Red Light Excitation Research Articles

A cyanobenzo[a]phenoxazine-based near infrared lysosome-tracker for in cellulo imaging

A cyanobenzo[a]phenoxazine-based pH probe with pKa = 5.0 exhibits OFF-ON emission at 625-850 nm upon excitation at 600 nm in aqueous buffers. The in cellulo imaging experiments with HeLa cells indicate that the probe can serve as a lysosome-specific probe under red light excitation (633 nm) with near infrared emission (650-790 nm).

Contrasting behaviour of the co-activators in the luminescence spectra of Y2O2S:Tb3+,Er3+nanometre sized particles under UV and red light excitation

Nanometre sized particles of terbium and erbium co-doped yttrium oxysulfide up-converting phosphors were prepared by a urea homogeneous-precipitation method. Results from X-ray powder diffraction (XRPD), scanning electron microscopy (SEM) and photoluminescence spectroscopy studies on the microstructure and luminescent properties of the materials are reported. Upconversion emission was observed from the Er(3+) cations when particles were excited with laser light of 632.8 nm wavelength. Under these conditions no interactions between the Er(3+) cations and the Tb(3+) cations were observed. In contrast there was evidence from the Stokes emission of the Er(3+) cations under 254 nm excitation for an interaction between the Er(3+) and Tb(3+) cations reducing intensity of the latter's blue and green emission bands by cross relaxation processes.

A photosensitive Cr3+ center in photorefractive Bi12SiO20 crystals co-doped with chromium and phosphorus

A trigonal Cr3+ (3d3) defect in sillenite type Bi12SiO20 crystals co-doped with chromium and phosphorus has been identified by means of multi-frequency X-band (9.4 GHz), Q-band (35 GHz) and W-band (94 GHz) electron paramagnetic resonance (EPR). A consistent analysis of the observed spectra and their angular dependence was reached using an S = 3/2 spin Hamiltonian with axial symmetry around a 〈111〉 crystallographic direction, an isotropic g-value g = 1.983, and a zero field splitting parameter B20 = 0.1950 cm−1. The spectra are attributed to a chromium ion in the unusual Cr3+ valence replacing a substitutional Si4+ in tetrahedral oxygen coordination. Evidence is found that the symmetry lowering from tetrahedral to trigonal is not spontaneous but induced by an associated defect, for which a P5+ ion in a nearest-neighbor Si4+ site is the most plausible candidate. Optical excitation results in a reversible charge transfer process directly correlated with a photochromic effect: near-UV light leads to a strong reduction of the Cr3+ EPR signals, and induces a broad band at 675 nm in the absorption spectrum, and both effects are reversed under red light excitation.

A new Os,Rh bimetallic with O2 independent DNA cleavage and DNA photobinding with red therapeutic light excitation

Many Ru and Os systems display photoactive (3)MLCT states. Systems activated by therapeutic window light in the absence of O(2) remain elusive. [(bpy)(2)Os(dpp)RhCl(2)(phen)](3+) photobinds and photocleaves DNA under red light in an oxygen independent manner, due to molecular design involving one Os chromophore coupled to a photoactive cis-Rh(III)Cl(2) moiety.

Chemiluminescence-based uphill energy conversion

The conversion of red excitation light into blue emission light (uphill energy conversion) using unstable 1,2-dioxetanes is described. The method is based on 1,2-dioxetane formation by red-light sensitized photooxygenation of adequate alkenes and subsequent blue-light emission due to thermal 1,2-dioxetane cleavage. The energy gain resulting from the chemical energy obtained in the transformation of an alkene into two carbonyl compounds transforms a red-light excitation laser beam into a blue-light chemiluminescence emission, producing thereby a formal anti-Stokes shift of 200–250 nm, opening up a whole spectrum of possible applications.

Multi-modal imaging of anoxic depolarization and hemodynamic changes induced by cardiac arrest in the rat cerebral cortex

We have reported previously that, in otherwise physiological conditions, spreading depression (SD) can be visualized directly by using a fluorescent, voltage-sensitive (VS) dye. However, in stroke models, where depolarizations occur spontaneously near the ischemic core, marked hemodynamic changes interfere significantly with VS dye imaging. This study provides the scientific basis necessary for accurate interpretation of VS dye images captured from ischemic brains. Using two cameras and carefully selected illuminations, multiple image sequences of the cortex were captured through a cranial window during cardiac arrest and subsequent anoxic depolarization (AD). This multi-modal strategy, used in anesthetized rats, allowed the study of synchronous changes in the following variables: (i) membrane potential (VS dye method); (ii) cerebral blood volume (CBV) with green (540–550nm) illumination; (iii) hemoglobin (Hb) deoxygenation with red (620–640nm) illumination, and cerebral blood flow (CBF) by laser speckle contrast imaging. Careful analysis of the data and their relationship revealed two important points: (i) as long as hemoglobin deoxygenation is not too pronounced, vascular changes interfere little with VS dye signals; (ii) in contrast, when the local, blood oxygen carrying capacity is close to exhaustion, higher absorption of both red light excitation and VS dye emission by deoxy-Hb, results in marked decreases of VS dye signals. Multiple, synchronous imaging of cellular depolarization, CBF, CBV and Hb deoxygenation is required for reliable data interpretation — but this combination is a powerful tool to examine the coupling between membrane potential and hemodynamic changes, with high spatial and temporal resolution.

Pulsed upconversion of Tm 3+-doped sol–gel silicate glasses

Upconversion processes allow materials to emit light of shorter wavelength than the light incident upon them. Materials with high upconversion efficiency have numerous potential applications in solid-state physics, such as blue upconversion lasers. We study the time-evolution of upconversion fluorescence of Tm 3+ in a sol–gel glass host following pulsed, red light excitation. The 1D 2→ 3F 4 intensity varies quadratically with the laser intensity, indicating a two-photon upconversion mechanism. Maximum upconversion intensity occurred for 0.5% Tm 3+ with 1% Al 3+. We analyzed the main relaxation processes affecting the upconversion emission, namely ion clustering and atmospheric water adsorption.

Photodiagnosis for frameless stereotactic biopsy of brain tumor

Stereotactic biopsy is a minimally invasive method of reaching a pathological diagnosis. However, it is not always possible with this method to obtain the tissue samples required for an exact pathological diagnosis. The factors that can make histological diagnoses uncertain are the heterogeneity of tumors and/or brain shifts in the case of small tumors. In this study, we investigated the usefulness of fluorescence in determining the existence of tumor components in obtained tissues. Six patients underwent stereotactic biopsy. 5-Aminolevulinic acid (5-ALA) was administered orally prior to operation. Frameless stereotactic biopsies were performed. The obtained samples were irradiated with 405nm light and all samples showed red light excitation. Intraoperative rapid pathological diagnosis was made in each case by microscopic examination of frozen section samples. The final pathological diagnoses were of three glioblastomas, one astrocytoma grade 3, and two malignant lymphomas. One case was initially thought to be gliosis on rapid pathological diagnosis, but the final pathological diagnosis reached by examination of a permanent HE stained section was astrocytoma grade 3. Another case, finally diagnosed as malignant lymphoma, was initially diagnosed as infiltration of lymphocytes. The discrepancies between rapid and permanent pathological diagnoses might be caused by the destruction of cells. 5-ALA photodynamic diagnosis is not influenced by the destruction of tissues, simply because it does not depend on the structure of tissues. Stereotactic fluorescence biopsy is very useful in that it enables rapid and exact biopsy and obviates the necessity of waiting for an intraoperative report from a pathologist.

Color of illumination during growth affects LHCII chiral macroaggregates in pea plant leaves

To determine whether the color of illumination under which plants are grown, affects the structure of photosynthetic antennae, pea plants were grown under either blue-enriched, red-enriched, or white light. Carotenoid content of isolated chloroplasts was found to be insensitive to the color of illumination during growth, while chlorophyll a/ b ratio in chloroplasts isolated from young illuminated leaves showed susceptibility to color. Color of illumination affects the LHCII chiral macroaggregates in intact leaves and isolated chloroplasts, providing light-induced alteration of the handedness of the LHCII chiral macroaggregate, as measured with circular dichroism and circularly polarized luminescence. The susceptibility of handedness to current illumination (red light excitation of chlorophyll fluorescence) is dependent on the color under which the plants were grown, and was maximal for the red-enriched illumination. We propose the existence of a long-term (growth period) color memory, which influences the susceptibility of the handedness of LHCII chiral macroaggregates to current light.

Non-exponential optical modification of the electrical properties in oxygen-deficient YBa2Cu3Ox

We present studies of the time dependent electrical resistivity of YBa2Cu3Ox during visible light excitation (photodoping). Illumination with a green semiconductor laser changes the resistivity in a non-exponential way, which is well described by a stretched-exponential function with parameters β (dispersion parameter) and τ (time constant). β showed an unusual behaviour: at temperatures below 220 K β was about 0.3 to 0.4, but increased near room temperature to 0.5 to 0.6. For comparison with results obtained by red-laser excitation we discuss the dependence of the resistivity on the cumulative photon dose, thereby introducing a ‘‘photon dose constant’’ Ne which corresponds to τ. The results indicate that green-light excitation is somewhat more effective than red-light excitation at low temperatures.

Water-Soluble Green Perylenediimide (PDI) Dyes as Potential Sensitizers for Photodynamic Therapy

[reaction: see text] A series of water-soluble green perylenediimide (PDI) dyes have been synthesized. On red light excitation, these dyes were shown to be efficient generators of singlet oxygen, and in cell culture media, they were shown to display significant light-induced cytotoxic effects on the human erythroleukemia cell line (K-562). It appears that highly versatile PDI dyes are likely to find new applications in photodynamic therapy.

Blue and red photoluminescence fromAl2O3:Ce3+:Mn2+ films deposited by spray pyrolysis

Al2O3:Ce3+:Mn2+ films deposited by the spray pyrolysis technique show blue and red emissionsunder ultraviolet light excitation. The blue emission is due to the de-excitation ofCe3+ ions from their excited state 5d to the split ground state2F. The usually weak red emission attributed to 3d 3d de-excitation of Mn2+ is enhanced through an efficient energy transfer fromCe3+ toMn2+ ions. The most probable mechanism of energy transfer is found to be electric dipole–quadrupole interaction. The quantumefficiency of this transfer was estimated as being near to 100%, which makes these filmsinteresting phosphors for the design of luminescent layers in flat-panel displays withtwo-colour emission.

Upconversion of Y[sub 2]O[sub 2]S:Tm, Mg, Ti Phosphor and Its Long-lasting Phosphorescence

We report the upconversion luminescence of Tm 3 + in Y 2 O 2 S:Tm, Mg, Ti phosphor. The upconversion luminescence of Y 2 O 2 S:Tm, Mg, Ti phosphor and its unusually long-lasting phosphorescence properties have been discussed.Two upconversion emission bands located at 466 and 545 nm from Tm 3 + in Y 2 O 2 S:Tm, Mg, Ti phosphor are observed after near infrared light (λ = 798 nm) or red light (λ = 648 nm) excitation. The afterglow light of Y 2 O 2 S:Tm, Mg, Ti phosphor is so strong that it can be seen by the naked eye for above an hour. The possible mechanism of the unusual upconversion long-lasting phosphorescence is also discussed.

Wavelength-dependent Raman scattering of hydrogenated amorphous silicon carbon with red, green, and blue light excitation

This study presents results of wavelength-dependent Raman scattering from amorphous silicon carbon (a-Si:C:H). The a-Si:C:H films were produced by radio-frequency plasma-enhanced chemical vapor deposition. Prior results with amorphous carbon indicate that laser excitation selectively probes clusters with differing sizes. Our measurements with a-Si:C:H indicate that when using red (632.8 nm), green (514.5 nm), and blue (488.0 nm) excitation, the Raman D and G peaks shift to higher wave numbers as the excitation energy increases. The higher frequency is associated with smaller clusters that are preferentially excited with higher photon energy. It appears that photoluminescence occurs due to radiative recombination from intracluster transitions in Si-alloyed sp2-bonded carbon clusters

Changes in properties of a 〈porous silicon〉/silicon system during gradual etching off of the porous silicon layer

Scanning electron microscopy has shown etching of a porous silicon layer in an HF solution to be irregular. The intensity of porous silicon photoluminescence significantly decreases during gradual etching off, and its peak initially shifts to shorter and then to longer wavelengths. Under red-light pulse excitation, photo-voltage measurements have shown that the boundary potential ϕs of the p-Si substrate is positive, and ϕs grows with the etching time and as the temperature decreases from 300 to 200 K. At T<230 K, the photomemory of ϕs caused by nonequilibrium electron capture by p-Si boundary traps is observed. The concentration of shallow traps and boundary electron states in p-Si increases as porous silicon is etched. At T<180 K, the system of boundary electron states is rearranged. Photovoltage measurements with white-light pulses have revealed electron capture at oxide traps of aged porous silicon.

Resonant electronic Raman scattering in optimally dopedBi2Sr2CaCu2O8+x superconductor

We report experimental results on resonant electronic Ramanscattering in superconducting single crystalsof Bi2Sr2CaCu2O8+x. The change of excitationwavelength results in a shift of the position for thesuperconductivity-induced 2Δ peak in A1g andB1g symmetries. In addition, in the red-light excitation anew Raman peak arises at approximately 130 K in the B1gspectra. Various explanations of these effects are discussed.

Soil reflectance and colouring of grape. Vine red light excitation could be decisive for grape berry quality

&lt;p style="text-align: justify;"&gt;Various conditions of vine « solarisation » with sun light reflecting clothes partially colored in blue, green or red, were performed in field conditions during 1998 and 1999 years.The experiments were conducted both on table grapes (Muscat de Hambourg , Italia and Danuta) and on wine grapes varieties (Carignane, Mourvèdre, Shiraz, Muscat à petits grains). The « solarisation » clothes were set up at the cluster closure stage and removed at the harvest time. Effect of various experimental conditions on changes &lt;em&gt;in situ&lt;/em&gt; berry colour was examined. The chromatic parameters using the Lab and LCH conventional systems were weekly measured on representative berry samples, and levels of significance of the obtained differences were determined by a variance analysis. Differences in the colouring dynamics and in the values of the chromatic parameters at harvest were statistically significant, in particular in function of the importance of the reflecting area set up per vinestock and also in function of the color of the reflecting cloth used. The results were compared to those obtained from various other analyses : reflectance spectra and composition of berries at harvest, tastings of the table grapes. As a main result, the red colour with a maximum of reflectance at 680 nm appeared as the more effective in improving quality of the berries. These results demonstrate the importance of the reflectance properties of the neighbours of the vine, in particular those of the soil of the parcel, on the composition and the quality of the grape. Moreover, they underline that these properties should be taken in account to explain some misunderstood terroir effects. Finally, they strongly suggest that the excitation of vine photoreceptor systems, specially with the clear red light, could be decisive in the signaling and regulatory mechanisms leading to an optimal ripeness of the grape.&lt;/p&gt;

Raman spectrum and stability of(C59N)2

Raman spectra of $({\mathrm{C}}_{59}\mathrm{N}{)}_{2}$ are presented for excitation with various laser lines and for temperatures between 100 and 500 K. The material exhibits a reliable stability versus laser irradiation for the full temperature range and a remarkable resonance enhancement of the scattering cross section for red light excitation. The spectra show a strong relation to those of ${\mathrm{C}}_{60},$ particularly in the spectral range of the tangential modes. Calculations of the mode frequencies with the semiempirical AM1 technique reveal good agreement with the observed Raman lines, in particular for the three intermolecular modes observed at 82, 103, and 111 ${\mathrm{cm}}^{\ensuremath{-}1}.$

Non-Monotonous Relaxation of the Luminescence Intensity ofPorous Silicon

The relaxation of the luminescence intensity for porous silicon wasfor the first time investigated with red light excitation. A new typeof relaxation behavior was observed under these excitation conditions.The data on the evolution of the photoluminescence intensity and theobservation under the same conditions of a persistent absorptionsaturation are described. A model is proposed to explain the observedeffects as manifestations of a general carrier relaxationprocess.

Tumour visualization in a murine model by time-delayed fluorescence of sulphonated aluminium phthalocyanine.

Mice bearing the MS-2 fibrosarcoma were administered 0.25, 0.5 or 1 mg kg(-1) body weight (b.w.) of sulphonated aluminium phthalocyanine (AlS(2)Pc) (with average degree of sulphonation of 2.1), and time-gated fluorescence images were acquired up to 6 h after the injection. Different excitation wavelengths (610, 650 and 670 nm) were tested. Red light excitation and 3 ns delayed detection allow one to minimize natural fluorescence and scattered laser light, respectively. The best conditions for tumour detection are reached under either 650 or 670 nm Excitation, 2-4 h after the administration of either 0.5 or 1 mg kg(-1) b.w. of AlS(2)Pc. In these situations, the average fluorescence contrast between tumour area and surrounding healthy tissue is > 2, providing a clear identification of the pathological region. However, tumour localization is possible even after the injection of 0.25 mg kg(-1) b.w. of sensitizer. In conclusion, under low power excitation (< 100MuW cm(-2)), the technique allows real time detection of an intradermal tumour with good contrast.