Humidity-Controlled Tunable Emission in a Dye-Incorporated Metal–Hydrogel–Metal Cavity

Abstract

Actively controllable photoluminescence is potent for a wide variety of applications from biosensing and imaging to optoelectronic components. Traditionally, methods to achieve active emission control are limited due to complex fabrication processes or irreversible tuning. Here, we demonstrate active emission tuning, achieved by changing the ambient humidity in a fluorescent dye-containing hydrogel integrated into a metal–insulator–metal (MIM) system. Altering the overlapping region of the MIM cavity resonance and the absorption and emission spectra of the dye used is the underlying principle to achieving tunability of the emission. We first verify this by passive tuning of cavity resonance and further experimentally demonstrate active tuning in both air and aqueous environments. The proposed approach is reversible, easy to integrate, and spectrally scalable, thus providing opportunities for developing tunable photonic devices.

Monolithic MOF-Based Metal–Insulator–Metal Resonator for Filtering and Sensing

“…Reflectivity of the MOF-based MIM resonator was over 95%, which was higher than that of the reported MOF-based photonic crystals. 37,38 simulated reflection agreed well with the experimental results. Also, optical images showed a tunable variable coloration from blue to red for the MOF-based MIM resonators (Figure 1d).…”

“…Figure b shows tunable reflection of the Au/SURMOFs/Au resonator with a main reflection band at λ = 408, 474, 543, 587, 644, and 690 nm by varying the number of spraying cycles for the SURMOFs growth. Reflectivity of the MOF-based MIM resonator was over 95%, which was higher than that of the reported MOF-based photonic crystals. , Figure c depicts the reflection spectra obtained by a finite-difference time-domain (FDTD) simulation for the planar MIM resonators with different insulator thicknesses. A plane wave is normally incident to the top surface of the MIM resonator, which excites a wide light source from the incidence of the resonators to reveal bright colors from blue to red.…”

Switchable unidirectional emissions from hydrogel gratings with integrated carbon quantum dots

“…Because the emission direction cannot be directly tuned by humidity based on hydrogel grating schemes, we employ the angle-dependent resonance from Fabry-Perot type nanocavity to tailor the direction of PL emission. With the RH increase, the angle-dependent resonance actively shifts and leads to a continuous emission angle variation from 0° to 40° due to the cavity-induced angular enhancement of the Purcell effect and excitation rate 39 , 45 . Figure 6b shows the measured angular-resolved PL emission under different RH conditions.…”

“…By employing polymer shrinkage under the e-beam exposure, the QDs-embedded polyvinyl alcohol (PVA) hydrogel film can be directly fabricated for asymmetric grating profile with single-step processing, imparting the grating momentum to the PL emission and allowing the PL in the guided mode to be unidirectionally coupled out into free space. Thanks to the humidity-responsive swelling capability of hydrogel materials 35 – 39 , the grating efficiency of hydrogel grating could be notably tuned with ambient humidity change due to the morphology alteration, enabling efficient control of emission, beyond typical grating schemes for static emission extraction 2 , 40 . Furthermore, the excitation position creates extra degree of freedom to manipulate the emission direction of the PL.…”

Hydrogels for active photonics

“…c Multilayered nanoslide for switchable image processing by tuning humidity 80 . d Dye-containing MHM cavity for emission tuning 86 . e Indirectly built MHM nanoarray plasmonic cavity with pH responsiveness 88 .…”