Development and Tuning of Broadband Near-Infrared Light Sources for Spectroscopy Applications

• Main Authors: Veeramani Rajendran, 韋拉馬尼•拉金德倫
• Other Authors: CHANG, HO
• Format: Others
• Language: en_US
• Published: 2019
• Online Access: http://ndltd.ncl.edu.tw/handle/zbqnr9

碩士 === 國立臺北科技大學 === 製造科技研究所 === 107 === In recent times, a lot of effective steps are initiated by the research community to narrow down the size of standard desktop near-infrared spectrometer into the miniature size. So, it can be employed for the practical applications by the non-scientific community for the real-time non-destructive examinations especially the analysis of foodstuffs and health monitoring. The deteriorating availability of traditional light sources makes phosphor converted near-infrared light-emitting diode (pc-NIR LED) as a superior and auspicious light source candidate for miniature spectrometers. Moreover, the growing technology of pc-NIR LED also opens up the possibility of new applications areas like facial/iris recognition by smartphones, infrared cameras for security, LIDAR (light, imaging, detection, and ranging) technology and so on. The two different La-gallogermanate host crystal systems are reported in this thesis work. In the first work, La3Ga5(1-x)GeO14： 5xCr3+ (0.005 ≤x≤ 0.09) is reported with the super broadband NIR luminescence in the range of 650 to 1200 nm with the wide full width half maximum (fwhm) of 330 nm and radiant flux of 18.2 mW for the first time. The observation of super broadband luminescence from two distinct luminescence centers is studied and evidenced by structural and spectroscopy investigations. In the second work, the crystal structure of La3Ga1-xGe5O16：x Cr3+ (0.005 ≤x≤ 0.13) is solved for the the actual crystallographic sites of all elements by joint Rietveld refinement and achieved the ultra-broadband NIR luminescence in the range of 620 to 1020 nm with the hyper radiant flux of 43.1 mW at the driving current of 350 mA. Noteworthy, the radiant flux is increased to 56.3 mW and 65.2 mW by the modifications of chemical compositions as La3(1-y)Ga0.93Ge5O16: 0.07 Cr3+, 3y Gd3+ (0.005 ≤y≤ 0.02) and La2.97Ga0.93Ge5(1-z)O16: 0.07 Cr3+, 0.03 Gd3+, 5z Sn4+ (0.005 ≤z≤ 0.03) respectively. The presence of multiple-luminescent centers (multi-excited state) of Cr3+ resulted in broadening of the emission spectrum along with increased intensity. Finally, the luminescence mechanism of Cr3+ is discussed with the relevant configurational coordinate diagrams. Moreover, it is observed that the phosphor host system with a higher number of the crystallographic site for Cr3+ ions can promote higher fwhm but lesser radiant flux and vice versa.