Measurements Of Emission Spectra Research Articles

Uniform and stable plasma reactivity: Effects of nanosecond pulses and oxygen addition in atmospheric-pressure dielectric barrier discharges

Uniform and stable reactivity of atmospheric pressure plasmas is a prerequisite for most applications in fields ranging from materials’ surface processing, environment protection, to energy conversion. Dielectric barrier discharges (DBDs) are among the most promising plasmas to satisfy these requirements. However, the unpredictable and uncontrollable transitions between discharge modes, the limited understanding of the DBD ignition and extinction processes, and the complexity of plasma chemistries and reactions with admixture gases restrict their adoption in industry. Here, we report a practically relevant and elegant solution based on using customized nanosecond (ns) pulse excitation and precise addition of oxygen to an Ar flow. The effects of ns pulses and oxygen on the uniformity and reactivity of the DBD are investigated via quantifying the gap voltage Ug and the discharge current Ig from the current–voltage measurements and quantitative discharge imaging. The electron density, ne, is estimated with Ug and Ig. With increasing Ug, more electron avalanches are ignited and overlap, which facilitate ne, Te, and discharge uniformity, while high Ug induces excessive electrons generated with high ionization rates, resulting in the distortion of the space electric field and reduced stability and uniformity. A small amount of added oxygen favors the production of electrons. Overdosed oxygen molecules capture electrons causing a drop in ne and Te and couple with the effect of the electrical field resulting in the filamentary discharges or complete plasma extinction. The mechanism of the effects of ns pulses and oxygen addition on the uniformity and reactivity of plasmas is based on the electrical measurements and discharge image analysis and is cross-validated by optical emission spectra measurements and the ratio of the Ar intensities’ calculations as indicators of the variation in ne and Te. The results in this work contribute to the realization and controllability of uniform, stable, and reactive plasmas at atmospheric pressure.

Random laser oscillation from an organic fluorescent dye loaded inside a porous zirconia medium.

Porous zirconia medium (PZrM) has been fabricated successfully using polystyrene microparticles (MPs) as templates. The emission spectra of rhodamine B (RhB) [optical amplifying medium] loaded inside PZrM [porous scatterers] were obtained at numerous excitation light intensities. The lasing thresholds (Ith) have been determined experimentally from the variations in the intensity of random laser oscillation peaks, which are suitably separated from the measured emission spectra. Ith is closely related to the pore sizes of PZrM and the added amount of PZrM powder, and it clearly provided the minimum against the pore size. This fact is explained reasonably by the simulation of scattering efficiency on the basis of the Mie scattering theory. Consequently, PZrM as a porous scatterer is superior to Zr MPs from the viewpoint of random laser oscillation.

Energy transfer from fluorescein dye dispersed with CdS nanoparticles as evidenced by emission spectrum measurements

Cadmium Sulphide (CdS) nanoparticles show very interesting optical properties due to quantum confinement effects, that make them useful for biomedical labelling, optoelectronic devices, etc. In this work we show that when CdS nanoparticles are dispersed in organic dyes, the optical properties of the dyes change considerably. We have synthesized CdS nanoparticles by co-precipitation method and characterized by XRD and TEM. Nanoparticles have been dispersed in aqueous solution of fluorescein dye and their absorption and photoluminescence (PL) spectra were recorded. The intensities of PL spectra and the peak wavelength of emission shifted remarkably from the spectra of corresponding pure dye solution. The observed shifts are attributed to the band structure modification by the formation of chemical complex when dye molecules get adsorbed onto nanoparticle surfaces. FRET mechanism is responsible for the rapid quenching of dye fluorescence.

Gas-discharge plasma diagnostics by a continuous spectrum of optical radiation

In the present work, plasma diagnostics method based on the measurement and theoretical analysis of continuous emission spectrum of a gas discharge was discussed. Using the method, electron temperatures of a DC glow discharge and ferromagnetic enhanced inductive discharge were determined for inert gases in the gas pressure range of 20–200 Pa. Experimental results were compared with the results of numerical calculations for the ferromagnetic enhanced inductive discharge and DC glow discharge. A satisfactory agreement between the optically measured and numerically calculated values of electron temperature was shown.

Mesosphere Ozone and the Lower Ionosphere under Plasma Disturbance by Powerful High-Frequency Radio Emission

We present the results of experiments on the Earth’s lower ionosphere at mesospheric heights by creating artificial periodic irregularities (APIs) of the ionospheric plasma and simultaneous measurement of the atmospheric emission spectrum in the ozone line by ground-based microwave radiometry when the ionosphere was disturbed by powerful high-frequency radio emission from the midlatitude SURA heating facility (56.15° N; 46.11° E). The diagnostics of the ionosphere was carried out on the basis of measuring amplitudes and phases of signals scattered by periodic irregularities in the altitude range of 50–130 km. For each heating session lasting 30 min, two ozone spectra were measured. These spectra were compared with the measured spectra the periods when heating was turned off. During the heating session of the ionosphere, a decrease in the intensity of the microwave radiation of the atmosphere in the ozone line was observed. The lower ionosphere was characterized by intense dynamics. Rapid variations in the amplitude of the scattered signal and the relaxation time of artificial periodic irregularities were observed. The velocity of a regular vertical movement in the D-region of the ionosphere constantly varied direction with average minute values up to 4–5 m/s. We assume the decrease in the ozone emission spectrum at the altitude of 60 km can be explained by an increase in the coefficient of electron attachment to oxygen molecules during heating sessions. The lower boundary of the region enriched with atomic oxygen was estimated from the height profile of the API relaxation time.

Multi-Stimuli Responsive Luminescent β-Diketones and Difluoroboron Complexes with Heterocyclic Substituents.

Emissive β-diketones (bdks) and difluoroboron complexes (BF2bdks) exhibit multi-stimuli responsive luminescence, including solvatochromism, viscochromism, aggregation induced emission, thermal and mechanochromic luminescence, halochromism and pH sensing. In this study, a series of six-membered heterocycle-substituted (piperidine, morpholine, 1-methyl piperazine) bdk ligands and boron complexes were synthesized, and their luminescent properties were investigated. All the compounds exhibited red-shifted emission in more polar solvents due to intramolecular charge transfer as well as higher emission intensity in more viscous environments. In response to solubility changes in water/tetrahydrofuran mixtures, while the piperazine bdk ligand showed aggregation caused quenching, the piperidine and morpholine bdks displayed enhanced emission upon aggregation. In the solid state, all ligands exhibited mechanochromism. More dramatic halochromism was observed for the piperidine boron dye spin cast film. In solution, for the boron dyes under varying pH values (1-13), different protonated and deprotonated forms were analyzed according to the measured emission spectra. Graphical abstract Multi-stimuli responsive luminescent properties were investigated for the six-membered heterocycle-substituted β-diketone ligands and difluoroboron complexes.

Measurement of two-photon properties of indocyanine green in water and human plasma excited at the 1700-nm window.

Indocyanine green (ICG) is a human compatible dye and is ideal for deep-tissue two-photon fluorescence (2PF) microscopy excited at the 1700-nm window in vivo. However, the two-photon excitation and emission properties of this dye remain unknown. Here we demonstrate measurement of the two-photon excitation and emission properties of ICG in both water and human plasma, using home-built two-photon action cross-sectional measurement and two-photon emission spectrum measurement systems. Our results show that excited from 1600 to 1800 nm, 2PF can be generated from ICG dissolved in both water and human plasma. The measured two-photon action cross-sectional ησ2 of ICG dissolved in human plasma is an order-of-magnitude larger than that dissolved in water. The measured two-photon emission spectrum overlaps with the one-photon emission spectrum for ICG dissolved in both human plasma and water. Our results will provide key two-photon parameters for the clinical use of ICG.

Luminescence and study of channels for cross-relaxation dependent on the concentration of Sm3+ under simultaneous UV-IR excitation in tellurite-germanate glasses

A spectroscopic evaluation of Sm3+ doped TeO2-GeO2-ZnO glasses (0.5, 1.0, 3.0 and 5.0%) was carried with aim to determinate the dominant process in the cross-relaxation mechanism at high and low concentrations of Sm3. A new experimental spectroscopic technique is proposed, based on the analysis of the time evolution of the 600 m emission, corresponding to the 4G5/2 → 6H7/2 transition, obtained under spatial and temporal simultaneous excitation at 355 nm and into the infrared (950, 1085 1236, 1380 nm). It was possible to determine that at low Sm3+ content the dominant channel for cross relaxation is 4G5/2 + 6H5/2 → 6F5/2 + 6F11/2 and at high concentrations are: 4G5/2 + 6H5/2 → 6F7/2 + 6F9/2, 4G5/2 + 6H5/2 → 6F9/2 + 6F7/2, 4G5/2 + 6H5/2 → 6F11/2 + 6F5/2, and the least contributor one being 4G5/2 + 6H5/2 → 6F5/2 + 6F11/2. It is reported the optical absorption and Raman spectroscopies, photoluminescence spectra and decay time profiles as a function of Sm3+ concentration. Emission spectra measurements indicated that concentration quenching is active in the samples, being 1.0 mol% the optimum concentration for luminescence of Sm3+ ions. The decay time of 4G5/2 level upon 403 nm excitation, at 0.5% of Sm3+, presents a decay curve single exponential, however, when the concentration increases, the time decay reduces and becomes non-exponential. The Inokuti-Hirayama model was used to infer that an electric dipole-dipole mechanism is the dominant interaction in the energy transfer process between Sm3+-Sm3+ ions.

Molecular structure and spectroscopic properties of new neodymium complex with 3-bromo-2-chloro-6-picolinic N-oxide showing the ligand-to-metal energy transfer

A new neodymium [Nd(BCPN)3(NO3)3(H2O)2] complex with 3-bromo-2-chloro-6-picolinic N-oxide was synthesized and characterized by means of spectroscopic studies and DFT quantum chemical calculations. The IR, Raman, electron UV-VIS and emission spectra measurements were performed. The femtosecond excitation was used to establish an excited energy level depopulation mechanism. The influence of the halo-groups position on the structural and optical properties of the studied compound was discussed. Ligand-to-metal energy transfer in the studied neodymium complex was analysed.

Enhanced luminescence performances of Mn4+-activated Sr4Al14O25 red phosphors by doping with Sc3+ ions

A series of non-rare earth Mn4+-activated strontium aluminate phosphors Sr4Al14O25:Mn4+ co-doped with Sc3+ ions were successfully synthesized by a high-temperature solid-state reaction method. XRD result reveals that there is no introduction of additional phase but expansion of lattice with incorporation of Sc3+ ions. Excitation and emission spectrum measurement shows that the synthesized phosphors can be efficiently excited by near-ultraviolet and blue light, and a deep red emission centered at 652 nm with a narrow full width at half maximum (FWHM) can be obtained, which is attributed to the transition 2E→4A2 of Mn4+ ions. In addition, the crystal field strength parameter (Dq) and Racah parameters (B, C) and energies of states were calculated based on experimental data. Moreover, the luminous intensity of Sr4Al14-xScxO25:Mn4+ is enhanced and increased by 60% compared with Mn4+ single incorporated sample at x = 0.06. A phenomenon of redshift is observed in the excitation spectrum and discussed systematically. Finally, the mechanism of the positive effects with Sc3+ ions incorporated into lattice is discussed in detail. All the results suggest that the Sr4Al13.94Sc0.06O25:Mn4+ phosphor will become one of the great candidates for backlight of LCD.

Structural and optical properties of Dy3+:YAlO3 phosphors for yellow light-emitting diode applications

The spectroscopic properties of a series of Dy3+ single-doped and Dy3+/Nd3+, Dy3+/Tb3+, and Dy3+/Tm3+ co-doped YAlO3 (yttrium aluminum perovskite, YAP) phosphors were investigated and compared through the measurements of optical absorption, emission spectra, and fluorescence decay curves. For the Dy3+ ion single-doped samples, the intensity of each absorption band increases with an increment in Dy3+ ion doping concentration, and the identified strong absorption peak at 447 nm indicates that Dy3+:YAP phosphors are suitable to be pumped by a blue laser diode (LD). For all co-doped samples, absorption peaks of Dy3+ ion along with some of the absorption bands of Nd3+, Tb3+, and Tm3+ ions are observed. Under 351 and 447 nm excitation, a prominent emission peak at 572 nm was obtained in all the samples, corresponding to Dy3+: 4F9/2 → 6H13/2 transition. Here, 2 at% Dy3+:YAP phosphor exhibits the highest yellow emission intensity under 447 nm pumping. Among the three kinds of Dy3+ co-doped phosphors, Dy3+/Tb3+:YAP phosphor possesses the dominant yellow emission. The fluorescence decay curves show exponential behaviour and are fitted well. The Commission International de L'Eclairage (CIE) chromaticity coordinates were calculated following the respective emission spectra, and it is found that all the coordinates locate in the yellow region. The energy transfer (ET) processes were investigated and the concentration quenching mechanism was discussed. The obtained results suggest that Dy3+-activated YAP phosphors are good candidates for yellow LED applications.

Phase-locked pair of terahertz quantum cascade lasers through evanescent-wave coupling

A phase-locked laser pair containing two terahertz distributed feedback (DFB) quantum cascade lasers (QCLs) has been realized via evanescent-wave coupling. The mode selection in the laser pair is dominated by the waveguide loss which can be controlled mainly by the ridge width, as well as the width of the gap between the two ridges. A judicious design enables the laser pair to stably operate on the out-of-phase supermode with a side mode suppression ratio (SMSR) of 34 dB, a peak output power of 8.06 mW, and an amplification factor of about 1.72. Due to the significant overlap of the electromagnetic fields caused by the two laser elements, the laser pair is phase-locked even when the two elements are differently biased, confirmed by the measured emission spectra and far-field beam patterns. This work represents a crucial step towards phase-locked arrays for high power single-mode terahertz radiation.

Characterization of the fluorescence intensity and color tonality in the exoskeleton of scorpions

Scorpions are a mesodiverse and nocturnal group of arachnids inhabiting most biomes worldwide. Different species of scorpions have divergent adaptations to the substrate they live in, but most of them share an intriguing characteristic: their exoskeleton contains fluorophores that emit blue-greenish fluorescence under ultraviolet radiation. Although there are some reports in the literature on the study of fluorescence in scorpions, the biological functionality of this light emission is currently unknown and is under debate. In this work, the properties of emission from the scorpion's exoskeleton are studied by means of digitally processed photographs taken of living specimens under ultraviolet illumination and complemented with standard spectroscopic measurements of emission and excitation spectra. With the aim of identifying possible correlations between the fluorescence, the characteristics color of the exoskeleton and the biology of the scorpions, 4 families, 9 genera and 24 species were studied. Our results suggest that the intensity of fluorescence is heterogeneous throughout the scorpion's exoskeleton studied here in such a way that pedipalps and metasomal segments fluoresce more intensely than the mesosomal segments. The spectrum of fluorescence across species is practically identical, suggesting that the same fluorophores are present in their exoskeletons. However, the fluorescence intensity emitted by each species varies according to their characteristic color (associated with the exoskeleton optical reflectance). Since the coloration of the exoskeleton is determined by the concentration of melanin and other pigments according to the substrate where scorpions live in, we conclude by suggesting that fluorescence may correlate directly to the ecomorphotype of the scorpions.

Thermal behaviour and photoluminescence properties of Er- and Nd-doped yttrium aluminate glasses

Yttrium aluminate glasses (76.8 mol% of Al2O3, 23.2 mol% of Y2O3) doped with Er3+ and Nd3+ ions at different concentration levels (0.25 mol%, 0.5 mol% and 0.75 mol% Er2O3/Nd2O3) were prepared by flame synthesis in the form of glass microspheres. The prepared samples were XRD amorphous, without presence of any crystalline phases in measured patterns. The two exothermic effects (~ 940, ~ 1010 °C), which can be assigned to the two steps of YAG crystallization, were observed in the DSC records of all prepared samples. The high temperature XRD measurements showed YAG (900–1200 °C) and α-Al2O3 (1300–1450 °C) phase crystallization. The emission spectra were measured in the VIS and NIR regions for Er-doped samples and in the NIR region for Nd-doped samples. All measured emission spectra contain of characteristic bands due to the typical 4f–4f transitions within the Er3+ and Nd3+ ions. Comparison of the measured intensities of Er-doped samples made it evident that the highest intensities were obtained for the 0.5 mol% Er2O3-doped sample (in both the NIR and VIS spectral regions). The maximum intensity for Nd-doped samples was found when the sample was doped with 0.75 mol% of Nd2O3. The slowly increasing of emission intensities in samples after 20 min annealing at 1000 °C and Stark splitting of emission bands in samples after 40 and 60 min annealing at 1000 °C and after 20, 40 and 60 min annealing at 1500 °C was observed.

Effects of oxygen vacancies on luminescent properties of phosphor Sr4Al14O25:Mn4+ co-doping with alkali metal ion

A series of Na+, Mn4+ ions co-doped Sr4Al14O25 phosphors are synthesized by conventional solid-state reaction and their luminescent properties are investigated in detail. XRD result reveal that there is no introduction of additional phase with incorporation of Na+ ions. Excitation and emission spectrum measurement shows that the synthesized phosphors can be efficiently excited by near-ultraviolet and blue light, and a deep red emission centered at 652 nm with a narrow full width at half maximum (FWHM) can be obtained. The ESR result shows that doping Na+ ions can lead to the creation of the oxygen vacancies due to the nonequivalent substitution between Na+ ions and Sr2+ ions, the oxygen vacancies can act as a sensitizer for the effective energy transfer from Sr4Al14O25 host to Mn4+ ions. Correspondingly, a possible mechanism for energy transfer between oxygen vacancies and Mn4+ is provided. The luminous intensity of Sr4-xNaxAl14O25-x/2: Mn4+ is enhanced and increase by 250% compared with Mn4+ single incorporated sample at x = 0.6. All the results suggest that this phosphor could be considered as a potential red phosphor for the backlight of LCD.

Scintillation and Energy-Storage Properties of Micro-Pulling-Down Grown Crystals of Sc3+- and La3+-Doped YAlO3 Perovskite

The scintillation and energy-storage properties of YAlO3 (YAP) crystals doped with Sc3+ and La3+ isoelectronic dopants were investigated in this work. The YAP:Sc and YAP:La crystals were grown from the melt with a nominal Sc and La content in the 0.2–5.0 mol.% range using the novel micro-pulling-down method. We found that the segregation coefficient of Sc ions in YAP:Sc (0.2–1.0 mol.%) crystals is about of 0.35–0.4 and decreases to around 0.2 at Sc content of 5.0 mol.% when the segregation coefficient of La ions in YAP:La (1.0–5.0 mol.%) crystals is 0.008–0.01. The scintillation and stimulated luminescence phenomena, like thermo- and photoluminescence, were utilized for the property characterization of the studied materials. The cathodoluminescence and X-ray-excited luminescence were used for the imitation of scintillation in the YAP:Sc and YAP:La crystals. The influence of Sc3+ and La3+ dopant concentration on the CL and RL emission spectra, as well as the shape of the measured thermoluminescence (TL) glow-curves, was also investigated. The measured emission spectra showed dominant emission of Sc3+ and La3+ ions in the UV range. For this reason, the YAP:Sc and YAP:La crystals can be considered for creation of ultraviolet (UV)-emitting scintillators. For the undoped YAlO3 crystals, the main TL emission peak occurs in a low-temperature range at 375 K. Meanwhile, even a small addition of dopants causes a strong suppression of luminescence of the YAP host and high-temperature peaks become dominant in the TL glow-curves of YAP:Sc and YAP:La crystals. Moreover, the amplitude of emission does not change monotonically with increasing dopant content. The kinetic parameters of emission were also evaluated, and the first-order behavior was confirmed in all cases. The dosimetric properties of investigated materials such as dose response, fading rate, and the lowest measurable dose are also discussed. The obtained results tend to suggest that the YAlO3 perovskite host, apart from its application for the development of efficient scintillators, may also be considered as a promising matrix for the creation of energy-storage phosphors for dosimetric applications.

Engineering and biological assessment of double core nanoplatform for co-delivery of hybrid fluorophores to human melanoma

We investigated new development in photodynamic therapy (PDT), aiming at enhanced tumor selectivity and biocompatibility, which included application of a third-generation photosensitizing agent, i.e. xanthene-origin Rose Bengal (RB) co-encapsulated with up-converting NaYF4 nanoparticles (NPs) co-doped with lanthanide ions: Er3+ (2%) and Yb3+ (20%). The hybrid fluorophores were applied as components of double core nanocarriers (NCs) obtained by double (multiple) emulsion solvent evaporation process. Next, to improve the biocompatibility and photodynamic activity, biodegradable polymer: poly(lactide-co-glycolide) – PLGA and non-ionic surfactants with different hydrophobicity: Span 80 and Cremophor A25, were used. After the engineering process, controlled by dynamic light scattering (DLS) measurements, ζ-potential evaluation, transmission electron and atomic force microscopy (TEM and AFM) imaging, as well as optical analysis provided by measurements of the up-conversion emission spectra and luminescence kinetics for encapsulated only NaYF4:Er3+,Yb3+ NPs and co-encapsulated RB + NaYF4:Er3+,Yb3+ molecules, spherical polyester NCs with average size <200 nm, were tested on human melanoma (Me-45 and MeWo) cells and a control human keratinocyte (HaCaT) cell line. The photodynamic action of the investigated NCs was assessed by oxidoreductive potential measurements with 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, that corresponds to percentage of the viable cells. Immunofluorescence and the NCs internalization studies were visualized by confocal laser scanning microscopy (CLSM studies). Our results indicated effective photosensitizer delivery into the cancer cells and significant photodynamic efficiency enhanced by the near infrared (NIR)-activation of the encapsulated hybrid cargo in the skin melanoma cells.

Spectral efficiency of lutetium aluminum garnet (Lu3Al5O12:Ce) with microelectronic optical sensors

The aim of the present work was to investigate the absolute luminescence efficiency (AE) of a lutetium aluminum Lu3Al5O12:Ce (LuAG:Ce) garnet, doped with cerium, combined with various microelectronic optical sensors. Two LuAG:Ce samples, with dimensions of 5 × 5 × 10 and 10 × 10 × 10 mm3 were examined. The light emitted by the crystals, was evaluated by performing measurements of the AE using X-rays from 50 to 130 kV. The spectral compatibility of the LuAG:Ce crystal, with various existing optical detectors, was investigated after emission spectra measurements. Results were compared with previously published data for commercially available lutetium based and cerium doped crystals, such as, (Lu,Gd)2SiO5:Ce and Lu2SiO5:Ce, frequently used in medical imaging applications. Absolute efficiency was found maximum at 130 kVp for the 5 × 5 × 10 mm3 LuAG:Ce crystal (31.86 efficiency units-E.U). AE of the 10 × 10 × 10 mm3 LuAG:Ce crystal was found higher than both LGSO:Ce and LSO:Ce crystals (of equal dimensions). The emission spectrum of LuAG:Ce is excellent matched with the spectral sensitivities of photocathodes, charge coupled devices (CCD), non-passivated amorphous hydrogenated silicon photodiodes (a-Si:H) and complementary metal-oxide semiconductors (CMOS) microelectronic devices employed in radiation detection. Considering the higher luminescence efficiency values than currently used crystals and the spectral compatibility with the various photodetectors, LuAG:Ce single crystal could be considered for use in imaging detectors, such as, PET/CT scanners.

Generation of a Nanosecond Pulsed Gliding Arc Discharge With a Repetition Frequency of 300 kHz in an Air Flow at Atmospheric Pressure

Characteristics of a repetitive nanosecond pulsed gliding arc discharge in an air flow at atmospheric pressure driven by a SiC MOSFET inverter power supply are reported for the first time. The gliding arc discharge is produced using two diverging electrodes. The repetition frequency of the pulsed voltage is set from 10 to 300 kHz, and the pulse duration is 500 ns. The propagation distance of the gliding arc discharge almost linearly increases with increasing the repetition frequency of the applied pulsed voltage, resulting in an increase in the discharge reaction area. Dynamics of ignitions and propagation of the gliding arc discharge are revealed with a high-speed camera imaging synchronized with the applied pulsed voltage. The result shows that a shortcut discharge with a different generation mechanism appears. It is found that formation of a shortcut current path between the two legs of the stretched arc discharge occurs, resulting in a new ignited arc discharge. Thus, the pulsed gliding arc discharge can be repeatedly generated without a reignition at the shortest gap between the electrodes. The probability of the occurrence of the shortcut discharge increases as the repetition frequency of the pulsed voltage increases. Additionally, measurements of optical emission spectra of the gliding arc discharge show the presence of excited N2, OH, and NH radicals. The OH emission dominates in the gliding arc discharge with the shortcut events. It can be concluded that the repetition frequency of the applied pulsed voltage becomes the control knob for chemical reactions in future industrial applications.

D-optimal design as a useful tool response surface methodology for the optimization of signals from synchronous fluorescence prior to simultaneous determination of avanafil and tadalafil.

A rapid, smart and sensitive first derivative spectrofluorimetric method has been carried out for the simultaneous estimation of avanafil and tadalafil either in their pure form, tablet dosage form or spiked human plasma. The measurements of normal emission spectra or synchronous fluorescence intensity of both drugs show severe overlap which hindered their determination using normal fluorescence or synchronous intensity. Therefore, a highly sensitive first derivative synchronous fluorescence procedure was used to resolve this overlap. The method is based upon measurement of the amplitude of the first derivative of synchronous fluorescence intensity of both drugs at Δλ=70nm and at suitable wavelength of 396nm and 364nm for avanafil and tadalafil, respectively. Under the optimum conditions, the linear determination ranges are 50-1800 and 5-400ngmL-1 with a detection limit of 12.93 and 1.46ngmL-1 for avanafil and tadalafil, respectively. A response surface methodology was used for optimization using D-optimal design which can be used for determination of the exact optimum parameters specifically designed for this method. In addition; it is a good way to graphically clarify the relationship between various experimental variables and the synchronous fluorescence intensity.