Compositional variations in optical characteristics of Mn doped spinel crystals

- Crystals were grown with various compositions and O2 concentrations.
- Colors of Mn doped spinel vary with compositions and O2 concentrations.
- Absorption and photoluminescence vary with composition and O2 concentrations.

Mn doped spinel (MgAl2O4) crystals have been grown by floating zone (FZ) techniques with various conditions of O2 concentrations in the growth atmosphere from 0 to 75 vol%, with a starting composition of molar ratio x=MgO/(MgO+Al2O3) from 0.3 to 1.0 and/or Mn concentrations from 1.0 to 6.0 at%. Optical absorption spectra and photoluminescence spectra were evaluated using crystals grown under various growth conditions. The color of the crystals is found to vary with their composition and the O2 concentration in the atmosphere. Crystals grown under a 100 vol% Ar atmosphere, were a pale green color and emitted a strong green luminescence at λ=520 nm. Colors of stoichiometric crystals, x=1.0, and Mg-poor crystals grown under an oxidizing atmosphere are yellow and red, respectively. Both optical absorption spectra and photoluminescence spectra of Mg-poor, x<1.0 crystals grown under an oxidizing (O2-Ar) atmosphere are found to vary greatly from those of the stoichiometric crystals.