of light due to the existence of a photonic bandgap (PBG) and have been widely used in ultralow reflection solar cells, [6] LED light output, [7] light extraction from scintillation materials, [8] and FL enhancement. [9][10][11][12][13] Studies have shown that light propagates near the PBG will be at reduced group velocity owing to resonant Bragg scattering, which can enhance optical gain leading to stimulated emission and amplify the excitation of incident light. [14][15][16] Adjusting the bandgap structure to match the maximum excitation and emission wavelengths of a fluorescent dye can enable strong FL signal enhancement. PCs can achieve FL enhancement in two ways: enhancing emission by matching the bandgap position with the fluorophore excitation wavelength (E) and enhancing the emission by blue bandgap matching the emission wavelength (F) or the Bragg mirror effect. [17] Zhou et al. [18] observed a 320-fold luminescence enhancement for [Ru(dpp) 3 ]Cl 2 dispersed on a PMMA PC with stopband matching with the E, and a 71-fold enhancement of rhodamine B (RhB) was observed by Tao et al. [19] Li et al. [20] demonstrated a PC-based light-amplification method for ultrasensitive DNA detection with stopband matching of the donor emission and acceptor absorbance. Song and co-workers [21] reported a 162-fold enhancement of Nile Red based on a heterostructure PC with dual stopbands overlapping the E and F of Nile Red. Eftekhari et al. [22] demonstrated an extraordinary FL amplification of RhB with a 3D E-F-E double heterostructure, which provided higher FL enhancement than monolithic E-PCs and F-PCs. However, the abovementioned PC architectures are effective only for a particular fluorescent medium. For different dyes, the stopband structure and position of the PC must be specifically prepared and regulated. On the one hand, a PC with a broadened stopband can overlap with both the excitation and emission maxima, thereby achieving simultaneous amplification of the excitation of incident light and enhancement of the extraction of light generated by fluorescent media. On the other hand, if this stopband is wide enough to cover the E and F of most dyes, it can serve as a universal FL enhancement substrate. Therefore, novel PC architectures with broadened stopbands should be explored further to obtain more remarkable and extensive FL enhancement.
Universal fluorescence (FL) enhancement is achieved based on a multiple heterostructure photonic crystal (MHPC) with a super-wide stopband. This MHPC film is fabricated by layer-by-layer deposition of annealed colloidal crystal monolayers with gradient sizes, and it displays a broadened stopband (from 280 to 650 nm) that can overlap with the excitation wavelength (E) and the emission wavelength (F) of most commonly used fluorescent media.More than 100-fold FL enhancement of [Ru(dpp) 3 Cl 2 ], rhodamine 6G (Rh6G), and rhodamine B (RhB) on the MHPC is observed compared to that on a glass substrate. This super-wide stopband MHPC may find significant applications for augmenting FL intens...