Graphene and MoS₂ coupled upconversion nanoparticles as photodetectors and nanoheaters
Surojit Chattopadhyay1*, Sandip Ghosh1, Akash Gupta1, Mukesh Kumar Thakur1
1Institute of Biophotonics, National Yang Ming University, Taipei, Taiwan
* Presenter:Surojit Chattopadhyay,
Zero dimensional (0D) and 2D materials are being conjugated to make hybrids that may have an enhanced and broader spectrum of properties inaccessible to pure materials. Conjugating the right materials to generate the desired properties is the key to such applications. We demonstrate that 2D materials such as graphene or molybdenum disulphide (MoS₂), in addition to plasmonic gold nanoparticles, can be used to enhance and quench fluorescence from upconversion nanoparticles (UCNPs) [1]. The control of the visible upconverted fluorescence in these infrared absorbing lanthanide doped NPs can result in enhanced functionality in optoelectronic and photothermal applications. First, we show that engineered UCNPs, with a silica shell, could be coupled to graphene and MoS2 to either enhance or quench the fluorescence from the UCNPs.
These UCNPs have shown promise as photodetectors requiring a charge transport layer, such as graphene, or MoS₂. The reported UCNP based photodetectors either have very low photoresponse or use complicated active core-shell structure and are based on fluorescence quenching. We have fabricated graphene-UCNP [2], and MoS₂-UCNP [3] composite devices, based on both fluorescence quenching (for core UCNPs) and fluorescence enhancement (for silica coated core-shell SiO₂@UCNPs) and found that the latter device has a significant enhancement in responsivity as compared to the former. The obtained photoresponsivity of the devices (~2.7 x 10⁴ A/W, at 980 nm, power density of ~31 µW/cm², and under 1.0 V bias for graphene-UCNP device) are the highest in its own class. These UCNP based hybrid devices could detect signals from domestic hand held appliances such as, laser pointers, mobile phone flash, and ac remote controllers.
Next, we show how the graphene-UCNP can generate heat photothermally with efficiencies in excess of 60 % to evaporate water from a concentrated saline solution demonstrating a ‘proof-of-concept’ desalination application of the material [4].
Key Words: Graphene; MoS₂; Up-conversion nanoparticles, Metal enhanced fluorescence; Hybrid photodetector; Desalination.
Acknowledgements: MOST 104-2112-M-010-002-MY3; MOST 107-2112-M-010-003-MY3.
[1] Gold Coated Cicada Wings: Anti-Reflective micro-environment for Plasmonic Enhancement of Fluorescence from Upconversion Nanoparticles; Akash Gupta, Hao-Yu Cheng, Kung-Hsuan Lin, Chien Ting Wu, Pradip Kumar Roy, Sandip Ghosh, and Surojit Chattopadhyay*, Mater. Sci. Engg. C 102, 569-577 (2019).
[2] Optically coupled engineered upconversion nanoparticles and graphene for high responsivity broadband photodetector; Mukesh Kumar Thakur, Akash Gupta, Muhammad Yusuf Fakhri, Ruei San Chen, Chien Ting Wu, Kung Hsuan Lin, and Surojit Chattopadhyay*, Nanoscale 11, 9716-9725 (2019).
[3] Ultrasensitive broadband photodetector using electrostatically conjugated MoS₂-upconversion nanoparticle nanocomposite; Sandip Ghosh, Wen Cheng Chiang, Muhammad Yusuf Fakhri, Chien Ting Wu, Ruei San Chen, and Surojit Chattopadhyay*; Under revision (2019).
[4] Graphene-Conjugated Upconversion Nanoparticles as Fluorescence-Tuned Photothermal Nanoheaters for Desalination; Mukesh Kumar Thakur, Akash Gupta, Sandip Ghosh, and Surojit Chattopadhyay*, ACS Applied Nanomaterials 2, 2250-2259 (2019).

Keywords: Up-conversion nanoparticles, Graphene, MoS2, photodetector, Metal enhanced fluorescence