Streak camera

Reflectance (R) and transmittance (T) measurements were performed at 8° angle of incidence using a dual-beam spectrophotometer with an integrating sphere accessory (Agilent Cary 5000 UV-Vis-NIR). Absorptance (A) was calculated as 1-R-T.
Time-resolved photoluminescence. Samples were mounted excited by a regenerative amplifier laser (Coherent Libra) delivering 100-fs-long pulses at a repetition rate of 1 KHz. Photoluminescence was dispersed with a grating spectrometer (Princeton Instruments Acton SpectraPro 2300i equipped with a 50 gr/mm grating blazed at 600 nm), dispersed and detected by a streak camera (Hamamatsu).
CW photoluminescence. Samples were excited by a diode-pumped Nd:YVO₄ CW laser at 532 nm (Spectra Physics Millennia). Photoluminescence was dispersed by a grating spectrometer (Princeton Instruments Acton SpectraPro 2300i) and detected by a LN-cooled CCD camera (Princeton Instruments PIXIS). At the highest excitation intensities, laser beam was chopped to reduce the overall thermal loading.

RIR films were deposited on sapphire substrates and cooled to 4 K in a closed-cycle helium cryostat (Advanced Research Systems). To excite the samples, a 70 fs, 1 kHz Ti:sapphire amplified laser was frequency doubled to an excitation wavelength of 405 nm and reduced to a 2 mm (diameter) excitation spot. The PL was relayed to an Avantes spectrophotometer for steady-state measurements, and to a Hamamatsu Photonics streak camera to measure the time-resolved spectral decay.

Absorption spectra of the samples were collected using a Lambda UV-Vis-NIR spectrometer. Photoluminescence data was collected using a pump generated from a frequency-doubled 2 kHz Ti: sapphire laser (800 nm doubled to 400 nm), with emission collected by fiber and directed onto a CCD array. Time-resolved emission was collected using the same configuration but directed instead to a streak camera (Hamamatsu). The index of refraction for the films was estimated from thin films spin-coated onto silicon using an Alpha-SE ellipsometer using a Cauchy model of the transparent region. This model was then applied to determine the film thickness of samples using a Filmetrics optical profilometer.

Time resolved photoluminescence measurements were conducted using a Hamamatsu streak camera containing a photocathode sensitized from the visible spectrum to 1300 nm and operated in the synchroscan mode. The samples were excited at 425 nm by the frequency-doubled output of a mode locked Ti:sapphire laser.

The time-resolved PL measurements were performed at room temperature. A wavelength-tunable mode-locked Ti:Sapphire laser was used as the excitation source, which has a repetition rate of 76 MHz and a pulse duration of 2 ps. Here, the laser wavelength was set at 725 nm. PL emission induced by the pulsed excitation laser was detected by a Hamamatsu streak camera combined with a single-grating monochromator.

The crystals were mounted into a cryostat (Oxford Instruments Hires or Optistat CF) and excited at 3.1 eV (400 nm) using the second harmonic of a mode-locked Ti:sapphire laser (Mira 900, coherent) at a repetition rate of 76 MHz. Steady-state spectra were recorded with a Hamamatsu EM-CCD camera that was spectrally calibrated. The excitation beam was spatially limited by an iris and focused with a lens of 150 mm focal length. The fluence was adjusted using grey filters and spectra were taken in reflection geometry. Time-resolved traces were taken with a Hamamatsu streak camera working either in synchroscan or single sweep mode. An optical pulse selector was used to vary the repetition rate of the exciting pulses where necessary. At room temperature, measurements occurred under nitrogen unless stated otherwise, and a helium atmosphere was used for the experiments at low temperature.
Low fluence excitation below the band gap was performed using a supercontinuum laser (NKT Photonics SuperK Extreme, 76 MHz repetition rate, 1–2 ps pulse duration) as excitation source and the photoluminescence^{46 (link)} was detected through a spectrograph (Shamrock SR303i, Andor) with 150 l mm⁻¹ grating (800 nm blaze) equipped with an EM-CCD camera (Luca R, Andor).

Absorption spectroscopy was performed using an Agilent spectrometer (Agilent Technologies, 8453) with the CND solution in a 1 × 1 cm quartz cuvette with two transparent facets. All spectra, including the reference from pure acetone solution were measurement from 300 to 900 nm. Photoluminescence spectrum was measured using a spectrofluorophotometer (Shimadzu, RF-5301), with the sample in quartz cuvettes having four transparent facets. Samples were excited at various different wavelengths (369, 390, 410, 430, and 450 nm). Time-resolved photoluminescence spectroscopy was performed by exciting the samples with Ti:Sapphire laser with a 80-fs pulsed laser and a repetition rate at 80 MHz. The fundamental laser source was doubled to obtain a laser wavelength at 345 nm for the excitation of the samples. The time-resolved PL intensity was dispersed through a spectrometer, and the spectrally resolved PL signal was collected using a Hamamatsu streak camera.