On the origin of temperature dependence of the emission maxima of Eu2+and Ce3+- activated phosphors

In this paper, temperature dependence of the emission maxima of Eu2+ and Ce3+-activated phosphors and various explanations for the thermal red-shift or blue-shift proposed by different authors are reviewed. Depending on the host lattice, doping concentration of Eu2+ or Ce3+, or the temperature range at which the PL spectrum was monitored, both the way and magnitude of emission spectrum shifting were quite different. Various explanations for the thermal shifts of the emission maxima were proposed. Nonetheless, a close inspection of a collection of the data indicates that some popular explanations seemingly plausible for the thermal red/blue-shifts of the emission maxima of Eu2+ and Ce3+-activated phosphors are highly questionable, because they either misused the Varshni equation or discussed the energy of the 5d-4f transitions of Eu2+ and Ce3+ in isolation without considering simultaneous change of the host lattice. An explanation of lattice dynamic induced thermal shifts of the emission maxima of Eu2+ and Ce3+-activated phosphors is proposed in this paper. By considering the dominant contribution to the energy of the 5d-4f transitions either from a lattice dilatation or from the interactions between the 5d electrons and phonons, the complex temperature dependences of the emission maxima of various Eu2+ and Ce3+-activated phosphors experimentally observed in literature could be explained reasonably.