Blue Light Excitation Research Articles

86‐4: Color Conversion Enhancement of Perovskite Quantum Dots by Integrating with Cholesteric Liquid Crystals

In this study, cholesteric liquid crystals (CLCs) are integrated with quantum dot color conversion (QDCC) display to increase the light efficiency. The CLC structure is designed to selectively reflect the blue excitation light, and thus the green emission from the perovskite quantum dots (QDs) is enhanced. An improvement of luminance by 21% is achieved.

Structural and spectroscopic characteristics of thermally stable Eu3+ activated barium zinc orthophosphate phosphor for white LEDs

Crystalline monoclinic phase of europium (Eu3+) doped barium zinc orthophosphate [BaZn2(PO4)2: BZP] phosphor has been synthesized via solid-state reaction technique. The phase purity, morphology and luminescent features of the as-synthesized phosphors have been examined using the results of X-ray diffraction (XRD), scanning electron microscopy (SEM) and photoluminescence (PL), respectively. The XRD results indicate pure phase formation of Eu3+ doped BZP (BZP:Eu3+) phosphor due to exact matching with the standard data of BZP. The SEM image specifies irregular shape of micro sized particles and non-uniform morphology. The BZP:Eu3+ phosphor exhibits intense emission at 592 nm wavelength under ultraviolet (UV), near-UV and blue light excitations. The emission spectra disclose that the emission intensity improved with increase in Eu3+ ions concentration up to 4.0 mol% and intensity decreases beyond it. The CIE coordinates (0.625, 0.363) calculated for the optimized BZP:Eu3+ phosphor, which fall in the pure red region and close to commercially available red phosphor Y2O2S: Eu3+ (0.647, 0.343). The PL intensity sustained up to 62.25% at 150 °C as compared to the intensity at room temperature indicating good thermal stability of BZP phosphor. All the above mentioned results signify the potential candidature of BZP:Eu3+ phosphors for white light emitting devices.

Efficient blue to near-infrared luminescence properties in Pr3+ - Yb3+ co-doped Li8Bi2(MoO4)7 phosphor

Abstract Down-conversion phosphors could absorb underutilized high-energy photons and convert to available near-infrared (NIR) photons in 900 – 1100 nm improving the spectral mismatch of silicon-based solar cells. Herein, we report the preparation of Pr3+-Yb3+ co-doped Li8Bi2(MoO4)7 molybdate phosphors by sol-gel method. The pure phases of all samples were confirmed by the X-ray diffraction. Under 453 nm blue light excitation, near infrared emission from Yb3+ and Pr3+can be generated. The NIR emission integral intensity of the Pr3+ - Yb3+ co-doped sample was 1.6 times than that of the corresponding Pr3+ single - doped sample. The optimal doping concentration of Yb3+ was 0.05 and the highest efficiency was 62.7%, furthermore the energy transfer process in Pr3+-Yb3+ was analyzed. The results indicate that Li8Bi2(MoO4)7: Pr3+, Yb3+ NIR phosphors have potential applications in the spectral converters of crystalline silicon solar cells.

Functional imaging of mitochondria in retinal diseases using flavoprotein fluorescence.

Mitochondria are critical for cellular energy production and homeostasis. Oxidative stress and associated mitochondrial dysfunction are integral components of the pathophysiology of retinal diseases, including diabetic retinopathy (DR), age-related macular degeneration, and glaucoma. Within mitochondria, flavoproteins are oxidized and reduced and emit a green autofluorescence when oxidized following blue light excitation. Recently, a noninvasive imaging device was developed to measure retinal flavoprotein fluorescence (FPF). Thus, oxidized FPF can act as a biomarker of mitochondrial dysfunction. This review article describes the literature surrounding mitochondrial FPF imaging in retinal disease. The authors describe the role of mitochondrial dysfunction in retinal diseases, experiments using FPF as a marker of mitochondrial dysfunction in vitro, the three generations of retinal FPF imaging devices, and the peer-reviewed publications that have examined FPF imaging in patients. Finally, the authors report their own study findings. Goals were to establish normative reference levels for FPF intensity and heterogeneity in healthy eyes, to compare between healthy eyes and eyes with diabetes and DR, and to compare across stages of DR. The authors present methods to calculate a patient's expected FPF values using baseline characteristics. FPF intensity and heterogeneity were elevated in diabetic eyes compared to age-matched control eyes, and in proliferative DR compared to diabetic eyes without retinopathy. In diabetic eyes, higher FPF heterogeneity was associated with poorer visual acuity. In conclusion, while current retinal imaging modalities frequently focus on structural features, functional mitochondrial imaging shows promise as a metabolically targeted tool to evaluate retinal disease.

Compositional dependence of red photoluminescence of Eu3+ ions in lead and bismuth containing borate glasses

Herein, heavy metal borate glasses activated with different concertation of Eu2O3 were prepared via the melt quench method. The Eu3+ concentration effect on photoluminescence (PL) properties of prepared glasses was investigated and discussed in detail to understand their utility in solid-state lighting and other photonic applications. The present work explains the suitability of two heavy metal oxides such as PbO and Bi2O3 for Eu2O3 doping to develop the glassy materials for photonic applications. The PL intensity was increased with an increase in Eu3+ content in PbO framed borate glasses while in Bi2O3 containing borate glasses the PL intensity was decreased at higher concentration due to concentration quenching. The Judd–Ofelt parameters and the radiative properties suggest the heavy metal borate glass hosts activated with 1 mol % of Eu3+ were potential materials for red light-emitting devices under blue light excitations. The Lifetime values of the PbO framed glasses were greater compared to Bi2O3 framed borate glasses which suggest the borate glass host containing high PbO content is more precisely suitable than Bi2O3 containing borate glass for solid-state lighting applications under blue light excitation.

Non-invasive red-light optogenetic control of Drosophila cardiac function

Drosophila is a powerful genetic model system for cardiovascular studies. Recently, optogenetic pacing tools have been developed to control Drosophila heart rhythm noninvasively with blue light, which has a limited penetration depth. Here we developed both a red-light sensitive opsin expressing Drosophila system and an integrated red-light stimulation and optical coherence microscopy (OCM) imaging system. We demonstrated noninvasive control of Drosophila cardiac rhythms using a single light source, including simulated tachycardia in ReaChR-expressing flies and bradycardia and cardiac arrest in halorhodopsin (NpHR)-expressing flies at multiple developmental stages. By using red excitation light, we were able to pace flies at higher efficiency and with lower power than with equivalent blue light excitation systems. The recovery dynamics after red-light stimulation of NpHR flies were observed and quantified. The combination of red-light stimulation, OCM imaging, and transgenic Drosophila systems provides a promising and easily manipulated research platform for noninvasive cardiac optogenetic studies.

A red-emitting phosphor Ba2HfF8:Mn4+ with a strengthened zero phonon line of Mn4+ for displays

Herein, a red-emitting phosphor Ba2HfF8:Mn4+ was successfully synthesized by the hydrothermal method. This phosphor is of the similar orthorhombic structure with that of Ba2ZrF8:Mn4+ confirmed by the Rietveld refinement. The as-prepared Ba2HfF8:Mn4+ exhibits excellent red emission with a strengthened zero phonon line of Mn4+ under the blue-light excitation, indicating that Mn4+ experiences the low symmetry environment in this phosphor. Meanwhile, Mn4+ in the sample Ba2HfF8:Mn4+ (8.7 mol%) has the shorter decay time, compared with that in some hexafluoride phosphors. The white light-emitting diode (wLED) based on Ba2HfF8:Mn4+ (8.7 mol%) and Y3Al5O12:Ce3+ presents the excellent photoelectric performances with wide color gamut. So, Ba2HfF8:Mn4+ as a new red phosphor could find potential application on the backlight for displays.

Red-emitting improvement of CaAlSiN3:Eu2+ phosphor-in-glass: Insight into the effect of atmospheric pressure preparation on photoluminescence properties and thermal degradation

The red-emitting phosphor-in-glass (PiG)s have been successfully prepared by a facile one-step co-sintering method on the basis of ultra-low melting Sn-P-F-O glass and CaAlSiN3: Eu2+ red phosphors synthesized under atmospheric-pressure (denoted as CASN-AP) and high-pressure (denoted as CASN-HP), respectively. The crystal structure, particle morphology, photoluminescence (PL) properties and surface states of the phosphors were investigated detail by X-ray powder diffraction (XRD), field emission electron microscopy (FESEM), fluorescence spectroscopy and X-ray photoelectron spectroscopy (XPS). Under excitation of blue light (460 nm), CASN-AP phosphor with red emission at 659 nm shows a higher luminescent intensity by 23 % than that of CASN-HP phosphor. Moreover, a shorter photoluminescence lifetime and red shift of 9 nm for emission peak can be also found for the CASN-APphosphor, which is ascribed to the increased Si-N bonds and surface Si/N ratio (1.86) demonstrated by the XPS analysis. Besides, the quantum yield and thermal degradation of both phosphors have been investigated. CASN-AP phosphor exhibits higher emission intensity because of its more emitting photons, but a lower quantum yields than CASN-HP phosphor due to its more absorbed photons. Based on the above, the low-temperature melting process for Sn-P-F-O glass does not damage the phosphor and the enhanced (≥35%) red-emitting CASN-AP PiG will be a promising candidate for essential red component in high quality white LEDs.

Photoswitchable Photon Upconversion from Turn-on Mode Fluorescent Diarylethenes

Photon upconversion (UC) is one kind of anti-Stokes shift process, which generally requires a combination of two or more low-energy photons to produce one high-energy photon. However, another inter...

N, S-codoped Carbon Dots for Nontoxic Cell Imaging and As a Sunlight-Active Photocatalytic Material for the Removal of Chromium.

Nitrogen-sulfur codoped carbon dots (NSCD) were synthesized via a single-step microwave-assisted method having a fluorescence quantum yield of ∼12%. The NSCD has been proven to be nontoxic and utilized as a fluorescent imaging nanoprobe for cancer cells (HeLa cells) under UV and blue light excitation (in vitro environment). In addition to the long-known cell imaging application, these NSCD have been used as a sunlight active photomaterial for the removal of toxic hexavalent chromium as Cr(VI). The experimental results reveal that the sunlight active NSCD shows good potential toward the photocatalytic removal of Cr(VI) ions from the wastewater. For the environment and water purification purpose, three different wastewater samples were tested that are synthetic wastewater (up to 100 ppm), laboratory wastewater, and Cr(VI) ion-spiked industrial wastewater for the photocatalytic removal of Cr(VI). The biocompatible NSCD as a fluorescent imaging probe of cancer cells along with its fruitful utilization in photocatalysis under sunlight (compared to the dark condition) demonstrates the overall sustainability of the presented process.

Double perovskite Ca2MgTeO6:Eu3+ red-emitting phosphors with high thermal stability for near UV/blue excited white LEDs

A series of Eu3+-doped double perovskite Ca2MgTeO6 (CMTO) red-emitting phosphors with high thermal stability were successfully prepared using the solid-state reaction at 1100 °C. The phase purity, surface morphology, and elemental mapping were investigated. Under near-ultraviolet (n-UV) (398 nm) and blue light (465 nm) excitation, the phosphors showed the strongest emission peak at 616 nm belonging to 5D0→7F2 transition. Besides, the ideal Eu3+ doping concentration was 0.30 mol. The major reason for the concentration quenching was the nearest neighbor ions interaction. More importantly, the CMTO:Eu3+ phosphors showed excellent thermal stability with a high value of activation energy (0.29 eV). The color purity of CMTO:0.30Eu3+ phosphor was up to 99.9% and the internal quantum efficiency (IQE) of CMTO:0.30Eu3+ was measured to be 53%. White light-emitting diodes (w-LEDs) based on the InGaN chip (λ = 398 nm) and GaN chip (λ = 465 nm) with high color rendering index (Ra) and low correlated color temperature (CCT) have been fabricated. Hence, the double perovskite CMTO:Eu3+ red phosphors have potential applications in the illumination field.

Autofluorescence of experimentally heated bone: Potential archaeological applications and relevance for estimating degree of burning

Assessing the degree of burning in archaeological bone is important for interpreting fire-related activities of humans in the past. Previous studies have explored a range of analytical methods to characterise burned bone, examining heat-induced changes to specific physical- or chemical properties. Autofluorescence is a property of bone tissue that has not received much attention in archaeological research despite its applicability on both hand-specimens and microscopic fragments in sediment thin-sections. In this study epifluorescence microscopy with blue-light excitation (400–440 nm) is applied in combination with fluorescence spectroscopy to investigate autofluorescence of experimentally heated cow bone. The results show that upon heating, a shift in fluorescence colour – from blueish-green to yellowish-green – occurs before combustion or charring, lasting up to the moment of calcination. The associated emission spectra suggest that this shift is caused by either or both the presence of pyrolysis products and changes to the bone mineral structure. These results support the use of epifluorescence microscopy as an analytical method for archaeology and contribute to a growing set of multi-proxy reference data to assess the degree of burning of bone.

Chiral Photomagnets Based on Copper(II) complexes of 1,2-Diaminocyclohexane and Octacyanidomolybdate(IV) Ions.

Chiral photomagnets compose a class of multifunctional molecule-based materials with light-induced alteration of magnetization and chiral properties. The rational design and synthesis of such assemblies is a challenge, and only few such systems are known. Herein, the remarkable octacyanide-bridged enantiomeric pair of 1-D chains [Cu((R,R)-chxn)2]2[Mo(CN)8]·H2O (1R) and [Cu((S,S)-chxn)2]2[Mo(CN)8]·H2O (1S) exhibiting enantiopure structural helicity, which results in optical activity in the 350-800 nm range as confirmed by natural circular dichroism (NCD) spectra, is reported. The photomagnetic effects of 1R, 1S, and 1rac result from the blue light excitation (436 nm) of the photomagnetically active octacyanidomolybdate(IV) ions. In the excited state MoIVHS centers with S = 1 couple antiferromagnetically with the neighboring CuII centers with JCuMo values of -1.3, -1.0, and -1.1 cm-1 for 1R, 1S, and 1rac, respectively. The values of thermal relaxation energy barriers have been estimated as 142 and 356 K for 1R and 1S, being comparable with the energy range of the thermal bath. The value for 1rac reveals a significantly lower value of 75 K. On the basis of these results the value of gMoHS has been estimated to be in the range 4.8-5.8.

Synthesis and Luminescence Properties of SrGd2O4:Eu3+ Red Phosphors

As one of the important raw materials for LED products, phosphors play an important role. At present, the spectrum of LED phosphors lacks red light, resulting in poor quality of white LED products and a low color rendering index (Ra <80), which affects lighting effects. To solve this problem, we synthesized the SrGd2O4:Eu3+ red phosphor by a high-temperature solid-phase method. The structure and luminescence properties of SrGd2O4:Eu3+ red phosphors were studied by means of X-ray diffraction (XRD) measurements of their emission and excitation spectra, and their spectra were analyzed. We also studied the Eu3+ doping concentration with the best luminous efficiency and the color coordinate of the SrGd2O4:Eu3+ phosphor. The experimental results show that SrGd2O4:Eu3+ is a new red phosphor material that can be used for near-ultraviolet or blue-light excitation and has good practicability.

Luminescence-enhancement and tunable-excitation of far-red emitting La2LiSbO6:Mn4+, Bi3+ phosphors for plant growth lighting

In this paper, Bi3+ ions were co-doped into La2LiSbO6:Mn4+ phosphors for purpose of improving luminescent properties in the near ultraviolet and blue light range. A significant enhancement from 25.89% to 58.71% in quantum yield under blue light excitation was achieved. Impressively, via increasing Bi3+ concentration, the excitation spectra can be effectively tuned from double to triple bands along with the maximum excitation peak changed. Besides, particle morphology and Raman vibration modes were investigated to reveal the luminescence enhancement and the excitation evolution mechanisms. The results show that Bi3+-induced structure symmetry change may play a dominant role in tunable excitation phenomenon of the samples, which makes La2LiSbO6:Mn4+, Bi3+ may have a potential application in plant growth lighting LEDs for different kind of excitation light sources.

Noninvasive multimodal imaging by integrating optical coherence tomography with autofluorescence imaging for dental applications

We report the development of an integrated multifunctional imaging system capable of providing anatomical (optical coherence tomography, OCT), functional (OCT angiography, OCTA) and molecular imaging (light-induced autofluorescence, LIAF) for in vivo dental applications. Blue excitation light (405 nm) was used for LIAF imaging, while the OCT was powered by a 1310 nm swept laser source. A red-green-blue digital camera, with a 450 nm cut-on broadband optical filter, was used for LIAF detection. The exciting light source and camera were integrated directly with the OCT scanning probe. The integrated system used two noninvasive imaging modalities to improve the speed of in vivo OCT data collection and to better target the regions of interest. The newly designed system maintained the ability to detect differences between healthy and hypomineralized teeth, identify dental biofilm and visualize the microvasculature of gingival tissue. The development of the integrated OCT-LIAF system provides an opportunity to conduct clinical studies more efficiently, examining changes in oral conditions over time.

Eu3+-activated Ca3Mo0.2W0.8O6 red-emitting phosphors: A near-ultraviolet and blue light excitable platform for solid-state lighting and thermometer

Eu3+-activated Ca3Mo0.2W0.8O6 phosphors, which presented bright red emissions mainly from the 5D0 → 7F2 transition of Eu3+ ions upon the near-ultraviolet and blue light excitation, were successfully prepared by a traditional high-temperature technology. The crystal structure, phase constitution, morphology, electronic structure, photoluminescent behaviors, decay time, internal quantum efficiency and thermal stability of the resultant phosphors were investigated in detail. Under the excitation of 365, 393 and 465 nm, the optimal doping concentration was 9 mol% and the electrical multipolar interaction contributed to the non-radiative energy transfer between Eu3+ ions in Ca3Mo0.2W0.8O6 host lattices. Additionally, through using the prepared compounds, commercial blue/green-emitting phosphors and light-emitting diodes (LEDs), the fabricated white-LEDs emitted warm white light with excellent performance, such as good CIE coordinates, high color rending index and low correlated color temperature, when driven by 30 mA of injection current. Ultimately, according to the response of the decay time to the temperature, the thermometric performances of the resultant phosphors in the temperature range of 298–573 K were studied. The maximum sensor sensitivity of the studied phosphors reached up to 1.16% K−1 at 523 K. These achievements revealed that Eu3+-activated Ca3Mo0.2W0.8O6 phosphors were promising candidates for solid-state lighting and thermometer.

Rapid Release of Ca2+ from Endoplasmic Reticulum Mediated by Na+/Ca2+ Exchange.

Phototransduction in Drosophila is mediated by phospholipase C (PLC) and Ca2+-permeable TRP channels, but the function of endoplasmic reticulum (ER) Ca2+ stores in this important model for Ca2+ signaling remains obscure. We therefore expressed a low affinity Ca2+ indicator (ER-GCaMP6-150) in the ER, and measured its fluorescence both in dissociated ommatidia and in vivo from intact flies of both sexes. Blue excitation light induced a rapid (tau ∼0.8 s), PLC-dependent decrease in fluorescence, representing depletion of ER Ca2+ stores, followed by a slower decay, typically reaching ∼50% of initial dark-adapted levels, with significant depletion occurring under natural levels of illumination. The ER stores refilled in the dark within 100-200 s. Both rapid and slow store depletion were largely unaffected in InsP3 receptor mutants, but were much reduced in trp mutants. Strikingly, rapid (but not slow) depletion of ER stores was blocked by removing external Na+ and in mutants of the Na+/Ca2+ exchanger, CalX, which we immuno-localized to ER membranes in addition to its established localization in the plasma membrane. Conversely, overexpression of calx greatly enhanced rapid depletion. These results indicate that rapid store depletion is mediated by Na+/Ca2+ exchange across the ER membrane induced by Na+ influx via the light-sensitive channels. Although too slow to be involved in channel activation, this Na+/Ca2+ exchange-dependent release explains the decades-old observation of a light-induced rise in cytosolic Ca2+ in photoreceptors exposed to Ca2+-free solutions.SIGNIFICANCE STATEMENT Phototransduction in Drosophila is mediated by phospholipase C, which activates TRP cation channels by an unknown mechanism. Despite much speculation, it is unknown whether endoplasmic reticulum (ER) Ca2+ stores play any role. We therefore engineered flies expressing a genetically encoded Ca2+ indicator in the photoreceptor ER. Although NCX Na+/Ca2+ exchangers are classically believed to operate only at the plasma membrane, we demonstrate a rapid light-induced depletion of ER Ca2+ stores mediated by Na+/Ca2+ exchange across the ER membrane. This NCX-dependent release was too slow to be involved in channel activation, but explains the decades-old observation of a light-induced rise in cytosolic Ca2+ in photoreceptors bathed in Ca2+-free solutions.

Salamanders and other amphibians are aglow with biofluorescence

Biofluorescence is the absorption of electromagnetic radiation (light) at one wavelength followed by its reemission at a lower energy and longer wavelength by a living organism. Previous studies have documented the widespread presence of biofluorescence in some animals, including cnidarians, arthropods, and cartilaginous and ray-finned fishes. Many studies on biofluorescence have focused on marine animals (cnidarians, cartilaginous and ray-finned fishes) but we know comparatively little about the presence of biofluorescence in tetrapods. We show for the first time that biofluorescence is widespread across Amphibia, with a focus on salamanders (Caudata), which are a diverse group with a primarily Holarctic distribution. We find that biofluorescence is not restricted to any particular family of salamanders, there is striking variation in their fluorescent patterning, and the primary wavelengths emitted in response to blue excitation light are within the spectrum of green light. Widespread biofluorescence across the amphibian radiation is a previously undocumented phenomenon that could have significant ramifications for the ecology and evolution of these diverse and declining vertebrates. Our results provide a roadmap for future studies on the characterization of molecular mechanisms of biofluorescence in amphibians, as well as directions for investigations into the potential impact of biofluorescence on the visual ecology and behavior of biofluorescent amphibians.

Highly Stabilized Gradient Alloy Quantum Dots and Silica Hybrid Nanospheres by Core Double Shells for Photoluminescence Devices.

This Letter reports the synthesis approach and application of colloidal suspensions containing gradient alloy quantum dots (QDs) and silica hybrid spheres with improved thermal and photostability, invisible QD aggregation, and high material compatibility. These hybrid nanospheres are characterized by using silica spheres as cores, adsorbing QDs as one shell, and then coating a silica layer as another shell (termed SiO2-QD-SiO2). They were synthesized by using Stöber and adsorption methods. The experimental conditions affecting the optical properties were fully investigated. A light-guiding microstructure array (LGMA) was fabricated and tested for photoluminescence demonstration. After accelerated aging tests for 240 h under 85 °C, 40% relative humidity, and 450 nm blue light excitation, the luminance of the SiO2-QD-SiO2 LGMA remained stable, which was 1.6 times greater than that of untreated QD samples. This structure with long-term photothermal stability could pave the way for displays or lighting applications.