Metallo-graphene enhanced upconversion luminescence for broadband photodetection under polychromatic illumination

We report electrostatically conjugated core- silica (SiO2) shell upconversion nanoparticle (UCNPs@SiO2), and gold nanorod (AuNR) nanocomposite (NC) combined with graphene to demonstrate > 200-fold UC fluorescence enhancement. Plasmonic AuNR and graphene, resulted in enhanced fluorescence in UCNP with a maximum for the SiO2 shell thickness of 7 nm supported by finite difference time domain simulation of electric field distribution. In addition to the conventionally reported spectroscopic evidence, the plasmon aided UC fluorescence enhancement was demonstrated by direct confocal fluorescence imaging also, which was corroborated by a similar to 40% decrease in fluorescence lifetime. Finally, we have fabricated a NC/graphene hybrid photodetector (PD) that showed broadband (455-980 nm) photoresponse, with photoresponsivity of similar to 5000 AW 1, and response times of 80-200 ms under 980 nm illumination. The multiphoton infrared (IR, similar to 980 nm) absorbing UCNPs also show interesting high energy (blue (B), green (G), and red (R)) photoresponse which is now conclusively attributed to one-photon absorption in the UCNPs. We report, probably for the first time, the performance of the hybrid PD under monochromatic and polychromatic illumination of B, G, R, B + G, B + R, G + R, and B + G + R, among others. The photocurrent under polychromatic conditions is dominated by the strongest monochromatic response, and does not scale with net power of the illumination. The loss in photocurrent is attributed to saturation in absorption, and photothermal heating. The fast response of the PD device has been demonstrated while detecting high frequency modulated AC remote controller signals, and attributed to the fast charge sweeping by the AuNRs.

Automated summary

In this study, electrostatically conjugated core-silica shell upconversion nanoparticles (UCNP@SiO2) and gold nanorod (AuNR) nanocomposites combined with graphene were used to demonstrate over 200-fold upconversion fluorescence enhancement. The enhanced fluorescence in UCNP, attributed to a plasmonic effect from AuNR and graphene, was supported by finite difference time domain simulations of electric field distribution. The performance of the hybrid photodetector (PD) with broad photoresponse and fast response times under various illumination conditions was also reported, with the potential application in remote sensing devices.