Comprehensive investigations of near infrared downshift and upconversion luminescence mechanisms in Yb3+ single-doped and Er3+,Yb3+ co-doped SiO2 inverse opals

Abstract

Comprehensive investigations of near infrared (NIR) downshift and visible upconversion luminescence (UCL) mechanisms were carried out for Yb³⁺ single-doped and Er³⁺,Yb³⁺ co-doped SiO₂ inverse opals under excitation at 256, 378, 520 and 980 nm. NIR emission at 976 nm from the Yb³⁺–O²⁻ charge transfer state and UCL emission at 500 nm due to the cooperative emission of two Yb³⁺ ions were observed in SiO₂:Yb³⁺ inverse opal upon excitation at 256 and 980 nm, respectively. The cooperative UCL of two Yb³⁺ ions was suppressed due to the photon trap created by the photonic band gap. For the SiO₂:Er³⁺,Yb³⁺ inverse opals, NIR emission of Yb³⁺ at 976 nm and of Er³⁺ at 1534 nm were observed upon excitation at 256, 378 and 520 nm, respectively. Upon excitation at 378 and 520 nm, the 976 nm NIR emission of Yb³⁺ does not arise from (²H_11/2/⁴S_3/2) + 2Yb³⁺(²F_7/2) → Er³⁺(⁴I_15/2) + 2Yb³⁺(²F_5/2) traditional quantum cutting. The NIR emission of Yb³⁺ at 976 nm may be due to the Er³⁺(²H_11/2) + Yb³⁺(²F_7/2) → Yb³⁺(²F_5/2) + Er³⁺(⁴I_11/2) cross-relaxation energy transfer process upon excitation at 520 nm. The NIR emission of Yb³⁺ at 976 nm may arise from the cross-relaxation energy transfer of Er³⁺(⁴G_11/2) + Yb³⁺(²F_7/2) → Yb³⁺(²F_5/2) + Er³⁺(⁴F_9/2) and Er³⁺(⁴F_9/2) + Yb³⁺(²F_7/2) → Yb³⁺(²F_5/2) + Er³⁺(⁴I_13/2) upon excitation at 378 nm.