Introduction The greatest powerful propriety of laser dyes is their tunability band laser emission which gives a varity of applications in many fields. Laser dyes are used efficiently within the isotope separation field. They also have applications in biology such that they modify the DNA by irradiation with ultraviolet light to prevent genetic mutations. The greatest successful, advanced and widely used application of laser in medicine is certainly eye surgery by photocoagulation, the laser dyes should be also used to coagulate blood vessels sequential to obstruct the flow of blood 1. They also should be used in monitoring non-residential pollution by means of differential absorption lidar DIAL technique 2.
According to these importances there exists different methods used for increasing the laser fluorescence intensity with specific wavelength. For example by creating use of the laser induced fluorescence LIF technique, the effect of concentration on the laser dye Rhodamine Be dissolved in ethanol should be studied such that the fluorescence emission intensity of Rhodamine Be gets broad and shifts to higher wavelength with concentration 3. Also a dye fluorescence spectrum shift should be obtained without fluorescence intensity enhancement below the influence regarding the solvent used 4. Corresponding authors: + Lotfi Z. Ismail: Department of Physics, Faculty of Science, Cairo University.
El Shaer: Department of Physics and Mathematics, Faculty of Engineering, Zagazig University. That enhancement regarding the fluorescence emission of molecules near a metal surface arises from interactions with surface plasmons sp resonance within the metal particles; these interactions shall also result in shortening regarding the excited-state lifetime thus improving the photostability regarding the dye 5. Within the spots, where regional fields are concentrated, most linear and nonlinear optical responses of molecules and atoms are gigantically enhanced which shall lead to a many important applications, the greatest important one is the surface enhanced Raman scattering SERS seven. The presence regarding the nanoparticles NPs shall increase the fluorescence quantum efficiency that is expected to hold a very important consequence in SERS 7. For example when silver NPs are added to the dye solution, dye molecules should be adsorbed on islands and films regarding the metallic NPs and when the surface plasmon resonance SPR regarding the metallic NPs coincides together with the dye absorption band that shall modify the intensity regarding the electromagnetic field EMF molecule diagram which shall increase the emitted fluorescence intensity 8.
That modification regarding the EMF is due to the very high field gradient near the metallic surfaces 9. Adding Ag NPs to the dye solution can cause neither an enhancement or a quenching regarding the fluorescence intensity regarding the dye depending on the distance between the dye molecules and the metal surfaces. When the metallic NPs are in close proximity to the fluorophores, quenching regarding the luminescence occurs due to the fact that the non-radiative decay regarding the excited molecules shall increase due to the life transfer from the dye molecules to silver NPs, whereas when the metallic NPs are located at sure distance, enhancement within the luminescence is observed due to the decrease regarding the non-radiative decay 10. Silver and gold NPs are used in most well-known dyes due to the fact that their plasmon resonance frequency is located within the visible spectrum which matches together with the absorption and the emission bands of these dyes. There exists important factors affecting the strength regarding the fluorescence intensity which are the volume and shape regarding the NPs, the orientation regarding the dye dipole moments relative to the NPs surface normal, the overlap regarding the absorption and emission bands regarding the dye together with the plasmon band regarding the metal and the radiative decay rate and the quantum yield Q regarding the fluorescent molecule 5, 11.
Since Rhodamine dyes are the greatest and wieldy used dyes in many fields such that they should be used in nonphotochemical hole burning experiments on the mitochondrial dye Rhodamine 800 incubated with 3 person ovarian surface epithetical cell lines. This dye is believed to be selective for the plasma and inner membranes regarding the mitochondria 12. Gold nanoparticles should be used like a colorimetric sensor for protein conformational change 13. So in this work we read the effect of adding silver NPs to Rhodamine 101 dye of concentration 10-4 M or L with different weighting factors between the Ag NPs and the dye solution. Experimental samples and setups Experimentally, we use Rh 101 dye of molecular mass of 591.
06 gm, which appears like a lime solid with maximum absorption wavelength of 568 nm when it is dissolved in absolute ethanol 99. The selected concentration regarding the dye solution is 10-4 M or L. The aggregated nanoparticles are prepared by vinylpyrrolidone reduction of AgNO3 in ethanol solution. AgNO3 six mg is dissolved in EtOH 100 ml, place in a reflux condenser and heated while stirring for 15 min. Then poly vinylpyrrolidone molecular weight, 40 000; 1.
2 g was added, with stirring, and kept in a reflux condenser for about 10 min. Subsequent to that NaOH two wt%; 0. 5 ml is added and kept at boiling while stirring for 30 min. Then the mix was kept stirred until it cooled to room temperature. That colloid prepared this method contains mostly isolated Ag particles.
Within the preparation of Ag aggregate, ethanol solution of AgNO3 25 mg in 25 ml of EtOH is mixed with 25 ml of initial colloid at boiling heat while stirring. Then, 5 ml of NaOH two wt % is added to the mixture, which was kept stirred at boiling heat for 30 min and then until it cooled to room temperature. The estimated concentration of Ag particles within the mix was 8. Interaction of Rhodamine 101 dye molecule with silver nanoparticles is schematically shown in figure 1. 1 Schematic representation regarding the formation of dye-Ag nanoparticles complex This molecule has 3 nitrogen atoms with which it can bind to silver nanoparticles.
Between these 3 nitrogen atoms two of them is more electropositive and can bind to silver nanoparticles preferentially to shape dye silver nanoparticles complex. Due to the affinity of dye molecule with silver nanoparticles, electron transfer mechanism becomes easier and enhancement is obtained. The pure dye solution and the dye aggregate mixtures are pumped by argon Ar ion laser of output wavelength 488 nm generated from Lexel 95 laser generator and the fluorescence spectrum is detected by SPEX 750M monochromator. An Acquisition card is used to analyze the fluorescence spectra with pc-computer software specially written to scan the wavelength as shown in figure 2. 2 Schematic diagram regarding the spectroscopic system and data acquisition component regarding the experiment.
Conclusions First, a pure Rh 101 dye solution of concentration 10-4 M or L is pumped with Ar ion laser, and then Ag NPs is added to the dye solution with ratios from 1:7 to 1:3 regarding the Ag NPs to the dye within the solution, the fluorescence intensities are recorded as shown in figure 4 which presents a comparison between the fluorescence emission curves regarding the 4 cases such that the lowest fluorescence intensity belongs to the pure dye solution black curve of concentration 10-4 M or L and equals to 1. and its peak at? = 627. 5 nm, lime curve the fluorescence intensity regarding the Ag aggregate to dye solution ratio is 1:7 increases to be 1. and its peak is shifted to be at? = 617. 5 nm, dark brown curve the fluorescence intensity regarding the Ag aggregate to dye solution ratio is 1:3.
and its peak is shifted to be at? = 615 nm, blue curve the fluorescence intensity regarding the Ag aggregate to dye solution ratio is 1:3 increases to be 2. - the highest price - and its peak is shifted to be at? = 614. 4 A comparison between the fluorescence intensity versus wavelength of different cases Black pure dye of concentration 10-4 M or L, Lime Ag aggregate to dye ratio 1:7, Dark brown Ag aggregate to dye ratio 1:3. 5, and Blue Ag aggregate to dye ratio 1:3. Figures 4, six represent the relation between the dye fluorescence intensity and its peak spectral wavelength shift versus the Ag aggregate percentage within the aggregate-dye solution respectively.
They showed that there is a linear relationship between the Ag aggregate percentage within the mix and the fluorescence intensity and its peak spectral wavelength shift. As the Ag aggregate nanoparticles percentage increased within the mixture, the fluorescence intensity increased and the peak spectral shift also increased. 5 The relation between Ag aggregate percentages and the fluorescence intensity. six The relation between Ag aggregate percentages and the shift regarding the maximum peak wavelength. As we dilute the dye solution to be of a concentration of 510-5 M or L and push it with Ar ion laser, and then adding Ag NPs to dye solution such that the Ag aggregate to dye ratio within the mix is 1:7, their fluorescence emission intensities are recorded as shown in figure seven which represents a comparison between the 3 cases such that the pure dye solution dark brown curve has the minimum fluorescence intensity with its peak at? = 612.
5 nm, and the fluorescence intensity regarding the aggregate dye mix of ratio 1:7 regarding the Ag NPs to dye black curve increases with percentage increase within the fluorescence intensity by only 5% with its maximum peak at? =610 nm, so we can speak that the intensity increased and the shift is obtained but with weak dependence on the Ag aggregate percentage within the solution. 6 A comparison between the fluorescence intensity of 3 cases, dark brown curve the fluorescence intensity of a pure dye of concentration of six 10-5 M or L, black curve the fluorescence intensity of an Ag aggregate to dye six 10-5 M or L mix of ratio 1:7. Discussion and Conclusion In this work, adding silver NPs to Rhodamine 101 dye solution is investigated. The measured values reveal that adding Ag NPs to the dye solution shall enhance the dye fluorescence to significant values accompanied by wavelength shift to higher values as the Ag NPs percentage increases within the dye aggregate mixture. The fluorescence enhancement should be due to the field enhancement in metallic nanostructures associated together with the surface plasmons, whereas the fluorescence spectrum shift should be obtained due to the overlapping between the electronic transition regarding the metal nanoparticles and the molecular transition regarding the dye molecules.
At similar time adding Ag NPs to diluted Rh 101 dye solution of concentration six 10-5 M or L with ratio 1:7 regarding the aggregated silver to the dye within the mix shall release an intensity increase within the fluorescence regarding the dye by only 5%, and a spectrum wavelength shift is obtained by only 2. 5 nm which gives a weak dependence on the Ag percentage within the solution due to the fact that dye dilution decreases fluorophores density compulsory to make bonds to the Ag nanoparticles to enhance the dye fluorescence intensity as seen in figure 1, accordingly the intensity enhancement is limited. Hillman, 1990, Academic press. Staicu, 2001, Journal of molecular structure, Vol. Ismail, 2009 , Journal of Fluorescence, Vol.
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