Usb4000 miniature fiber optic spectrometer

The blue (BaMgAl₁₀O₁₇:Eu²⁺) and yellow ((C₄N₂H₁₄)₄SnBr₁₀) phosphors were blended with a Sylgard 184 polydimethylsiloxane (PDMS) encapsulant, and put in a polytetrafluoroethylene (PTFE) mold to control the shape and thickness. The whole mold was heated at 100 °C for 40 min in an oven to cure PDMS. The phosphor doped PDMS films were then attached to a UVTOP® UV LED with a window, 340 nm, 0.33 mW (THORLABS) to form UV pumped LEDs. The LEDs were driven by a Keithley 2400 sourcemeter and emission spectra were recorded on an Ocean Optics USB4000 Miniature Fiber Optic Spectrometer. For the device stability test, a white light LED was continuously powered by a Keithley 2400 at a stable current power to give a brightness of ∼400 cd m^–2. Emission spectra were recorded at periodic intervals using an Ocean Optics USB4000 Miniature Fiber Optic Spectrometer.

In order to calibrate the recorded wavelengths, the spectrum of each laser line of the SOLE-6 (405, 488, 514, 561, 594 and 638 nm) was recorded once with a spectrometer (USB4000 Miniature Fiber Optic Spectrometer, Ocean Optics, USA). On each day of measurements, all filters were removed and the scattered signal of all six laser lines was recorded simultaneously on the camera chip. The intensities of both measurements were fitted with Gaussian distributions to determine the centre positions using a MATLAB (MathWorks, USA) script. The acquired centre positions were fitted linearly to obtain the calibration curve (Supplementary Fig. 3). This calibration is fast and can be easily repeated on each day of measurements to ensure precise and reproducible spectra.

The spectra of the front and back surfaces of E. angustifolia leaves were measured using a USB4000 miniature fiber optic spectrometer (Ocean Optics, Inc., Dunedin, FL, USA), with a spectral range of 200–850 nm. Before measurement, a standard whiteboard was used for calibration, and the viewing angle was 25°. Three replicates were performed for each sample, and the mean value was taken as the spectral reflectance of this sample. R v3.6.0 and Origin v20.0 were used to analyze and plot the different data.