Elementary tellurium is attracting increasing attention due to its unconventional properties with three two-dimensional phases and the existence of Weyl nodes around its Femi level. Unlike chemically synthesized tellurium crystals (Chem-Te) which employ harsh reagents, high temperatures, and high costs for considerable hazardous waste disposal, biologically synthesized tellurium (Bio-Te) nanostructures are much environmentally friendly. These properties make Bio-Te nanostructures promising candidates as the material of choice for next-generation optoelectronic and photonic devices. However, their physical characteristics are largely unexplored.

Recently, a collaborative study, led by Prof. WANG Jun and Prof. ZHANG Long from Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, revealed the excellent ultrafast nonlinear optical properties of these Bio-Te nanostructures and their conjugated polymer composites, realized ultrafast pulse generation by building infrared fiber and solid-state lasers using Bio-Te as the saturable absorber, and demonstrated an all-optical switch based on the Bio-Te in optical fiber system. Their study was published in Nature Communications.

In their experiment, Bio-Te nanocrystals were synthesized by growing haloalkaliphilic anaerobic bacterium, Bacillus Selenitireducens, in a lactate–tellurite medium. The obtained materials exhibited strong saturable absorption in a wide range of visible to mid-infrared (515 nm to 2.8 μm), and was superior to graphene at 800 nm, 2.5 μm, and 2.8 μm wavelengths. In addition, the conjugated composites of Bio-Te with poly(mphenylenevinylene)-co-2,5-dioctoxy-phenylenevinylene (PmPV), Bio-Te-PmPV displayed excellent optical limiting properties both in the visible and near infrared bands, which exceeded those displayed in optical limiting materials C⁶⁰ fullerene, single-walled carbon nanotubes and metal phthalocyanine, etc.

By using Bio-Te as a saturable absorber, researchers have successfully generated pulse trains by mode-locking/Q-switching in a 1.5 μm erbium-doped fiber laser and a 2 μm Tm: YAP solid-state lasers. At the same time, a thermo-optical switch based on Te nanocrystals was also implemented, and its thermo-optical response speed and thermo-optical coefficient were higher than WS₂ and graphene, which were previously considered to have excellent performance.

This work indicates that Te nanostructures synthesized by microorganisms have excellent ultrafast nonlinear optical properties and good performance in photonics devices such as infrared ultrafast pulse mode-locking device, wide-band strong laser protective optical limiter and thermal optical switch.

It innovatively introduced green microbial synthesis technology into the preparation of high-performance photonic functional materials, filling the gap in the research on the photonic properties and applications of microbial synthesis nanomaterials.

This work was supported by the Chinese National Natural Science Foundation, the Strategic Priority Research Program of CAS, the Key Research Program of Frontier Science of CAS, and the Program of Shanghai Academic Research Leader.

Fig. 1 (a) Synthesis biological synthesized tellurium (Bio-Te).
(b) Saturation properties in the broad range of visible to mid-infrared.
(c) Ultrafast laser pulse generation. (d) Excellent all-optical switch feature.

Article website: https://www.nature.com/articles/s41467-019-11898-z
Contact:
Mr. Cao Yong
General Administrative Office
Shanghai Institute of Optics and Fine Mechanics, CAS
Email: caoyong@siom.ac.cn