Carbon quantum dot-sensitized and tunable luminescence of Ca19Mg2(PO4)14:Ln3+ (Ln3+ = Eu3+ and/or Tb3+) nanocrystalline phosphors with abundant colors via a sol–gel process

Abstract

Herein, we demonstrate the characteristic blue luminescence of carbon quantum dots embedded in the Ca₁₉Mg₂(PO₄)₁₄ nanocrystalline phosphor and carbon quantum dot-sensitized luminescence of Ca₁₉Mg₂(PO₄)₁₄:Ln³⁺ (Ln³⁺ = Eu³⁺ and/or Tb³⁺) nanocrystalline phosphors with abundant colors. A series of Ca₁₉Mg₂(PO₄)₁₄ and Ca₁₉Mg₂(PO₄)₁₄:Ln³⁺ (Ln³⁺ = Eu³⁺ and/or Tb³⁺) nanocrystalline phosphors was prepared via a Pechini-type sol–gel process. With UV light excitation, the prepared Ca₁₉Mg₂(PO₄)₁₄ nanocrystalline phosphors exhibited novel blue luminescence with a broad band from 374 to 600 nm peaking at 439 nm, which is ascribed to the embedded carbon quantum dots. Also, the obtained Ca₁₉Mg₂(PO₄)₁₄:Ln³⁺ (Ln³⁺ = Eu³⁺ and/or Tb³⁺) nanocrystalline phosphors not only exhibited the characteristic broad band emission of the carbon quantum dots, but also the characteristic narrow line emission of the doped rare earth ions, i.e., the characteristic red emission of Eu³⁺ (⁵D_J → ⁷F_J′ transitions, J, J′ = 0, 1, 2, 3) and the characteristic green emission of Tb³⁺ (⁵D₄ → ⁷F_J transitions, J = 3, 4, 5, 6). Thus, energy transfer occurred from the carbon quantum dots to the doped Eu³⁺ and/or Tb³⁺ ions in the Ca₁₉Mg₂(PO₄)₁₄:Ln³⁺ (Ln³⁺ = Eu³⁺ and/or Tb³⁺) nanocrystalline phosphors. The luminescence color of the Ca₁₉Mg₂(PO₄)₁₄:Ln³⁺ (Ln³⁺ = Eu³⁺ and/or Tb³⁺) nanocrystalline phosphors could be tuned from blue to blue-green, green, white, pink, orange, red, etc. by changing the doping rare-earth ion concentration, species, and relative ratio of Eu³⁺ to Tb³⁺ ions. Furthermore, single-phase white-light luminescence was demonstrated in the Eu³⁺/Tb³⁺ codoped Ca₁₉Mg₂(PO₄)₁₄:Ln³⁺ nanocrystalline phosphors. Finally, the luminescence properties and mechanisms of the Ca₁₉Mg₂(PO₄)₁₄ and Ca₁₉Mg₂(PO₄)₁₄:Ln³⁺ (Ln³⁺ = Eu³⁺ and/or Tb³⁺) nanocrystalline phosphors were discussed.