磷光Phosphorescence

分子吸收光到达 S₁ 后，经系间窜越进入能量较低的 T₁，再缓慢发光回到 S₀。T₁ 能量低于 S₁，所以磷光波长比荧光更长。室温溶液中三重态易被氧气和分子碰撞淬灭，有机分子磷光通常需在低温刚性玻璃（如 77 K 液氮冷冻的乙醇）中才能观察到。含重原子（Ir、Pt、Br、I）的分子自旋-轨道耦合强，能在室温下高效发磷光。无机长余辉材料（如 SrAl₂O₄:Eu²⁺,Dy³⁺）则依靠陷阱能级缓慢释放电子。

After absorbing light to S₁, a molecule crosses into the lower-lying T₁ by intersystem crossing and then emits slowly back to S₀. T₁ lies below S₁, so phosphorescence is at longer wavelength than fluorescence. In room-temperature solution, triplets are easily quenched by oxygen and collisions, so organic phosphorescence usually needs a rigid glass at low temperature, such as ethanol frozen at 77 K. Molecules with heavy atoms (Ir, Pt, Br, I) have strong spin–orbit coupling and phosphoresce efficiently at room temperature. Inorganic afterglow materials such as SrAl₂O₄:Eu²⁺,Dy³⁺ instead release trapped electrons slowly.

1603 年意大利鞋匠卡肖罗洛煅烧重晶石得到“博洛尼亚石”，在黑暗中发光，引起轰动。1669 年布兰德从尿中提取出在黑暗中发光的白磷，并以希腊语“携光者”命名为 phosphorus——但白磷的发光实际是缓慢氧化的化学发光，而非真正的磷光。1944 年刘易斯和卡沙证明有机分子的磷光源于三重态。

In 1603 the Italian shoemaker Casciorolo roasted barite to make the 'Bologna stone', which glowed in the dark and caused a sensation. In 1669 Brand extracted from urine a white substance that glowed in the dark and named it phosphorus, Greek for 'light-bearer', though white phosphorus glows by chemiluminescence from slow oxidation, not true phosphorescence. In 1944 Lewis and Kasha showed that organic phosphorescence comes from triplet states.

磷光材料用于夜光表盘、应急疏散标志、发光玩具；铱配合物磷光 OLED 使显示器内量子效率接近 100%，是手机和电视屏幕红绿光的主要发光材料；磷光探针用于氧气传感（磷光被 O₂ 淬灭）和时间分辨生物成像（避开短寿命背景荧光）；荧光灯和白光 LED 中的荧光粉。早期夜光表使用放射性镭激发硫化锌，导致“镭女孩”职业病悲剧。

Phosphorescent materials light watch dials, emergency exit signs and glow-in-the-dark toys; iridium-complex phosphorescent OLEDs give displays internal quantum efficiencies near 100% and supply most of the red and green emitters in phone and television screens; phosphorescent probes sense oxygen (which quenches them) and enable time-resolved bioimaging free of short-lived background fluorescence; and phosphors coat fluorescent lamps and white LEDs. Early luminous dials used radium to excite zinc sulfide, causing the occupational tragedy of the 'Radium Girls'.