Visible quantum cutting through downconversion in GdPO4:Tb and Sr3Gd(PO4)3:Tb

Visible quantum cutting has been observed in GdPO₄:Tb³⁺ upon Tb³⁺ 4f⁸–4f⁷5d¹ excitation and host excitation, and in Sr₃Gd(PO₄)₃:Tb³⁺ upon Tb³⁺ 4f⁸–4f⁷5d¹ excitation. In the quantum cutting process, Tb³⁺ acts as a quantum cutter, which converts one short wavelength ultraviolet photon or one vacuum ultraviolet photon into more than one visible photon. The quantum cutting involves a cross-relaxation process between two neighboring Tb³⁺ and direct energy transfer between Tb³⁺ and Tb³⁺ or Tb³⁺ and Gd³⁺, depending on the excitation wavelength. The quantum efficiency variation of GdPO₄:xTb³⁺ and Sr₃Gd(PO₄)₃:xTb³⁺ shows a growing trend with increasing of Tb³⁺ content from x=1.5% to 13%.