8.3: Flexible Infrared Emitting ZnS:ErF[sub 3] Alternating Current Thin Film Electroluminescent Devices

Abstract

We have developed ZnS:ErF 3 electroluminescent thin films by pulsed laser ablation (PLD), which have been incorporated into flexible, inorganic alternating current thin film electroluminescent devices (ACTFELDs). The ZnS:ErF 3 phosphor emits green at 550nm ( 4 S 3/2 → 4 I 15/2 ), and infrared at 980nm ( 2 F 7/2 → 4 I 11/2 ) and 1540nm ( 4 I 13/2 → 4 I 15/2 ). The fabricated devices could be flexed in tension and compression without mechanical failure or deterioration of optical output, and flex radii of a few centimeters are routinely achieved. Thus, the feasibility of an inorganic, flexible, electroluminescent device with both visible and infrared emission has been demonstrated. For 700nm thick phosphor films the threshold voltage was typically 140V. At 40V above threshold the radiant flux at 980nm was typically in the 7µW/cm 2 range, and at 1540nm it was 23 µW/cm 2 . The corresponding phosphor field and conduction charge at 40 V above threshold was 2.1MV/cm and 5.23µC/cm 2 respectively. Flexible devices were fabricated using molybdenum, tungsten and steel foils as substrates.