Enhanced emission from fcc fluorescent photonic crystals

We fabricated a high quality fcc photonic crystal composed of ruthenium tris-bipyridine ${\left[\text{Ru}{\left(\text{bpy}\right)}_3\right]}^{2+}{\left({\text{PF}}_6^{-}\right)}_2$. Solid-angle-resolved spectroscopy was performed over 76% of $2\pi$ sr, with $\sim 2°$ resolution. Anisotropic emission patterns are explained with an analytic model of two plane waves coupled by diffraction from a Bragg plane. Two distinct types of emissive enhancements are observed, one due to modes coupling confined directions into leaky directions and the other due to maxima in the optical mode density adjacent to partial photonic band gaps.

Figure 1

SEM micrographs of (a) polystyrene colloidal template and (b) FPC cross-section. (c) Normalized emission spectra, integrated over 76% of $2\pi$ sr, from FPC, RuBpy film, and their ratio. Also in (c), normal-incidence reflectance from FPC and template.

Figure 2

Parts (a)–(e) each have subparts (i), (ii), (iii). FPC emission at (a) 712 (b) 690 (c) 650 (d) 617 and (e) 560 nm. (a)(i)–(e)(i) Normalized intensity vs $\theta$ and $\phi$. (a)(ii) Comparison with model16. (b)(ii)–(e)(ii) Satisfaction of Bragg condition (white) comparable to (b)(i)–(e)(i) but plotted at half-scale; Bragg planes labeled with Miller index; high-symmetry points U, K, and W identified. (a)(iii)–(e)(iii) $\phi$-averaged intensity vs $\theta$ (black, with vertical bars depicting min. and max.), normalized to theoretical BLB (gray); over-bars depict theoretical width of TE (upper bar) and TM (lower bar) stopgaps. Tables point to the stopgap, mode enhancements (ME), and mode density enhancements (DE) where obscured features were extrapolated and reported in parentheses. ${\text{ME}}_{111}$ points to vertices of bright arcs nominally at $\phi =90$, 210, and $330°$; ${\text{ME}}_{200}$ vertices at $\phi =30$, 150, and $270°$.

Figure 3

Momentum space dispersion surface for TE (left of ${\mathbf{G}}_{111}$) and TM (right) for energy $\lambda =690\text{nm}$ and diffraction in (111), shown relative to $k{\epsilon }_{000}^{1/2}$ plane wave dispersion (dots). A mode point on the dispersion surface is identified with the coupling and DOM by drawing a vertical line. Inset: dispersion for $\left(11\overline{1}\right)$ Bragg plane at $70.5°$ to FPC surface.