Kinetically stabilized aliovalent europium-doped magnesium oxide as a UV sensitized phosphor.Doping of size mismatched aliovalent ions is challenging due to the associated elastic and electronic stress making the thermodynamics unfavorable.  In light of such a possibility, we utilize sol-gel synthesis for preparing a size mismatched trivalent europium doped MgO (Mg(1-x)Eu(x)O:(x/2)V"(Mg)) system, which can be potentially used in optical applications. It is found that such a doped system can be metastabilized and the extent of metastability can be correlated with critical temperature (Tc) required for phase segregation which decreases with the dopant concentration. For x = 0.005, 0.01, and 0.02, Tc is above 1200 °C, 500-800 °C and less than 500 °C, respectively. As the synthesis temperature is 500 °C, these trends in critical temperatures make it impossible to metastabilize europium in MgO with x > 0.01. Doping is evident from X-ray diffraction data, excitation spectra, high resolution emission spectra, and luminescence lifetimes. A characteristic strong red emission of Eu(3+) has been observed via energy transfer from the MgO matrix to Eu(3+). Density functional theory based simulations suggest stabilization of Eu(3+) in MgO at lower doping concentration through the formation of cation vacancies which is also evident from optical studies. Furthermore, thin films deposited using the e-beam evaporation technique from the Mg(1-x)Eu(x)O:(x/2)V"(Mg) (x = 0.005) system show UV sensitized emission with CIE coordinates (0.26, 0.21).
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