Spectroscopic investigation of CaAl12O19:M3+upon UV/vacuum–UV excitation: a comparison with SrAl12O19:M3+(M = Pr,Cr)

In order to evaluate the possibility of using Cr³⁺ co-doping to modify the emission properties of Pr³⁺-based quantum cutting phosphors, which emit one ultraviolet (UV) and one visible photon from each vacuum-UV photon absorbed, into phosphors that emit two visible photons, the optical spectroscopies between 150 and 750 nm of CaAl₁₂O₁₉:M³⁺ (M = Pr,Cr) were investigated and compared with those of SrAl₁₂O₁₉:M³⁺ using synchrotron radiation as one of the excitation sources. When Pr³⁺ is excited to its 4f5d states, cascade emission of UV photons from the ¹S₀ state followed by visible photons from the ³P₀ state are both observed in (Ca,Sr)Al₁₂O₁₉:Pr³⁺. Similar to SrAl₁₂O₁₉:M³⁺, there exist desirable spectral overlaps between Pr³⁺ ¹S₀ emissions and the Cr³⁺ higher multiplet absorptions in CaAl₁₂O₁₉, which should be favourable to the energy transfer from Pr³⁺ ¹S₀ to Cr³⁺, converting the UV photon from Pr³⁺ ¹S₀ into the red Cr³⁺ emission. However, the host absorption band and the Cr³⁺-related charge transfer band have an unfavourable overlap with the Pr³⁺ 4f5d states in the vacuum-UV region, preventing efficient selective Pr³⁺ excitation under radiation of Xe discharge, a prerequisite for the quantum cutting process.