Advanced Materials for Optical Sensing – AMOS

We evaluated the influence of temperature and illumination on the emission of various compounds. The optical response of the materials was related to the synthesis method, which determines the surface type and structure. Emission by nano-objects in semi-conductor matrices depends on competition between energy transfer to active centres and trapping. Using specially designed instruments, we recorded simultaneously the fluctuations of the electrical and optical responses of screen-printed thick films under controlled atmospheres. Surface passivation or neutralisation leads to stable emission. Photocatalytic properties were tested, for reduction of organic solvents. Some fluorinated compounds showed luminescence hysteresis. After proper calibration, the kinetics of reactions modifying emissions can be used as a marker of the history of UV irradiation of the materials (threshold and exposure time).

Titanium dioxide and zinc oxide materials were examined. Synthesis routes led to luminescence centres in the visible spectrum. Monitoring intensity fluctuations can be used to determine the composition of mixtures of gases. Neutralisation of surface states gives rise to stable UV emission (zinc oxide). The kinetics of reversible redox phenomena on elpasolites could be a possible marker of the UV radiation undergone by the material. A possible application is long- or short- term data storage.

The continuation of the project will concern the quantification of the optical properties and the correlation which exists between the detected emissions and the activities of surface or of « bulk « of the selected matrices. Studies under controlled atmosphere and in temperature will be performed.

This work was reported in papers and oral communications at international meetings. Seven papers were published in high impact journals covering materials synthesis and characterisation, one in a conference proceedings. There were six conference talks, two invited lectures, a seminar and eight poster presentations. Conference contributions were chosen to reach solid state chemists and optics specialists.

In the recent years a big effort was devoted to develop tools, skills and initiate research projects in the upcoming new fields of organic electronics and the new functional materials for the information, communication, energy and optic. At the international level, such subject is growing of interest in the scientific community investigating luminescent materials.
Multiple research groups are coming to the subject of chemical sensors based on luminescent properties especially in Asia (China and Japan). ICMCB was part of an European consortium, FAME, from which several collaborations were developed and many scientific advances were published on the nanomaterials topic. Our team is one of the first to publish on a new field studying the relation between catalytic properties of TiO2 and luminescent properties with the scope of developing innovative sensing materials.
At the regional level, the topic investigated by the coordinator for developing photonic materials which act as sensors, will be in perfect accordance with the development of Photonic in Aquitaine. The certification of the project by the competitiveness cluster “Route des lasers” will be sought.
Since 2008, the University of Bordeaux 1 together with the Aquitaine Region have decided to reinforce this area of materials for photonics with the financing of two GIS programs devoted to optical applications. In one of them (LasINOF: program coordinated by T Cardinal, optical materials group of the ICMCB), strong collaborations already exist with different laboratories ISM, IMS, CPMOH and a new international education MASTER program based on topics developed in these research groups has been initiated to educate and prepare the young generation to promising photonic field.
Non-doped and rare earth doped materials will be used to evaluate the irradiation impact and their emission stability under controlled atmosphere and temperature. Several synthetic routes will be performed to modify and control the surface nature of nanosized semiconductor that can be used as optochemical gas sensor. The electron-hole recombination will be studied by luminescence as a function of the nature (gas) and the oxidizing or reducing effect of the atmosphere. Crystallized dielectric materials potentiality as high temperature sensors exhibiting hysteresis effect will be analysed. In this case, we will follow the redox mechanism of the Ce-In pairs in an elpasolite matrix to determine the thermal stability threshold of the visible luminescence under several gaseous atmospheres.
The goal is to bring to the academic community and the society expertise in the field of sensing materials based on luminescent properties.
For such an objective, two different approaches corresponding to two families of materials will be developed by looking for:
i. excitation through the matrix of nanoscale semiconductors and transfer to the dopant. In that case the surface reactivity of the matrix is the main issue
ii. co-doping of materials for thermal hysteresis

Our strength remains on the capability to gather together, material synthesis, materials shaping, luminescence properties, analysis of photo-produced species and material characterization expertise. In the present project, we will benefit from this unique environment in Aquitaine for the development of materials, to conduct a fundamental approach for understanding the relation between luminescence properties, material composition and design and take advantage of innovative discover at the frontier of catalysis and luminescence to become leader in this new emerging field.