*λ*~em~ = Δ*λ* = 0), a PMT voltage of 000 v, both excited and emission slit width of 0 nm, emission filter of 0%T attenuator on fluorescence spectrophotometer. The RRS intensity at 000 nm (*I*~000 nm~) and the blank value (*I*~000 nm~)~0~ without Pb^0+^ were recorded. The value of Δ*I*~000 nm~ = *I*~000 nm~