Comprehensive investigations of near infrared downshift and upconversion luminescence mechanisms in Yb 3+ single-doped and Er 3+ ,Yb 3+ co-doped SiO 2 inverse opals.

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 (2 H11/2 /4 S3/2 ) + 2Yb3+ (2 F7/2 ) → Er3+ (4 I15/2 ) + 2Yb3+ (2 F5/2 ) traditional quantum cutting. The NIR emission of Yb3+ at 976 nm may be due to the Er3+ (2 H11/2 ) + Yb3+ (2 F7/2 ) → Yb3+ (2 F5/2 ) + Er3+ (4 I11/2 ) 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+ (4 G11/2 ) + Yb3+ (2 F7/2 ) → Yb3+ (2 F5/2 ) + Er3+ (4 F9/2 ) and Er3+ (4 F9/2 ) + Yb3+ (2 F7/2 ) → Yb3+ (2 F5/2 ) + Er3+ (4 I13/2 ) upon excitation at 378 nm.