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 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 showed 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 in part tunneling of excited electrons from nano-ZnS into porous silicon and in part direct excitation of porous silicon layer. Time-resolved photoluminescence also showed that radiative recombination was effectively dominated by the nano-ZnS. Photoluminescence excitation result revealed the presence of two excitation levels; one belonged to nano-ZnS at near uv region, and another at about 520 nm from the surface states of porous silicon and nano-ZnS. The doping of nano-ZnS into porous silicon demonstrates that luminescence color tuning is possible when an appropriate functional material is introduced into porous silicon.