White light luminescence from nano-ZnS doped porous silicon

Nano-ZnS was deposited into porous silicon. By varying the concentration of Zn2+ ion solution during nano-ZnS formation, the amount of nano-ZnS in the porous silicon host can be controlled. The doped porous silicon exhibited a gradual shift in its photoluminescence peak from red to blue as a function of the nano-ZnS coverage. At an optimum doping, white light photoluminescence was obtained. A study in the luminescence lifetime has shown that the radiative recombination at the blue end of the visible spectrum was due to nano-ZnS, whereas luminescence emission at the red end of the visible spectrum came from porous silicon. The latter luminescence was due to the tunnelling of excited electrons from nano-ZnS into porous silicon. Time-resolved photoluminescence has also shown that radiative recombination was effectively dominated by the nano-ZnS. The photoluminescence excitation results revealed the presence of two excitation levels: one belonging to nano-ZnS at the near-ultraviolet region, and another at about 520 nm from the surface states of porous silicon. The doping of nano-ZnS into porous silicon demonstrates that luminescence colour tuning is possible when an appropriate functional material is introduced into porous silicon.