N-lines in the luminescence spectra of Cr3+-doped spinels: IV. Excitation spectra

Excitation spectra (T = 75–300 K; λ_exc = 450–630 nm) which were measured for the R-lines of Cr³⁺-doped oxides (α-Al₂O₃, β-Ga₂O₃) and for different luminescence lines (R-lines, N-lines) of Cr³⁺-doped spinels (MgAl₂O₄, ZnAl₂O₄, ZnGa₂O₄) are reported. The excitation maxima observed for different luminescence lines of a given compound exhibit considerable differences: 530 nm ? λ^max_exc ? 565 nm for MgAl₂O₄; 530 nm ? λ^max_exc ? 580 nm for ZnAl₂O₄; 545 nm ? λ^max_exc 555 nm for ZnGa₂O₄. According to the interpretation of N-lines to arise from different classes of Cr³⁺ ion swith different short range orderd, the excitation maximum of one distinct line should entirely correspond to the transition Δ : ⁴T₂ ← ⁴A₂ of that Cr³⁺ class from which the line arises. By this method spectroscopic data about the different kinds of Cr³⁺ ions present in a given sample can, therefore, be obtained which are not available from absorption measurements. The experimetal data were found to be in agreement with the results of model calculations. Restrictions which limit the accuracy and relevance of the data are discussed.