| Summary: | 碩士 === 國立臺灣大學 === 化學研究所 === 107 === For near-infrared (NIR) spectroscopy, the interactions between NIR with samples have been noted in several ways, involving absorption, reflection, and transmission. Light illuminates on samples, then the detector receives the specific spectrum for material identification and/or quantification. The behavior is also called “Molecular fingerprint”. The range of the NIR spectrum is from 650 to 3000 nm. Given the advantages of minimum damage to samples and deep penetration, NIR radiation is widely used for analytical techniques, such as food safety inspection, bioimaging, environmental test, agriculture analysis, and digital healthcare. Nowadays, conventional analysis techniques must overcome challenges to get out of the lab by reducing the size of spectrometers for applying to mobile devices. The traditional light sources, halogen lamps, incandescent bulbs, and lasers, however, have their own weaknesses to some extent. In order to deal with them, NIR light-emitting diodes (NIR LEDs) are chosen as the solution which is credited to its merits of lightweight, robustness, energy-efficiency and environment protection. Moreover, the applied spectrum technique must cover the spectral range of the analyte, that is, a broad spectrum. Developing NIR phosphors can reach the needs of different wavelength and broaden the full width at half maximum. A phosphor-converted LED is fabricated to realize a blueprint for a mobile micro-spectrometer.
Two types of NIR phosphors, namely, Cr3+-doped K3AlF6 and K3GaF6 fluoride-based materials, were developed in this research. Different from the general synthesis for fluoride phosphors, HF was replaced with H2O as the solvent in the wet chemical steps with merits of high production and eco-friendly. Due to the octahedral crystal field environment of fluoride and trivalent chromium, the emission band is located at 650 to 1000 nm, which belongs to the near-infrared region. In addition, the symmetry of the two phosphors was also investigated by using electron paramagnetic resonance measurements, and the results were mutually confirmed by the results of the temperature- and pressure-dependent spectra. For the phosphor-converted light-emitting diodes (LED) fabricated from these two phosphors, the spectral range is from 650–1000 nm, which resulted in the radiant flux of 7–8 mW with the input current of 350 mA.
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