N-lines in the luminescence spectra of Cr 3+ -doped spinels (I) identification of N-lines

Abstract

Low-temperature luminescence spectra ( T=75 K) which have been measured at various excitation wavelengths in the range 450 nm⩽λ exc ⩽650 nm are reported for the chromium-doped spinels MgAl 2O 4, ZnAl 2O 4, ZnGa 2O 4 and for chromium-doped samples with the general composition AB 2O 4 · xB 2O 3 (A=Mg,Zn; B=Al,Ga). It is shown that the measurement of luminescence spectra at various excitation wavelengths provides a very powerful and highly sensitive method for the detection and identification of lines which arise from different kinds of luminescence centers. By their differing intensity dependences on the excitation wavelength, a number of N-lines which must be due to different kinds of Cr 3+ ions with slightly different short-range order can be identified in the spectra of the three stoichiometric spinels at frequencies v(R 1)− v<250 cm −1 .