Efficient Nd3+ sensitized Yb3+ emission and infrared-to-visible energy conversion in gallium nano-garnets

Abstract

Nanocrystalline RE₃Ga₅O₁₂ (RE = Gd, Y and Lu) garnets co-doped with 1 mol% of Nd³⁺ and 10 mol% of Yb³⁺ ions have been synthesized via a sol–gel method and their structural and luminescence properties studied. Upon laser excitation at 805 nm, an intense near-infrared emission from Yb³⁺ ions at 1025 nm is observed, which is due to efficient Nd³⁺ → Yb³⁺ energy transfer with a probability of about 90%. Lifetimes of the ⁴G_7/2 and the ⁴F_3/2 emitting levels of Nd³⁺ ions and the ²F_5/2 excited level of Yb³⁺ ions have been evaluated upon pulsed laser excitations. The non-exponential nature of the decay curves has been studied to understand the multipolar interaction between Nd³⁺ and/or Yb³⁺ ions using the Inokuti–Hirayama model. Moreover, under 970 nm laser excitation, green upconverted luminescence is observed in Nd³⁺–Yb³⁺ co-doped RE₃Ga₅O₁₂ nano-garnets, which can be related to both phonon-assisted excited-state absorption and energy transfer upconversion mechanisms. The results show that the as-synthesized nano-garnets could be useful for infrared detectors, solar energy converters and green phosphor applications.