Excitonic Sensors (Platform 3.1)

What’s this platform about?

The goal of this platform is to develop emerging emissive materials, robust strategies and analysis procedures for miniaturising and simplifying luminescence chemical sensors with lower economic cost than existing large laboratory instruments, higher sensitivity than ordinary paper tests and better selectivity than electrochemical detectors.

In partnership with the Defence Science and Technology Group (DSTG), the Centre is in a unique position to develop portable and robust chemical sensors with high sensitivity and specificity.

DSTG is investigating technologies that can be included in such a device, with a particular focus on a photoluminescence-based response system.

We have developed a new device that allows the use of solution chemistry for chemical detection, greatly expanding the variety of probe materials that can be used. In addition to the detection of chemical species, an extension of the project has been devised to detect biological species.

Progress in 2023

Work in 2023 has focused on two projects:

1. Supporting the development of a sensor device that can detect biological agents. The SARS-Cov2 virus is the primary target, with detection enabled by loop-mediated isothermal amplification (LAMP) assays. We demonstrated that the LAMP assay can be performed on the sensor filter which results in fluorescence if the sample is positive.
2. Validation of the fluorescein aerosol sensor in the chemical suit testing facilities at DSTG. We had previously optimised and calibrated the detection of fluorescein aerosols in University of Melbourne lab tests. The experiments at DST group are performed in a large aerosol chamber which is used for chemical suit testing. Once validated, the final stage is to miniaturise the device so that they can be used for in-suit testing.

Research Highlights

Manuscripts describing work from both projects are in preparation, with publication due in 2024.

Issues

No issues to report.

Collaboration

Industry: DSTG

Outlook for next year

Exciton Science contributions to the fluorescein aerosol detection and biological agent detection projects will conclude by mid-2024, which coincides with the end of the PhD candidature of the student working on the project and the end of Centre funding.

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Novel Security Features for RBA (Platform 3.2)

What’s this platform about?

Australia leads the way in the development of polymer banknote technology. With counterfeiters gaining improved access to lower cost technologies, more sophisticated forgeries are possible.

To maintain confidence in the currency, development of new security features is needed. The most important security features that act as a first line of defence in identifying counterfeits are overt features. These features must be straightforward and intuitive for the public or cash handler to use in helping them identify the banknote is genuine. The security features must be durable, printable, difficult to replicate, and cost-effective.

Platform 3.2 is focused on the development of new overt optical security features for Australian polymer banknotes. The overarching goal is to produce banknote security features that are difficult to counterfeit and simple to verify. Such security features must be able to meet multiple requirements such as cost effectiveness, efficacy, durability, printability, sustainability and public safety.

Progress in 2023

The machine-readable near infrared ink project progressed well in 2023, where ink scale up and pilot scale trials were performed on banknote production presses. Further optimisation trials, durability and machine transport/functionality performance testing are scheduled for early 2024.

The magnetic nanoparticles ink (MNI) project is aimed at developing an overt security ink using magnetically aligned nanoparticles to produce bright optical effects. Magnetic nanoparticles are being successfully synthesised with highly controlled physical properties, and the potential scaling up of such processes required to meet demand of high-volume banknote production is under investigation.

A new experimental approach for the MNI project commenced during 2023 where an “offline” process is being developed for producing an optically bright magnetic pigment, moving away from incorporating the nanoparticles directly into the base ink. Various methods for producing the pigment are being investigated, along with the optimisation of the nanoparticle synthesis method. Researchers from Monash University have recently began assisting with development of the pigment production process.

Research Highlights

Research highlights include:

• Further pilot scale trials of the near infrared inks using a pigment supplier capable of supporting banknote production volumes, and able to supply a pigment compatible with safe handling procedures for formulation into a finished ink.
• Development of a new experimental approach for the MNI project designed to overcome the previous issues regarding ink efficacy.
• Progressing development of the synthesis processes for the magnetic nanoparticles, and demonstrating impacts of scale up of the process in the laboratory.

Issues

The primary risks associated with the projects are:

• For the MNI project new materials may not be scalable, too costly for use in banknote technologies, or unable to generate the desired durability, efficacy or security merit for the project to progress. Additionally there may be challenges formulating a security ink with the pigment in terms of dispersion and stability;
• The RBA may change research directions in response to changing national and international demands on currency protection and/or actual or perceived counterfeiting risks

Collaboration

Industry: Reserve Bank of Australia

Outlook for next year

Our goals for 2024 include:

• Completing the durability and machine testing of printed material for the near infrared ink project. If testing is successful the near infrared ink project will enter production scale testing.
• Producing an MNI prototype sample with the desired efficacy to undertake a preliminary focus group study and security assessment.
• Completing planning for a small-scale print trial of MNI features on production equipment pending developmental outcomes.

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Light-Emitting Devices (Platform 3.3)

What’s this platform about?

This platform aims to deliver solutions for future lighting and display technologies by developing materials and devices beyond current efficiency, brightness and stability limits with spectral coverage from the ultraviolet to visible and infrared range.

These next-generation light-emitting devices (LEDs) will open new architectures and applications, such as tunable lasers. For example, we employ a combined theoretical and experimental approach towards the realisation of a stable blue LED, which has been challenging traditionally due to triplet losses and defect emission. We will employ strong light-matter interactions, or polaritons, to achieve improvements over conventional optoelectronics. One such target, an electrically pumped polariton laser, remains a ‘Holy Grail’ in optoelectronics.

Progress in 2023

In 2023, projects were undertaken to exploit strong light-matter coupling in various photophysical processes, energy transfer and charge transfer dynamics in organic solar cells and photodetectors, and intersystem crossing in thermally activated delayed fluorescence (TADF) molecules.

CIs Lakhwani and Hutchison and AI Gomez published two reviews on polaritonic energy transfer and polaritonic chemistry in ACS Chemical Reviews, a flagship chemistry review journal.

CI Hutchison and AI Gomez began collaborations with Dr James Quach of CSIRO to develop polaritonic LEDs (‘quantum batteries’). Dr Kieran Hymas and Dr Jack Muir were employed by CSIRO from the beginning of 2023 as postdocs to contribute to this work.

PhD student Engin Akinoglu (Hutchison group) worked on mid-infrared photonic structures for strong light-matter interactions, leading to a publication. MSc students Jianfei Yu (graduated in November) and Dali Quan continued work on sustainable and flexible polaritonics respectively. Dr Shi Tang was employed as an Exciton Science Fellow, working on polaritonic and perovskite LEDs. Dr Sam Brooke was also employed as an Exciton Science Fellow to contribute to this platform.

CI Wong supplied TADF compounds to CI Lakhwani for study in optical cavities. Lakhwani and Dr Inseong Cho published a manuscript on this and they (along with Dr Alex Stuart) are also working on a manuscript on transient absorption studies on those compounds.

Wong group students involved in Platform 3.3 in 2023 included:

• Dr Will Kendrick (finished in April 2023). He supplied the compounds for Inseong’s publication.
• Jungwoo Ma, MSc student, who finished in November. He was working on MR-TADF derivatives similar to Will’s. Compound synthesis is complete but more evaluation is needed to see whether they are viable to continue exploring.
• Aitor Gutierrez Valero, an MSc exchange student from Edinburgh, is continuing Will’s project and aiming to supply more TADF compounds to CI Lakhwani in 2024.

CI Lakhwani has worked with Tim van der Laan (CSIRO) towards 2D material/chiral plasmonic hybrids and chiral light-emitting devices, Dr Yahui Tang (USyd) has been heavily involved in this work.

CI Mulvaney has been active in the area of nanodrum resonators involving Dr Jialu Li, and in collaboration with James Bullock and Ken Crozier, in the area of MIR photodetectors involving Dr Wei Luo. These activities led to several publications in 2023, the latter project successfully made photodetectors using InSb quantum dots which exhibit tunable photoresponse. The project has now extended to exploring various 2D materials in phototransistors.

Research Highlights

Issues/risk mitigation

Coming into the final year of the Centre, highly experienced research fellows have begun to depart (see for example Dr Will Kendrick). Transfer of knowledge to PhD and MSc students will be important in finalising the goals of Platform 3.3.

Collaboration

International: Prof. Hiroshi Ujii & A/Prof. Kenji Hirai (Uni. of Hokkaido, Japan) with CI Hutchison: Article in press (Chem. Eur. J.) on polaritonic cavities.

Prof. Markus Retsch & Prof. Georg Herink (Bayreuth, Germany), with CI Mulvaney, using quantum dots for probing resonant and propagating THz field excitations.

Local: Dr James Quach, CSIRO Clayton, polaritonic LEDS/quantum batteries, with CI Hutchison

Dr Tim van der Laan, CSIRO Linfield, 2D materials and chiral emitting devices, with CI Lakhwani

Outlook for next year

By the end of 2024, which also marks the end of the Centre, we hope to extend the impact of strong light-matter coupling via polaritons to a range of light-emitting and energy detection/storage devices. These include polaritonic solar cells, LEDs, photodetectors, and lasers, and taking advantage of polariton-modified intersystem crossing, exciton fission/fusion, valley exciton protection, and more.

We also hope to finalise the successful fabrication of stable blue LEDs based on quantum dots, with full characterisation of their lifetime and spectral properties. This will be allowed by an in-house developed ligand exchange method and in-depth analysis of the electrical properties of LEDs.