Absolute absorption and fluorescence measurements over a dynamic range of 106^6 with cavity-enhanced laser-induced fluorescence

We describe a novel experimental setup that combines the advantages of both laser-induced fluorescence and cavity ring-down techniques. The simultaneous and correlated measurement of the ring-down and fluorescence signals yields absolute absorption coefficients for the fluorescence measurement. The combined measurement is conducted with the same sample in a single, pulsed laser beam. The fluorescence measurement extends the dynamic range of a stand-alone cavity ring-down setup from typically three to at least six orders of magnitude. The presence of the cavity improves the quality of the signal, in particular the signal-to-noise ratio. The methodology, dubbed cavity-enhanced laser-induced fluorescence (CELIF), is developed and rigorously tested against the spectroscopy of 1,4-bis(phenylethynyl)benzene in a molecular beam and density measurements in a cell. We outline how the method can be utilised to determine absolute quantities: absorption cross sections, sample densities and fluorescence quantum yields.Comment: 12 pages, 6 figures, submitted to J. Chem. Phy

Laser diagnostics and minor species detection in combustion using resonant four-wave mixing

Peer reviewedPostprin

Emerging technologies for the non-invasive characterization of physical-mechanical properties of tablets

The density, porosity, breaking force, viscoelastic properties, and the presence or absence of any structural defects or irregularities are important physical-mechanical quality attributes of popular solid dosage forms like tablets. The irregularities associated with these attributes may influence the drug product functionality. Thus, an accurate and efficient characterization of these properties is critical for successful development and manufacturing of a robust tablets. These properties are mainly analyzed and monitored with traditional pharmacopeial and non-pharmacopeial methods. Such methods are associated with several challenges such as lack of spatial resolution, efficiency, or sample-sparing attributes. Recent advances in technology, design, instrumentation, and software have led to the emergence of newer techniques for non-invasive characterization of physical-mechanical properties of tablets. These techniques include near infrared spectroscopy, Raman spectroscopy, X-ray microtomography, nuclear magnetic resonance (NMR) imaging, terahertz pulsed imaging, laser-induced breakdown spectroscopy, and various acoustic- and thermal-based techniques. Such state-of-the-art techniques are currently applied at various stages of development and manufacturing of tablets at industrial scale. Each technique has specific advantages or challenges with respect to operational efficiency and cost, compared to traditional analytical methods. Currently, most of these techniques are used as secondary analytical tools to support the traditional methods in characterizing or monitoring tablet quality attributes. Therefore, further development in the instrumentation and software, and studies on the applications are necessary for their adoption in routine analysis and monitoring of tablet physical-mechanical properties

Confocal and multiphoton imaging of intracellular Ca²⁺

This chapter compares the imaging capabilities of a range of systems including multiphoton microscopy in regard to measurements of intracellular Ca<sup>2+</sup> within living cells. In particular, the excitation spectra of popular fluorescent Ca<sup>2+</sup> indicators are shown during 1P and 2P excitation. The strengths and limitations of the current indicators are discussed along with error analysis which highlights the value of matching the Ca<sup>2+</sup> affinity of the dye to a particular aspect of Ca<sup>2+</sup> signaling. Finally, the combined emission spectra of Ca<sup>2+</sup> and voltage sensitive dyes are compared to allow the choice of the optimum combination to allow simultaneous intracellular Ca<sup>2+</sup> and membrane voltage measurement

Study of TADF Emitters in OLEDs

Delayed fluorescence through thermally activated delayed fluorescence (TADF) has great potential for the creation of inexpensive and highly efficient white lighting applications, with superior colour rendering. Currently the highest external quantum efficiencies are achieved with small donor-acceptor-donor molecules utilising intramolecular charge transfer (ICT) states, and these molecules require a suitable host matrix to reside in. This thesis studies the effect of host material on the model molecule 2d, a proven efficient TADF emitter through diligent photophysical investigation. A combination of steady state and nanosecond time resolved spectroscopic studies confirm the importance of a high host triplet level to ensure that the ICT state is the lowest energy excited state to avoid high levels of quenching. More interestingly it is shown that the functional group combination of emitter and host is crucial in achieving efficient TADF in OLED devices. In particular combinations where both the host and dopant are carbazole-based should be avoided due to the formation of carbazole dimer. The effect of such dimerisation is to lower the host triplet level significantly, and further to deactivate the ability of the 2d dopant to produce the ICT state required for TADF by locking the 2d dopant in the ‘planar’ configuration. It is therefore clear that the chemical composition of the host is of critical importance for the design of future OLED devices. Experiment also suggests that there is a complex interplay between exciplex and ICT emission in 2d systems in the solid state, insofar as CT emission of any description has so far only been observed in conditions where exciplex can and does occur

Validation of phosphor thermometry for industrial surface temperature measurements

Surface temperature measurements are required by the aerospace and automotive industries to guarantee high-quality products and optimize production processes. Accurate and reliable measurement of surface temperature is very challenging in an industrial environment. Surface contact probes are widely used but poorly characterized, while non-contact infrared thermometry is severely hampered by the unknown emissivity of the surface and by problems caused by stray radiation from the background. An alternative approach to the above techniques is phosphor thermometry, used here in a hybrid contact/non-contact approach. In this work, the development of a lifetime-based phosphor thermometer, its application to industrial surface temperature measurement and its validation are reported in a metrologically sound manner. The phosphor thermometer was initially calibrated by contact on a reference calibrator system at the Istituto Nazionale di Ricerca Metrologica to provide SI traceability to the measurements at the industrial level; the system was later validated by exploiting a metal phase-change method. The robustness of the approach against a strong radiative background was also investigated. A comprehensive uncertainty analysis was carried out, resulting in an expanded uncertainty (k  =  2) lower than 1.4 °C over the temperature range from the ambient to 450 °C. The phosphor-based thermometer was then tested at industrial manufacturing premises to measure the surface temperature of aluminium alloy billets during the pre-heating phase before forging. The phosphor-based approach was compared with radiation and contact thermometry in both static and dynamic measurement conditions. The experimental results proved that phosphor thermometry, besides being a valid alternative to conventional techniques, may offer better performance in an industrial setting

TRIGA-SPEC: A setup for mass spectrometry and laser spectroscopy at the research reactor TRIGA Mainz

The research reactor TRIGA Mainz is an ideal facility to provide neutron-rich nuclides with production rates sufficiently large for mass spectrometric and laser spectroscopic studies. Within the TRIGA-SPEC project, a Penning trap as well as a beam line for collinear laser spectroscopy are being installed. Several new developments will ensure high sensitivity of the trap setup enabling mass measurements even on a single ion. Besides neutron-rich fission products produced in the reactor, also heavy nuclides such as 235-U or 252-Cf can be investigated for the first time with an off-line ion source. The data provided by the mass measurements will be of interest for astrophysical calculations on the rapid neutron-capture process as well as for tests of mass models in the heavy-mass region. The laser spectroscopic measurements will yield model-independent information on nuclear ground-state properties such as nuclear moments and charge radii of neutron-rich nuclei of refractory elements far from stability. This publication describes the experimental setup as well as its present status.Comment: 20 pages, 17 figure