aggregates were observed. Strong red emissions were detected under 404 nm violet light-emitting diode (LED) excitation for those Ag-Eu3+ co-doped samples. It was found that these red emissions of Eu3+ well compensated the deficiency of the red spectral components in glasses containing Ag aggregates. In addition, it was confirmed that stable white light could be achieved from the combination of a specific Ag-Eu3+ co-doped fluoroborate glass phosphor and LEDs with different output wavelengths. By adjusting the luminescence intensity ratio of the glass phosphor to the 404 nm violet LED, tunable emitting color was realized, and the studied glass phosphors showed excellent emitting color stability toward LED drive currents. Our results demonstrated that this kind of easy fabrication, low-cost, and highly stable Ag-Eu3+ co-doped fluoroborate glass phosphors had potential application in white LED.

Physical and optical properties of lithium borosilicate glasses doped with Dy3+ ions

The borosilicate glasses with Dy3+ ions were prepared by the melt quench technique with varying concentration of Dy2O3. The glasses were characterized by the density calculation, absorbance and photoluminescence (PL) spectroscopy measurements. Density and molar volume of the glasses increases with increase in Dy3+ ions in the glass matrix. This behavior is correlated with the higher molecular weight and larger ionic radius of Dy3+ ion compared to the other constituents of glass matrix. Emission of Dy3+ doped glasses showed three bands at 482, 573 and at 665nm which correspond to 6H15/2 (blue), 6H13/2 (yellow) and 6H11/2 (red) transitions. The emission spectra of glasses with different concentration of Dy3+ ions shows that, glasses with 0.5mol% of Dy2O3 shows highest emission and decreases with further doping. CIE 1931 chromaticity diagram showed that the emission of these glasses was in the white region. Photographs of these glasses under 349nm Light emitting diode excitation also confirmed the white light emission from these glasses.

Low-cost photoacoustic imaging systems based on laser diode and light-emitting diode excitation

Photoacoustic imaging, an emerging biomedical imaging modality, holds great promise for preclinical and clinical researches. It combines the high optical contrast and high ultrasound resolution by converting laser excitation into ultrasonic emission. In order to generate photoacoustic signal efficiently, bulky Q-switched solid-state laser systems are most commonly used as excitation sources and hence limit its commercialization. As an alternative, the miniaturized semiconductor laser system has the advantages of being inexpensive, compact, and robust, which makes a significant effect on production-forming design. It is also desirable to obtain a wavelength in a wide range from visible to near-infrared spectrum for multispectral applications. Focussing on practical aspect, this paper reviews the state-of-the-art developments of low-cost photoacoustic system with laser diode and light-emitting diode excitation source and highlights a few representative installations in the past decade.

In vivo photoacoustic imaging of vasculature with a low-cost miniature light emitting diode excitation.

In this Letter, we present a photoacoustic imaging (PAI) system based on a low-cost high-power miniature light emitting diode (LED) that is capable of in vivo mapping vasculature networks in biological tissue. Overdriving with 200ns pulses and operating at a repetition rate of 40kHz, a 1.2W 405nm LED with a radiation area of 1000 μm×1000 μm and a size of 3.5 mm×3.5 mm was used to excite photoacoustic signals in tissue. Phantoms including black stripes, lead, and hair were used to validate the system in which a volumetric PAI image was obtained by scanning the transducer and the light beam in a two-dimensional x-y plane over the object. In vivo imaging of the vasculature of a mouse ear shows that LED-based PAI could have great potential for label-free biomedical imaging applications where the use of bulky and expensive pulsed lasers is impractical.

Pr3+/Ho3+ co-doped glass phosphors for application in warm white light-emitting diodes

Pr3+/Ho3+ co-doped fluorozirconate glasses were prepared and their luminescence properties studied. Blue, green and red luminescence in the wavelength region of 470–750nm were achieved in these glasses under 443nm light-emitting diode (LED) excitation. The ratio of Pr3+–Ho3+ was changed in order to determine the appropriate combination for realizing color-controlled white LEDs. The color temperature of the white light can be adjusted by changing the LED-excitation wavelength or the ratio of the Ho3+/Pr3+ ions. Thus, Pr3+/Ho3+co-doped fluorozirconate glasses are potential materials for use in white LEDs.