Blue Wavelength Range Research Articles

With Blue Light against Biofilms: Berberine as Natural Photosensitizer for Photodynamic Inactivation of Human Pathogens

Evolving antibiotic resistance of bacteria is a prevailing global challenge in health care and requires the development of safe and efficient alternatives to classic antibiotics. Photodynamic Inactivation (PDI) has proven to be a promising alternative for treatment of a broad range of microorganisms. Photodynamic Inactivation uses photoactive molecules that generate reactive oxygen species (ROS) upon illumination and in the presence of oxygen, which immediately kill pathogenic target organisms. Relevant photoactive properties are provided by berberine. Originally extracted from Barberry (Berberis vulgaris), it is a natural compound widely used in Traditional Chinese Medicine for its antimicrobial and anti-inflammatory effects. With this study, we demonstrated the potential of berberine chloride hydrate (Ber) as a photosensitizer for PDI of important human pathogens, Gram(+) Staphylococcus capitis subsp. capitis, Gram(+) Staphylococcus aureus, and Gram(−) Escherichia coli. In vitro experiments on planktonic and biofilm cultures were conducted focusing on Ber activated with visible light in the blue wavelength range. The number of planktonic S. capitis cells was reduced by 7 log10 steps using 100 µM Ber (5 min incubation, illumination with 435 nm LED array, radiant exposure 25 J/cm2). For an antibacterial effect of 4 log10 steps, static S. capitis biofilms required 1 mM Ber, a drug-to-light interval of 60 min, and illumination with 100 J/cm2. Almost all planktonic cells of Staphylococcus aureus could be photokilled using 100 µM Ber (drug-to-light interval of 30 min, radiant exposure 25 J/cm2). Biofilms of S. aureus could be phototreated (3 log10 steps inactivation) when using 1 mM Ber incubated for 5 min and photoactivated with 100 J/cm2. The study is highlighted by the proof that PDI treatment using Ber showed an antibacterial effect on Gram(−) E. coli. Planktonic cells could be reduced by 3 log10 steps with 100 µM Ber (5 min incubation, 435 nm, 25 J/cm2). With 5 mM ethylenediamine tetraacetic acid disodium salt dihydrate (Na2EDTA) or 1.2% polyaspartic acid (PASA) in addition, a relative inactivation of 4 log10 steps and 7 log10 steps, respectively, was detectable. Furthermore, we showed that an antibacterial effect of 3.4 log10 towards E. coli biofilms was given when using 1 mM Ber (5 min incubation, 435 nm, 100 J/cm2). These results underscore the significance of PDI-treatment with Ber as a natural compound in combination with blue light as valuable antimicrobial application.

Improved piezoelectric and photoluminescence properties in Ce-doped PSN-PMN-PT piezoelectric ceramics by multiscale coordination

The large piezoelectric coefficient (d33) and high mechanical quality factor (Qm) are essential for piezoelectric ceramics used in high-power devices. It is pity that the two parameters are usually opposite, with higher d33 corresponding to lower Qm. In order to well-balance the d33 and Qm, the rare-earth element Ce with multi-valence was introduced into the 0.06 Pb(Sc1/2Nb1/2)O3-0.61 Pb(Mg1/3Nb2/3)O3-0.33PbTiO3 (xCe-PSN-PMN-PT) ceramics in this work. The structure, electrical properties and optical properties of ceramics were systematically analyzed. Optimal electrical performances (d33 = 719 pC/N, Qm = 256, and dielectric loss tanδ = 0.007) were obtained in 0.02Ce-PSN-PMN-PT ceramics. These excellent performances originate from the multiscale coordination effects among defect dipoles, local structural heterogeneity, domain structure, phase structure, and grain size. The xCe-PSN-PMN-PT ceramics exhibit excellent photoluminescence properties in the blue wavelength range. Our research provides a new paradigm for deep-sea electro-optical communication.

Efficient and Traceable Tamoxifen Delivery to Breast Cancer Cells Using Folic Acid‐Decorated and PEGylated Graphene Quantum Dots

AbstractGraphene quantum dots (GQDs) possess potential properties for the targeted transport and tracking of anticancer medication to tumor cells. For this purpose, the synthesized GQDs were decorated with folic acid (FA) and methoxy polyethylene glycol (mPEG2000), and finally loaded with tamoxifen (TMX) drug. The synthesized nano‐drug was characterized using FTIR, XRD, UV‐Vis, PL, HRTEM, FESEM, and DLS analytical devices. Based on the obtained data, the average hydrodynamic diameter of particles dissolved in water was 294.7 nm and the size of dehydrated particles was between 53 and 210 nm. PL data showed that prepared nanoparticles have an emission wavelength of 438 nm, which is in the blue fluorescent wavelength range, thus making these nanoparticles suitable for cell imaging. The encapsulation efficiency and loading percentage of tamoxifen in nanoparticles were calculated at about 52.5 % and 30 %, respectively, and cumulative drug release reached 89 % within 42 hours. The cytotoxicity effects of nanoparticles were investigated. According to IC50 results, the targeted mPEG‐GQDs‐FA/TMX (TMX‐FPGs) nano‐drug was more toxic than free TMX on MCF‐7 cells and had reduced side effects on healthy HDF cells. TMX‐FPGs induced apoptosis cell death, significantly. The confocal imaging experiments showed that TMX‐FPGs are appropriate for monitoring and targeting MCF‐7 cells.

Optical and Structural Properties of Europium-Doped Silicon Oxide Fabricated Using Integrated Sputtering and Chemical Vapour Deposition

Europium (Eu) doped silicon oxide (SiOx) thin films containing Eu concentrations of 0.2 to 6.4 at% were fabricated using a hybrid deposition system combining a magnetron sputtering gun serving as the doping source with electron cyclotron resonance plasma enhanced chemical vapour deposition (ECR-PECVD). The influence of annealing conditions on the structural and luminescence properties was thoroughly studied. The optical properties of the films were investigated by performing variable angle spectroscopic ellipsometry (VASE) and photoluminescence (PL) measurements. The Eu-related emission was found to be highly dependent on the deposition parameters and annealing conditions. Eu2+ and Eu3+ emissions, which are attributed to blue and red light emissions, respectively, were observed. The structural properties were investigated by X-ray diffraction (XRD) and transmission electron microscopy (TEM) analyses, and the formation of nanoclusters was confirmed. At annealing temperatures of 900 °C and beyond, EuxSiyOz crystals were formed, and Eu ions were optically activated. As the light emissions of these thin films are in the blue and red wavelength range, they are promising candidates to be used as greenhouse covers and transparent solar cells.

What drives the variance of galaxy spectra?

ABSTRACT We present a study aimed at understanding the physical phenomena underlying the formation and evolution of galaxies following a data-driven analysis of spectroscopic data based on the variance in a carefully selected sample. We apply principal component analysis (PCA) independently to three subsets of continuum-subtracted optical spectra, segregated into their nebular emission activity as quiescent, star-forming, and active galactic nuclei (AGNs). We emphasize that the variance of the input data in this work only relates to the absorption lines in the photospheres of the stellar populations. The sample is taken from the Sloan Digital Sky Survey (SDSS) in the stellar velocity dispersion range 100–150 km s−1, to minimize the ‘blurring’ effect of the stellar motion. We restrict the analysis to the first three principal components (PCs) and find that PCA segregates the three types with the highest variance mapping SSP-equivalent age, along with an inextricable degeneracy with metallicity, even when all three PCs are included. Spectral fitting shows that stellar age dominates PC1, whereas PC2 and PC3 have a mixed dependence of age and metallicity. The trends support – independently of any model fitting – the hypothesis of an evolutionary sequence from star formation to AGN to quiescence. As a further test of the consistency of the analysis, we apply the same methodology in different spectral windows, finding similar trends, but the variance is maximal in the blue wavelength range, roughly around the 4000 Å break.

Study on the luminescence characteristics of Tb3+-doped TeO2-Bi2O3-BaF2 glass for blue-green laser emission

In this study, we prepared Tb3+-doped bismuth tellurite glasses by a high-temperature melting method. The matrix glass was characterized by higher thermal stability (ΔT = 102 °C) and lower maximum phonon energy (614 cm−1). Based on absorption spectra, Judd-Ofelt analysis revealed the spontaneous radiation transition probability (269.34 s−1) and fluorescence branching ratio (41.55%) of 5D4→7F5 transition. The luminescence peaks of the samples were located at 486 nm and 545 nm blue-green bands. Meanwhile, the luminescence intensity increased with the increase of Tb3+ concentration and reached the maximum at 4mol% Tb4O7. In addition, emission cross-section and gain coefficients were calculated in blue wavelength range, the maximum values were 2.01 × 10−22 cm−1 and 2.92 cm−1, respectively. Combining all the above results, Tb3+ doped bismuth tellurite glass had potential application value in the field of blue-green communication.

Fabrication of tunable bandgap epitaxial β‐(AlxGa1−x)2O3 films using a spin‐coating method

Abstractβ‐(AlxGa1−x)2O3 films have several critical properties of interest to the research community, including a wide bandgap that may be used in the development of new electronic, optoelectronic, and photonic devices. Here we demonstrate the first time fabricated metal‐alkoxide‐based spin‐coated single‐phase epitaxial β‐(AlxGa1−x)2O3 films on c‐sapphire substrates with orientation and good crystallinity that is comparable to the films fabricated using other film deposition techniques, such as molecular beam epitaxy and chemical vapor deposition. Using this technique, we generated films with broad Al compositions (x) of 0.3, 0.5, and 0.7 with bandgap energies of 5.15, 5.56, and 6.16 eV, respectively, estimated from the X‐ray photoelectron spectroscopy inelastic energy‐loss spectra. Photoluminescence emission spectra in the ultraviolet and visible (blue) wavelength range highlighted several intrinsic defects in the film structure that functioned as luminescence centers, including self‐trapped exciton and recombining donor‐to‐acceptor band. Detailed analysis of the structural and optical properties of β‐(AlxGa1−x)2O3 epitaxial films revealed that this low‐cost and scalable solution‐deposition approach coupled with a spin‐coating technique could be used to fabricate β‐(AlxGa1−x)2O3 films with tunable properties.

Polarization Image Laser Line Extraction Methods for Reflective Metal Surfaces

In this work, we propose a novel pipeline method for laser line extraction from images with a polarization image sensor. The proposed method is specifically developed for strong laser beam reflections from metal surfaces. For the preprocessing stage, we propose a demosaicing algorithm for color polarizer filter array (CPFA) sensors. This can be implemented by using either one-quarter or full resolution of the sensor. In addition, we propose two methods for optimizing the information available in a 12-channel color polarization image. The first method is based on the minimum linearly polarized irradiance, and the second method is based on the linear polarization intensity. These preprocessing and optimization methods are combined with laser line extraction methods. The laser line extraction is done with either the polarized finite impulse response (FIR) center of gravity (COG), where the laser line coordinates are computed from the filtered laser intensity distribution, or with the polarized FIR-Peak, where the laser line coordinates are calculated from the first derivative of the filtered laser signal. The performance of the proposed algorithms is studied experimentally using a laser line scanner assembly, made of a polarization camera, and a laser line projector operating in the blue wavelength range.

Synthesis of n-type [60]Fullerene Derivatives with Sterically Bulky tert-Butyl Groups for Vacuum Deposition Processes.

[60]Fullerene derivatives with high thermal stability can be used for vacuum deposition under heating to fabricate thin films for organic electronic devices. Here, we investigated the thermal stability of [60]fullerene derivatives with various bulky substituents for thermal evaporation under vacuum by means of thermogravimetric analysis under reduced and normal pressure. We found sterically bulky groups such as tert-butyl groups of [60]fullerene derivatives lowered the vacuum deposition temperature. Also, we performed isothermal thermogravimetric analysis to examine the long-term thermal stability of the designed compounds under heating conditions. Furthermore, we investigated the UV-Vis absorption patterns of the deposited films. Absorption in the blue wavelength range, which was attributed to intermolecular HOMO-LUMO transitions among the molecular orbitals of adjacent [60]fullerenes, was dramatically modified. These results were associated with the prevention of aggregation among neighboring [60]fullerene by the sterically bulky groups. This concept could contribute to expanding the use of evaporable [60]fullerene derivatives in organic thin-film electronics research fields.

Spectral tuning of biotemplated ZnO photonic nanoarchitectures for photocatalytic applications.

The photocatalytic activity of a flat surface can be increased by micro- and nanostructuring the interface to increase the area of the contact surface between the photocatalyst and the solute, and moreover, to optimize charge carrier transfer. Further enhancement can be achieved by using photonic nanostructures, which exhibit photonic band gap (PBG). Structurally coloured butterfly wings offer a rich ‘library’ of PBGs in the visible spectral range which can be used as naturally tuned sample sets for biotemplating. We used conformal atomic layer deposition of ZnO on the wings of various butterfly species (Arhopala asopia, Hypochrysops polycletus, Morpho sulkowskyi, Polyommatus icarus) possessing structural colour extending from the near UV to the blue wavelength range, to test the effects arising from the nanostructured surfaces and from the presence of different types of PBGs. Aqueous solutions of rhodamine B were used to test the enhancement of photocatalytic activity that was found for all ZnO-coated butterfly wings. The best reaction rate of decomposing rhodamine B when illuminated with visible light was found in 15 nm ZnO coated M. sulkowskyi wing, the reflectance of which had the highest overlap with the absorption band of the dye and had the highest reflectance intensity.

A dark target Kalman filter algorithm for aerosol property retrievals in urban environment using multispectral images

Natural and anthropogenic aerosol atmospheric emissions play a fundamental role in directly modulating the incoming solar radiation and affecting the air quality, especially in large metropolitan regions. Likewise, aerosols indirectly impact cloud lifetime, atmospheric column thermodynamics and precipitation patterns. For these reasons, it is of particular importance to assess the aerosol spatial and temporal variability in the first instance to reduce the associated global climate models uncertainty to correctly forecasting future scenarios and then to react fast in applying mitigation strategies. In this paper, an aerosol optical depth (AOD) retrieval algorithm for high-spatial resolution images in the blue wavelength range for urban environments is developed for the first time. The proposed approach is completely blind because does not use look-up-tables or complex radiative transfer models, which require the setting/estimation of many parameters. The multi-wavelength (exploiting the coastal and the blue bands) AOD retrieval permits to retrieve also important aerosol micro-physical properties, e.g., the size. The proposed method leverages on the use of Kalman filters to deal with the unavoidable sensor's noise improving the accuracy of the estimation of the AOD. The approach is assessed on four different test cases acquired by Landsat 8 involving two metropolitan areas. A strong agreement to ground-based AERONET measurements is observed on several performance metrics. Clear advantages in comparison with the baseline approach relied upon the simple inversion of the explored model are pointed out.

Highly selective and responsive detection of simetryn in tobacco samples based on molecularly imprinted photonic crystal hydrogels

A novel sensor was developed based on the combination of photonic crystal templating and molecular imprinting technique (MIT) for the detection of simetryn in tobacco samples. The molecularly imprinted photonic crystal hydrogels (MIPHs) was prepared with methacrylic acid (MAA) as monomers, ethylene glycol dimethylacrylate (EGDMA) as cross-linkers, simetryn as imprinting template molecules and polystyrene (PS) microspheres as photonic crystal template. The ordered three-dimensional macro-porous structure of MIPHs with simetryn imprinting template can generate Bragg diffraction, showing a bright structural color. The results show that the MIPHs have high selectivity and excellent sensing performance and can be used for the detection of simetryn from actual tobacco samples. Among the four triazine herbicides with similar structure, MIPHs only produced obvious Bragg diffraction peak wavelength change to simetryn, and MIPHs have good recoverability with four cycle times. When the concentration of simetryn in the actual tobacco increased from 0 to 1.0 μg/mL, the wavelength was red-shifted from 457 nm to 499 nm, which was in the blue and green visible light wavelength range. This new sensor is expected to be used to directly detect pesticide residues in tobacco.

Light Transmittance and Depth of Cure of a Bulk Fill Composite Based on the Exposure Reciprocity Law.

The objective of this study was to evaluate the effect of the exposure reciprocity law of a multi-wave light-emitting diode (LED) on the light transmittance (LT), depth of cure (DOC) and degree of conversion in-depth (DC) of a bulk fill composite. A bulk fill composite (EvoCeram® bulk fill, Ivoclar Vivadent) was photoactivated using the multi-wave LED (VALO™ Cordless, Ultradent). The LED was previously characterized using a spectrophotometer to standardize the time of exposure when using the Standard or Xtra-Power modes with the same radiant exposure of 20J/cm2. LT was evaluated through samples of the bulk fill composite every millimeter till 4 mm in-depth. DOC was evaluated according to the ISO 4049. DC of the central longitudinal cross-section from each sample of the DOC test was mapped using FT-NIR microscopy. Data were statistically analyzed according to the experimental design (α=0.05; ß=0.2). The radiant exposure in the violet wavelength range for Standard and Xtra-Power was 4.5 and 5.0 J/cm2, respectively; for the blue wavelength range the radiant exposure for Standard and Xtra-Power was 15.5 and 15.0 J/cm2, respectively. There was no statistical difference in the DOC using Standard or Xtra-Power light-curing modes, but the DOC was lower than the claimed by the manufacturer (4 mm). The DC was not significantly affected by the light-curing mode up to 4 mm in depth (p>0.05). According to exposure reciprocity law, the reduction in exposure time using the same radiant exposure did not affect the depth of cure of the bulk fill composite.

Correlation of the mechanical and biological response in light-cured RBCs to receiving a range of radiant exposures: Effect of violet light

ObjectiveThis study correlates the mechanical and biological response of commercially available resin-based composites (RBCs) to clinically relevant light-curing conditions. MethodsTwo RBCs (Venus and Venus Pearl; Kulzer) that use different monomer and photo-initiator systems, but have a similar filler volume and shade, were exposed to either just blue light, or violet and blue light from two different LCUs (Translux Wave and Translux 2Wave; Kulzer). Distance and exposure times were adjusted so that both LCUs delivered 5 similar levels of radiant exposures (RE) between 1.5 J/cm²–25 J/cm² in the blue wavelength range. Thus, the violet light was additional light. The top and bottom of 2-mm thick specimens were subjected to a depth-sensing indentation test (Martens hardness/HM, Vickers hardness/HV, indentation modulus/YHU, mechanical work/Wtotal, plastic deformation work/Wplas, creep/Cr). The viability of human gingival fibroblasts was assessed after three days of exposure to RBC eluates. One and multiple-way analysis of variance (ANOVA), the Tukey honestly significant difference (HSD) post-hoc tests (α = 0.05), t-test and a Spearman correlation analysis were used. ResultsAs the RE increased, the mechanical properties increased at a greater rate at the top compared to the bottom of the RBCs. Values measured at the bottom of 2-mm increments approached the values measured at the top only when RE > 25 J/cm² of blue light was delivered. Toxicity decreased with RE and elution cycles and was lower for Venus Pearl. Within one RE level, addition of violet light resulted in significantly improved properties (in 131 out of 150 comparisons, p < 0.05). This effect was stronger for Venus Pearl. There was a good correlation between mechanical and biological parameters. This correlation decreased as the number of eluates increased. Clinical significanceThe mechanical and biological response to variation in RE is interrelated. The addition of violet light has a positive effect, particularly at low RE.

Effect of evening light exposure on sleep in bipolar disorder: A longitudinal analysis for repeated measures in the APPLE cohort.

Sleep disturbance, a core feature of bipolar disorder, is associated with residual mood symptoms, mood episode recurrence and suicide ideation. We investigated the effect of evening light exposure on sleep in patients with bipolar disorder. In this longitudinal analysis, we measured the sleep parameters of 207 outpatients with bipolar disorder using actigraphy at their homes for seven consecutive nights. We measured the white-light illuminance and the irradiance of each wavelength during the 4 hours before each participant's bedtime. We used mixed-effect linear regression analysis for repeated measures to evaluate the effect of evening light exposure on subsequent sleep parameters. The median white-light illuminance was 25.8 lux (interquartile range, 12.9-50.1 lux). In a multivariable model adjusted for potential confounders, we found higher white-light illuminance to be significantly associated with lower sleep efficiency (per log lux: 95% confidence interval = [-1.328, -0.133]; p = 0.017), prolonged sleep-onset latency (95% confidence interval = [0.006, 0.172]; p = 0.035) and longer wake after sleep onset (95% confidence interval = [1.104, 4.459]; p = 0.001). This effect size was larger in the younger age group (aged < 44 years) stratified by median age. Higher irradiance of the blue wavelength range was significantly associated with longer wake after sleep onset, a result similar to those for the green and red wavelength ranges. We observed significant associations between evening light exposure and subsequent sleep in patients with bipolar disorder. The effects of various light wavelengths on sleep in bipolar disorder require further investigation.

Post-consumer polymers (PCR) for color retention of delicatessen meats and elucidation of the light blocking mechanism

Increased light blocking properties of extruded films can be realized by sustainable, post-consumer recycled (PCR) polymers. This study elucidates the light blocking mechanism of these films within the ultraviolet-visible region (UV–Vis) via a novel optical measurement and electron microscopy analysis. A spectrometer and integrating sphere were mounted on a translational stage opposite a light source to measure the apparent absorbance as a function of distance. It was determined that a mixed scattering/reflection mechanism is present for virgin/PCR high density polyethylene (HDPE) blends with increased scattering in the ultraviolet and both scattering and reflection in the blue-visible. An electron microscopy study further suggests that the unique optical properties may be due to the well-dispersed nano-domains of aluminum, oxygen, and silica with increasing PCR content in addition to changes in crystalline domains reported previously. This inspired the application of the material as a light fixture filter for preserving light sensitive products. The preservation efficiency of light sensitive specimens under light emitting diode (LED) illumination was evaluated quantitatively (CIE L*a*b* color space) and qualitatively (digital imaging) as a function of time. Using roast beef as a model system, the maximum red color change (a*) of non-filtered roast beef specimens was realized approximately 55% faster than the filtered (Δa* = 7.1) in simulated retail display conditions. The improved color retention under filtered light can be attributed to increased light scattering across the blue wavelength range (440–485 nm) reducing light exposure near the maximum absorption band of myoglobin. Reduction of blue light exposure inhibits metmyoglobin production and meat discoloration. Data presented in this study suggest that PCR polymers can tune light blocking properties, providing a means to increase the color retention of light sensitive foods while simultaneously diverting food and plastic waste from landfills.

Identifying and Reducing Interfacial Losses to Enhance Color-Pure Electroluminescence in Blue-Emitting Perovskite Nanoplatelet Light-Emitting Diodes.

Perovskite nanoplatelets (NPls) hold promise for light-emitting applications, having achieved photoluminescence quantum efficiencies approaching unity in the blue wavelength range, where other metal-halide perovskites have typically been ineffective. However, the external quantum efficiencies (EQEs) of blue-emitting NPl light-emitting diodes (LEDs) have reached only 0.12%. In this work, we show that NPl LEDs are primarily limited by a poor electronic interface between the emitter and hole injector. We show that the NPls have remarkably deep ionization potentials (≥6.5 eV), leading to large barriers for hole injection, as well as substantial nonradiative decay at the NPl/hole-injector interface. We find that an effective way to reduce these nonradiative losses is by using poly(triarylamine) interlayers, which lead to an increase in the EQE of the blue (464 nm emission wavelength) and sky-blue (489 nm emission wavelength) LEDs to 0.3% and 0.55%, respectively. Our work also identifies the key challenges for further efficiency increases.

Self-trapped state enabled filterless narrowband photodetections in 2D layered perovskite single crystals

Filterless narrowband photodetectors can realize color discrimination without filter or bulk spectrometer, thus greatly reducing the system volume and cost for many imaging applications. Charge collection narrowing has been demonstrated to be a successful approach to achieve filterless narrowband photodetections; nevertheless, it sacrifices the sensitivity of the photodetectors. Here we show a highly tunable narrowband photodetector based on two-dimensional perovskite single crystals with high external quantum efficiency (200%), ultralow dark current (10−12 A), and high on–off ratio (103). The spectral response of the narrowband photodetectors can be continuously tuned from red to blue with all full-width at half-maximum < 60 nm and especially < 20 nm in blue wavelength range. The excellent performance can be ascribed to self-trapped states within bandgap and extremely low electrical conductivity in the out-of-plane direction. Our findings open the exciting potential of 2D perovskites for next-generation optoelectronics.

Effect of Hf4+ doping on structure and enhancement of upconversion luminescence in Yb:Tm:LiNbO3 crystals**Project supported by Special Funds of Harbin Innovation Talents in Science and Technology Research, China (Grant No. 2015RQQXJ045) and Science Funds for the Young Innovative Talents of HUST, China.

A series of Yb:Tm:LiNbO3 crystals doped with x mol% Hf4+ ions (x = 2, 4, and 6) were grown by the Czochralski method. The dopant occupancy and defect structure of Hf:Yb:Tm:LiNbO3 crystals were investigated by x-ray diffraction and infrared transmission spectra. The influence of Hf4+ ions concentration on UV–VIS–NIR absorption spectra of Hf:Yb:Tm:LiNbO3 crystals was discussed. The upconversion luminescence of Hf:Yb:Tm:LiNbO3 crystals was obtained under 980 nm excitation. Strong emissions were observed at 475 nm in the blue wavelength range and 651 nm in the red wavelength range. Remarkably, enhancement of the red and blue upconversion luminescence was achieved by tridoping Hf4+ ions.

An aposematic colour‐polymorphic moth seen through the eyes of conspecifics and predators – Sensitivity and colour discrimination in a tiger moth

Abstract Although predation is commonly thought to exert the strongest selective pressure on coloration in aposematic species, sexual selection may also influence coloration. Specifically, polymorphism in aposematic species cannot be explained by natural selection alone. Males of the aposematic wood tiger moth (Arctia plantaginis) are polymorphic for hindwing coloration throughout most of their range. In Scandinavia, they display either white or yellow hindwings. Female hindwing coloration varies continuously from bright orange to red. Redder females and yellow males suffer least from bird predation. White males often have higher mating success than yellow males. Therefore, we ask whether females can discriminate the two male morphs by colour. Males approach females by following pheromone plumes from a distance, but search visually at short range. This raises the questions whether males discriminate female coloration and, in turn, whether female coloration is also sexually selected. Using electroretinograms, we found significantly larger retinal responses in male than female A. plantaginis, but similar spectral sensitivities in both sexes, with peaks in the UV (349 nm), blue (457 nm) and green (521 nm) wavelength range. According to colour vision models, conspecifics can discriminate white and yellow males as separate morphs, but not orange and red females. For moths and birds (Cyanistes caeruleus), white males are more conspicuous against green and brown backgrounds, mostly due to UV reflectivity, and red females are slightly more conspicuous than orange females. The costly red coloration among females is likely selected by predator pressure, not by conspecifics, whereas male colour polymorphism is probably maintained, at least partly, by the opposing forces of predation pressure favouring yellow males, and female preference for white males. Whether or not the preference for white males is based on visual cues requires further testing. The evolution of polymorphic aposematic animals can be better understood when the visual system of the species and their predators is taken into consideration. A plain language summary is available for this article.