Universal Fluorescence Enhancement Substrate Based on Multiple Heterostructure Photonic Crystal with Super‐Wide Stopband and Highly Sensitive Cr(VI) Detecting Performance

Abstract 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 intensity in chemical and biochemical sensing, imaging, disease diagnosis, and environmental monitoring. The function of MHPC/rhodium B hydrazide composites is further demonstrated in the semiquantitative detection of Cr(VI), and the limit of detection of Cr(VI) is effectively improved to 0.2 ppb.