Scientists in Romania and France have investigated the development of new chalcogenide glass-ceramics for use in IR optical components. The study has been published online in the journal Materials.
Study: New Chalcogenide Glass-Ceramics Based on Ge-Zn-Se for IR Applications. Image Credit: Yalcin Sonat/Shutterstock.com
Infrared Materials and Optical Components
Infrared (IR) components are required in the electronics industry and consumer market. Smartphones in particular need reliable integrated optical components which are constructed of environmentally friendly and abundant materials.
Initially, the development of transparent infrared sensing materials was limited to the military, with consumer demand growing in recent years. Aside from smartphones, they have found applications in markets such as the automotive sector for night-time driving assistance.
Infrared devices are also used in the medical industry due to their thermovision capabilities, which detect elevated body temperatures which can be indicative of fevers, thereby aiding in disease outbreak control. Another feature of these devices is their night vision abilities which can detect objects and bodies with elevated temperatures above room temperature.
Infrared transparent materials possess a few key requirements. These are high transmittance over a range of wavelengths including longer wavelengths, optical homogeneity, purity, devitrification resistance, sufficient dispersion parameters and refractive index in IR regions, and excellent durability against mechanical stresses and water incursion.
Glass-Ceramics and Chalcogenide Glasses
Amongst the various transparent materials explored for IR devices, glass-ceramics and chalcogenide glasses have become an increasing focus of research. These materials can be easily molded and therefore can be produced on an industrial scale. Moreover, issues with mechanical properties can be easily overcome and therefore present no impediment.
There are constraints with these materials, however. They have issues with reduced stability and, currently, transparency over the entire visual spectrum range is currently difficult to realize. Ideally, these materials should be constructed from abundant and eco-friendly materials.
The new paper in Materials has evaluated two novel chalcogenide glass-ceramics for use as transparent IR-sensing materials for the commercial market. The materials were both doped and undoped with iodine and barium and are variants of Ge-Zn-Se glasses.
Mechanical alloying and spark plasma sintering methods were employed by the authors to prepare the materials, which possess a nano-sized crystalline structure. Processing routes significantly affect the final color of the prepared samples. Black, dark red, and light red samples were prepared in the study.
The authors have stated that the preparation route, which involves three milling stages along with SPS sintering, is the most efficient approach for producing transparent IR materials. Optical and structural analysis of the prepared materials under ambient conditions, considering aging, demonstrated that these materials are highly promising for constructing commercial IR devices.
Doping with iodine and barium was discovered to be a key influencing factor in the chalcogenide glass-ceramic materials, along with processing temperature. Doping affects the stability of the materials in the glass-ceramic’s amorphous phase.
The authors have identified a number of key difficulties associated with the materials. Firstly, zinc and selenium have a tendency to form ZnSe. They have noted that using selenium and germanium powders as raw materials could favor this process. This causes problems as once formed, it is difficult to achieve amorphous ZnSe using milling processes. This is likely due to the torsional force constant.
In addition, milling processes have difficulty producing amorphous o-GeSe. Even after extended milling processes (up to three hundred hours) fully amorphous o-GeSe cannot be produced. Additionally, only fifteen to eighteen percent of the total volume of powder transforms into amorphous Ge using ball milling.
Whilst these energetic barriers cause problems with the efficient production of homogenous chalcogenide glass-ceramics, the authors have stated that this can be overcome by reactions between ZnSe, BaSe, Se, and Ge powders at high temperatures. Doping is a powerful approach to meeting these challenges.
Further improvements in the doping process will be necessary for future studies, the authors have stated. Optimization of this process will improve the commercial viability of these novel materials.
Chalcogenide glass-ceramics are a promising class of transparent materials that can be used in commercial applications such as smartphones and automobiles. Imparting these products with enhanced infrared-sensing capabilities provides several benefits for multiple industries.
Whilst challenges still need to be overcome, the new study provides researchers in this field of materials science with key information which will help to realize the industrial-scale production of both thin film and bulk chalcogenide glass-ceramics.
Velea, A et al. (2022) New Chalcogenide Glass-Ceramics Based on Ge-Zn-Se for IR Applications Materials 15(14) 5002 [online] mdpi.com. Available at: https://www.mdpi.com/1996-1944/15/14/5002
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