Ultraviolet Light and its Use with Fluorescent Minerals
Ultraviolet Light and its Use with Fluorescent Minerals
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紫外线及其与荧光矿物的应用
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发表时间：
2008
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通讯作者：
A. Wilkins
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作者：
A. Wilkins
有趣的是，尽管人类几万年来一直在寻找矿物中的颜色，但矿物中最耀眼和最戏剧性的颜色现象之一直到最近才为人所知。这就是荧光现象。在迄今已确定的大约4200种矿物中，有566种(来自6500多个地点)在1989年出版的《汉高荧光矿物词汇表》中被报告为荧光矿物。其中一些荧光物种(例如方解石、透明蛋白石)分布广泛，而其他荧光物种(例如埃格利石、斜长石、世辉石、榴辉石)仅在世界上一个或几个地方发现。荧光是某些矿物在紫外线(UV)光源的不可见光线照射下产生的可见光。1852年，乔治·斯托克斯爵士(1820-1903)在观察到英格兰坎伯兰州阿尔斯顿穆尔的萤石后创造了这个词，类似于已经被认为是蛋白石的“蛋白石”。荧光发生时，荧光矿物中的“激活剂”原子吸收紫外线，从而将电子从较低的振动带转移到不太稳定的较高(即较高能量)的振动带。结果，电子被抛入增强的振动中，进而将能量传递给邻近的原子。因此，被带电的电子逐渐放弃了大部分新发现的能量作为热量，并逐渐滑向上振动带的下缘。接下来，电子以可见光的形式在一次爆发中放弃所有或几乎所有从紫外线辐射中获得的剩余能量，同时返回到它最初的“基态”。因此，这就是荧光。根据斯托克斯荧光定律，产生的光必须比先前从被吸收的紫外线吸收的光具有更低的能量(即更长的波长)，其余的能量以热的形式耗散。因此，斯托克斯定律允许蓝光产生红色荧光，但反之亦然。有些矿物质的荧光强度如此之大，以至于在阳光下这种影响是显而易见的。一些硅锌矿的荧光绿色，一些萤石的蓝色，以及一些红宝石在白天的红色，都与太阳紫外线的激发有关。磷光是当紫外线灯被置于荧光矿物上方，然后关闭或移开时产生的余辉。磷光是由阻止被紫外线激发的电子迅速释放能量的原子过程产生的，通常涉及到被激发的电子在某些位置上的“陷阱”，在那里它们不能迅速返回到低能状态。这可能是由于晶体缺陷、原子缺失或矿物晶体中的外来“杂质”原子被取代所致。一只适应黑暗的眼睛被证明能够在暴露后36000小时内探测到来自康涅狄格州特朗布尔的萤石中的磷光。西南方向的磷光比LW方向的磷光更明显。为了理解荧光，回顾一下电磁光谱是有用的。可见光包含彩虹的所有颜色，从紫罗兰色以一种
It is interesting to consider that while man has sought color in minerals for tens of thousands of years, one of the most brilliant and dramatic color phenomena in minerals has been unknown until recently. This is the phenomenon of fluorescence. Of the roughly 4,200 mineral species thus far identified, 566 of them (from more than 6,500 localities) are reported as fluorescent in The Henkel Glossary of Fluorescent Minerals, published in 1989. Some of these fluorescent species (e.g., calcite, hyalite opal) are widespread, while others (e.g., agrellite, benitoite, esperite, tugtupite) are found in only one or a few places in the world. Fluorescence is the visible light produced by certain minerals when they are illuminated by the invisible light rays of an ultraviolet (UV) light source. The term was coined in 1852 by Sir George Stokes (1820-1903) after observations on fluorite from Alston Moor, Cumberland, England, by analogy with the term “opalescence” already attributed to opal. Fluorescence occurs as “activator” atoms in the fluorescing mineral absorb UV, thereby transferring an electron from a lower vibration band to a less-stable upper (i.e., higher-energy) vibration band. As a result, the electron is thrown into increased vibration which, in turn, transfers energy to neighboring atoms. Thus, the energized electron gradually gives up much of its new-found energy as heat and gradually slips down to the lower edge of the upper vibration band. Next, the electron gives up all, or nearly all, of its remaining surplus energy derived from UV radiation in one burst, in the form of visible light, while returning to its original “ground state.” This, then, is fluorescence. In accordance with Stokes’ law of fluorescence, the light produced must be of lower energy (i.e., longer wavelength) than that taken in earlier from the absorbed UV, with the remainder of the energy dissipated as heat. Stokes’ law, then, allows a blue light to produce a red fluorescence, but not vice-versa. Some minerals fluoresce with such intensity that the effect is noticeable in sunlight. The fluorescent green of some willemites, the blue of some fluorites, and the red of some rubies in daylight is related to excitation by solar UV. Phosphorescence is the afterglow produced when a UV lamp is held over a fluorescent mineral and is then turned off or moved away. Phosphorescence results from atomic processes that prevent electrons energized by UV from rapidly discharging their energy, usually involving “traps” of their energized electrons at some location from whence they cannot return quickly to their low-energy state. This can happen as a result of crystal defects, missing atoms, or substitution of foreign “impurity” atoms in the crystal of the mineral. A dark-adapted eye has been shown to be able to detect phosphorescence in fluorite from Trumbull, Connecticut for an amazing 36,000 hours after exposure. Phosphorescence is generally more prominent under SW than LW. To understand fluorescence, it is useful to review the electromagnetic spectrum. Visible light, containing all of the colors of the rainbow, extends from violet at a