Spectroscopic Study of New, Effective Up-Conversion Charging Process in Persistent Phosphors

非技术描述：余辉(即持久发光)是一种自我维持的发光现象，其中在激励光源被关闭后，材料(即持久荧光粉)在黑暗中发光数小时。如今，在可见光和近红外光谱范围内发射的持久性荧光粉正被用于日常生活中，例如安全标志、紧急路线标志、交通标志、刻度盘和显示器以及医学研究。然而，由于需要高能激发光(主要是紫外光)来给材料充电，永久荧光粉的广泛使用受到了极大的阻碍。因此，需要用低能光，特别是可见光来实现有效激发的解决方案。本项目研究一种新的充电工艺，使低能量可见光光源(如激光二极管)在给持久性荧光粉充电方面与常用的高能紫外线光源(如紫外线灯)一样有效。这项研究的结果有可能为研究和利用持久性荧光粉开辟新的战略。该项目为研究生、本科生和K-12级学生提供发光材料研究和应用方面的跨学科培训经验。本科生和K-12教育是通过佐治亚大学现有的计划实施的，如NSF赞助的桃州-路易斯·斯托克斯少数民族参与联盟计划，NSF赞助的本科生网站研究经验，以及Young Dawgs计划(K-12教育)。技术描述：高能紫外光通常是必要的，以有效地为永久荧光粉充电。然而，由于高能激发的需要，在紫外光不可用或不适合的情况下，某些应用会受到影响。该项目旨在通过研究一种新的双光子上转换充电(UCC)工艺来解决这一限制，在该工艺中，低能量可见光光源(例如激光二极管)与常用的高能紫外线光源(例如紫外灯)在为持久性荧光粉充电方面具有同等的效率。在UCC概念中，来自可见光激光二极管的两个可见光光子被UCC使能离子(例如三价铬离子)连续吸收，从而达到离子的高能离域状态，并填充荧光粉中的电子陷阱。UCC使能离子包括三价铬、二价锰、四价锰、三价钯和三价钕。用几个波长在400-700 nm范围内的功率可调谐可见光激光二极管作为激发源。UCC的新的光学测量技术，如UCC激发光谱，正在开发中，以获取对于理解UCC所涉及的能量吸收、电子转移、电子捕获和去捕获过程至关重要的光谱数据。

Non-technical Description: Afterglow (i.e. persistent luminescence) is a self-sustained luminescence phenomenon whereby a material (i.e. persistent phosphor) glows in the dark for hours after the excitation light source has been switched off. Nowadays persistent phosphors emitting in the visible and near-infrared spectral ranges are being used in daily life, e.g., security signs, emergency route signs, traffic signage, dials and displays, and medical research. However, the widespread use of persistent phosphors is greatly hindered because of the need of high-energy excitation light, mostly ultraviolet light, to charge the materials. Therefore, solutions to achieving effective excitation with low-energy light, particularly the visible light, are in demand. This project investigates a new charging process that enables low-energy visible-light sources (e.g. laser diodes) to be as effective as the commonly used high-energy ultraviolet light sources (e.g. ultraviolet lamps) in charging persistent phosphors. The outcomes of this research have a potential to open new strategies for studying and utilizing persistent phosphors. The project provides an interdisciplinary training experience to graduate, undergraduate and K-12 students in luminescent materials research and applications. The undergraduate and K-12 education is implemented through the existing programs at University of Georgia, such as the NSF-sponsored Peach State-Louis Stokes Alliance for Minority Participation program, NSF-sponsored Research Experiences for Undergraduates sites, and Young Dawgs program (for K-12 education).Technical Description: It is a general knowledge in persistent luminescence that high-energy ultraviolet light is usually necessary in order to effectively charge a persistent phosphor. However, the need of high-energy excitation compromises some applications where the ultraviolet light is unavailable or unsuitable. This project aims to tackle this limitation by investigating a new, two-photon up-conversion charging (UCC) process where low-energy visible-light sources (e.g. laser diodes) are as effective as the commonly used high-energy ultraviolet light sources (e.g. ultraviolet lamps) in charging persistent phosphors. In the UCC concept, two visible photons from a visible-light laser diode are successively absorbed by a UCC enabling ion (e.g. trivalent chromium ion) so that the high-energy delocalization state of the ion is reached and the electron traps in the phosphor are filled. The UCC enabling ions include trivalent chromium, divalent manganese, quadrivalent manganese, trivalent praseodymium, and trivalent neodymium. Several power-tunable visible-light laser diodes with wavelengths in the range of 400-700 nm are used as the excitation sources. New optical measurement techniques for UCC, such as UCC excitation spectroscopy, are under development in order to acquire spectral data that are essential for understanding the energy absorption, electron transfer, electron trapping and de-trapping processes involved in the UCC.