The principal unstability of some polyvalent triple impurity systems against the possibility of radiative tunnel transitions (RTTs) is discussed. As an example, a three-centre system of neutral, negatively charged and positively charged F-, F′- and α-colour centres in an alkali halide crystal is considered. If the distance between F- and F'-centres is much smaller than the F'-α distance then, along with a very slow RTT process, F′ + α → 2F, a much faster RTT process F′(h) + F(1) → F(h) + F′(1) is also a possible one. Here, h and 1 denote the relatively higher and lower energy position of the trapping level for an extra electron at two F-sites caused by their different distances from the charged α-centre. This type of radiative unstabilities could be relatively significant in areas of defect clustering.