在本篇論文中，我們是第一位成功合成出具有形狀控制的無機鈣鈦礦CsPbBr3粒子。藉由改變界面活性劑的比例或者是合成溫度，能快速的合成出CsPbBr3立方體、菱形十二面體與八面體。由紫外光吸收光譜可以明顯看到三者的吸收位置不同，是因為三者所組成的晶面不同造成的差異。而可藉由控制菱形十二面體的大小改變吸收位置，進而利用Tauc plot推算出相對應的能隙，隨著粒子尺寸越大，能隙逐漸下降。CsPbI3立方體也可以直接合成。我們更進一步的利用陰離子交換法來探討光學晶面效應，170奈米的CsPbBr3菱形十二面體可藉由陰離子交換法轉換成CsPbI3菱形十二面體，而10奈米的CsPbI3立方體可轉換成相同大小的CsPbBr3立方體。比較CsPbBr3的菱形十二面體與立方體，不論是紫外吸收光譜或是螢光放射光譜，粒徑較大的170奈米菱形十二面體反而較粒徑超小的立方體藍位移，此項例子對於光學晶面效應提供了一個強而有力的證明。最後，我們將合成出的CsPbBr3菱形十二面體、立方體與期刊合成出的粒子做比較。將粒子尺寸大小與紫外光吸收位置作圖，會發現當具有{110}晶面的菱形十二面體與具有{100}晶面的立方體隨著粒徑尺寸越大，粒子的光吸收趨勢差異極大。相較於相同大小的菱形十二體與立方體，兩者的吸收光譜竟差距了70奈米。這除了證明了光學晶面效應的存在，也顯示藉由改變晶面也可調控LED的顏色。

In this study, we are the first one to synthesize CsPbBr3 rhombic dodecahedra and octahedra. By tuning the ratio of surfactant or controlling the reaction temperature, we have demonstrated fast synthetic methods for the fabrication of CsPbBr3 crystals with various morphologies. We can see it is obvious that the absorption band depends on the crystal facets. We also can change the positon of absorption wavelength by tuning particle size, and a modified band diagram for CsPbBr3 can explain the observed optical properties of CsPbBr3. Furthermore, CsPbI3 particles can be made by anion exchange method for optical facet-dependent effect observation. Through the anion exchange method, 170 nm CsPbBr3 RD can lead to CsPbI3 RD, and 10 nm CsPbI3 cubes can change to CsPbBr3 cubes of the same size. Compared with CsPbBr3 rhombic dodecahedra and cubes, remarkably the much bigger RD are more blue-shifted than the ultrasmall cubes in light absorption and emission. This is one powerful demonstration of optical facet effects. Lastly, we compared our synthesized rhombic dodecahedra and cubes with reported cesium lead halide particles. Cubes with {100} crystal faces can produce a large shift in absorption position by slightly changing their particle size. Conversely, RD with {110} crystal faces require a large size variation to cause similar absorption shifts. The comparison also reveals ultralarge band separation of 70 nm for similar-sized CsPbBr3 rhombic dodecahedra and cubes. This phenomenon not only proves the optical facet effects, but also provides us a new way to tune the emission color of LEDs through crystal face control.

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