The achievement of Si-based white light emission is one of the challenging goals in the field of display and lighting technologies.Generally

there are two methods to produce white light from light-emitting diodes(LEDs):combining three LED chips(red

green

and blue) in one discrete package or as a cluster LED chips

and coating blue indium-gallium-nitride(In-GaN) LED chips with phosphors.In addition

fabricating multilayer devices using different materials that emit lights with different colors

based on the principle of tricolor(red

green

and blue) overlay

white light can also be obtained.ZnS films were deposited on porous silicon(PS) substrate by pulsed laser deposition(PLD)

and the room-temperature photoluminescence spectra of ZnS films

PS and ZnS/PS composite system were measured.The results show that

after ZnS films were deposited

a blueshift of the red emission from PS layer occurs.Then the ZnS/PS sample was cut into three pieces

and annealed in vacuum at 400℃ for 10

20 and 30 min respectively.In the PL spectra of the three annealed samples

there appeared a new green emission band located at about 550 nm compared with the PL spectra of ZnS/PS composite system before annealing

which is ascribed to the defect-center emission of ZnS.With the increase of annealing time

the intensity of the red emission from PS layer decreases

and a redshift of the peak occurs

which is attributed to the optical band gap shrinking of a-Si:H as a function of hydrogen loss during annealing.Combining the blue

green emission from ZnS films with the red emission from PS layers

a broad PL band from 450 nm to 700 nm in the visible region is obtained

exhibiting intensively white light emission.This work offers a cheap route for fabricating a white LED

which is significant for display and lighting technology.