Asymmetric Bilayer Films for Directional Control and Spectral Conversion of Persistent Luminescence

Persistent luminescence (PersL) enables the storage and delayed release of photonic energy, offering opportunities for time-resolved and excitation-free optical systems. However, PersL phosphors with sufficiently long and bright afterglows for practical applications are largely limited to blue or green emission. One approach to overcoming this limit is to couple PersL phosphors with organic fluorescent dyes to achieve spectral conversion. However, previously reported phosphor-dye systems remain inefficient because of incomplete energy transfer and residual phosphor emission. Here, we present a bilayer hybrid photonic structure design that enables efficient afterglow harvesting and spectral conversion. A blue-emitting Sr 2 MgSi 2 O 7:Eu 2+,Dy 3+ (SMSO) phosphor is coupled with a boron difluoride hydrazone (BODIHY) dye, forming an asymmetric architecture that selectively filters and re-emits the stored luminescence. When viewed from the dye side, the system exhibits PersL exclusively from the dye. The bilayer design further introduces direction-dependent photoluminescence (PL) and afterglow, enabling multiple distinct emission colors from only two components. The films are easily fabricated and compatible with various substrates and exhibit good chemical stability.This design provides a simple strategy for manipulating the spectral, temporal, and directional characteristics of PersL, with potential relevance to optical encoding, display, and energy conversion.