Shift In Emission Spectra Research Articles

Multi-cation doped CuCrO[formula omitted] crystallite matrix: Exploring bandgap tunability through Ni-Zn and Ni-Zn-Mg doping for optoelectronic application

Bandgap tuning is a key approach to optimizing materials for advanced technologies, enabling the development of more efficient and specialized devices. In this study, we demonstrate the tunability of the bandgap of CuCrO2 from 2.38 to 4.37 eV via single cation-doping with Ni and Zn, and multi-cation doping with Ni-Zn and Ni-Zn-Mg. XRD analysis reveals structural changes due to lattice distortions by cationic substitution, while FESEM shows the impact of doping on particle size, surface morphology, and crystallinity. The lamellar structure observed with multi-cation doping in FESEM investigations indicates increased structural disorder and defects, causing tailing above the valence band and below the conduction band, significantly reducing the bandgap. The effect of Zn-Ni doping on the lattice is reversed with Mg2+ insertion due to p-p orbital interactions between Mg2+-O, replacing the d-p interaction in the Cr3＋-O bond, as confirmed by optical studies. UV–Vis and photoluminescence analyses reveal significant shifts in bandgaps and emission spectra, with Ni doping yielding a bandgap of 3.97 eV, Zn doping 3.16 eV, Zn-Ni doping expanding it to 4.37 eV, and Zn-Ni-Mg doping reducing it to 2.38 eV. The dopants also affect emission characteristics, including band edge and deep-level emissions. This study provides valuable insights into the relationship between cationic doping and material properties, guiding the design of CuCrO2-based materials with tailored functionalities.

Structure regulation and luminescence improvement of Gd3Ga5O12:Cr3+: An anti-thermal quenching NIR phosphor for multifunctional applications

Near-infrared (NIR) phosphors converted light emitting diodes (LEDs) are booming as next NIR light sources. But the quantum efficiency and thermal stability of the NIR phosphors need to be improved. Here, thermally stable garnet Gd3Ga5O12 is selected as the matrix and Cr3+ as the luminescent center to obtain Gd3Ga5O12:Cr3+ NIR phosphor. Equivalent smaller Lu3+ was adopted to regulate the structure of Gd3Ga5O12 to further improve the luminescence performance. By regulating the structure the emission spectra shift toward blue region and the intensity is improved. Optimized GdLu2Ga5O12:Cr3+ exhibits anti-thermal quenching behavior and the internal quantum efficiency reaches 73.69 %. Relative sensitivity value of the phosphor GdLu2Ga5O12:Cr3+ reaches 3.353 % K−1 at 423 K based on lifetime mode. LED device is fabricated by combining the phosphor GdLu2Ga5O12:Cr3+ and the commercial red phosphor with blue chip. Electroluminescence spectrum can cover the absorption spectra of the plant dyes well. The lettuce grow faster by adopting this LED device as compensating light source. This work provides an anti-thermal quenching NIR phosphor for multiple applications.

Cm(III) speciation in the presence of citrate from neutral to hyperalkaline conditions and the effect of calcium

We investigated the binary Cm-citrate system using time-resolved laser fluorescence spectroscopy (TRLFS), parallel factor analysis (PARAFAC), and quantum chemical calculations. Evidence collectively suggests the stepwise coordination and deprotonation of citrate alcohol groups in Cm-cit complexes with two bound citrate moieties upon increasing pH, which is supported by a bathochromic shift in emission spectra, an observed increase in lifetime measurements, and lower energy minima for citrate alcohol involvement versus hydrolysis of the Cm-citrate species. Our PARAFAC results agree with a 3-component model for the Cm-citrate system and offer pure component decompositions, yielding fraction species across the studied pH range that have a correlated slope = 1 as a function of pH. For the first time, evidence of ternary Ca-Cm-citrate complexes was revealed by TRLFS with increasing calcium concentration at fixed pHm. The formation of these ternary complexes was substantiated with density functional theory (DFT) calculations on simple model systems of the complexes. Shared citrate carboxylate groups between calcium and curium were proposed for all three ternary Ca-Cm-cit complexes based on DFT-determined Ca–O and Cm–O distances. Moreover, we found that the ternary complex with both alcohol groups deprotonated is most stable when it shares both two carboxylate and two alcohol groups between Ca and Cm. The presence of shared functional groups highlights the enhanced stability of these ternary complexes. Additional work is warranted to further constrain the stoichiometry, stability constants and dependence on ionic strength of these complexes for purposes of thermodynamic modeling of repository settings.

Effects of donor substituents on the conformational heterogeneity, photophysical, mechanochromic and electroluminescent properties of the donor-substituted fluorine-containing triphenylpyrimidines

Three derivatives of fluorinated triphenylpyrimidine with the attached carbazole, phenothiazine, or acridan donor moieties are synthesized by Buchwald-Hartwig reactions. The impact of the donor units on emissive and other properties of the compounds is reported. The compounds exhibit excellent thermal stability, competitive photophysical phenomena such as room temperature phosphorescence (RTP) appearing when compounds are molecularly dispersed in the rigid polymer matrix and thermally activated delayed fluorescence (TADF). The compounds with carbazole and phenothiazine donor moieties show the manifestation of triplet–triplet annihilation in the electroluminescence when used as emitters in organic light-emitting diodes (OLEDs). The phenothiazine-containing compound exhibit dual photoluminescence with the blue-shifted peak corresponding to the quasi-axial conformer and a red-shifted peak to the quasi-equatorial conformer. This derivative shows reversible shifts of emission spectra exceeding 100 nm due to the stable (at least 4 cycles) mechanochromic luminescence under the application of external stimuli. After grinding the emission intensity maximum is observed at 555 nm, after fuming at. ca 448 nm and after melting at 555 nm. The photoluminescence shifts and ON/OFF delayed fluorescence of the phenothiazine-based emitter occur due to the alteration between the crystalline and amorphous states. Optimization of the device structure allows to control the charge balance resulting in external quantum efficiency of up to 5.7 % observed for the OLED based on the phenothiazine-based emitter. This compound also shows the biggest response to the presence of oxygen acting as the quencher of triplet excited energy. The film of the compound doped in rigid Zeonex shows an 8.4-fold increase in emission intensity after evacuation. The optical sensor fabricated using the derivative of fluorinated triphenylpyrimidine and phenothiazine is characterized by the Stern-Volmer constant 1.37 × 10-4 ppm−1.

Electric charges of the lipid headgroup modulate Melittin adsorption to lipid vesicle membranes

Peptide lipid membrane interactions are modulated by factors such as peptide hydrophobicity and the electric charge of both the peptide and the membrane surface. We investigated the influence of lipid headgroup charge on the adsorption of Melittin (Mel) on the surface of artificial lipid vesicles in conditions that mimic the interaction with biological cells, such as ionic strength, pH, and peptide concentration. Taking advantage of Mel TRP residue fluorescence, we used several fluorescence techniques (FRET, fluorescence quenching, time-resolved fluorescence) to investigate Mel adsorption on the surface of the DMPC and DMPC with fractions of positively charged lipids (EPC) or negatively charged lipids (DPPG) vesicles. Our results show that the DMPC:DPPG vesicles allow a deeper localization of TRP residues in the lipid membrane, proven by the blue shift of the TRP emission spectrum and the exclusion radius evaluated from FRET. We also showed that even for positively charged surfaces Mel tends to adsorb on the lipid surface. The results were confirmed indirectly by quencher accessibility to TRP. Finally, we discuss the results in correlation to the Mel effects on biological cells

Humidity Sensing Using a Multimode Fiber Ring Laser with Thermal Compensation

We propose a multimode fiber laser sensor utilizing PI-SMF (polyimide-coated single mode fiber) for low-error relative humidity (RH) measurement, which is temperature compensated based on FBG. The PI-SMF in the laser cavity is used as a sensing element, and its length varies with humidity and temperature by volume-variation induced strain, which leads to frequency shift of the longitudinal mode beat frequency signal (BFS). When the 2000 MHz BFS is selected as the sensing signal, a RH sensitivity of −2.68 kHz/%RH and a temperature sensitivity of −14.05 kHz/°C are achieved. The peak shift of the FBG-based laser emission spectrum is only sensitive to temperature rather than RH with a temperature sensitivity of 9.95 pm/°C, which is used as the temperature compensation for RH measurements. By monitoring the response of the BFS and the laser wavelength, the cross-sensitivity effect of RH and temperature is overcome, and low-error RH measurement in the temperature range of 20 to 65 °C is realized with errors within ±0.67 %RH (25 to 85 %RH). The scheme does not require the design and production of complex structures and hygroscopic material coating processes, owning the advantages of simple structure, easy operation and high accuracy, and is expected to be practically applied in food safety and environmental monitoring.

Formation of gel and solid phases in acrylic cuvettes upon exposure to DMSO, oxygen and light: implications for fluorescence spectroscopy

We here report the formation of a turbid-gel phase in acrylic cuvettes upon exposure to pure Dimethyl Sulfoxide (DMSO) at room temperature. The observed phenomenon occurred over a 10 h to 14 h incubation in the presence of environmental oxygen. After the turbid gel was removed from the cuvette, it became a white solid exhibiting unique emission behavior. The formation of the turbid-gel phase was accelerated upon exposure to UV 295 LED pulses of light from 6 h to 8 h. Surprisingly, subsequent exposure of the white solid to a few microliters of pure DMSO and vortexing resulted in its transformation into a transparent gel state in just a few minutes, eventually acquiring transparent and liquid properties. Additionally, the white-solid phase can load other molecules, such as Resveratrol and Quercetin, leading to shifts in the respective emission spectra compared with the same molecule in liquid and pure DMSO. These novel findings highlight the interaction between UV photons, oxygen, DMSO and Acrylic, and potentially distort fluorescence spectroscopy experiments.

Engineering of Multidimensional Core-Shell Perovskite Precursors to Obtain Superior Luminescence and Incorporating in Luminescent Solar Concentrators

The luminescence feature of perovskite NPs with high PLQY directs them to lighting and display applications. 2D A2MAn−1PbnBr3n+1 (n=1−6) perovskites with A as octylammonium and benzylammonium cations are synthesized by the LARP method, in which the highest PL emission is attained to the n=6 sample with benzylamine cation. XRD results reveal the appearance of diffraction peaks related to 3D perovskites with increasing n value. Mixing 3D perovskites with 2D ones leads to the formation of core-shell MAPbBr3−A2MAn−1PbnBr3n+1 (n=1−6) nanostructures, confirmed by TEM images and optical properties. Incorporation of Zn to core-shell perovskites improves the PL intensity and induces higher crystallinity. A blue shift in absorption and emission spectra of Zn-doped perovskites is observed. The highest PLQY (94%) is attributed to the Zn-doped core-shell perovskite with n=6 among the all-synthesized samples. Luminescent solar concentrators with thicknesses of 2 mm and 5 mm are fabricated with benzylamine-based perovskites, because of their greater PLQY versus octylamine-based perovskites. The performance of LSC devices is boosted for the LSC with 5 mm thickness. The relative PCE obtained for the core-shell perovskite-based LSC with thickness of 5 mm reaches to almost 60%.

Solid-State [2+2] Photoreaction of Isostructural Cd(II) Metal Complexes and Solid-State Fluorescence.

A green method to synthesize cyclobutane derivatives has been developed over the past three decades in the form of solid-state [2+2] photochemical reactions. These solid-state reactions also play a major role in the structural transformation of hybrid materials. In this regard, crystal engineering has played a major role in designing photoreactive molecular systems. Here, we report three novel binuclear Cd(II) complexes with the molecular formula [Cd2(4spy)4L4], where 4spy = 4-styryl pyridine and L = p-toluate (1); 4-fluorobenzoate (2); and 3-fluorobenzoate (3). Although three different benzoates are used, all three complexes are isostructural, as corroborated through SCXRD experiments. Structural analysis also helped in identifying two potential photoreactions. These are both intra- and intermolecular in nature and are driven by the head-to-head (HH) and head-to-tail (HT) alignment of 4spy linkers within these metal complexes. 1H NMR spectroscopy studies showed evidence of a quantitative head-to-head photoreaction in all these three complexes, and SCXRD analysis of the recrystallization of the photoproducts also provided confirmation. TGA studies of these photoreactive complexes showed an increase in the thermal stability of the complexes due to the solid-state photoreaction. Photoluminescence studies of these complexes have been conducted, showing a blue shift in emission spectra across all three cases after the photoreaction.

The effect of polarity and hydrogen bonding on the electronic and vibrational structure of the salicylate anion in acetonitrile and water: implicit and explicit solvation approaches.

This study investigates the fluorescence quenching of the salicylate anion in water compared to acetonitrile (ACN) and the stability of its keto structure in ACN using DFT and TD-DFT methods at the 6-311++G(d,p) basis set. Computational simulations in implicit and explicit environments of ACN and water reveal the effects of solvent polarity and hydrogen bonding on enol [Od-H⋯Oa] and keto [Od⋯H-Oa] tautomerization, fluorescence quenching, and the spectral profile of the salicylate anion. Implicit solvation models show a barrier height of approximately 1.9 kcal mol-1 in ACN and 3.6 kcal mol-1 in water for enol-keto tautomerization in the ground state, with no barrier in the excited state, leading to an ESIPT reaction in both solvents, but only ground state proton transfer in ACN. Simulated absorption spectra for both enol and keto forms are similar in both solvents, while the emission spectrum is red-shifted in water. Explicit solvation studies indicate greater stabilization of the salicylate anion in water than in ACN, with a blue shift in absorption and emission spectra and varying oscillator strengths. Solvent molecule positioning affects enol-keto stabilization in the ground state, but only the keto structure is stabilized in the excited state. Simulated IR spectra in water show a blue shift in Od-H stretching frequency and increased water molecule vibrational frequencies, suggesting non-radiative excitation energy transfer from salicylate ions to water molecules via n → σ* intermolecular hydrogen bonding interactions. This mechanism explains the fluorescence quenching observed in water and results align with experimental data, indicating hydrogen-bonded keto form stabilization both in water and ACN.

Precisely Regulation of Peripheral Decoration of Multi‐Resonance Molecules and Construction of Highly Efficient Solution‐Processed Orange–Red OLEDs with External Quantum Efficiency Approaching 20%

AbstractThe advent of multi‐resonance thermally activated delayed fluorescence (MR‐TADF) materials, heralding cutting‐edge emitters with superior efficiency and color fidelity, represents a momentous stride in the realm of organic light‐emitting diodes (OLEDs). In this particular investigation, substantial advancements have been made by enhancing, synthesizing, and characterizing three distinct MR‐type emitters through meticulous control of peripheral decorations using frontier molecular orbital engineering. Through strategic attachment of various pyrimidine derivatives to the positions of the lowest unoccupied molecular orbitals (LUMO) of the parent molecule, the molecular excited state attributes are meticulously tailored, leading to the development of orange‐red MR‐TADF emitters. These designed molecules have demonstrated an emission spectrum shift from orange‐red to orange, exhibiting peak wavelengths spanning the range of 585–608 nm and full width at half‐maximums (FWHM) between 36 and 43 nm. This signifies a remarkable precision in managing the emission maxima of MR‐TADF emitters. Astonishingly, the solution‐processed OLEDs have showcased vibrant orange‐red electroluminescence, characterized by peak wavelengths ranging from 587 to 611 nm, accompanied by a notable external quantum efficiency nearing 20%.

A near-infrared fluorescent probe for rapid and on-site detection of sulfur dioxide derivative in biological, food and environmental systems

Emission of toxic gaseous sulfur dioxide (SO2) and its derivative bisulfite (HSO3–) from various industrial applications, like food processing, transportation, and the coking process, has raised substantial concerns regarding environmental quality and public health. The probes for specific and sensitive detection of SO2 derivatives plays an essential role in their regulation, and ultimately mitigating their environmental and health implications, but the one that can detect SO2 derivatives onsite by end users remains limited. Herein, we report a new near-infrared fluorescence probe (SL) for rapid and onsite detection of SO2 derivative, HSO3– in industrial wastewater, food samples and for sensing its interaction with biological organisms. The SL is developed through coupling of quinolinium and coumarin moiety through an electron deficit CC bond that can specifically react with HSO3− via a Michael addition. By recording the blue shift of absorption and emission spectra, SL can sensitively detect HSO3– (limit of detection, 38 nM) in aqueous solution within 40 s SL is biocompatible, can be used for evaluating toxicity of SO2 derivatives in living organisms. The preparation of SL-stained test paper allows the colorimetric/fluorometric analysis for quantification of HSO3– onsite in food, river and coking wastewater samples using a smartphone. The successful development of SL not only provides a new tool to investigate HSO3– in biological, food and environmental systems, but also potentially promotes the application of fluorescence technique for rapid and onsite analysis of real-world samples by end users.

Multimodal fluorescence imaging and spectroscopic techniques for oral cancer screening: a real-time approach

The survival rate of oral squamous cell carcinoma (OSCC) patients is very poor, but it can be improved using highly sensitive, specific, and accurate techniques. Autofluorescence and fluorescence techniques are very sensitive and helpful in cancer screening; being directly linked with the molecular levels of human tissue, they can be used as a quantitative tool for cancer detection. Here, we report the development of multi-modal autofluorescence and fluorescence imaging and spectroscopic (MAF-IS) smartphone-based systems for fast and real-time oral cancer screening. MAF-IS system is indigenously developed and offers the advantages of being a low-cost, handy, non-contact, non-invasive, and easily operable device that can be employed in hospitals, including low-resource settings. In this study, we report the results of 43 individuals with 28 OSCC and 15 oral potentially malignant disorders (OPMDs), i.e., epithelial dysplasia and oral submucous fibrosis, using the developed devices. We observed a red shift in fluorescence emission spectra in vivo. We found red-shift of 7.72 ± 6 nm, 3 ± 4.36 nm, and 1.33 ± 0.47 nm in the case of OSCC, epithelial dysplasia, and oral submucous fibrosis, respectively, compared to normal. The results were compared with histopathology and found to be consistent. Further, the MAF-IS system provides results in real-time with higher accuracy and sensitivity compared to devices using a single modality. Our system can achieve an accuracy of 97% with sensitivity and specificity of 100% and 94.7%, respectively, even with a smaller number of patients (28 patients of OSCC). The proposed MAF-IS device has great potential for fast screening and diagnosis of oral cancer in the future.

Temporal‐Spatial‐Resolved Lasing Dynamics in Customized Solution Grown Perovskite Single‐Crystal Microcavities

AbstractSingle‐crystal halide perovskites are among the most promising semiconductor candidates for highly efficient optoelectronic devices due to their higher stability against moisture and light radiation and lower trap density than their polycrystalline counterparts. In this work, single‐crystal MAPbBr3 microcavities with controllable geometries and sizes are fabricated using a template‐limited method combined with an anti‐solvent diffusion growth method. The single‐crystal microcavities emit lasers around 550 nm under femtosecond laser excitation, with a lasing threshold of ≈35 µJ cm−2 and a quality factor of 1135, as well as excellent long‐term operation stability. The temporal‐spatial evolution of the lasing process in an individual microcavity is achieved by the microscopic optical Kerr‐gating technique. The temporal behaviors including pulse duration and build‐up time, emission spectra shift, and lasing mode evolution as a function of pump fluence are unveiled, and the complex relationship between the light‐induced carrier dynamics and lasing properties is clarified. Spatial heterogeneous lasing dynamics are also observed in an individual microdisk, which is attributed to the non‐uniform optical losses and carrier densities driven by structural imperfections. This study can provide a fabrication strategy for perovskite on‐chip optoelectronic devices, as well as a deeper understanding of the carrier‐density‐driven lasing dynamics in microcavities.

Beyond Universal Volume Scaling: Tailoring Two-Photon Absorption in Nanomaterials by Heterostructure Design.

Colloidal semiconductor nanomaterials present broadband, with large cross-section, two-photon absorption (2PA) spectra, which turn them into an important platform for applications that benefit from a high nonlinear optical response. Despite that, to date, the only means to control the magnitude of the 2PA cross-section is by changing the nanoparticle volume, as it follows a universal volume scale, independent of the material composition. As the emission spectrum is connected utterly to the nanomaterial dimensions, for a given material, the magnitude of the nonlinear optical response is also coupled to the emission spectra. Here, we demonstrate a means to decouple both effects by exploring the 2PA response of different types of heterostructures, tailoring the volume dependence of the 2PA cross-section due to the different dependence of the density of final states on the nanoparticle volume. By heterostructure engineering, one can obtain 1 order of magnitude enhancement of the 2PA cross-section with minimum emission spectra shift.

Tunable emission and high chromogenic laser lighting of transparent ceramics for high-brightness white LEDs/LDs

Transparent ceramics possess highly luminescent and safe for museum lighting and be considered excellent color converters for laser diode (LD) devices. However, the current LD lighting has a low color rendering index for the lack of red component that affects the original appearance of the artwork. Here, a series of Lu3-xGdxAl5O12:Ce3+, Mn2+ (x = 0–1.5) photoluminescent transparent ceramics were prepared with an improvement display index due to the red shift of emission spectrum, the emission peak of Ce3+ and Mn2+ has a red shift by 30 and 20 nm respectively. The transmittance of transparent ceramics is 70% and the spectrum adjustable from 500 to 800 nm. Their photoluminescence property is retained at 96% of the initial value at 425 K when the doping of Gd3+ is 0.25. The color rendering index of the Lu1.38Gd1.5Al5O12:0.02Ce3+, 0.1Mn2+ can reached 81.5, while the correlated-color temperature is 3465 K. These characteristics show the LD system is promising for application in museum lighting.

Non-Phenomenological Description of the Time-Resolved Emission in Solution with Quantum-Classical Vibronic Approaches-Application to Coumarin C153 in Methanol.

We report a joint experimental and theoretical work on the steady-state spectroscopy and time-resolved emission of the coumarin C153 dye in methanol. The lowest energy excited state of this molecule is characterized by an intramolecular charge transfer thus leading to remarkable shifts of the time-resolved emission spectra, dictated by the methanol reorganization dynamics. We selected this system as a prototypical test case for the first application of a novel computational protocol aimed at the prediction of transient emission spectral shapes, including both vibronic and solvent effects, without applying any phenomenological broadening. It combines a recently developed quantum-classical approach, the adiabatic molecular dynamics generalized vertical Hessian method (Ad-MD|gVH), with nonequilibrium molecular dynamics simulations. For the steady-state spectra we show that the Ad-MD|gVH approach is able to reproduce quite accurately the spectral shapes and the Stokes shift, while a ∼0.15 eV error is found on the prediction of the solvent shift going from gas phase to methanol. The spectral shape of the time-resolved emission signals is, overall, well reproduced, although the simulated spectra are slightly too broad and asymmetric at low energies with respect to experiments. As far as the spectral shift is concerned, the calculated spectra from 4 ps to 100 ps are in excellent agreement with experiments, correctly predicting the end of the solvent reorganization after about 20 ps. On the other hand, before 4 ps solvent dynamics is predicted to be too fast in the simulations and, in the sub-ps timescale, the uncertainty due to the experimental time resolution (300 fs) makes the comparison less straightforward. Finally, analysis of the reorganization of the first solvation shell surrounding the excited solute, based on atomic radial distribution functions and orientational correlations, indicates a fast solvent response (≈100 fs) characterized by the strengthening of the carbonyl-methanol hydrogen bond interactions, followed by the solvent reorientation, occurring on the ps timescale, to maximize local dipolar interactions.

Red-Emitting Tetraphenylethylene-Based Boron Thioketonates: Effect of Substitution and Study of Nonlinear Optical Properties

We present tetraphenylethylene (TPE) and N,N-dimethylaniline (DMA)-substituted monothio-β-diketonate boron compounds. All O,S-chelated boron compounds showed red emission in solution as well as in the solid state. A comparison of O,O-chelated vs O,S-chelated compound reveals that the latter showed a pronounced red shift in both absorption and emission. Furthermore, the O,S-chelated compound showed the reduction potential at a less-negative position over the O,O-chelated compound. The marked red shift in O,S-chelated compounds indicates that there is a discernible enhancement in linear polarizability upon optical excitation, and consequently, we explore the nonlinear optical properties of the compounds at infrared wavelengths. The open-aperture Z-scan measurements using ultrashort pulses reveal the optical-limiting behavior of these compounds along with a greater nonlinear absorption for those variants, which exhibits a greater red shift in absorption and emission spectrum.

Effect of surface modification on the photoluminescent properties of γ-Ga2O3 nanocrystals

Ga2O3 nanocrystals with compelling optical properties attract broad attention from the scientific and industrial community. However, the influence of surface modification on the photoluminescent properties of Ga2O3 NCs remains unexplored. Here, we report comparative investigations of the photoluminescent properties of oleylamine-capped and ligand-free γ-Ga2O3 nanocrystals. The removal of oleylamine ligand on the Ga2O3 nanocrystal surface via a post-synthesis reaction is accompanied by the accumulation of positive surface charges and a reduction of oxygen vacancies. The change of nanocrystal surface leads to an appreciable red shift of emission spectrum along with a substantial increase in photoluminescence lifetime. Modeling the photoluminescence decay dynamics of Ga2O3 nanocrystals indicate the change of photoluminescent property is correlated to the decrease of the number density of donors and donor Bohr radius resulting from the change of nanocrystal surface.

HIGH ANTIOXIDATION-CAPACITY STEM CELLS ENHANCE CARTILAGE REGENERATION

Stem cells are known to have low levels of intracellular reactive oxygen species (ROS) and high levels of glutathione. ROS are thought to interact with several pathways that affect the transcription machinery required for stem cell differentiation, and are critical for maintaining stem cell function. In this study, we are developing a new fluorescent probe that rapidly and reversibly reacts with glutathione (GSH), the most abundant non-protein thiol in living cells that acts as an antioxidant and redox regulator.Multipotent perivascular progenitor cells derived from human ESCs (hESC-PVPCs): Differentiated ESCs as embryoid bodies in the presence of BMP4 to induce mesoderm differentiation followed by a simple cell selection strategy using attachment of single cells onto collagen-coated dishes. Differential gene expression profiling was performed among H9 hESCs, EBs induced by BMP4 and naturally selected CD140B+CD44+ population at Day 7 (PVPCs). Colony-forming assay: GSHhigh and GSHlow PVPCs were plated on 10-cm tissue culture-treated polystyrene dishes in triplicate in growth medium and cultured for 14 days. Transwell migration assay: GSHhigh and GSHlow PVPCs at passage 4 were resuspended at 1 × 106/mL in the migration medium and seeded in the upper chamber. The following human recombinant SDF-1 and PDGF-AA proteins were used as chemoattractants in the lower compartment.Probe-GSH conjugate shows shifts in fluorescence excitation and emission spectra that enables ratiometric measurement of GSH levels. Using these properties, stem cells can be purified by FACS-based technology according to intracellular GSH level. We are developing a protocol both for comparing GSH level in stem cell from different culture conditions and for preparing stem cells with high-GSH level . Our results reveal that GSHhigh PVPC purified by FACS show increased colony forming ability compared with that GSHlow PVPC, indicating that intracellular GSH contributes to the maintenance of stemness. Moreover, transplantation of GSHlow PVPC is more effective than that of GSHlow PVPC for cartilage regeneration in osteochondral defect.This technique enable FACS-based sorting of stem cells according to intracellular GSH levels and thus investigation of functional role of GSH (high antioxidant capacity) in the stem cell maintenance and chondrogenic differentiation.