ABSTRACT
Numerous fascinating optical devices have firmly entered our everyday life. It is unthinkable to spend even a short time without those already ordinary and/or yet fancy things, which just a few decades ago could only have been a result of rich imagination of a novelist writing the scientific fiction novels or stories. Rather than discussing and describing the applications of the optical materials, the reader’s attention will be brought to the so-called activators or active ions, responsible for the absorption and emission of light. Many people are quite advanced users of those mentioned devices, but very few think about the physical principles of their operation and those substances producing bright colored emissions that make watching modern TVs or playing with modern computers/mobile phones so amusing. As a result, the optical spectra of the ions with those partially filled electron shells exhibit remarkable diversity from the point of view of possible transitions, their intensities and spectral ranges covered by those transitions.
