Preparation of transparent suspensions of tunable-emission CaMoO4:(1−x)Eu3+,(x)Tb3+ nanophosphors

Abstract The synthesis of transparent suspensions of tunable-emission nanophosphors for application in transparent displays is scarcely investigated. We developed a new method for preparing transparent suspensions of CaMoO4:(1−x)Eu3+,(x)Tb3+ (x = 0, 0.50, 0.60, 0.70, 0.80, 0.90, 0.92, 0.94, 0.96, 0.98, and 1) nanophosphors. The CaMoO4:(1−x)Eu3+,(x)Tb3+ nanophosphors were prepared by reacting Ca-oleate (with Eu-oleate and/or Tb-oleate) complexes in hexane with an aqueous (NH4)6Mo7O24 solution via a solvothermal reaction in a hexane–water bilayer system. The Ca-oleate (with Eu-oleate and/or Tb-oleate) complexes were prepared by a phase-transfer reaction. TEM revealed slightly elongated spherical particles with a mean length and width of 9.5 ± 3.6 and 4.1 ± 1.2 nm, respectively. The hydrophobic CaMoO4:(1−x)Eu3+,(x)Tb3+ nanophosphors were soluble in nonpolar solvents because of the presence of long alkyl chains of the capping agents coating the outer surfaces of the nanophosphor particles. The photoluminescence emission spectra of the CaMoO4:Eu3+ and CaMoO4:Tb3+ nanophosphors exhibited intense peaks in the red (614 nm) and green (545 nm) regions, respectively; these emissions originated from the 5D0 → 7F2 transition of the Eu3+ ion and the 5D4 → 7F5 transition of the Tb3+ ion in the CaMoO4 host, respectively. The emission colors in the green–red spectral region could be finely tuned by adjusting the molar fraction of Tb3+ ions in the CaMoO4:(1−x)Eu3+,(x)Tb3+ nanophosphors.