Ldh p c 405

The time-resolved confocal fluorescence microscope was custom-built. The used light source was a pulsed laser diode (LDH P–C-405, PicoQuant GmbH, Germany) with an excitation wavelength of 405 nm and at a repetition frequency of 40 MHz. The pulse duration was 50 ps. The beam was focused on the sample by an oil immersion objective lens (Zeiss Plan-Apochromat, 100 × , 1.4 Oil DIC, Carl Zeiss AG, Germany). An additional long-pass filter (EdgeBasic™ Long Wave Pass 405) separated the excitation light from the sample emission. Confocal imaging was achieved using a single photon avalanche diode (SPAD; PDM series, Micro Photon Devices, Italy). By coupling the SPAD with a time-correlated single photon counting (TCSPC) unit (HydraHarp 400, PicoQuant GmbH, Germany) and the pulsed laser diode, time-resolved measurements were performed. The scanning stage, SPAD, laser diode, and TCSPC unit were controlled by SymphoTime® software (PicoQuant GmbH, Germany). Time-resolved measurements were also analyzed and evaluated with the SymphoTime® software.

Steady-state and time-resolved photoluminescence measurements where performed with a photon counting system (Fluotime 300, PicoQuant GmbH). The samples were excited with a 398 nm laser diode (LDH-P-C-405, PicoQuant GmbH, pulse duration 40 ps). Emission spectra were measured in front illumination mode where emitted light is collected from the side where the laser beam excites the crystal or in back illumination where the light is collected from the rear of the crystal. The distance traveled by the emitted light through the sample is approximately d_eff = d/cos(θ) where d is the crystal thickness and θ the angle between the crystal and the incident laser beam (Supplementary Fig. 6). Time-resolved measurements were acquired with a 447 nm laser diode (LDH-P-C-450B, PicoQuant GmbH, pulse duration 68 ps) at an excitation fluences between 7 and 500 nJ cm⁻². We estimate the excited volume to be larger than the volume defined strictly by the penetration depth at the excitation wavelength (d_1/e≈80 nm), due to the fast diffusion of charges within the crystal. Thus, the initial carrier density is estimated to be N₀≈0.15–10.7 10¹⁶ cm⁻³. For time-resolved emission spectra, the crystals were excited at a fluence of 260 nJ cm^-2 (N₀≈5.6·10¹⁶ cm⁻³) and decay traces were recorded with 5 nm wavelength intervals. The single crystals were kept in air during the measurements.