應用於發光二極體之寬帶近紅外光摻鉻氟化物螢光粉

Abstract

近紅外光譜技術藉材料與光之特定吸收、反射與穿透行為，將光譜照射於樣品，並藉收集其光譜進而定性或定量待測成分，亦稱為分子之指紋特徵，其近紅外光譜範圍為650至3000奈米。因紅外光具非破壞性與具一定穿透性之優點，至今已廣泛使用於分析技術，如應用於食品成分監測、生物顯影、環境檢測、農業與數位醫療。然而隨科技之演進，使近紅外光譜技術面臨尺寸縮小之挑戰，為搭載於手持裝置，須克服鹵素燈、白熾燈、雷射等傳統光源不同面向之缺點，以兼具輕薄、穩定、節能與環保之綠色光源，即近紅外光發光二極體(near infrared light-emitting diodes; NIR LEDs)取代。而應用於光譜技術則須涵蓋待測物之光譜範圍，即為寬光譜，可由研發近紅外螢光粉達成不同波段與半高寬之需求，並製成螢光粉轉換發光二極體元件，進而實現行動微型光譜儀之藍圖。 本研究主研發近紅外光螢光粉，即K3AlF6:Cr3+與K3GaF6:Cr3+(KAFC與KGFC)。以新型共沉澱法以水取代有害之溶劑氫氟酸合成之氟化物螢光粉，具產率高與友善環境之優勢。因氟化物與三價鉻之八面體晶場環境，使其放射波段皆位於650 至1000奈米，屬近紅外光區，而以理論計算求得之理論能階，可呼應實驗光譜之躍遷過程。此外亦藉電子自旋光譜性質探討二螢光粉之結構對稱性，其結果與變壓放射光譜之結果相互應證。最終將所合成之近紅外光螢光粉搭配藍光晶片應用於近紅外光發光二極體，於輸入電流為350毫安培之條件可得光通量7－8毫瓦。

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.