3D Luminescence Spectroscopy. A Thermo Aminco Bowman II (ABII) luminescence spectrometer (figure 2E) was used to investigate the samples’ fluorescence. The analyses were conducted at room temperature to simulate typical observation conditions. Three-dimensional fluorescence spectra were recorded in the 300–750 nm emission range (2 nm resolution, 4 nm bandpass) using an excitation of 220 to 500 nm (5 nm intervals, 4 nm bandpass). Detector voltage was adjusted so that the highest peak in the spectrum comprised 80%–90% of the instrument’s maximum fluorescence intensity range. The ABII spectrometer is not configured with excitation filters, so most of the 3D spectra collected contained first-, second-, and sometimes third-order artifacts produced by the spectrometer grating at 1×, 2×, and 3× the excitation wavelength. In most of the spectra presented, the 2× and 3× artifacts have been removed. The 1× artifact was retained to avoid potential data loss.