Semiconductor electrodes having regions of graded composition exhibiting photoluminescence and electroluminescence

A method of forming a photoelectrochemical cell, comprising the steps of:

• (a) providing a base substrate comprising a solid solution of metal and a non-metal having a characteristic emission spectrum;
• (b) diffusing a substituent element into a surface of the base substrate for a period of time and at a temperature selected such that the concentration of the substituent in the substrate declines from a level of substantially complete substitution for the like metal or non-metal element at the surface to substantially no substitution at a selected distance into the substrate to form an emissive electrode;
• (c) mounting an electrical conductor into ohmic electrical contact with the surface of the emissive electrode substrate opposite that into which the substituent has been diffused;
• and
• (d) immersing the emissive electrode in an electrolyte.

A method of providing emitted light of varying color in response to incident light, comprising the steps of:

• (a) providing an emissive electrode having a substrate formed of a solid solution of three metal and non-metal elements in which the concentration of two like elements varies with depth from an exposed surface of the substrate such that the band gap energies between the valence and conduction bands changes with depth from the exposed surface, and wherein the band gap energies are such that the material of the substrate, to a selected depth beneath the exposed surface, provides emission spectra in the visible range in response to light stimulation;
• (b) maintaining an electrolyte in contact with the exposed surface of the emissive electrode;
• (c) applying light to the exposed surface at an intensity sufficient to cause photoluminescence from the exposed surface;
• and
• (d) applying a voltage of varying magnitude between the electrolyte and the emissive electrode substrate to produce emissions from the exposed surface of varying color.