Red-emitting Sr2MgGe2O7:Mn4+ phosphors: Structure, luminescence properties, and application in warm white light emitting diodes

To achieve efficient phosphors that address the shortage of red emission for use in white light emitting diodes (WLED), a series of red-emitting phosphors of Sr2MgGe2O7 doped with different concentrations of Mn4+ have been successfully fabricated by a high-temperature solid-state method. The crystal structure properties including the phase purity were analysed by X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). Absolute quantum yield, temperature stability, and lifetime were utilized to characterize the samples. Furthermore, the excitation spectra of the samples exhibit two broad absorption bands with peaks located at approximately 308 nm and 419 nm, which could be excited by near-UV/blue LED light. The emission spectra range from 600 nm to 700 nm and exhibited a sharp peak at 659 nm due to the 4E→4A2 spin- and parity-forbidden transition of Mn4+. The optimal Mn4+ doping concentration in the Sr2MgGe2O7 host is determined to be 0.7%. The critical energy transfer distance of these phosphors is calculated to be about 26.61 Å, and the concentration quenching mechanism is proved to correspond to a dipole-dipole interaction. The luminescence of the Sr2MgGe2O7:Mn4+ phosphors decrease gradually with increasing temperature, and the Sr2MgGe2O7:Mn4+ sample exhibits better thermal stability than the commercial Sr2Si5N8:Eu2+ red phosphors. The warm WLED is fabricated by combining the Sr2MgGe2O7:0.7%Mn4+ and YAG:Ce3+ phosphor with a 420-nm blue LED chip to explore its possible applications in warm WLED.