Abstract: This work investigates pressure-induced phase transition PT and excited-state-crossover effects on the photoluminescence PL properties of LiCaAlF6 :Cr3+. We report a PL study by means of time-resolved emission, excitation, and lifetime measurements as a function of pressure. We focus on Cr3+ PL variations around pressure-induced trigonal-to-monoclinic first-order PT in LiCaAlF6 at 7 GPa. Moreover, the structural requirements for changing Cr3+ PL from a broadband emission at 1.59 eV 781 nm at ambient conditions, to a rubylike narrow-line emission at 1.87 eV 663 nm are analyzed in the 0?35 GPa range. We show how pressure progressively transforms Cr3+ broadband PL into a rubylike emission that becomes the dominant feature of the room-temperature emission spectrum at 28 GPa. This behavior, together with the pressure dependences of the 2 E and 4 T2 excited-states energy and PL lifetime, are explained on the basis of the electron-phonon coupling associated with the 4 T2 and 2 E states. We demonstrate that both excited states interact through spin-orbit coupling yielding Fano resonance rather than antiresonance as is frequently assumed.

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