  In this work, a reversible control over the visible luminescence of phosphor
ZnO is achieved by the application of a few volts (<5V) to nanostructured ZnO
film sandwiched between ITO and LiClO4/PEO solid electrolyte. Since ZnO is a
good absorbing material but ITO-Glass substrate is transparent in the range of
320-375 nm, the ZnO-ITO interface has been illuminated by a 345 nm light
passing through the ITO glass substrate and the emitted light near 545 nm has
been collected in reflection mode. When the solid polymer electrolyte is
negatively biased, up to 107 percent enhancement in the visible luminescence
has been observed, whereas a complete quenching (87 percent reduction) of the
visible emission has been seen when it is positively biased. The sharp near
band edge (NBE) emission in the ultraviolet region however has no dependence
within the voltage range we are working. The luminescence output follows
variations in the applied voltage up to maximum frequency limited by response
time of the device which lies within the range of 20-30 sec. The upward band
bending created by application of negative bias to the conductive polymer
populates increasing number of defect levels above the Fermi level which
enhances the visible photoluminescence and vice versa.
