I have added Ag nano particles in Photo luminescent dye solution in order to increase its florescence emission intensity. But unexpectedly its intensity start decreasing. I have use 15ppm to more then 200ppm for finding optimum value. but in all cases intensity decreases. but according to literature, it should increase. can anybody guide me please.. I thought i may be using high concentration which causes aggregation quenching effect but when use low concentrations, results were still opposite to literature.
Dear Mateen,
A distance between a fluorophore dye and the metal (gold or silver) nanoparticle determines whether the fluorescence is enhanced due to local electromagnetic field produced by the metal nanoparticle or, alternatively, if the energy is efficiently transferred from the fluorophore to the metal nanoparticle, which would occur fluorescence quenching.
I guess your case shall be the later, which a Quenching was resulted in.
Ref:
Pons, T.; Medintz, I.L.; Sapsford, K.E.; Higashiya, S.; Grimes, A.F.; English, D.S.; Mattoussi, H. On the quenching of semiconductor quantum dot photoluminescence by proximal gold nanoparticles. Nanoletters 2007, 7, 3157–3164.
Dulkeith, E.; Morteani, A.; Niedereichholz, T.; Klar, T.; Feldmann, J.; Levi, S.; van Veggel, F.; Reinhoudt, D.; Möller, M.; Gittins, D. Fluorescence quenching of dye molecules near gold nanoparticles: Radiative and nonradiative effects. Phys. Rev. Lett. 2002, 89, 203002:1–203002:4.
Dear Mateen,
A distance between a fluorophore dye and the metal (gold or silver) nanoparticle determines whether the fluorescence is enhanced due to local electromagnetic field produced by the metal nanoparticle or, alternatively, if the energy is efficiently transferred from the fluorophore to the metal nanoparticle, which would occur fluorescence quenching.
I guess your case shall be the later, which a Quenching was resulted in.
Ref:
Pons, T.; Medintz, I.L.; Sapsford, K.E.; Higashiya, S.; Grimes, A.F.; English, D.S.; Mattoussi, H. On the quenching of semiconductor quantum dot photoluminescence by proximal gold nanoparticles. Nanoletters 2007, 7, 3157–3164.
Dulkeith, E.; Morteani, A.; Niedereichholz, T.; Klar, T.; Feldmann, J.; Levi, S.; van Veggel, F.; Reinhoudt, D.; Möller, M.; Gittins, D. Fluorescence quenching of dye molecules near gold nanoparticles: Radiative and nonradiative effects. Phys. Rev. Lett. 2002, 89, 203002:1–203002:4.
It seems that your silver nanoparticles may have lost their nanoparticle behavior/properties and achieved bulk status. Probably your Silver nanoparticles are optically inactive. Total internal reflection could also play role in the reported low intensity? Please check your SEM images and thereby the Ag nanoparticle and/or bulk properties could be ascertained.
Dear Mateen,
When you add Ag NPs to your dye solution, dye molecules may adsorb on the NPs, which results in the quenching of their fluorescence due to fast, nonradiative charge or energy transfer to the metal (because molecules are too close or in direct contact to metal).
Therefore, you may fix this issue by using Ag-silica core-shell NPs, like those reported in, e.g.: Liu et al, Organic Electronics, 12(7) 1279–1284 (2011), or Niitsoo et al, J Colloid Interface Sci. 354(2) 887-90 (2011), or Rainville et al, RSC Adv. 3, 13953-13960 (2013).
In this way, even if dye molecules adsorb on the NPs, you will control the molecule-metal distance (the silica shell acts as a spacer) and you will achieve optimal fluorescence enhancement.
What is the reason for the fluorescence enhancement in the presence of Ag-nanoparticles?
I can suggest why the fluorescence intensity was quenched by Ag-nanoparticles.
1. The heavy atom effect. Quenching of fluorescence by a heavy atom (Ag).
2. A reaction of a fluorescent dye (in the ground or excited state) with Ag-nanoraticles.
3. The inner filter effect and/or light scattering due to nanoparticles.
4. Ground-state complex formation (static quenching).
To get any idea what occurs in your system you need to record the absorption spectrum of your sample as well as the absorption spectrum of nanoparticles before and after adding the nanoparticles to the sample. If there are changes in the position or shapes of the spectra, then it means that there should be some reaction/interaction between components in the ground state. Also, it is necessary to check the absorption spectrum of the sample after fluorescence measurement to see if there are any changes that could indicate a reaction in the excited state.
The absorbance of the sample should be less than 0.1 at the excitation and/or emission wavelengths, otherwise you will have fluorescence quenching due to the inner filter effect. So, you will need to make a correction of the fluorescence intensity for IFE.
I agreed with above comments that the quenching of the luminescence is due to the non-radiative energy transfer from the dye molecules to the Ag nanoparticles. Did you have excited your dye molecule at the absorption wavelength of Ag nanometal? Please you check this observation.
What is the size of the Ag nanoparticles you added? At which energy does their SPR peak when taken separately and in the dye solution? Which dye are you using (which absorption/fluorescence spectra), and what are the fluorescence measurement conditions (excitation and detection energies, geometric conditions of incidence and collection)?
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