Down-shifting and down-conversion emission properties of novel CdO–P₂O₅ invert glasses activated with Pr³⁺ and Pr³⁺/Yb³⁺ for photonic applications

The down-shifting and down-conversion emission properties of novel CdO–P₂O₅ invert glasses activated with Pr³⁺ and Pr³⁺/Yb³⁺ were respectively studied. The down-shifting emission spectra of Pr₆O₁₁ singly doped glasses upon 443 nm excitation (Pr³⁺: ³H₄ → ³P₂), displayed the feature Pr³⁺ transitions in the visible and near-infrared (NIR) regions, reaching the optimum intensity at 0.7 and 0.3 mol% of Pr₆O₁₁, respectively. The emission tonality can be adjusted from the reddish-orange to orange-pink region, depending on the Pr₆O₁₁ content. Such fact coupled with the superposition of the blue light excitation might be attractive for white light-emitting diodes (W-LEDs) applications. The cross-relaxation processes involved between Pr³⁺-Pr³⁺ pairs seem to be mediated by an electric quadrupole-quadrupole interaction, as revealed by the Inokuti-Hirayama model. The emission spectra of the Pr₆O₁₁ and Yb₂O₃ doped glasses upon 443 nm excitation showed, in addition to the Pr³⁺ related transitions, a band at 977 nm associated with the Yb³⁺: ²F_5/2 → ²F_7/2 transition, which gradually grows at expenses of non-radiative energy transfer from Pr³⁺. This process might lead to a down-conversion (quantum cutting) emission with theoretical quantum efficiencies up to 144%. Analysis complemented by the Inokuti-Hirayama or Dexter model revealed that the non-radiative Pr³⁺ → Yb³⁺ energy transfer process arisen from Pr³⁺: ³P₀ and ¹D₂ levels are most likely dominated by electric dipole-dipole and quadrupole-quadrupole interactions, respectively. The global emission properties suggest that the Pr³⁺ and Pr³⁺/Yb³⁺ activated CdO–P₂O₅ invert glasses might be interesting for WLEDs and crystalline silicon (c-Si) solar cell applications.