Fluorescence Lifetime Measurements
Typically the excitations of the materials we look at have a natural lifetime of about 1 to 1.5 ns, but this is reduced by various quenching mechanisms. To measure this time regime accurately we use the time correlated single photon counting technique. Sample excitation is performed using a tuneable Mira-900 picosecond laser (2 ps), which in conujunction with second harmonic generation allows for site-specific excitation (350 – 475 nm). Low pulse energies combined with a 76MHz repitition rate allow for aquisition of high signal-to-noise data. Emission is aquired via a double subtractive monochromator (Acton) and a Hamamatsu 3900 MCP. TCSP is controlled using Becker&Hickl electronics. This system has an instrument response function of ~21ps, which can be improved to ~3ps with excitation pulse deconvolution.
Streak Camera 2-Dimensional measurements
In order to measure the spectral dynamics of fluorescence we use a Hammamatsu C5860 Streak Camera. This allows for the fluorescence lifetimes across a large near-continuous range of emission energies to be measurement simultaneously, providing significant insight into key photophysical processes such as exciton migration which have direct bearing on key device properties such as the photoluminescence quantum efficiency. This system operates with a ~5ps day-to-day time resolution for broad emission spectra.
Coherent Mira 900D Ti:Sapphire Coherent Verdi VIII pump laser
Hamamatsu 3809 MCP with Becker & Hickl SPC630 acquisition Acton 2300 subtractive double monochromater
Hamamatsu C5860 Streak Camera
Ocean Optics HR4000
Janis LN2 cryostat CryoMech 405 displex cryostat (2.5K)
Excitation range 240-320nm, 340-500nm Emission range 400-850nm