Dear Mohammad,

the information that you present is very poor. There are very many metals with different electriniсs structure and different nature of interaction with other substances. Also, the concentration of metal salts (includind anion nature) or its ratio to gold NCs can have important role. Everybody who can help should have more information about your system.

I'm using metal chloride solutions, in the start from uM to mM there is a sense, i.e. increase in metal ion concentration decreases the fluorescent. but the region of nM to uM is showing totally opposite results,. i.e. increase in conc. increases fluorescence. 

An increase with increase is expected (Beer's law). A decrease with increase is consistent with what would be seen in agglomeration of particles or multiparticle quenching.

SO both trends are there at different ranges of concentrations, how Beer's law justify this? I'm talking about fluorescence, not absorbance... 

I tell, again, that the nature (s-, p-, d-, f-metals) and concentration of the salts can effect on the size of nanoclasters and excited energy transfer in solution, as well as other resons can inflyence on the fluorescence intensity.

My apologies. I read too quickly. Fluorescence intensity is proportional to number of emitters (OK, call it an "inverse Beer's law"). Number of emitters depends on surface area. Surface area depends on particle size. For exactly the same mass concentration in solution, individual and small particles have greater surface area than agglomerated or large particles.