Pixis 400b

(Time-integrated) photoluminescence measurements were conducted by directing the excitation laser pulses to SCs or thin films. The laser pulses were generated by a 1-kHz regenerative amplifier (Coherent Libra, 800 nm, 50 fs, 4 mJ). A mode-locked Ti-sapphire oscillator (Coherent Vitesse, 80 MHz) was used for the amplifier. For 800 nm pump, the laser from the regenerative amplifier was directly used. For 400 nm, a BBO crystal was used to double the frequency of 800 nm. The photoluminescence was collected at a backscattering angle by a spectrometer (Acton, Spectra Pro 2500i) and CCD (Princeton Instruments, Pixis 400B). For circular-polarized pump and circular-polarized PL measurements, a quarter-waveplate and polarizer were placed in the path of the excitation beam and another pair of quarter-waveplate and polarizer were placed at the PL detection path. Time-resolved photoluminescence was collected using a streak camera system (Optronis Optoscope), which has an ultimate temporal resolution of 6 ps. For the temperature-dependent PL and TRPL measurements, the crystals were adhered to the cryostat (Janis) copper sample mount with silver paste. The temperature was cooled down using liquid nitrogen.

A CW frequency-doubled Nd:YVO₄ laser (532 nm, Spectra-Physics, Millenia) was used as a light source for all the experiments. An imaging spectrophotometer (Bunko Keiki, MK-300) equipped with a cooled CCD camera (Princeton Instruments, PIXIS400B) was used for detecting Raman spectra. A total of 400 Raman spectra were measured simultaneously in one exposure. Two edge filters (Semrock, LPD01-532RU-25) were used to separate the laser and the Raman scattering light before the spectrophotometer. A commercial inverted microscope (Nikon, ECLIPSE Ti) was used for mounting the objective lens and sample, and a focus stabilization system (Nikon, Perfect Focus System) was used to keep the focal plane in the sample constant during the measurement. In all Raman imaging experiments, the slit width was set to the Airy size with the centre wavelength (591 nm) detected in the spectrophotometer, which corresponds to a spectral resolution of 3.1 cm⁻¹ at the centre wavelength.

Time-integrated photoluminescence measurement was conducted by directing the excitation laser pulses to thin films. The photoluminescence was measured at a backscattering angle of 145° by a pair of two lenses via an optical fiber coupled by a spectrometer (Acton, Spectra Pro 2500i) and CCD (Princeton Instruments, Pixis 400B). Time-resolved photoluminescence was collected using an Optronis Optoscope streak camera system with an ultimate temporal resolution of 10 ps.

For femtosecond optical spectroscopy, the laser source was a Coherent Libra regenerative amplifier (50 fs, 1 KHz, 800 nm) seeded by a Coherent Vitesse oscillator (50 fs, 80 MHz). 800 nm wavelength laser pulses were from the regenerative amplifier while 400 nm wavelength laser pulses were obtained with a BBO doubling crystal. 650-nm laser pulses were generated from a Coherent OPerA-Solo optical parametric amplifier. The laser pulses (circular spot, diameter 2 mm) were directed to the films. The emission from the samples was collected at a backscattering angle of 150° by a pair of lenses into an optical fiber that was coupled to a spectrometer (Acton, Spectra Pro 2500i) and detected by a charge coupled device (Princeton Instruments, Pixis 400B). TRPL was collected using an Optronis Optoscope streak camera system which has an ultimate temporal resolution of around 10 ps.

Time-integrated steady-state PL from the samples was collected at the edge of the film by using a pair of lenses into an optical fiber that was coupled to a spectrometer (Acton, Spectra Pro 2500i) and detected by a charge-coupled device (Princeton Instruments, Pixis 400B). TRPL was measured using an Optronis Optoscope streak camera system.