Synthesis, Characterization, Photoluminescence Properties of Rare-Earth Free Activated Sr2GeO4 for Lighting Applications.

Abstract

Strontium orthogermanate (Sr₂GeO₄) doped with Mn⁴⁺ and Cu²⁺ phosphors were prepared by high temperature solid state reaction. All the prepared phosphors were crystallized in the orthorhombic lattice with space group Pbn2₁. The surface morphology of prepared phosphors contains irregular shaped objects with considerable agglomeration. The FT-IR and Raman profiles of the compositions gave characteristic bands belonging to GeO₄^4- tetrahedra. Photoluminescence profiles of Sr₂GeO₄: Mn⁴⁺ compounds are characterized by red emission at 647 nm upon excitation at 433 nm, while Sr₂GeO₄: Cu²⁺ compositions gave orange emission at 603 nm under excitation at 403 nm. The emission mechanism of Sr₂GeO₄: Mn⁴⁺ was explained by Tanabe-Sugano energy level diagram of Mn⁴⁺ ion. The CIE chromaticity coordinates, color purity (CP) and correlated color temperature (CCT) values were deduced. Thermoluminescence profiles are characterized and trap depth parameters were evaluated. These compositions may be useful in the manufacturing of cool and warm solid state lighting sources.