Synthesis and VUV Spectral Properties of Red-Emitting K2Gd0.97Zr (PO4)3:3mol%Eu3+ Phosphor via Down-Conversion

K2Gd0.97Zr (PO4)3:3mol% Eu3+ were prepared by the solid-state diffusion method and under a vacuum ultra-violet (VUV) region, photoluminescence properties of the phosphor were examined. The phenomenon of visible quantum harvesting via DC was observed in synthesized phosphor for the Gd3+–Eu3+ pair. In the process of quantum harvesting, the two visible light photons are emitted per absorbed VUV photon. This phenomenon occurred upon the 190 nm excitation of Gd3+ at the 6GJ level through a two-step energy transfer from Gd3+ to Eu3+ by cross-relaxation and sequential transfer of the remaining excitation energy. The consequences are that the quantum efficiency of the K2Gd0.97Zr (PO4)3:3mol% Eu3+ phosphor in the energy transfer process from Gd3+ to Eu3+ could reach 233%. The quantum efficiency goes to more than 200% (i.e., 233%) at just low concentration Eu3+ ions (i.e. 3% only). This novelty was found in the prepared phosphor. Therefore, the phosphor K2Gd0.97Zr (PO4)3:3mol% Eu3+ was a potential quantum harvester and potential candidate for mercury free fluorescent lamp and plasma display panel.