Exploring new nuances glass with controllable relaxation

Exploring new nuances of glass with controllable relaxation

12:03 PM, 26th October 2016
Optical Materials Group members (From right to left) Shichao Lu, Yongze Yu, Qiannan Mao, Liting Lin, Jiejie Chen, B Shanmugavelu, Shifeng Zhou, and Zaijin Fang.
Optical Materials Group members (From right to left) Shichao Lu, Yongze Yu, Qiannan Mao, Liting Lin, Jiejie Chen, B Shanmugavelu, Shifeng Zhou, and Zaijin Fang.

In an interview Professor Shifeng Zhou from the school of materials science and engineering, South China University of Technology, Guangzhou, China with Chemical Today magazine talks about the complexities that a crystal-clear pane of glass holds. Along with his team of researchers, he explores the great potentials that glass has and various fields of science where the use of glass that brings in a revolutionising change.

Give us an idea about your current research.

Glass, in itself, is very interesting and fascinating as the nature of glass and the glass transition are recognised as the deepest and most interesting unsolved problem in solid state theory. For glass technology, one of the paramount challenges is the search for approaches that can produce new glasses. Our current research focuses on the glass functionalization through controllable relaxation, because we recognised that the non-equilibrium glassy state relaxes spontaneously to the metastable supercooled liquid and even more stable state.

We are particularly interested in bulk crystallisation, surface crystallisation, ageing, space-selective relaxation, and also phase separation of meta-stable glass. For example, partial crystallisation of rare earth ions doped glasses greatly enhances the high-energy photon absorbing capacity. Controllable relaxation of transition metal/main group ions doped glasses leads to great emission enhancement and ultra-broadband optical amplification. We tried to fabricate various novel glass-based materials, including films for UV-blocking and planar photonics, and fibres for fibre optics.

In what ways is your re­search technology different from other research works?

Our current research technology is controllable relaxation in a glass. In contrast to other works, which suffers from the difficulty in rational microstructure engineering in a glass, the protocol is shown here allows simultaneous control of phase transition, dopant distribution, and even the chemical state and chemical environment of dopant in glass phase.

We noted that the research technology should be general to various pure glass and glass-based composite, which have been tested in our group recently. For example, transparent composites embedded with CeO2:F nanocrystalline phase with unusual core-shell-like multi-scale structure can be successfully fabricated. Furthermore, chemical state evolution of dopant (eg, Bi) in glass can be engineered. The chemical environment of dopant (eg, Ni, Cr) can also be modified. By using this technology, we have demonstrated the success in improvement of optical performance through controllable relaxation in various pure glass phase including borate, silicate, germanium, germanium silicate and borosilicate glasses doped with various metal ions. We have designed and succeeded in a fabrication of various functional glass composites embedded with Ga2O3, ZnO, TiO2,(Ga2O3)3 (GeO2)2, LiTaO3, Li2Ge4O9 and Mg2SiO4 crystalline phases.

Elaborate on the chemical materials used in your research.

The chemical materials used in our research are multi-component glass and their derived composite doped with various metals elements, such as Ce Ni, Bi, and Cr. The selection of multi-component glass as the host is critically important since it allows high dopant concentration. Furthermore, the rich microstructure in this glass system provides unique advantages for control of the chemical state and chemical environment of dopants, which dominates the optical performance of glass system.

What are the potential applications of your research?

Metal ion doped multi-component glass with robust absorption feature (e.g., CeO2:F glass-ceramics) can be potentially applied in various fields such as biological shield, cultural relics preservation and radiation hardening of electronic devices. For example, in the space station, the high-energy radiation from aerospace is very strong and can cause serious damage to electronic equipment. Fortunately, in the future, if you add a UV-blocking coating film on the surface of the package (transparent glass/polymer material), the device would be protected well and its service lifetime may be potentially prolonged.

Metal ion doped multi-component glass with high efficient and broadband luminescence is highly attractive for applications in high-resolution medical tomography, tunable lasers, and modern super-high-capacity information transmission system. As another example, we have achieved ultra-broad band luminescence in Ni2+-doped glass-ceramics and Bi-activated glass. The broadband optical amplification from 1050 nm to 1425 nm with the bandwidth of 75THz can be expected.

In contrast to the conventional rare-earth doped optical amplifier which generally offers limited bandwidth of 11 THz, the newly developed material provides notable advantages, including a dramatic increase in bandwidth, flat gain and tunable gain profile. In addition, the success in

broadening the emission band is also highly promising to advance the optical coherence tomography (OCT) technique for noninvasive diagnostic imaging with improved depth resolution.

Describe the methods for large-scale fabrication of this type of film.

The materials, in the form of a film, show various promising applications such as smart coating, the base materials for planar photonics. For large-scale fabrication of the composite film, the stable and homogeneous solution is crucially important. As mentioned above, we are especially interested in multi-component glass system. However, this type of glass system shows great phase separation and/or crystallisation tendency. Thus, one of the key issues is to develop various new stable multi-component solutions. We are currently focusing on this issue.

Shed some light on the self-limited nanocrystallization of glass and its importance?

Self-limited nanocrystallization is a unique phase evolution process in a glass. We name it as “self-limited” because it occurs in a solid-state matrix in which the ionic diffusion is highly limited. As it is well known, the conventional material synthetic ways are mostly conducted in solution and vapour conditions, we focus our attention on a solid-state matrix, for taking advantage of the rigid environment to modulate the ionic migration kinetics.

The viscous glass matrix would pose a considerable constraint for ionic movement and remarkably increase the diffusion activation barrier. This intriguing feature can be expected to provide distinct advantages for the amorphous-crystalline phase transition. Furthermore, the solid-state matrix offers the convenience for achieving doping control.

For example, the intentional introduction of various cation/anion impurities (e.g., F-, In3+, and Ni2+) can be realised. In addition, the reverse doping can also be achieved. In this process, fluorite is gradually etched by O2- ions in an oxide matrix and finally F--doped nanostructure would be obtained in a controllable manner. Moreover, the process also allows fine-tuning of the aggregation state of doping centres over a wide range of length scales, from ions to clusters to nanoparticles, via carefully regulating the topological structure feature of the glass matrix.

What are some of the challenges you faced while carrying out your research?

There are still some of the challenges about our research. Firstly, glass structure is extremely complicated, which is characterised by the absence of long-range disorder while presences of rich short- and medium-range order. Thus, we still need to make a further study of the multi-scale structure and detailed phase transition process in a glass. Secondly, the multi-component glass presents many distinct advantages such as continuously tunable composition and high dopant solubility.

However, it usually shows great devitrification tendency. There are still many works to do for preventing undesirable phase evolution and crystallisation. It is extremely important if we want to fabricate low optical loss glass film or glass fibre. We believe these fundamental researches have great significance to the current glass industry.

Do you plan on commercialising your technology?

We are trying to commercialise our technology. Now our plan is to modify the fabrication procedure for meeting the large-scale processing requirement.

© Chemical Today Magazine

See the Interview Coverage in Chemical Today magazine (Pg 58)


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