Rare-earth-doped oxide phosphors are important for solid-state lighting and photonic applications because their spectroscopic properties are strongly governed by the interplay between local structure, lattice vibrations, electronic structure, and crystal-field (CF) interactions. We present a comprehensive investigation of the structural, electronic, vibrational, and spectroscopic properties of $R^{3+}$ ($R$ $=\mathrm{Dy}$, Eu)-doped ${\mathrm{CaAl}}_4{\mathrm{O}}_7$ phosphors using complementary first-principles density functional theory (DFT) computations and CF parameters (CFPs) modeling approaches. Electronic-structure computations were performed within DFT employing the LDA+$U$ and LDA–1/2 formalisms, while lattice vibrations were analyzed using both DFT-LDA computations and the semiempirical GF-matrix force-field methods. The DFT geometry-optimized structures preserve the monoclinic space group $C2/c$ while introducing local distortions around the substitutional $\mathrm{C}{\mathrm{a}}^{2+}$ sites. The computed electronic structures reproduce the experimentally observed wide band-gap features and reveal distinct differences between $\mathrm{D}{\mathrm{y}}^{3+}$- and $\mathrm{E}{\mathrm{u}}^{3+}$-doped systems. In $\mathrm{D}{\mathrm{y}}^{3+}$-doped ${\mathrm{CaAl}}_4{\mathrm{O}}_7$, the $4f$ states remain well separated from the band edges, whereas in the $\mathrm{E}{\mathrm{u}}^{3+}$-doped system, Eu($4f$) states appear within the band gap, associated with O($2p$) → Eu($4f$) charge-transfer transitions. The calculated Raman- and infrared-active phonons agree well with experiment. The modeled CFPs successfully reproduce the observed Stark splitting patterns and $4f\text{−}4f$ transition energies of $\mathrm{D}{\mathrm{y}}^{3+}$ and $\mathrm{E}{\mathrm{u}}^{3+}$ ions. The standardized monoclinic CFP sets and rotational invariants reveal stronger CF for $\mathrm{D}{\mathrm{y}}^{3+}$ than for $\mathrm{E}{\mathrm{u}}^{3+}$, correlating with differences in local coordination distortions. Overall, the present study establishes structure-property relationships by demonstrating how local coordination distortions induced by rare-earth substitution govern the electronic structure, lattice dynamics, crystal-field strength, and the resulting spectroscopic properties of $\mathrm{D}{\mathrm{y}}^{3+}$- and $\mathrm{E}{\mathrm{u}}^{3+}$-doped ${\mathrm{CaAl}}_4{\mathrm{O}}_7$ phosphors.

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• Electronic structure
• Lattice dynamics
• Crystal-field theory
• Density functional theory
• First-principles calculations