Researchers devise a full-color night vision goggle

研究人员开发出全彩夜视镜

Human eyes don’t register the infrared portion of the light spectrum because infrared photons don’t carry enough energy to trigger the signaling pathway inside our light-sensing cells. But we’ve been able to make devices that give us a visual representation of what’s happening in the infrared. 人眼无法感知光谱中的红外部分，因为红外光子的能量不足以触发我们感光细胞内的信号传导通路。但我们已经能够制造出一些设备，将红外波段发生的情况转化为视觉呈现。

A team at the Beijing Institute of Technology, led by Xin Tang and Ge Mu, has now built a device that lets people see infrared in a new way. Instead of just translating it to visible shades of green as it’s done in standard night-vision goggles, it translates different infrared wavelengths into distinct parts of the visual spectrum, giving the eye something closer to natural vision. 由北京理工大学的唐鑫（Xin Tang）和穆格（Ge Mu）领导的研究团队，现已开发出一种让人们以全新方式观察红外光的新型设备。与标准夜视镜仅将其转换为可见的绿色阴影不同，该设备能将不同的红外波长转换为可见光谱中的不同部分，从而为眼睛提供更接近自然视觉的图像。

Researchers achieved that by combining mercury telluride colloidal quantum dots, which absorb infrared light, and a dual-layer OLED, which converts that absorbed energy into visible color. Stacked together with the right internal wiring, they make incoming infrared radiation come out the other side as an ordinary-looking, full-color image. 研究人员通过结合吸收红外光的碲化汞胶体量子点和将吸收能量转换为可见颜色的双层OLED实现了这一目标。通过适当的内部布线堆叠在一起，它们能将入射的红外辐射在另一端转化为外观自然的彩色图像。

Invisible light

不可见光

Vision begins when a photon strikes a light-sensitive pigment in the retina and causes it to change shape. That alters a protein that the pigment is embedded in, starting a nerve impulse that eventually contributes to an image in the brain. The molecular shape change that starts it all needs a minimum amount of energy, roughly 1.6 electron volts; infrared photons with wavelengths longer than 700 nanometers don’t carry enough energy to do it. That leaves over half of the Sun’s radiant energy outside our visual reach, along with anything that emits or reflects heat rather than visible light. 视觉始于光子撞击视网膜中的感光色素并使其形状发生改变。这一过程改变了色素所嵌入的蛋白质，从而引发神经冲动，最终在大脑中形成图像。启动这一过程的分子形状改变需要最低限度的能量，大约为1.6电子伏特；波长超过700纳米的红外光子携带的能量不足以达到这一要求。这意味着太阳超过一半的辐射能量，以及所有发射或反射热量而非可见光的物体，都处于我们视觉范围之外。

Most existing devices that allow us to see infrared use IR photodetectors wired to visible-light LEDs. This approach makes infrared light visible, but only as brightness: A warmer object glows a bit more, a cooler one glows a bit less, and we represent them all in the same (usually greenish) color. One problem with this is that human eyes are far better at distinguishing subtle differences in hue than they are at picking out brightness differences, so a device that only modulates brightness is leaving most of the eye’s sensitivity unused. 目前大多数允许我们观察红外光的设备，使用的是连接到可见光LED的红外光电探测器。这种方法虽然能让红外光可见，但仅限于亮度表现：较热的物体发光稍强，较冷的物体发光稍弱，而我们用同一种（通常是绿色）颜色来表示它们。这种方法的一个问题是，人眼在区分细微色调差异方面的能力远强于区分亮度差异，因此仅调节亮度的设备浪费了人眼大部分的敏感度。

Selective quantum dots

选择性量子点

Bulk semiconductors routinely used in IR detectors have continuous energy bands, which means they absorb a broad, undifferentiated swath of the infrared spectrum. This doesn’t preserve much information about which specific wavelength arrived. The mercury telluride colloidal quantum dots the Chinese team picked for their device behave differently. Due to their tiny size, roughly 4 nanometers across, quantum confinement breaks their energy levels into discrete steps rather than a continuous chunk. 红外探测器中常用的块状半导体具有连续的能带，这意味着它们吸收的是红外光谱中宽泛且无差别的部分，无法保留关于具体入射波长的信息。中国团队为其设备选择的碲化汞胶体量子点则表现不同。由于其约4纳米的微小尺寸，量子限域效应将其能级分解为离散的阶梯，而非连续的块状。

Photons of different infrared wavelengths and intensities excite different electronic transitions, moving an electron between discrete energy levels within the dot, rather than just producing more or less of a single signal. At wavelengths of around 2 micrometers, the longest the team tested, incoming photons have just enough energy to bump an electron across the dot’s fundamental bandgap, producing a modest number of charge carriers, either negatively charged electrons or positively charged holes that move around the dot. 不同红外波长和强度的光子会激发不同的电子跃迁，使电子在量子点内的离散能级之间移动，而不仅仅是产生单一信号的强弱变化。在团队测试的最长波长——约2微米时，入射光子刚好有足够的能量将电子推过量子点的基本带隙，产生适量的电荷载流子（即在量子点内移动的带负电电子或带正电空穴）。

At shorter infrared wavelengths, photons carry more energy per particle, and they can access additional, higher-energy electronic transitions inside the dot. In some cases the excess energy in a carrier can be enough to kick loose more than one electron-hole pair per photon. These processes open extra channels for generating charge carriers. The effect is that shorter infrared wavelengths and more intense infrared light push more positively charged holes out of the quantum dot layer and toward the OLED side of the device. 在较短的红外波长下，每个光子携带的能量更高，它们可以激发量子点内部额外的、更高能级的电子跃迁。在某些情况下，载流子中的多余能量足以使每个光子释放出不止一对电子-空穴对。这些过程为产生电荷载流子开辟了额外通道。其结果是，较短的红外波长和更强的红外光会将更多的带正电空穴从量子点层推向设备的OLED侧。

The barrier

能量势垒

The team achieved this by building the OLED with two separate emissive layers stacked on top of each other. One layer, closer to where the holes enter, was doped with a red-emitting phosphor. The other one, positioned farther away, was doped with phosphor-emitting cyan light. The key component that made full-color vision work was an energy barrier of about 0.82 electron volts between these two layers. 研究团队通过构建两个堆叠在一起的独立发光层来实现这一目标。靠近空穴进入端的一层掺杂了红色发光磷光体，而位置较远的一层则掺杂了青色发光磷光体。实现全彩视觉的关键组件是这两层之间约0.82电子伏特的能量势垒。

When only a small number of holes arrive from the infrared detector because of dim illumination or long-wavelength photons, they are all captured by the red layer, and the device emits a low-brightness red glow. As the number of incoming holes grows, whether because the infrared light is brighter or because it contains shorter wavelengths, additional carrier-generating pathways in the quantum dots are unlocked, and the barrier gets saturated. Holes start finding their way through it and into the cyan layer, and the device begins emitting a mixture of red and cyan simultaneously, shifting the overall color and increasing the luminance. 当由于光照暗淡或长波长光子导致从红外探测器到达的空穴数量较少时，它们会被红色层全部捕获，设备发出低亮度的红光。随着入射空穴数量的增加（无论是由于红外光更强还是包含更短波长），量子点中额外的载流子产生路径被解锁，势垒达到饱和。空穴开始穿过势垒进入青色层，设备开始同时发出红色和青色的混合光，从而改变整体颜色并提高亮度。

Because this color shift is tied to carrier number rather than a fixed lookup table, the resulting color space encodes both the wavelength and the intensity of the incoming infrared light. The team’s calculations presented in the study show the device should enable users to distinguish infrared power differences roughly 200 times smaller than they would be able to if using a single-color, brightness-only design. 由于这种颜色偏移与载流子数量相关，而非依赖固定的查找表，因此产生的色彩空间同时编码了入射红外光的波长和强度。研究中展示的计算结果表明，与使用单色、仅调节亮度的设计相比，该设备能让用户分辨出约200倍精细的红外功率差异。

Glasses and implants

眼镜与植入物

The eyeglass is semi-transparent and weighs only 23 grams, with an active viewing area of about 3.57 square centimeters. 这款眼镜呈半透明状，重量仅为23克，有效视场面积约为3.57平方厘米。