Ceramic holds promise for greener optical devices

(Nanowerk News) A lead-free ceramic that could be used in applications ranging from optical sensors and switches to creams for protecting against ultraviolet (UV) light has been developed by A*STAR researchers (Journal of Applied Physics, "Lead-free perovskite ceramics with ultraviolet-tunable optical and magnetic properties at room temperature").
Ceramics made from potassium sodium niobate (KNN) are promising alternatives to lead-based ceramics in electro-optical applications. However, it is both challenging and costly to improve KNN’s performance by ensuring it has a high density, fine-grained, chemically uniform microstructure.
potassium sodium niobate crystals
Researchers modified the shape and size of KNN crystals into nano-sized, nearly spherical particles arranged in a perovskite structure, similar to image above. (Image: Niethammer Zoltan0
Known as PLZT, lanthanum modified lead zirconate titanate is one of the most widely used electro-optic ceramics. Yet there are serious ecological concerns regarding toxicity to the environment and living organisms once devices made with it are discarded; PLZT contains around 60 per cent of lead (by weight). The search is on to find lead-free replacements for PLZT.
Santiranjan Shannigrahi, and his colleagues from A*STAR’s Institute of Materials Research and Engineering and Institute of High Performance Computing, have developed a method for making a KNN based ceramic material that has the potential for replacing PLZT.
“Developing a lead-free, stable ceramic for practical applications was our key aim,” explains Shannigrahi. “For some time now KNN has shown promise as a potential alternative to PLZT, but KNN-based ceramics suffer from a number of intrinsic issues, such as the low density of large, cube-shaped particles that allow moisture to be absorbed, making them unstable and therefore unsuitable for practical use.”
The KNN crystals are modified into nano-sized, nearly spherical particles arranged in a perovskite lattice arrangement. Potassium and sodium ions are located at the corners of the cubed-shaped lattice, oxygen ions at the faces, and niobium ions at the center. The researchers then replaced a proportion of the niobium ions with lanthanum ions, changing the crystal size and structure and creating a completely new material whose magnetic and optical properties can be tuned when exposed to UV.
The new material completely absorbs UV light when illuminated, turning into a deep blue color. This is accompanied with a significant increase in magnetization. Interestingly, it returns to its original color and magnetization once illumination ceases.
KNN crystals after modification and addition of lanthanum ions
KNN crystals after modification and addition of lanthanum ions. (Image: A*STAR)
“These modifications produced a semitransparent ceramic with nano-sized, spherical particles with a density of approximately 98 per cent of the theoretical potential,” says Shannigrahi.
The new material could be used in a range of applications, including powerless UV sensors, optical switches and detectors, and for UV protection in sunscreens.
“Our work could lead to a more environmentally friendly alternative to PLZT, and we are now engaging industrial partners for further development,” says Shannigrahi.
Source: A*STAR
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