Enhanced light extraction efficiency of thin film phosphor by reverse nano-imprint lithography

Abstract

Over the past few decades, the excellent luminescence of Y2O3:Eu3+ powder phosphors has lead to their widespread use as a red components of RGB triads in display and lighting devices. More recently there has been growing interest in the use of Y2O3:Eu3+ thin film phosphors in flat panel displays (FPD) such as field-emission displays (FED) and plasma display panels (PDP) due to their superiority over the powder phosphors in terms of thermal stability, reduced out-gassing, improved uniformity, smaller grains, and better adhesion to substrates. However, for these applications, it is necessary to increase the light intensity from the thin-film phosphor layers. The two-dimensional (2D) PC patterns have been demonstrated to enhance extraction efficiency of thin film luminescent materials in various light emitting devices. At this time when integration of elements is important issue of process, the nano-imprint lithography (NIL) process which has low cost and simple process and is the process of production of minute structure is drawing attention as the next-generation lithography process. In this study, a zirconium oxide (ZrO2) nanoparticle assisted photonic structure for improving the light extraction efficiency of Y2O3:Eu3+ thin film phosphors by reverse nano-imprint lithography approach. The structural effect of a 2D ZrO2 nanoparticle photonic crystal (PC) pattern on the extraction efficiency of photoluminescence (PL) from the underlying Y2O3:Eu3+ thin film phosphors was investigated. The 2D photonic crystal structure was fabricated using a reverse nano-imprint process with a ZrO2 nanoparticle solution as a nano-imprint resin and a patterned trimethylolpropane propoxylate triacrylate (TPT)/polydimethyl-siloxane (PDMS) stamp as a mold. The upward and downward surfaces of Y2O3:Eu3+ thin film phosphors were coated with 2D ZrO2 nanoparticle PCLs using a reverse nano-imprint lithography. The 2D ZrO2 nanoparticle PCLs were generated on the Y2O3:Eu3+ thin film phosphors or quartz substrates by reverse nano-imprint lithography. This simple process results in a double-side 2D ZrO2 nanoparticle PCLs, where the extraction efficiency was improved by 8.49 times compared to the conventional Y2O3:Eu3+ thin film phosphors.