Transition series ions, colours

Ligands coordinated to transition metal ions may also be arranged in order of increasing A. This order is called the spectrochemical series, reflecting colour variations in chemical compounds of individual cations with different ligands. Thus, for Cr3+ and Co3+ cations in octahedral coordination with different ligands, the order of increasing A0 is... 

The series of ten elements from scandium to zinc is known as the First Transition Series. Most of these show distinctive properties such as variable valency, coloured compounds, and complex ion formation. 

It has long been known that many lanthanide ions fluoresce under ultraviolet light, the fluorescence coming from f -> f transitions some ions which do not normally fluoresce at room temperature do so when they are cooled. This fluorescence property has led to lanthanide ions being incorporated in the phosphor of domestic fluorescent tubes and in the screens of colour televisions. When an ion is in an electronically excited state there is a competition between deactivation by radiative and non-radiative processes. For an ion to be a good emitter, any non-radiative process must be a poor second in the competition. If studies are carried out using aqueous solutions, it is found that the lanthanide ions at the centre of the lanthanide series are... 

Table 1. Colours and outer configurations of some of the Ions of first transition series.

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