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

Abstract

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.

Optical properties of Pr and Eu-doped SrAl12O19: A theoretical study

“…This paper has presented a computational study of defect and optical properties in 220 [25] 215 [27] 214.0(t) [22] 214.1(e) [22] 253.4 [29] 254 [27] 253 [28] 250.5(t) [22] 250.5(e) [22] 273.6 [28] 276.6 [25] 275 [27] 273.6 [28] 270.9(t) [22] 271.0(e) [22] 343.4 [28] 333.5(t) [22] 333.0(e) [22] 1 S 0 → 3 P 0 383.8 382.6(t) [22] 382.6(e) [22] 1 S 0 → 1 I 6 390.8 402 [29] 404 [25] 403 [26] 402(e) [27] 406.3(e) [28] 390.8(t) [22] 390.9(e) [22] 1 S 0 → 3 P 1 392.4 392.9(t) [22] 392.9(e) [22] 1 S 0 → 1 I 6 395.0 396.0(t) [22] 395.5(e) [22] 1 S 0 → 3 P 2 412.9 411.6(t) [22] 411.3(e) [22] …”

Pr3+ 1S0→Cr3+ energy transfer and ESR investigation in Pr3+ and Cr3+ activated SrAl12O19 quantum cutting phosphor

“…[30]) replace trivalent Al ions (67.5 pm, 6-coord.) instead of the divalent and considerably large Sr ions ($132 pm) in the host [25].…”

“…unit cell. Besides the ESR spectra, according to ligand field theory [41], the spectral properties of the energy states of Cr 3+ in SAO also indicate that the Cr 3+ ions enter Al 3+ sites with octahedral symmetry [25]. Anyway, the two tetrahedral sites of the M.P.…”

“…unit cell should be excluded first. Although there are three possible octahedral Al 3+ sites in the host lattice, only one site of Cr 3+ emission is observed [25]. Among the three sixfold-coordinated Al sites, the Al1(2a) site (regular octahedron) must be discarded because it is too regular to be accountable for the high Cr 3+ D value [40].…”

“…An appropriate codopant which can convert this first step photon to proper visible photon through energy transfer (ET) could be a solution for this situation. Many codopants, such as Sm 3+ [13,14], Eu 3+ [13][14][15], Gd 3+ [16], Dy 3+ [13,14], Er 3+ [13,14,17], Yb 3+ [13][14][15], Mn 2+ [13,14,[18][19][20][21][22][23], Cr 3+ [24,25], etc, have been tried in various matrixes, in which the absorption of codopants have sufficient spectral overlaps with the near-UV emission of Pr 3+ (the prerequisite of the occurrence of ET [26]). However, in most co-doped materials, efficient ET cannot be observed.…”