All Publications

  • Spatially Controlled Uv Light Generation at Depth Using Upconversion Micelles. Advanced materials (Deerfield Beach, Fla.) Zhou, Q., Wirtz, B. M., Schloemer, T. H., Burroughs, M. C., Hu, M., Narayanan, P., Lyu, J., Gallegos, A. O., Layton, C., Mai, D. J., Congreve, D. N. 2023: e2301563


    Ultraviolet (UV) light can trigger a plethora of useful photochemical reactions for diverse applications, including photocatalysis, photopolymerization, and drug delivery. These applications typically require penetration of high energy photons deep into materials, yet delivering these photons beyond the surface is extremely challenging due to absorption and scattering effects. Triplet-triplet annihilation upconversion (TTA-UC) shows great promise to circumvent this issue by generating high energy photons from incident lower energy photons. However, molecules that facilitate TTA-UC usually have poor water solubility, limiting their deployment in aqueous environments. To address this challenge, a nanoencapsulation method is leveraged to fabricate water-compatible UC micelles, enabling on-demand UV photon generation deep into materials. Two iridium-based complexes are presented for use as TTA-UC sensitizers with increased solubilities that facilitate the formation of highly emissive UV-upconverting micelles. Furthermore, this encapsulation method is shown to be generalizable to nineteen UV-emitting UC systems, accessing a range of upconverted UV emission profiles with wavelengths as low as 350 nm. As a proof-of-principle demonstration of precision photochemistry at depth, UV-emitting UC micelles are used to photolyze a fluorophore at a focal point nearly a centimeter beyond the surface, revealing opportunities for spatially controlled manipulation deep into UV-responsive materials. This article is protected by copyright. All rights reserved.

    View details for DOI 10.1002/adma.202301563

    View details for PubMedID 37548335

  • Water additives improve the efficiency of violet perovskite light-emitting diodes MATTER Hu, M., Fernandez, S., Zhou, Q., Narayanan, P., Saini, B., Schloemer, T. H., Lyu, J., Gallegos, A. O., Ahmed, G. H., Congreve, D. N. 2023; 6 (7): 2356-2367
  • Controlling the durability and optical properties of triplet-triplet annihilation upconversion nanocapsules. Nanoscale Schloemer, T. H., Sanders, S. N., Narayanan, P., Zhou, Q., Hu, M., Congreve, D. N. 2023


    Deep penetration of high energy photons by direct irradiation is often not feasible due to absorption and scattering losses, which are generally exacerbated as photon energy increases. Precise generation of high energy photons beneath a surface can circumvent these losses and significantly transform optically controlled processes like photocatalysis or 3D printing. Using triplet-triplet annihilation upconversion (TTA-UC), a nonlinear process, we can locally convert two transmissive low energy photons into one high energy photon. We recently demonstrated the use of nanocapsules for high energy photon generation at depth, with durability within a variety of chemical environments due to the formation of a dense, protective silica shell that prevents content leakage and nanocapsule aggregation. Here, we show the importance of the feed concentrations of the tetraethylorthosilicate (TEOS) monomer and the methoxy poly(ethyleneglycol) silane (PEG-silane) ligand used to synthesize these nanocapsules using spectroscopic and microscopy characterizations. At optimal TEOS and PEG-silane concentrations, minimal nanocapsule leakage can be obtained which maximizes UC photoluminescence. We also spectroscopically study the origin of inefficient upconversion from UCNCs made using sub-optimal conditions to probe how TEOS and PEG-silane concentrations impact the equilibrium between productive shell growth and side product formation, like amorphous silica. Furthermore, this optimized fabrication protocol can be applied to encapsulate multiple TTA-UC systems and other emissive dyes to generate anti-Stokes or Stokes shifted emission, respectively. These results show that simple synthetic controls can be tuned to obtain robust, well-dispersed, bright upconverting nanoparticles for subsequent integration in optically controlled technologies.

    View details for DOI 10.1039/d3nr00067b

    View details for PubMedID 37000152

  • Nanoengineering Triplet-Triplet Annihilation Upconversion: From Materials to Real-World Applications. ACS nano Schloemer, T., Narayanan, P., Zhou, Q., Belliveau, E., Seitz, M., Congreve, D. N. 2023


    Using light to control matter has captured the imagination of scientists for generations, as there is an abundance of photons at our disposal. Yet delivering photons beyond the surface to many photoresponsive systems has proven challenging, particularly at scale, due to light attenuation via absorption and scattering losses. Triplet-triplet annihilation upconversion (TTA-UC), a process which allows for low energy photons to be converted to high energy photons, is poised to overcome these challenges by allowing for precise spatial generation of high energy photons due to its nonlinear nature. With a wide range of sensitizer and annihilator motifs available for TTA-UC, many researchers seek to integrate these materials in solution or solid-state applications. In this Review, we discuss nanoengineering deployment strategies and highlight their uses in recent state-of-the-art examples of TTA-UC integrated in both solution and solid-state applications. Considering both implementation tactics and application-specific requirements, we identify critical needs to push TTA-UC-based applications from an academic curiosity to a scalable technology.

    View details for DOI 10.1021/acsnano.3c00543

    View details for PubMedID 36800310

  • Triplet Fusion Upconversion Nanocapsule Synthesis. Journal of visualized experiments : JoVE Schloemer, T. H., Sanders, S. N., Zhou, Q., Narayanan, P., Hu, M., Gangishetty, M. K., Anderson, D., Seitz, M., Gallegos, A. O., Stokes, R. C., Congreve, D. N. 2022


    Triplet fusion upconversion (UC) allows for the generation of one high energy photon from two low energy input photons. This well-studied process has significant implications for producing high energy light beyond a material's surface. However, the deployment of UC materials has been stymied due to poor material solubility, high concentration requirements, and oxygen sensitivity, ultimately resulting in reduced light output. Toward this end, nanoencapsulation has been a popular motif to circumvent these challenges, but durability has remained elusive in organic solvents. Recently, a nanoencapsulation technique was engineered to tackle each of these challenges, whereupon an oleic acid nanodroplet containing upconversion materials was encapsulated with a silica shell. Ultimately, these nanocapsules (NCs) were durable enough to enable triplet fusion upconversion-facilitated volumetric three-dimensional (3D) printing. By encapsulating upconversion materials with silica and dispersing them in a 3D printing resin, photopatterning beyond the surface of the printing vat was made possible. Here, video protocols for the synthesis of upconversion NCs are presented for both small-scale and large-scale batches. The outlined protocols serve as a starting point for adapting this encapsulation scheme to multiple upconversion schemes for use in volumetric 3D printing applications.

    View details for DOI 10.3791/64374

    View details for PubMedID 36155426

  • A biomineral-inspired approach of synthesizing colloidal persistent phosphors as a multicolor, intravital light source. Science advances Yang, F., Wu, X., Cui, H., Ou, Z., Jiang, S., Cai, S., Zhou, Q., Wong, B. G., Huang, H., Hong, G. 2022; 8 (30): eabo6743


    Many in vivo biological techniques, such as fluorescence imaging, photodynamic therapy, and optogenetics, require light delivery into biological tissues. The limited tissue penetration of visible light discourages the use of external light sources and calls for the development of light sources that can be delivered in vivo. A promising material for internal light delivery is persistent phosphors; however, there is a scarcity of materials with strong persistent luminescence of visible light in a stable colloid to facilitate systemic delivery in vivo. Here, we used a bioinspired demineralization (BID) strategy to synthesize stable colloidal solutions of solid-state phosphors in the range of 470 to 650 nm and diameters down to 20 nm. The exceptional brightness of BID-produced colloids enables their utility as multicolor luminescent tags in vivo with favorable biocompatibility. Because of their stable dispersion in water, BID-produced nanophosphors can be delivered systemically, acting as an intravascular colloidal light source to internally excite genetically encoded fluorescent reporters within the mouse brain.

    View details for DOI 10.1126/sciadv.abo6743

    View details for PubMedID 35905189

  • Tether-free photothermal deep-brain stimulation in freely behaving mice via wide-field illumination in the near-infrared-II window. Nature biomedical engineering Wu, X., Jiang, Y., Rommelfanger, N. J., Yang, F., Zhou, Q., Yin, R., Liu, J., Cai, S., Ren, W., Shin, A., Ong, K. S., Pu, K., Hong, G. 2022


    Neural circuitry is typically modulated via invasive brain implants and tethered optical fibres in restrained animals. Here we show that wide-field illumination in the second near-infrared spectral window (NIR-II) enables implant-and-tether-free deep-brain stimulation in freely behaving mice with stereotactically injected macromolecular photothermal transducers activating neurons ectopically expressing the temperature-sensitive transient receptor potential cation channel subfamily V member 1 (TRPV1). The macromolecular transducers, ~40 nm in size and consisting of a semiconducting polymer core and an amphiphilic polymer shell, have a photothermal conversion efficiency of 71% at 1,064 nm, the wavelength at which light attenuation by brain tissue is minimized (within the 400-1,800 nm spectral window). TRPV1-expressing neurons in the hippocampus, motor cortex and ventral tegmental area of mice can be activated with minimal thermal damage on wide-field NIR-II illumination from a light source placed at distances higher than 50 cm above the animal's head and at an incident power density of 10 mW mm-2. Deep-brain stimulation via wide-field NIR-II illumination may open up opportunities for social behavioural studies in small animals.

    View details for DOI 10.1038/s41551-022-00862-w

    View details for PubMedID 35314800

  • Anisotropy and anharmonicity in polystyrene stable glass JOURNAL OF CHEMICAL PHYSICS Raegen, A. N., Zhou, Q., Forrest, J. A. 2020; 153 (21): 214508


    We have used ellipsometry to characterize the anisotropy in stable polymer glasses prepared by physical vapor deposition. These measurements reveal birefringence values (as measured by the magnitude of in-plane vs out-of-plane refractive index) less than 0.002 in vapor-deposited polystyrenes with N from 6 to 12 and with fictive temperatures between 10 K and 35 K below the Tg values. We have measured the thermal expansivity of these stable glasses and compared to ordinary rejuvenated glass. The thermal expansivity of the stable glasses is less than that of ordinary glass with a difference that increases as the fictive temperature Tf decreases.

    View details for DOI 10.1063/5.0032153

    View details for Web of Science ID 000597328700003

    View details for PubMedID 33291898

  • Ultrastable monodisperse polymer glass formed by physical vapour deposition NATURE MATERIALS Raegen, A. N., Yin, J., Zhou, Q., Forrest, J. A. 2020


    Stable glasses prepared by vapour deposition are an analogue of glassy materials aged for geological timescales. The ability to prepare such materials allows the study of near-ideal glassy systems. We report the preparation and characterization of stable glasses of polymers prepared by physical vapour deposition. By controlling the substrate temperature, deposition rate and polydispersity, we prepared and characterized a variety of stable polymer glasses. These materials display the kinetic stability, low fictive temperatures and high-density characteristic of stable glasses. Extrapolation of the measured transformation times between the stable and normal glass provides estimates of the relaxation times of the equilibrium supercooled liquid at temperatures as much as 30 K below the glass transition temperature. These results demonstrate that polymer stable glasses are an exciting and powerful tool in the study of ultrastable glass and disordered materials in general.

    View details for DOI 10.1038/s41563-020-0723-7

    View details for Web of Science ID 000546427400004

    View details for PubMedID 32632279

  • A highly sensitive double-layer structured nanodevice for moisture induced power generation NANOTECHNOLOGY Zhou, Q., Hui, Z., Xiao, M., Zhou, N. Y. 2020; 31 (26): 265401


    With the increasing global energy demand, traditional energy sources are gradually failing to meet society's needs while also having a potential of being harmful to the environment. As such, energy generating technologies capable of converting ubiquitous environmental energy into usable forms, such as electricity, have received increasing attention. In this research, a power generating device composed of a graphene (G) and titanium dioxide nanowire (TiO2 NWs) double-layer structure is prepared by an electrophoretic deposition method. Since both materials have special nanochannel structures and non-zero zeta potential, they can convert environmental energy into electricity through the diffusion, ionization, and natural evaporation of water. Furthermore, the efficiency of this novel sensor is much higher than their respective single-layer devices. By application of only 6 μl of water, the open circuit voltage (UOC) generated on the G-TiO2 sensor is as high as 1.067 ± (0.008) V. In comparison, TiO2 NWs single layer can only generate a UOC around 500 mV, and graphene itself can only produce a UOC no more than 250 mV under the same condition. Additionally, the effect of different deposition times of graphene on the surface morphology and thickness of graphene film is explored, and the effects of these changes in microstructure on performance is discussed in depth. Aside from power generation, the high sensitivity of the device to different volumes of water brings its use in the detection of trace amounts of water, and its high efficiency of energy conversion suggests a potential application as a power supply. This research not only provides a satisfactory candidate for inexpensive and efficient evaporative power generation, but also builds a foundation for developing new, intelligent, and self-powered electronic technologies.

    View details for DOI 10.1088/1361-6528/ab7fcd

    View details for Web of Science ID 000528541500001

    View details for PubMedID 32168494