Mn^(4+)在尖晶石和钙钛矿相关结构铝酸盐中的发光

Luminescence of Mn^(4+) Ions in Spinel Type and Perovskite-related Aluminates

Mn4+在MgAl2O4,ZnAl2O4和LiAl5O8等尖晶石结构中的发光呈现很大的差异。在LiAl5O8中,Mn4+的发射光谱由一个660nm线峰叠加在一个带谱上构成。前者是由于2E→4A2跃迁,后者可归于声子副带发射。跃迁具有中等的强度。而在MgAl2O4中Mn4+的发光很弱,在ZnAl2O4中几乎观察不到Mn4+的发射。这种差异是由于它们在微结构上的差异和组分元素的不同而引起的。钙钛矿相关结构稀土正铝酸盐LaAlO3和GdAlO3中,Mn4+离子发射分别呈现2个和3个线峰,位于深红色区间。这些线峰可归于2E→4A2跃迁和声子参与的发射。Mn4+的激发光谱均有两个带组成,一个在300nm附近的UV区,另一个位于500nm附近的可见区。前者为Mn4+→O2-的电荷迁移带,后者为Mn4+的4A2→4T2跃迁。Mn4+在LaAlO3和GdAlO3中的晶场强度参数Dq分别为2000cm-1和2040cm-1。

The luminescence of Mn4+ ions shows different features for MgAl2O4,ZnAl2O4 and LiAl5O8 which all have a spinel structure. In LiAl5O8, the emission spectrum of Mn4+ consists of a sharp line at 660nm overlapped on a broad band with maximum at 680nm. The former is assigned to the 2E→4A2 transition of Mn4+ and the latter is attributed to the vibronic side band. The emission of Mn4+ showed a higher intensity in LiAl5O8, and however, only a weak emission was observed in MgAl2O4 and almost no luminescence was recorded in ZnAl2O4. The differences in the intensity of the Mn4+ emissions for the three spinel compounds can be illustrated by the fact that the compounds have different microstructures and composition elements. In the perovskiterelated aluminates LaAlO3 and GdAlO3, The Mn4+ ions show 2 and 3 sharp emission lines, respectively, under 254nm excitation at room temperature. The Mn4+ emission peaks locate at 695 and 725nm for LaAlO3∶Mn,Ca and at 680, 700 and 715nm for GdAlO3∶Mn,Ca. These lines are assigned to the 2E→4A2 transition of Mn4+ ions and its phononcoupling transitions. Energies of the phonons associated with the 2E→4A2 transition have been estimated. Both the excitation spectra of Mn4+ in LaAlO3∶Mn,Ca and GdAlO3∶Mn,Ca show two broad bands. One locates at about 300nm and the other at about 500nm. The strong band at about 300nm is assigned to the O2-→Mn4+ chargetransfer band and the weaker band at about 500nm is due to the 4A2→4T2 transition of Mn4+. The 4A2→4T1 absorption transition is almost hidden under the chargetransfer band and exhibits only a little peak or shoulder at about 330nm. From the energy of the 4A2→4T2 transition we estimate crystal field parameter Dq to be equal to 2 000cm-1 for LaAlO3∶Mn,Ca and 2 040cm-1 for GdAlO3∶Mn,Ca.