Photoluminescence and optical absorption/reflection techniques provide access to several material properties, such as color or fluorescence/phosphorescence. They can be used to get information on the atoms or molecules in the material being studied, as well as their concentrations.
Optical spectroscopy focuses on the interaction between light and matter, enabling us to study the electronic and vibronic transitions of a material. These techniques are non-destructive: a beam of light (from UV to near IR) is directed onto the sample.
In absorption, part of the light beam is analysed after its absorption or reflection by the material. It can be used for colorimetric measurements, bandgap measurements for semiconductors and solution titration.
In photoluminescence, following excitation due to the absorption of part of the beam, a light emission can be observed at an other wavelength than the one of the incident beam. This technique provides information on excitatory impurities introduced into a matrix, excitons created in semiconductors, or reveals the presence of certain atoms in natural samples. Time-resolved photoluminescence studies of decays enable us to monitor the dynamics of photogenerated species (lifetimes, exciton migration, understanding of energy or charge transfers).
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Collaboration with the Kyushu Institute of Technology in Kitakyushu (Japan) to study the luminescence of rare-earth-doped inorganic matrices.
Optical absorption:
Optical absorption reveals the increase in bandgap width in semiconductor nanoparticles as their diameter decreases due to quantum confinement. This effect can be seen in the opposite figures: studies of the optical properties of CdSe (left, read the publication) and ZnO (right, read the publication).
Steady-state photoluminescence:
Hybrid materials based on halogenated lead, one of which has a high photoluminescence quantum yield of 45% ((TDMP)PbBr4), have been synthesized and studied. The target application is lighting, as both have white luminescence. The opposite figure shows the evolution of their excitation and emission spectra depending on temperature.
Left: excitation and emission spectra of (TDMP)PbBr4.
Right: evolution of emission intensity depending on temperature.
Time-resolved photoluminescence :
A hybrid material based on thermochromic luminescent halogenated copper (i.e., the emission color changes depending on temperature) shows two types of emission duration: a long one centered at 620 nm (21 µs) and a short one centered at 490 nm (0.28 µs).
Emissions in the material [C6H16N2]3[Cu4Br6][Cu2Br6]:
(a) Streak camera images for two different time ranges. (b) and (c) mono-exponential decays obtained by integrating the two framed ranges (red and green).
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