Spectroscopic characterization

Raman spectra were recorded at room temperature and ambient pressure on a Horiba JobinYvon Lab Ram Aramis spectrometer with a He-Ne laser providing excitation light at 633 nm with the 1200 l/mm grating.

Photoluminescence excitation spectra were acquired using a FluoroMax-4P TCSPC spectrofluorometer produced by Horiba, containing Czerny-Turner monochromators for excitation and emission. An excitation source in this system was a 150-W ozone-free Xenon lamp. Fluorescence intensity was measured using a R928 Side-on photomultiplier. Steady state luminescence spectra were excited with He-Cd laser with the wavelength of 442 nm. The photoluminescence spectra were recorded on a SR-750-D1 luminescence spectrometer with an Andor CCD camera DU420A-OE type, which can detect signal on large wavelength range 250–1000 nm with an accuracy of 0.5 nm. The spectra were corrected for instrumental spectral response using a standard lamp.

The experimental setup for luminescence kinetics consists of a PL 2143 A/SS laser as the excitation source and a PG 401/SH parametric optical generator. This system can generate 30 ps laser pulses, with the frequency of 10 Hz with wavelengths ranging from 220 to 2200 nm. The emission signal was analyzed by a Bruker Optics 2501S spectrometer and the Hamamatsu Streak Camera model C4334-01 with a final spectral resolution 0.47 nm. Luminescence decays were obtained by the integration of streak camera images over the wavelength intervals. Details of the experimental setup are described in the paper³¹. High hydrostatic pressure was applied in a Merrill Bassett type DAC³². Polydimethylsiloxane oil was used as the pressure-transmitting medium, and pressure was measured by the shift of the R₁ luminescence line of ruby.