Team of scientists from various research institutions work together to inspect a novel cascade optical field modulation strategy integrating the superlensing effect of polymeric micro-lens arrays (MLAs) and the plasmonic effect of gold nanorods (Au NRs) to boost up-conversion luminescence.
Narrow-band near infrared (NIR) photodetectors capable to simultaneously detect light in multi-spectral bands, for example in the NIR I and NIR II regions. Applications of these photodetectors are attracting a lot of attention in diverse areas including biological analysis, multicolour bio-imaging and sensing, and encrypted communications.
UCNCs (Unconventional Computation and Natural Computation), due to their unique two-photons or multi-photons excitation nature as well as their non-toxic characteristics and low preparation cost, have emerged as a superior solution by converting NIR photons into easily detectable visible photons. However, the relatively high pumping threshold to realize detectable up-conversion luminescence (UCL), originating from the lower absorption cross section of 4fn-4fn transitions of rare earth (RE) ions and lower luminescent quantum efficiency of UCNCs because of the anti-Stokes nature, poses a fundamental limitation for weak NIR light detection in photoelectric devices.
In a study published in Light Science & Applications, a team of scientists, led by Professors Song Hongwei and Xu Wen from State Key Laboratory of Integrated Optoelectronics, College of Electronic Science and Engineering, Jilin University, China, Dr Liu Haichun from Department of Theoretical Chemistry and Biology, KTH Royal Institute of Technology, Stockholm, Sweden, Department of Applied Physics, KTH Royal Institute of Technology, Stockholm, Sweden and co-workers have explored a novel cascade optical field modulation strategy integrating the superlensing effect of polymeric micro-lens arrays (MLAs) and the plasmonic effect of gold nanorods (Au NRs) to boost UCL. This cascade modulation strategy was found to readily lead to a UCL enhancement by more than four orders of magnitude.
They designed and synthesized multi-wavelength responsive core-shell-shell (CSS) structured UCNCs that emit visible light under excitation of 808, 980, or 1540 nanometres, and constructed NIR photodetectors on top. Realizing that each UCNC constitutes an information-rich kinetic system, possessing characteristic responses to optical signals in the temporal and frequency domains of different excitation wavelengths, they exploited the possibility of separating the channels of multi-wavelengths photodetection to implement selective detection. They proved that the modulation frequency response can be used to well distinguish the detected wavelengths. In addition, the UCL kinetics of the UCNCs was also optimized by manipulating the concentrations of lanthanide dopants, whereby short response times of 80 to 120 metre per second for the final photodectors were achieved.
These scientists summarize the operational principle of their NIR photodetectors by sharing that in comparison, the employment of the LSPR effect can typically enhance UCL by one order of magnitude, while the usage of the superlensing effect can lead to UCL enhancement by two or three orders of magnitude, when using the same routine and easily obtained nano- or micro-structures.
Importantly, the incident light wavelength can be well distinguished by a proposed novel approach, which was through examining the response to the excitation modulation frequency. Our work highlights new concepts to conquer the relatively high pumping threshold of UCNCs, enabling to build high-photoresponsivity and -detectivity multi-band responsive and distinguishable photodetectors on top of them, and can also stimulate other applications of up-conversion nanotechnology. [APBN]