Opto-impedance spectroscopy and equivalent circuit analyses of AC powder electroluminescent devices.

High energy photons can affect the dielectric response of AC powder electroluminescent devices (ACPELDs). In this paper, electroluminescent (EL), phosphor and dielectric films are photo-excited at peak wavelengths of 399 nm, 520 nm and 625 nm to identify the dielectric relaxation processes occurring in ACPELDs. The 399 nm illumination changes the frequency-dependent dielectric responses of both EL and phosphor films due to the photo-induced excitation of ZnS:Cu,Al phosphor particles. A higher illumination intensity increases the dipolar polarization in the resin matrix and enhances the Maxwell-Wagner-Sillars (MWS) effect at the particle/resin interfaces. Equivalent circuits relating to the relaxation processes present in the EL and phosphor films are derived. From the analyses of the circuit component values, a charge generation and accumulation process is proposed to explain these opto-impedance behaviors.