The two major conditions for lasers are sufficient pumping to obtain population inversion,and minimized quenching.Energy transfer between simultaneously present lanthanides,chromium(III) or manganese(II) are useful for feeding energy to the emitting level, and storing energy beyond its intrinsic life-time .Quenching of lanthanide J-level emission is well understood since the multi-phonon de-excitation was rationalized by Weber(1967) but can also involve cross-relaxation and other energy transfer (including resonant migration to dark traps).Both emission spectra and quenching (especially with increasing temperature,sometimes already above 100 K) is far more complicated in Cr(III) than in Mn(II) and can be related to the 16-dimensional Born-Oppenheimer potential surface of local MX6 clusters. Glasses preserve a dispersion of nuclear positions from their hot melt, enhancing quenching (it impedes energy transfer much less) with an optimized exception of low Cr(III) content in lithium lanthanum phosphate glass.Tunable Cr(III) lasers seem now accessible with limpid glass-ceramics.
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