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这5种岩石如何发光

How 5 Rocks Get Their Glow

[ ♪ intro ]
【片头曲】
There are a lot of great rocks out there
地球上有很多很棒的岩石
and we’ve even talked about some of them here on SciShow before.
我们之前在《科学秀》上也讨论过其中一些
But in our opinion, some of the coolest rocks are the ones that glow.
但在我们看来 有些最酷的岩石是能发光的
Any rock will glow if you heat it up enough,
只要受热充足 所有岩石都会发光
but there are a few types that are especially good at giving off light,
但是有几种岩石特别擅长发光
and they do it in all different ways.
而且他们以完全不同的方式发光
Here are five of our favorite rocks — and how they get their glow.
下面介绍五种我们最喜欢的石头以及它们是如何发光的
The most famous glowing rock might be fluorite,
最著名的发光岩石应当属萤石
which is actually where the word fluorescence comes from.
这也是荧光这个词的由来
When this mineral is exposed to ultraviolet, or UV light,
当这种矿物质暴露在紫外线下
it gives off an eerie blue, like your shoelaces under a blacklight.
它会发出一种诡异的蓝光 像是黑光下的鞋带
Essentially, it’s absorbing the UV light and then re-emitting it at a different frequency.
本质上 它吸收紫外线后以不同的频率重新把光发射出来
But fluorite and other rocks that fluoresce tend to only absorb and emit specific colors of light.
但萤石和其他发出荧光的岩石往往只吸收和发射特定颜色的光
Shine the wrong color on them, and they just look like an ordinary rock.
如果用错误的颜色照射它们 它们只会像一块普通的石头
And that’s actually a big hint about what gives them their glow.
这实际上很大程度上暗示我们是什么让它们发光
Anything that’s sensitive to certain frequencies of light
任何对特定频率的光敏感的事物
has probably got something quantum mechanics-y going on.
都可能与量子力学有关
See, in every material, electrons are bound to atoms in certain energy levels.
在每一种材料中 电子都在特定的能级与原子结合
And for an electron to step up or down from one energy level to another,
一个电子从一个能级上升或下降到另一个能级
it has to gain or lose a specific amount of energy.
必须获得或失去特定数量的能量
Absorbing light is one way electrons gain energy.
吸收光能是电子获得能量的一种方式
But different colors of light have different amounts of energy,
但是不同颜色的光有不同的光能
so electrons can only absorb light with the exact right amount of energy
而电子只能吸收能量合适的光
to take them up to a higher energy level.
来跃迁到更高的能级
Once they get there, though, electrons don’t typically stay there.
然而 电子一旦到达那里 通常也不会停留在那儿
They tend to lose energy and fall back to a lower energy state.
它们往往会失去能量 然后回落到较低的能态
And as they fall back down, they often emit photons of light.
当它们落回低能级时 通常会发射光子
For fluorescent materials, you only need to wait a nanosecond or so to see that happen.
对于荧光材料 你只需要等一纳秒左右就能看到发光
But the light they emit doesn’t necessarily have the same energy as the light they absorbed.
但它们发出的光不一定和它们吸收的光能量相同
Materials like rocks have lots of energy levels in them,
像岩石这样的物质有很多能级
so an electron might lose a little energy to heat and drop down one level,
所以一个电子可能以热能形式散失一些能量来下降一个能级
and then drop down the rest of the way by emitting a photon.
然后通过发射一个光子来跃迁剩下的能级
So the photons they emit each have lower energies than the ones they originally absorbed.
所以它们发出的光子比它们最初吸收的光子的能量要低
That’s why you can shine UV light on fluorite, but then see it glow in blue.
这就是你用紫外线照射萤石 它却发出蓝光的原因
And because UV light is invisible to humans, it looks to us like fluorite glows in the “dark.”
因为人类看不见紫外线 所以在我们看来就像萤石在“黑暗”中发光
Overall, though, fluorescence is actually pretty common:
总的来说 荧光实际上很常见
There are tons of fluorescent rocks out there, and they glow in all different colors.
地球上有很多荧光岩石 它们发出各种颜色的光
And what’s amazing is they just look like ordinary rocks
令人惊讶的是 它们一直看起来就像普通的岩石
until you see them under the right kind of light.
直到你在正确的光线下观察它们
Another mechanism that makes rocks glow is called phosphorescence
另一种岩石发光的机制叫做磷光现象
and it was also named after a natural substance: phosphorus.
它也以一种天然物质命名 磷
Except, confusingly, while phosphorus does glow,
不过 令人困惑的是 虽然磷确实会发光
we now know it’s actually not from phosphorescence
但我们现在知道它实际上并不是来自磷光现象
— it’s from chemical reactions with the air.
它的发光是来自磷与空气的化学反应
So that’s another story.
这就是另一种机理了
But lots of other rocks do truly phosphoresce, like calcite.
但其他很多岩石确实是发出磷光的 比如方解石
Just like fluorite, calcite and other phosphorescent rocks glow under UV light.
就比如萤石 方解石和其他磷光岩石在紫外线下发光
But unlike fluorite, these rocks can truly glow in the dark.
但与萤石不同的是 这些岩石是真的能在黑暗中发光
Because even after you turn off the light, they’ll keep glowing for a while.
因为即使你关了灯 它们还会发光一段时间
The reason for this is that phosphorescence works almost exactly like fluorescence,
原因是磷光的工作原理和荧光几乎一样
But with one key difference, in phosphorescent rocks,
但有一点非常不同 在磷光岩石里
electrons that have jumped up to a higher energy level
跃迁到更高能级的电子
don’t fall down in a split-second the way they do in rocks like fluorite.
并不会像在萤石等岩石中那样瞬间下落
Their structure lets them hold on to that energy for a lot longer.
它们的结构让它们能更长时间地保持这种能量
That’s because, before they drop down to where they started,
这是因为 在他们回到开始的能级之前
they usually have to go through what’s known as a forbidden transition
它们通常要经历禁阻跃迁
A forbidden transition is one that’s just very unlikely to happen.
禁阻跃迁是很难发生的
And it’s unlikely because it requires a change in the electron’s spin
它很难发生是因为它需要改变电子的自旋
—that weird, quantum mechanical property all particles have that’s vaguely like ordinary rotation.
所有粒子都具有的奇怪的量子力学性质——这有点像普通的旋转
And the thing is, transitions that involve a change in spin are less likely than ones that don’t.
事实上 涉及自旋变化的跃迁比不涉及自旋变化的跃迁更不可能发生
Which means you have to wait longer to see it happen.
这意味着你要等更长的时间才能看到它发生
As a result, a phosphorescent rock that’s been charged up
因此 磷光岩石在充电后
will slowly release that pent-up energy as light over time,
会慢慢地以光的形式释放被压抑的能量
so you can see it glow for minutes or even days since it was last exposed to light.
所以你可以在几分钟甚至几天后看到它发光
Phosphorescence in nature is actually fairly rare,
在自然界中 磷光实际上是相当罕见的
because it’s hard to get a rock with forbidden transitions
因为很难找到一种岩石
at just the right energies needed to emit visible light in that way.
在吸收合适的能量后发出可见光的同时还要经历禁阻跃迁
But if you ever had glow-in-the-dark stars on your ceiling at night, you’ve seen phosphorescence at work.
但如果你曾经在天花板上看到黑夜中闪烁的星星 那就是磷光现象
Now, if you’ve tried shining a UV light on a rock but you’re not having any luck,
现在 如果你试着用紫外线照射岩石 但你运气极差
you’re not out of options.
你也无计可施
You can always try hitting it with something!
不过你可以用什么东西打它
That’s the essence of triboluminescence,
这就是摩擦发光的本质
which is the type of glow you get when you hit a rock hard enough
当你以足够的力度撞击岩石时 你会得到这种光
—or rub it, pull it apart, or generally apply mechanical stress to it in some way.
或者你也可以摩擦它 把它掰开 或者以某种方式对它施加机械压力来得到这种光
The term covers a lot of bases.
这个术语涵盖了很多原理
Scientists actually don’t understand triboluminescence perfectly,
科学家们对摩擦发光并不是很了解
and it may work differently for different materials.
不同的材料可能会有不同的发光原理
But we have a decent idea of how it works for rocks like quartz
但我们比较了解像石英这种
that give off light when you rub them together.
在摩擦下发光的岩石的发光原理
As the rocks scrape against each other,
当岩石相互摩擦时
some charged atoms and electrons on the surface get knocked free.
表面上的一些带电原子和电子被击离
Then they collide with molecules in the air and knock loose even more charged particles.
它们与空气中的分子碰撞 释放出更多的带电粒子
As they recombine, those charged particles create little electric shocks,
当它们重新结合时 这些带电粒子会产生微小的电击
like mini-lightning, that we see as flashes of light.
就像迷你闪电 我们会看到闪光
But this doesn’t just happen with any rock.
但不是任何一块石头都能发生这种现象
To get triboluminescence, scientists think you need a rock
科学家认为 要获得摩擦发光 你需要一块
whose crystal lattice structure is asymmetric in some way
晶体晶格结构在某种程度上不对称的岩石
—in other words, it’s not just made of nice, neat rows of atoms.
换而言之 它不仅仅是由漂亮整齐的原子组成的
That’s how some parts of the material end up with excess electric charge,
这就是物质的某些部分最终带有多余电荷的原因
which can break free and produce that light when the material is put under stress.
当材料受到压力时 它就会断裂并产生光
Unlike fluorescence and phosphorescence, triboluminescence tends to be a brief flash of light.
与荧光和磷光不同 摩擦发光往往是短暂的闪光
And it’s a very common phenomenon
这是一种非常普遍的现象
—it’s possible that around half of all inorganic compounds triboluminesce in some way,
可能大约一半的无机化合物以某种方式摩擦发光
including rocks like quartz and feldspar, as well as some everyday organic compounds like sugar.
包括像石英和长石这样的岩石 以及一些日常生活中的有机化合物 比如糖
Today, scientists are still studying this phenomenon and learning more about how it works.
至今 科学家们仍在研究这一现象 进一步了解它的工作原理
Which is pretty cool—because it’s not often you can do science just by smashing rocks together!
这很酷 因为仅仅通过把石头砸在一起就能进行科学研究的情况并不多见!
Now, as we mentioned at the start of this episode, one way to make a rock glow is by heating it up.
现在 正如我们在本期视频开始时提到的 加热可以让岩石发光
But heated rocks can actually glow for more than one reason.
但加热使岩石发光的原因有很多
Things like lava or hot coals glow because of what’s called blackbody radiation:
像熔岩或热煤这样的东西会发光是因为所谓的黑体辐射
heat makes their molecules vibrate, and that releases energy in the form of light.
热使它们的分子振动 从而以光的形式释放能量
But there’s another, slightly safer way to get light from a rock by heating it,
但还有另一种稍微安全一点的通过加热使岩石发光的方法
called thermoluminescence.
叫做热致发光
This happens specifically when an object is heated after absorbing energy in some other way.
当物体以其他方式吸收能量受热时就会发生这种情况
That energy usually comes from some kind of radiation, like X-rays,
这种能量通常来自某种辐射 比如x射线
but light, friction, and even pressure can sometimes do the trick, too.
但光线 摩擦甚至压力有时也能起到作用
Any of these processes can free electrons from the crystal lattice that makes up a rock.
这些过程中的任何一种都可以从组成岩石的晶格中释放电子
But in thermoluminescent rocks,
但在热致发光的岩石中
those freed electrons quickly get re-captured in imperfections in the lattice.
这些被释放的电子很快就被晶格中的缺陷所俘获
The thing is, these new bonds are weaker than the original ones,
问题是 这些新键比原来的键弱
meaning the electrons actually become easier to free again.
这意味着电子实际上更容易再次释放
So a little heat is enough to vibrate the atoms making up the rock and set them loose.
所以一点热量就足以使构成岩石的原子发生振动而释放
This time, the electrons fall back down into their original positions.
这一次 电子会回到它们原来的位置
Once again, like in fluorescent rocks, those electrons give off photons as they drop down.
就像荧光岩石一样 这些电子再一次在下落时释放光子
The amount of light these rocks give off depends on
这些岩石发出的光的数量取决于
how long they were exposed to the initial source of energy.
它们接触原始能量源的时长
The more electrons there are trapped in different imperfections,
被困在不同缺陷中的电子越多
the more light the rock will release when you heat it.
岩石受热时释放的光子就越多
And it takes only a little bit of heat to release a lot of stored energy,
它只需要一点点热量就能释放出大量储存的能量
so it’s actually pretty easy to get a bright glow out of a thermoluminescent rock.
因此 很容易从热释光的岩石中获得明亮的光
For example, a rock called chlorophane will visibly glow just from the heat of your hand.
例如 一种叫做绿萤石的石头会因为你手的热量而发光
So if you pick up a rock and it starts glowing,
所以如果你捡起一块石头 它开始发光
it probably doesn’t mean you’re the chosen one destined to save the world…
这可能并不意味着你就是命中注定要拯救世界的那个人……
Probably.
也许是这样
Finally, if heating, lighting, and hitting a rock still won’t make it glow,
最后 如果加热 照明和撞击岩石都不能让它发光
you can always try passing an electric current through it.
你可以试试电击
If it glows, that means your rock is electroluminescent.
如果它发光 说明你的石头是电致发光的
Just like heating or shining light on a rock,
就像加热或用光照射岩石一样
passing an electric current through it is a pretty good way to charge up its atoms with energy,
电击是给原子充电的一种很好的方式
as long as it conducts electricity in the right way.
只要它以正确的方式导电
In electroluminescent rocks, the electric energy is enough to free electrons from their atoms,
在电致发光岩石中 电能足以将电子从原子中释放出来
leaving behind a bunch of positively-charged atoms and negatively-charged free electrons.
留下一堆带正电荷的原子和带负电荷的自由电子
Since positive and negative attract,
因为正负相吸
those particles will quickly recombine and become neutral
这些粒子会很快重新结合 变成中性的
—and once again, you get that mini-lightning, that quick release of light.
你会再次看到微型闪电一闪而过
The molecular structure needs to be just right,
分子结构必须恰到好处
so this doesn’t happen very often in naturally occurring rocks,
因此这在天然岩石中并不经常发生
but some colored diamonds are an exception.
但一些彩色钻石却是例外
See, in certain cases, diamonds aren’t actually completely transparent.
在某些情况下 钻石并不是完全透明的
They can have flaws in their structure that make them white or pink,
它们的结构可能有缺陷 导致它们变成白色或粉色
and they can also have trace amounts of stray elements
也可能含有微量的游离元素
that make them other colors, like yellow or blue.
使它们变成其他颜色 比如黄色或蓝色
And those impurities are the key: Those little interruptions in the crystal lattice
而这些杂质是关键: 当电流通过晶格时
are what emit light when the electric current passes through them.
这些微小的中断就会发光
What’s pretty wild about this is that the electroluminescence of diamonds
最疯狂的是 钻石的电致发光
could potentially make them useful for quantum computing.
有可能使它们在量子计算中发挥作用
That’s because quantum computing relies on super precise control over individual particles.
这是因为量子计算依赖于对单个粒子的超精确控制
And a well-made artificial diamond with a specific impurity can be sensitive enough
一颗含有特定杂质的精良人造钻石可以足够敏感到
to emit one photon at a time through electroluminescence,
通过电致发光一次发射一个光子
which could help us build more robust quantum computers.
这可以帮助我们建造更强大的量子计算机
So there are lots of glowing rocks out there, and lots of weird ways that they glow.
所以有很多发光的岩石 而它们发光的方式也很不可思议
We actually didn’t get around to talking about a few other neat examples,
我们实际上没有时间讨论其他一些简单的例子
like how the radioactive element actinium glows as its radiation reacts with the air around it.
比如放射性元素锕在辐射与周围空气反应时发光
But you know, there are plenty of safe ways to get glowing rocks,
但你知道么 有很多安全的方法可以得到发光的岩石
so maybe leave actinium to the experts.
所以也许把锕留给专家讲吧
Thanks for watching this episode of SciShow!
感谢收看本期科学秀!
And to find out even more about some of the coolest rocks out there,
想要了解更多关于最酷岩石的信息
you can check out our video on color-changing minerals right after this.
你可以观看接下来我们的关于变色矿物质的视频
[ outro ♪]
【片尾曲】

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视频介绍了一些岩石的发光原理,一起来看看吧!

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