Is it possible to create blackness using a bulb??
If not, how do they make the colour "Black" in TVs and mobilephone screens?
Do they make use of some destructive interference or something ?
Black light is not possible. In current LCD technology, the light from the screen is actually a panel of white light behind the pixels called the back light. The light shines through the colored pixels which filter out light to give what ever color you see. The black in this case is a total blockout of the back light for those pixels that are black.
In OLED technology, the pixels themselves produce light and black in that case is an off state of the pixel.