Abstract: We present a spectroscopic study of the doubly Mn4+ and Cr3+-doped Sr4Al14O25, synthesised via solid state reaction, as a function of pressure and temperature to check its potential as a red emitting phosphor. The strong crystal field acting on Cr3+ yields a ruby-like narrow R-line emission that is used as an intrinsic temperature sensor and, in comparison to ruby, provides a fair estimate of the bulk modulus K = 172 GPa for Sr4Al14O25. The photoluminescence (PL) and associated excitation spectra of Sr4Al14O25:Mn4+,Cr3+ unravel a strong-field 3d3 configuration with R1 and R2 emission lines largely separated by 10.7 meV, which characterizes the non-centrosymmetric distorted Al4 site in the Sr4Al14O25 structure. Eighteen Raman modes have been detected at ambient pressure. They correspond to the stretching modes of the Al?O bonds and show frequency shifts with pressure consistent with Grüneisen parameters (? = 0.65), similar to those measured for other aluminates. The variations of PL intensity and lifetime with temperature exhibit a similar concomitant behaviour indicating an efficient pumping to the 4T2 level and hence down to the 2E emitting level in both Mn4+ and Cr3+ ions at low and moderate temperatures. Multiphonon non-radiative processes yield a quenching temperature of 400 K for Mn4+ with an effective activation energy of 0.57 eV. Unexpectedly, this energy decreases with pressure enhancing the non-radiative processes and thus PL intensity reduction. A thoroughly coordinate configurational energy diagram is presented for explaining the main spectroscopic features and excited-state dynamics.

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