Spectroscopic investigation of CaAl₁₂O₁₉:M ³⁺ upon UV/vacuum-UV excitation: A comparison with SrAl ₁₂O₁₉: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 750nm of CaAl₁₂O ₁₉: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 ¹S ₀ state followed by visible photons from the ³P ₀ state are both observed in (Ca,Sr)Al₁₂O ₁₉:Pr³⁺. Similar to SrAl₁₂O₁₉:M ³⁺, there exist desirable spectral overlaps between Pr^{3+ 1}S₀ emissions and the Cr³⁺ higher multiplet absorptions in CaAl₁₂O₁₉, which should be favourable to the energy transfer from Pr^{3+ 1}S₀ to Cr ³⁺, converting the UV photon from Pr^{3+ 1}S ₀ 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.