The light sensor developed by Prof. Surojit Chattopadhyay and Ph.D. student Sandip Ghosh (schematic diagram on the right)
Prof. Surojit Chattopadhyay (middle) with the lab members
Light sensing technology has been widely applied in daily life, such as in remote controls, automatic doors, and phototherapy. However, the sensing and application of lights of different wavelengths remain problematic. The Institute of Biophotonics, National Yang-Ming University (NYMU; which merged with National Chiao Tung University and became National Yang Ming Chiao Tung University on February 1, 2021) researched and developed a brand-new nanomaterial that transfers light waves such as ultraviolet, visible light, and infrared into a current, creating a prototype of a new-generation photosensor. This result, as a collaborative achievement between NYMU, National Taiwan University of Science and Technology, and National Applied Research Laboratories, has been published in Nano Energy, an esteemed journal in the field of nanomaterial science.
A photosensor is a device that can transform light into electric current, with remote controls being one of its most recognizable applications. The infrared emitted by a remote control allows for household appliances to be controlled remotely. Light is classified by wavelength into the ultraviolet of short waves, visible light of a wavelength of 400 to 800 nm, and infrared of longer wavelengths. An effective photosensor must be able to absorb light signals of different wavelengths and simultaneously convert the light signals into the electric current; this ability is called photoresponsivity.
Photosensors require unique materials, but some materials only respond to light of a certain wavelength and high-energy ultraviolet and visible light are easily absorbed; thus, many challenges are faced in regards to infrared development. Prof. Surojit Chattopadhyay at the Institute of Biophotonics, NYMU, and his Ph.D. student Sandip Ghosh integrated MoS2 with upconversion nanoparticles, creating a photosensor a mere 4.5 µm in size. The light absorption range of this photosensor encompasses wavelengths from ultraviolet to infrared, greatly improving the shortcomings of inefficient infrared conversion into electric current.
Chattopadhyay stated that the light absorption range of MoS2 was approximately 650 nm. Through the integration of MoS2 with upconversion nanoparticles that could absorb infrared, the light absorption range of the photosensor reached 1064 nm. With the infrared radiation of a wavelength of 980 nm, a photocurrent of 1254 AW-1 was generated. According to Chattopadhyay, commercial materials generally cannot absorb a broad spectrum, which motivated him to apply two or more materials to achieve a broader light absorption range.
Ghosh explained that it takes 18 to 20 hours to integrate the two materials to construct the 4.5-µm photosensor. The photosensor can be applied in fields such as electronics, medicine, and optoelectronics. This result not only accelerates research and development of optoelectronics, but when applied commercially, can also improve smartphones, remote controls, and even night-vision equipment for military use.
Link: https://enews.ym.edu.tw/w/ymnews429/focus_20102810214357645
