Effectively Leveraging Solar Energy through Persistent Dual Red Phosphorescence: Preparation, Characterization, and Density Functional Theory Study of Ca2Zn4Ti16O38:Pr3+

To effectively leverage and convert cheap, abundant, and environmentally friendly solar energy is still an unaccomplished endeavor. In this work, we prepare and characterize the long-lasting red-light-emitting, single-phase Ca2Zn4Ti16O38 phosphor by the sol−gel method with nonstoichiometry or addition of H3BO3 as flux. Excitation and emission mechanisms are proposed and supported by the computational results from density functional theory. Phase identification of powders was performed by X-ray powder diffraction analysis, confirming the existence of single-phase Ca2Zn4Ti16O38 crystals in samples of every series. Unit cell parameters of the crystal were subsequently determined, together with its excitation spectra in the blue-green region with the maximum peak at 474 nm monitored by 644 nm light. The corresponding emission spectra showed a wide emission range with two narrow bands at 614 nm (1D2 → 3H4) and 644 nm (3P0 → 3F2) after the addition of H3BO3. If excited at 474 nm, the phosphor displays a superlong afterglow with the emission peak at 614 nm, enabling it to be a novel persistent red long phosphor for visible-light conversion. Luminescent properties of the phosphor were thoroughly examined. The mechanism of the dual persistence phosphorescence originated at 614 and 644 nm wavelengths induced by two separate kinds of doping defects was proposed. Density functional theory calculations under the periodic boundary condition provide insights about their excitation, emission, and long-lasting phosphorescence mechanisms.