Multi-color luminescence evolution of SrGdAlO4:Ln3+ (Ln3+ = Eu3+ and/or Tb3+) nanocrystalline phosphors via a sol-gel process

Highlights: • The nanocrystalline phosphors were prepared by a regular sol-gel process. • The obtained nanocrystalline phosphors show a multi-color luminescence evolution. • A new single-phase white-light-emitting was realized in nanocrystalline phosphors. A series of rare-earth (Eu³⁺ and/or Tb³⁺) ions doped SrGdAlO₄ nanocrystalline phosphors have been synthesized via a Pechini-type sol-gel process. X-ray diffraction, field-emission scanning electron microscopy, transmission electron microscopy and fluorescence spectrophotometer were utilized to characterize the prepared phosphors. XRD reveals that the samples begin to crystallize at 900 °C and the pure SrGdAlO₄ can be obtained at 1000 °C. FE-SEM images indicate that the SrGdAlO₄:Ln³⁺ (Ln³⁺ = Tb³⁺ and/or Eu³⁺) samples consist of fine and spherical grains with size around 100–200 nm in diameter. Under the excitation of the near ultraviolet light, the prepared SrGdAlO₄:Ln³⁺ (Ln³⁺ = Eu³⁺ and/or Tb³⁺) phosphors show both the characteristic red emission of Eu³⁺ (⁵D_J→⁷F_J′ J, J′ = 0, 1, 2, 3 transitions) and characteristic green emission of Tb³⁺ (⁵D₄→⁷F_6,5,4,3 transitions). There exists energy transfers from Gd³⁺ to Tb³⁺, and Tb³⁺ to Eu³⁺ ions in SrGdAlO₄:Ln³⁺ (Ln³⁺ = Eu³⁺ and/or Tb³⁺) phosphors. The luminescence color of SrGdAlO₄:Ln³⁺ (Ln³⁺ = Eu³⁺ and/or Tb³⁺) phosphors can be tuned from blue to blue-green, green, white, orange, etc. by varying the doping species, concentration, and relative ration of the codoping Eu³⁺/Tb³⁺ ions in SrGdAlO₄ host lattice to some extent. A single-phase white-light-emission has been realized in Tb³⁺/Eu³⁺ codoped SrGdAlO₄ nanocrystalline phosphors. The obtained SrGdAlO₄:Eu³⁺, SrGdAlO₄:Tb³⁺, and SrGdAlO₄:Eu³⁺,Tb³⁺ nanocrystalline phosphors have potential application in the areas of UV white-light-emitting diodes and other optoelectronics lighting and display devices.