To produce a high-key portrait you need to direct a light at the background. To produce a bit of a gradient texture try using a light with a wide reflector but no softbox. For the best effect use the light on full power, and turn down the other lights a bit, so that the background is lit a stop or two brighter than the model's face.
A high-key portrait works well with fair-skinned models and blondes, or with light coloured clothing. It produces a clean modern look, but can be a bit impersonal and antiseptic.