When crystalline or amorphous solids are doped with atomic or molecular ions, the ionic energy levels are broadened and shifted, becoming similar to the dyes described earlier. Optical pumping of excited states leads to many overlapping fluorescence bands terminating on lower "vibronic levels" (as seen in the diagram below). These rapidly relax back to the ground state. If there is sufficient overlapping of the fluorescence bands then it is possible to tune the laser continuously over a range determined by the choice of hosts and implanted ions. Below is a table of the properties of five lasers with different hosts and dopants.