物质颜色的基础是什么？

Colours all around us do fascinate us but have you ever wondered that even though the natural light is colourless then what it is that imparts different colours to different materials. In reality the colourless light that we see is composed of different colours. All of you would have seen the resolution of colourless beam of light into its constituent colours when it passes through a prism. The basic realization that white light is actually composed of different colours is the starting point that will provide answer to the basic question on what is responsible for the colour of materials.

Colour of a material arises from both physical and chemical characertistics and these are discussed in the present article.

Physical Characteristics

Absorption

A liquid or solid medium which is transparent will transmit all the constituent colours of white light without resolving them and will appear colourless. A medium which selectively absorbs some colours but reflects or transmits other colours will appear to be coloured. The colours which are transmitted or reflected are referred to as complimentary colours.A Complementary colour wheel depicts the colour of the material on absorption of wavelengths that appear on the wheel diagonally opposite to the colour of appearance.

吸收特定波长的强烈吸收分子称为颜料或染料。无机颜料以多晶粉的形式出现或聚集在可溶油中。另一方面，有机颜料本质上更为普遍。例子是植物和叶片中血红蛋白的红色和叶绿素的绿色。

扩散Reflectance

Rough surfaces reflect incident light back in multiple directions. Common salt appears white as its crystals reflect light without absorption. On the other hand, copper sulphate crystals appear blue as they absorb higher wavelengths such as red to yellow to green and reflect the blue wavelengths

Light Scattering

光在其路径中被颗粒散射。一个经典的例子是天空的蓝色外观。与光波长相比，入射阳光的蓝色波长比红色波长更强烈。较大的颗粒或污染物具有光波长的直径，甚至在大气中的较大的直径沿向前方向散射光和散射的颜色不大，因此云或污染羽通常似乎是朦胧的白色。

Chemical Characteristics

All matter is composed of atoms or groups of atoms arranged in different molecular configurations. Some of these arrangements or functional groups are responsible for colours of compounds. Such groups are referred to as发色团. A chromophore is capable of electronic transitions in the UV – visible spectral region when irradiated with light and thereby imparts colour to the compound.Some typical examples are ß-carotene, quinonones, porphyrins and azo dyes.