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)3Cl2], 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.