Infrared wavelengths have been used for many industrial purposes, including optical fiber communications, photovoltaic power generation and night vision devices, above. Credit: Photo By: Army Sgt. Thomas Stubblefield.

It’s a discovery that’s a bit difficult for the novice to understand, but it could lead to improved technology and a cleaner environment.

To begin with, many existing infrared semiconductors capable of emitting infrared radiation (i.e., direct transition semiconductors) — contain toxic chemical elements, such as cadmium and tellurium.

Secondly, infrared wavelengths have been used for many industrial purposes, including optical fiber communications, photovoltaic power generation and night vision devices.

As the need for IR applications grows and technology advances, manufacturers have also begun to utilize IR materials in the design of plano-optics (i.e. windows, mirrors, polarizers, beamsplitters, prisms), spherical lenses (i.e. plano-concave/convex, double-concave/convex, meniscus), aspheric lenses (parabolic, hyperbolic, hybrid), achromatic lenses, and assemblies (i.e. imaging lenses, beam expanders, eyepieces, objectives).

Enter the scientists at NIMS (National Institute for Materials Science) and the Tokyo Institute of Technology, who have jointly discovered that the chemical compound Ca3SiO is a direct transition semiconductor, making it a potentially promising infrared LED and infrared detector component, reported.

The benefit, of course, is that this compound — composed of calcium, silicon and oxygen — is cheap to produce, safer and non-toxic.

Infrared semiconductors free of toxic chemical elements are generally incapable of emitting infrared radiation (i.e., indirect transition semiconductors), the report said.

Conventionally, the semiconductive properties of materials, such as energy band gap, have been controlled by combining two chemical elements — yes, that element table you had to learn in high school — that are located on the left and right side of group IV elements, such as III and V or II and VI.

In this conventional strategy, energy band gap becomes narrower by using heavier elements: consequently, this strategy has led to the development of direct transition semiconductors composed of toxic elements, such as mercury cadmium telluride and gallium arsenide, the report said.

To discover infrared semiconductors free of toxic elements, this research group took an unconventional approach: they focused on crystalline structures in which silicon atoms behave as tetravalent anions rather than their normal tetravalent cation state.

An anion is an ion that has gained one or more electrons, acquiring a negative charge. A cation is an ion that has lost one or more electrons, gaining a positive charge.

According to the report, the group ultimately chose oxysilicides (e.g., Ca3SiO) and oxygermanides with an inverse perovskite crystalline structure, synthesized them, evaluated their physical properties and conducted theoretical calculations, the reoprt said.

These processes revealed that these compounds exhibit a very small band gap of approximately 0.9 eV at a wavelength of 1.4 μm, indicating their great potential to serve as direct transition semiconductors.

These compounds with a small direct band gap may potentially be effective in absorbing, detecting and emitting long infrared wavelengths even when they are processed into thin films, making them very promising near-infrared semiconductor materials to be used in infrared sources (ie., LEDs) and detectors, the report said.

This project was carried out by a research team consisting of Naoki Ohashi (Director of the Research Center for Functional Materials, NIMS) and Alexander Shluger (Professor, University College London (UCL)).

It was supported by the MEXT Element Strategy Initiative (core research center: Tokodai Institute for Element Strategy) and the JSPS Core-to-Core Program which enabled the NIMS-UCL collaboration, the report said.

This research was published in the online version of Inorganic Chemistry, a journal of the American Chemical Society, on December 10, 2020.

Sources:,, Wikipedia