Eu3+-doped SrGe4O9 red emitting phosphors: structural, luminescence properties, theoretical calculation and applications

Eu3+-doped germanate based red emitting phosphors SrGe4O9: xEu(3+) (0 <= x <= 0.5 mol%) were prepared by high-temperature solid-state procedure. Moreover, the Density Functional Theory (DFT) calculation, X-ray diffraction (XRD) Rietveld refinement, scanning electron microscopy (SEM), and photoluminescence (PL) measurement were discussed in detail to fully investigate the crystal structure and PL properties of SrGe4O9: xEu(3+). Furthermore, the Judd-Ofelt (J-O) analysis demonstrated that the Eu3+ ions in the SrGe4O9 host possessed lower sites symmetry. In addition, the phosphor SrGe4O9: 0.35%Eu3+ displayed superior thermal stability with PL intensity at 423 K is around 90% of its initial value at 298 K. As a result, the white light emitting diodes (WLED) device based on SrGe4O9: 0.35%Eu3+ achieved an expected result of a correlated color temperature (CCT) of 4573 K and a color rendering index (CRI) of 80.8 under a voltage of 3 V and a driven current of 20 mA.