Peak Emission Wavelength Research Articles

Computational identification of key residues regulating fluorescence emission in a red/green cyanobacteriochrome.

Cyanobacteriochromes (CBCRs) are linear tetrapyrrole bilin-binding photoreceptors of cyanobacteria that exhibit high spectral diversity, gaining attention in optogenetics and bioimaging applications. Several engineering studies on CBCRs were attempted, especially for designing near-infrared (NIR) fluorescent proteins with longer fluorescence wavelengths. However, despite continuous efforts, a key component regulating fluorescence emission property in CBCRs is still poorly understood. As a model system, we focused on red/green CBCR Slr1393g3, from the unicellular cyanobacterium Synechocystis sp. PCC 6803 to engineer Pr to get far-red light-emitting property. Energy profiling and pairwise structural comparison of Slr1393g3 variants effectively reveal the mutations that are critical to the fluorescence changes. H497 seems to play a key role in stabilizing the chromophore environment, especially the α3 helix, while H495, T499, and Q502 are potential key residues determining fluorescence emission peak wavelength. We also found that mutations of α2 and α4 helical regions are closely related to the chromophore binding stability and likely affect fluorescence properties. Taken together, our computational analysis suggests that the fluorescence of Slr1393g3 is mainly controlled by the stabilization of the chromophore binding pocket. The predicted key residues potentially regulating the fluorescence emission property of a red/green CBCR will be advantageous for designing improved NIR fluorescent protein when combined with in vitro molecular evolution approaches.

Design and Analysis of Rapid Production Single Wall Carbon Nanotube Sensor Platforms

Single-wall carbon nanotubes (SWNT) have a strong and stable near-infrared (nIR) signal and can interact with target analytes selectively, even at the single molecule level, to alter fluorescence intensity and/or emission peak wavelength. SWNT have been employed as nIR optical sensors for detecting a variety of analytes. However, high cost, long fabrication time, and poor fluorescence yield limit the current methods for immobilizing SWNT sensors on solid substrates. Recently, our group reported a protocol for SWNT immobilization resulting in high fluorescence yield, signal longevity, fluorescence distribution, and quick sensing response time. However, it takes 5 days to fabricate these sensor arrays. We have improved our previously reported protocol to immobilize SWNT sensors with a method that takes only 2 days, results in a platform with similar surface morphology, and has a higher fluorescence intensity than the previous platforms without sacrificing the sensing capabilities.

Optoelectronic and structural characterization of trapezoidal defects in 4H-SiC epilayers and the effect on MOSFET reliability

To this day, trapezoidal defects are found in clusters and high counts in wafers representing the industry standard in terms of material quality being produced. This study sheds light on the nature, origin, behavior, and impact of this defect on device yield and reliability. Trapezoidal defects in 4H-SiC epitaxial layers were investigated by photoluminescence (PL) imaging, scanning electron microscopy (SEM), cathodoluminescence spectrum imaging (CLSI), SEM electron beam induced current (EBIC) imaging, and by transmission electron microscopy (TEM) observation. The bar-shaped stacking faults were identified by the PL and CL measurements with a peak emission wavelength of 420 and 450 nm. An optoelectronic behavioral study based on the recombination enhanced dislocation glide mechanism revealed how expanding dislocations and stacking faults interact with each other. Combining the luminescence and microscopy results, the nature of the stacking faults was identified as being a combination of Shockley-type and Frank-type stacking faults. The TEM analysis showed that these defects originate from the substrate and the stacking sequences of some of the faults were determined as (…2, 4, 2…) and (…2, 3, 2…) in the Zhdanov's notation by high-resolution TEM. The origin of this defect is speculated based on our results and previous reports. The EBIC imaging showed that the high density of SFs in these towers is a strong site of carrier recombination, which presumably has an impact on the transfer characteristics of SiC devices. Furthermore, these defects have shown to impact metal oxide semiconductor field effect transistors electrical performance via an increase in the on-state resistance depending on the coverage percentage of the tower of defects in the active area of the device.

On the role of perfusion index for estimating blood glucose levels with ultrasound-assisted and conventional finger photoplethysmography in the near-infrared wavelength range

Background and objectivesThe perfusion index (PI) has recently attracted considerable interest and started to be investigated as a cost-effective diagnostic tool due to its non-invasive character. However, its potential as a painless marker of blood glucose concentration remains to be explored. This study aimed to assess the usefulness of perfusion index (PI) in estimating blood glucose using conventional and ultrasound-assisted finger photoplethysmography (PPG) in the near-infrared (NIR) wavelength range. MethodA customized module combining a reflective PPG sensor with a peak emission wavelength of 940 nm and an ultrasonic sensor with an operating frequency of 40 kHz was developed. 4-min PPG recordings (two minutes with ultrasound; two minutes without ultrasound) were acquired from 53 volunteers, including 19 diabetic patients, after conventional blood sample collection via an invasive glucometer. We computed Pearson's coefficient (r), the mean absolute error (MAE), Bland-Altman plots, and Clarke error grids to explore the relationship between PI and glucose values and evaluate the performance of the proposed approach, with and without ultrasound. ResultsWhen ultrasonic waves were applied, PI showed a higher correlation with blood glucose levels (r = −0.90, p < 0.001), MAE significantly decreased (p = 0.0051), the bias was slightly closer to zero, the LOA interval became narrower, and predicted glucose levels deviating from reference values by more than 20 % decreased in number. ConclusionsThere is an association between PI and the blood glucose level, and 40 kHz ultrasound can significantly increase the accuracy in estimating the blood glucose level through PI.

Ozone Generation from a Germicidal Ultraviolet Lamp with Peak Emission at 222 nm.

Recent interest in commercial devices containing germicidal ultraviolet lamps with a peak emission wavelength at 222 nm (GUV222) has focused on mitigating virus transmission indoors while posing minimum risk to human tissue. However, 222 nm light can produce ozone (O3) in air. O3 is an undesirable component of indoor air because of health impacts from acute to chronic exposure and its ability to degrade indoor air quality through oxidation chemistry. In seven four-hour experiments we measured O3 produced from a single filtered GUV222 lamp in a 31.5 m3 stainless steel chamber. Using an emission model, we determined an O3 generation rate of 19.4 ppbv h-1 ± 0.3 ppbv h-1 (equivalent to 1.22 mg h-1 ± 0.02 mg h-1). We estimated the fluence rate from the lamp using two methods: (1) chemical actinometry using tetrachloroethylene (actinometry) and (2) geometric projection of the irradiance field from radial and angular distribution measurements of the GUV222 lamp fluence (irradiance). Using the estimated lamp fluence rates of 2.2 μW cm-2 (actinometry) and 3.2 μW cm-2 (irradiance) we predicted O3 production in our chamber within 20 % of the average measured mixing ratio. Future studies should evaluate the indoor air quality impacts of GUV222 technologies.

Photoluminescence Induced in Mineral Oil by Ionizing Radiation

We have studied photoluminescence (PL) properties of vacuum pump mineral oil as a function of the type and intensity of ionizing radiation exposure. The mineral oil has a simple aliphatic structure, which possesses no chromophore in the traditional sense. Unexpected PL in the mineral oil has characteristic features such as variation of the emission peak wavelength depending on the excitation wavelength and intensity dramatically increasing with radiation dose. The observed behavior can be understood in the framework of a previously suggested model introducing aggregation-induced PL and the formation of conjugated clusters comprising nontraditional chromophores. Our findings can be used for the development of optical sensors for real-time monitoring of oil utilized in vacuum pumps in nuclear fusion reactors.

Fluorescence-Based Accurate Estimation of Chlorophyll in Tea Leaves Using Smartphone

Estimation of plant leaf chlorophyll is critical for assessment of overall health condition of plants. The existing detection methods demand relatively expensive and bulky instruments, thus restricting its use for onsite investigations. Present work demonstrates a low-cost, compact fluorescence-based sensor using a smartphone to estimate the chlorophyll content in plant leaves. The extracted plant chlorophyll samples have been optically excited by using an external LED with peak emission wavelength of 475 nm, and the corresponding emitted fluorescence signals at 679 nm have been recorded by the ambient light sensor of the phone. A 3D printed compact set-up has been designed to couple it with the phone to record the emitted fluorescence signal intensity from the sample. Chlorophyll concentrations in the range of 1-12 mg/g prepared from fresh tea leaves have been accurately estimated with a sensitivity of 0.068 AU g/mg and Limit of Detection (LoD) of 0.618 μg/L. The performance of the proposed smartphone sensor has been assessed by comparing the data with the commercial chlorophyll meter.

Correlative Imaging of Individual CsPbBr3 Nanocrystals: Role of Isolated Grains in Photoluminescence of Perovskite Polycrystalline Thin Films.

We report on the optical properties of a CsPbBr3 polycrystalline thin film on a single grain level. A sample composed of isolated nanocrystals (NCs) mimicking the properties of the polycrystalline thin film grains that can be individually probed by photoluminescence spectroscopy was prepared. These NCs were analyzed using correlative microscopy allowing the examination of structural, chemical, and optical properties from identical sites. Our results show that the stoichiometry of the CsPbBr3 NCs is uniform and independent of the NCs' morphology. The photoluminescence (PL) peak emission wavelength is slightly dependent on the dimensions of NCs, with a blue shift up to 9 nm for the smallest analyzed NCs. The magnitude of the blueshift is smaller than the emission line width, thus detectable only by high-resolution PL mapping. By comparing the emission energies obtained from the experiment and a rigorous effective mass model, we can fully attribute the observed variations to the size-dependent quantum confinement effect.

Performance Improvement of InGaN-Based Red Light-Emitting Diodes via Ultrathin InN Insertion Layer

The serious separation of electron–hole wavefunctions, which is caused by the built-in electric field, prevents electron–hole radiative recombination in quantum wells (QWs) in high-In-content InGaN-based red light-emitting diodes (LEDs). Here, we propose a staggered structure that inserts an ultrathin InN layer in the single quantum well (SQW) to reduce the piezoelectric polarization and suppress the quantum confined Stark effect (QCSE). We have numerically simulated the effects of SQW with the InN insertion layer (IL) on the energy band structure and electron–hole wavefunctions of the red LED. Owing to alleviated piezoelectric polarization and improved overlaps of electron–hole wavefunctions, the simulation results have revealed that the internal quantum well (IQE) of the red LED with InN IL exhibits 42% higher than that of the red LED with a square-shaped QW (SSQW) at 60 A/cm2, and the efficiency droop ratio of red LED with InN IL is 48% lower than that of red LEDs with SSQW. Furthermore, we have found that the position of InN IL can affect the energy states of carriers, which has a great influence on the IQE and peak emission wavelength of red LEDs.

86‐3: Why perovskite quantum dots will be key for LCD‐, OLED‐ and microLED displays

Green perovskite quantum dots are well known to be the best green color conversion material with respect to color purity (FWHM) and conversion efficiency (quantum yield). These two properties are essential for picture quality (color gamut and peak brightness) but also for minimizing the display power consumption which is getting more and more important for ecological reasons but also for regulatory reasons (especially in the EU). Furthermore there is also a development trend for displays equipped with a so‐called low‐ blue‐light function where the blue primary peak emission wavelength is increased in order to minimized the short‐wave blue light intensity which has a negative influence on the human circadian rhythm. However, such blue wavelength change intrinsically reduces the color gamut of the display and increases the power consumption at the same time. These two adverse effects can be mitigated and even improved by replacing the commonly used green B‐Sialon phosphor by green perovskite quantum dots.Over the last 7 years we have intensively worked on our green perovskite quantum dots and achieved a near‐unity quantum efficiency, an FWHM of 22nm and last but not least a sufficient stability against humidity, temperature and blue flux turning our perovsite QDs commercially viable now. In this presentation we give an overview about our technical perovskite solutions for miniLED backlight films (LCD displays) and also QD pixelated color converters for microLED displays and QD‐OLED displays.

Van der Waals Heterostructure Mid-Infrared Emitters with Electrically Controllable Polarization States and Spectral Characteristics.

Modern infrared (IR) microscopy, communication, and sensing systems demand control of the spectral characteristics and polarization states of light. Typically, these systems require the cascading of multiple filters, polarization optics, and rotating components to manipulate light, inevitably increasing their sizes and complexities. Here, we report two-terminal mid-infrared (mid-IR) emitters, in which tuning the polarity of the applied bias can switch their emission peak wavelengths and linear polarization states along two orthogonal orientations. Our devices are composed of two back-to-back p-n junctions formed by stacking anisotropic light-emitting materials, black phosphorus and black arsenic-phosphorus with MoS2. By controlling the crystallographic orientations and engineering the band profile of heterostructures, the emissions of two junctions exhibit distinct spectral ranges and polarization directions; more importantly, these two electroluminescence (EL) units can be independently activated, depending on the polarity of the applied bias. Furthermore, we show that when operating our emitter under the polarity-switched pulse mode, the time-averaged EL exhibits the characteristics of broad spectral coverage, encompassing the entire first mid-IR atmospheric window (λ: 3-5 μm), and electrically tunable spectral shapes.

Synthesis, structures and thermal dependence of photoluminescence of copper(I) halide metallacycle and 1-D chain complexes

In this work, we report the synthesis, X-ray crystal structures, and temperature dependence of solid-state photoluminescence properties of two cuprous iodide complexes, namely, [(mpbi)CuI]n (1) and [(bimb)CuI]n (2) (mpbi = 1,1′-(5-methyl-1,3-phenylene)bis (1H-imidazole), bimb = 1,2-bis((imidazole-1-yl)methyl)benzene). The complexes exhibit efficient solid-state emission at room temperature, with peak emission wavelengths at 580 and 650 nm, respectively. Two complexes display outstanding thermal stability. The X-ray diffraction analysis revealed that the structure of 1 is a discrete metallacycle with the copper atom in the structure adopting a less common triangular configuration, while the structure of 2 is a one-dimensional chain structure of Cu2I2 binuclear rhomboid. The temperature dependence of photoluminescence in the wide temperature range is investigated, which demonstrates that the thermal quenching of luminescence of copper complexes can be regulated by cuprophilic interaction.

Nonvolatile Tunable Wavelength‐Selective Emitter with Phase‐Changing Material Ge2Sb2Te5 Designed by Bayesian Optimization Method

The ability to tune the emission wavelength of infrared emitter while maintaining wavelength‐selectivity remains a challenge. By incorporating the nonvolatile phase‐changing material Ge2Sb2Te5 (GST), a nonvolatile tunable wavelength‐selective emitter (gold (Au)‐GST‐Au structure) based on Fabry–Perot (FP) resonance theory is demonstrated. An algorithm based on Bayesian optimization (BO) and transfer matrix method (TMM) for optimal design is proposed. First, the influence of amorphous proportion on tunability is investigated. It is found that the peak emission wavelength shifts from 5.3 to 3.8 μm and peak emissivity increases from 0.75 to 0.98 with an increase of the amorphous proportion. Second, the influence of the thickness of the top and middle layer on the emission spectrum is studied. It is illustrated that the thickness of each layer has a significant impact on the emission spectrum. Finally, an objective function considering wavelength‐selectivity in atmospheric and nonatmospheric windows as well as tunability is proposed. The optimal structure can be realized within calculations for less than 0.027% of total candidate structures. When the weight w = 0, the optimal structural parameters are dAu = 0.0018 μm and dGST = 0.4318 μm; and the effect of the weight factor in objective function is also investigated.

NIRDye 812: A molecular platform tailored for multimodal bioimaging applications of targeted fluorescence- and photoacoustic-guided surgery.

The primary treatment for malignant tumors remains to be surgical removal of the diseased tissue. The presence or absence of residual diseased tissue at the tumor margin is the strongest predictor of postoperative prognosis and recurrence. Accordingly, reliance on the ability of surgeons to visually distinguish diseased tissue from healthy tissue unambiguously in real time is crucial. Near infrared-I (NIRI) fluorescence-emitting targeting biomolecular constructs such as anticancer antibody-fluorophore conjugates, namely cetuximab-IRDye® 800CW (CTB-IRDye® 800CW), are FDA-approved for clinical trial usage in the fluorescence-guided resection of diseased tissue due to affording improved direct visualization of tumor tissue when compared to the use of either the unaided eye under standard white light illumination (WLI) surgical techniques or non-targeting fluorophores. Unfortunately, though helpful, CTB-IRDye® 800CW affords limited (i) identification of diseased tissue and (ii) tumor margin delineation, because the immunoconjugate generates suboptimal tumor-to-background ratios (TBRs) as a result of its spectral/photophysical profiles poorly aligning with the fixed optical windows of pre-/clinical setups. As such, CTB-IRDye® 800CW is more prone to affording incomplete resection compared to if TBRs were higher due to otherwise. To aid in accurately identifying deep-seated diseased tissue, photoacoustic (PA) tomography has been implemented alongside CTB-IRDye® 800CW to achieve PA signals that could result in higher TBRs. However, in clinical trial practice, using IRDye® 800CW for PA imaging also yields subpar TBRs due to it affording low PA signals. To overcome such limitations, we developed NIRDye 812, a structurally-modified topological equivalent of IRDye® 800CW, to confer it the capability to yield both higher TBRs and superior PA signal than that of the equivalent CTB-conjugate and fluorophore IRDye® 800CW itself, respectively. To do so, we substituted the oxygen atom at its meso-position with a sulfur atom. CTB-NIRDye 812 demonstrated a red-shifted absorption wavelength at 796nm and a peak NIR-I fluorescence emission wavelength at 820nm, which better dovetails with the fixed windows of preinstalled fixed emission filters within commercial pre-/clinical NIR-I fluorescence imaging instruments. Overall, CTB-NIRDye 812 provided a∼2-fold increase in TBRs compared to those of CTB-IRDye® 800CW in vivo. Also, NIRDye 812 displayed an ∼60% higher PA signal than that of IRDye® 800CW. Collectively, we achieved our goal of improving upon the spectral/photophysical and PA properties of IRDye® 800CW via introducing a subtle modification to its electronic core such that its CTB immunoconjugate could potentially allow for fast track or breakthrough designation by the FDA due to its near-identical structure displaying considerably improved efficacy.

Multifunctional and Multicolor Perovskite-CdSe Quantum Dots Diodes for Pulse Oximetry.

A conventional pulse oximeter system is composed of two light sources with different peak emission wavelengths and a photodetector. Integrating these three independent components into one single device will absolutely simplify the system design and create a miniaturized size of the product. Here, we demonstrate a bilayer perovskite-CdSe quantum dot (hereafter perovskite-QD) diode capable of voltage-tunable green/red emission and photodetection. The proposed diode also presents an intriguing feature of simultaneous light emission and detection, which is explored as regards the diode being used as a photoconductor when the positive bias is larger than the built-in voltage. The multifunctional and multicolor diode is further employed in a reflective pulse oximeter system, as either the multicolor light sources or the sensing unit in the system provide accepted and trustful results for heart rate and arterial blood oxygenation. Our work provides a possible avenue for the simplification of the pulse oximetry with a compact and miniaturized design in the future.

Impact of binding interaction modes between whey protein concentrate and quercetin on protein structural and functional characteristics

The utilization rate of proteins can be effectively improved through the interaction between proteins and polyphenols. In this study, non-covalent and covalent whey protein concentrate (WPC)-quercetin (Q) complexes were prepared. The binding principle between WPC and Q and the structural and functional properties alteration of WPC on binding with different concentrations of Q were evaluated. Fluorescence spectroscopy results demonstrated significant structural alterations of WPC characterised by fluorescence quenching and a red-shifted maximum wavelength of emission peak after the interaction between WPC and Q, and a significant decrease in β-sheet and a remarkable increase in random curl content with the increase of Q concentration in fourier transform infrared spectroscopy (FTIR). Moreover, WPC and Q were more likely to form covalent complexes rather than non-covalent ones, which was featured with higher Q binding quantity and lower sulfhydryl group content at the same Q content. The binding sites number under covalent interaction mode was about 4.75 times that of the non-covalent counterparts. Combination of Q to WPC decreased surface hydrophobicity and improved foaming capability and emulsifying activity as well as antioxidant capability both for non-covalent and covalent interaction. However, non-covalent binding increased foam stability and emulsifying stability and decreased the protein solubility characterised by protein aggregation, while opposite trends were found for covalent interaction. The interfacial stability index variations were explained by the changes of zeta-potential of complexes with the increase of Q concentration. This study provides clarifies the principle behind the binding of WPC with Q and the possible application of WPC-Q complexes in food.

Emission peak shifted incoherent random laser through the combined effects of coupling of surface plasmons in a triangular shaped silver nanostructure, microbubbles, and the waveguiding mechanism

The random laser (RL) is now becoming an essential tool for various photonics applications, and a plethora of research advancements in RL coupled with developments in the field of techniques of syntheses of various nanostructured materials is taking place. But the realization of tuning the peak emission wavelength of RL is still very challenging. However, in this report we have demonstrated an emission peak shifted tunable low threshold incoherent RL in the visible region in a gain medium of a commercially available dye laser material and by employing the rarely used scatterer materials of triangular silver nanoparticles (TSN), microbubbles, and the waveguiding mechanism. The scattering properties of trapped microbubbles, along with the localized surface plasmon resonance property of TSN of appropriate concentration within waveguided thin films composed of glass substrates, have been methodically investigated to demonstrate the reduction in lasing threshold and tunability in the peak emission wavelength. A two-fold reduction in RL threshold by addition of TSN in the disordered system, along with a considerable narrowing down of the emission spectra to a few nanometers, are obtained. Furthermore, the peak emission wavelength shift of 6 nm is reported by suitably changing the system configuration by the addition of an optimum concentration of TSN along with trapped microbubbles. The as-developed system shows high-quality laser performance with the maximum value of η=0.64, a quantity describing the ratio of the number of stimulated radiative photons within RL and the total number of emissive photons. We propose that the total internal reflections from the microbubble surface, along with plasmonic enhancement and scattering from the TSN, mediate the waveguided RL to achieve the low threshold. Therefore, this report is an early step towards demonstrating efficient RL in a ternary scattering system. Many more avenues for investigating this developing research issue may be helpful for the future development of affordable and robust optoelectronic devices.

Design of InGaN-ZnSnGa2N4 quantum wells for high-efficiency amber light emitting diodes

A novel type-II InGaN-ZnSnGa2N4 quantum well (QW) structure is proposed based on recent experimental achievements for the successful epitaxy of ZnSnN2-GaN alloys and the determination of their band offsets with GaN. The simulation results indicate that this structure is promising as the active region for high-efficiency InGaN-based amber (λ ∼ 590 nm) light-emitting diodes (LEDs). The hole wavefunction in the valence band is better confined with the insertion of a monolayer scale of ZnSnGa2N4 into the InGaN QW while the electron wavefunction in the conduction band is better confined with the incorporation of an AlGaN layer in the GaN quantum barrier. The band structure of the InGaN-ZnSnGa2N4 QW is numerically simulated based on the experimentally measured band offsets between ZnSnGa2N4 and GaN. With the InGaN-ZnSnGa2N4 QW design, a low In content (20%) is required in the InGaN layer to reach a peak emission wavelength of ∼590 nm, yet an In composition of 25% is needed to reach the same emission wavelength for a conventional InGaN QW with the same layer thicknesses. Moreover, the electron-hole wavefunction overlap (Гe1−hh1) for the InGaN-ZnSnGa2N4 QW design reaches 18% for an emission wavelength at ∼590 nm. This result is much improved over the conventional InGaN QW overlap of 5% emitting at the same wavelength. The increase in electron-hole wavefunction overlap results in an approximately 14 times enhancement in the predicted spontaneous emission radiative recombination rate of the InGaN-ZnSnGa2N4 QW as compared to that of the conventional InGaN QW. This InGaN-ZnSnGa2N4 QW structure design can be promising to pave a new way to achieve high efficiency amber LEDs.

The influence of LEDs with different blue peak emission wavelengths on the biomass, morphology, and nutrient content of kale cultivars

Light-emitting diodes (LEDs) enhance plant production in vertical farms by regulating photosynthetic rate and phytochemistry. Specific light recipes can be formulated using LEDs for high output by fine-tuning spectral composition and irradiance. In this study, the growth, development, and nutritional quality of three kale cultivars (‘Toscano’, ‘Redbor’, and ‘Winterbor’) were examined under different blue peak emission wavelengths (λpeak). Photosynthetic photon flux density (PPFD) was maintained at 200 ± 10% μmol m − 2s − 1 over a 16-hr photoperiod. The LED light treatments had blue λpeak centered at 400, 420, and 450 nm wavelengths, all with spectral ratios of 20% blue, 20% green, 60% red in the visible light region, and 15% of total PPFD in the far-red region. The control light was cool-white fluorescent (CWF) light with blue λpeak at 436 nm and a slightly higher amount of PPFD in the blue region (23%). The biomass yield and leaf physical characteristics were largely unaffected by the light treatments with different blue λpeak. However, the concentration of carotenoids and chlorophylls in kale leaves was influenced by the type and amount of blue light during growth. Future research should investigate the effect of different blue light percentages in pre- and post-harvest LED treatments (continuous or pulsed) on high-value, nutritious crops.

Temperature dependence of the emission cross-section and fluorescence lifetime in Cr:LiCAF, Cr:LiSAF, and Cr:LiSGaF between 78 K and 618 K

Cr:Colquiriites (Cr:LiCAF, Cr:LiSAF, and Cr:LiSGaF) are well-known for their broad emission bands in the near-infrared region. Unfortunately, due to their relatively weak thermomechanical strength, average powers from Cr:Colquiriite lasers have been so far limited to sub-5 W level in continuous-wave operation at room temperature. In this study, the promise of cryogenic operation, which shows significant power scalability in Yb-based systems, is investigated in detail for Cr-doped Colquiriite crystals in terms of the temperature dependence of the fluorescence lifetime and emission cross-section (σ e ) in the 78-618 K range. The lifetime measurements showed that the fluorescence, as well as the radiative lifetimes of Cr:Colquiriites are temperature dependent. The emission cross-section measurements revealed that while cooling the crystals from 300 K to 78 K, the peak σ e in E||c polarization increases moderately for all crystals: from around 1.3 × 10−20 cm2 to 1.6 × 10−20 cm2 in Cr:LiCAF, from around 4.5 × 10−20 cm2 to 6.3 × 10−20 cm2 in Cr:LiSAF and from around 3.1 × 10−20 cm2 to 3.95 × 10−20 cm2 in Cr:LiSGaF. We provide analytical formulas describing the measured temperature dependence of all relevant quantities such as fluorescence/radiative lifetime, peak emission wavelength, peak emission cross-section, and emission full-width at half-maximum. Overall, the reported results constitute a solid basis for the modeling of Cr:Colquiriite-based laser and amplifier systems, especially for the assessment of their potential at cryogenic temperatures.