Stretchable and Thermally Stable Dual Emission Composite Films of On-Purpose Aggregated Copper Nanoclusters in Carboxylated Polyurethane for Remote White Light-Emitting Devices

Abstract

Stretchable, mechanically stable films with thermally stable dual emission peaked in the blue and orange spectral range are fabricated by condensation and aging of carboxylated polyurethane in the presence of on-purpose aggregated copper nanoclusters. The aggregation of copper clusters leads to the enhancement of their emission in the orange, while polyurethane matrix contributes with the blue emission band, with an overall photoluminescence quantum yield of the films as high as 18%. Composite Cu nanoclusters/polyurethane films are sufficiently transparent over the visible spectral range and are absorbing in the UV range; more than 90% of their emission intensity is preserved after 10 times of cycle of stretch and recovery, as well as aging of up to 10 h at 90 °C, making them useful for optoelectronic devices. Remote white light-emitting devices (LEDs) have been fabricated by placing a down-conversion layer of composite Cu nanoclusters/polyurethane film separated through a silicone resin spacer from the UV LED chip, with Commission Internationale de l'Eclairage color coordinates of (0.34, 0.29), and a high color rendering index of 87.