Two-dimensional photonic crystal phosphors for efficient and polarization-insensitive excitation

As a continuing effort to improve the performance of photonic crystal (PhC) phosphors—an engineered nanophotonic phosphor structure developed by the authors' group—we hereby introduce two-dimensional (2D) PhC phosphor films. In particular, the excitation polarization dependence inherent to and suffered by the precedent one-dimensional PhC phosphors can be eliminated using a square lattice PhC structure due to its four-fold rotational symmetry. In addition, the thickness of the high index PhC backbone layer is intentionally increased so that dual excitation resonances occur for both the transverse-electric (TE) and transverse-magnetic (TM) waveguide modes, thereby effectively doubling the phosphor efficiency. We implemented and examined 2D PhC phosphor structures with colloidal quantum dots (CQDs) as phosphor material. We observed ∼4 times enhanced and excitation-polarization-insensitive CQD fluorescence at dual resonance wavelengths for the TE- and TM-guided modes. We confirmed the validity of the observed results through simulations.