POLARIZED ELECTRONIC-SPECTRA OF THE (CH3NH3)(2)CD1-XMNXCL4 (X=0-1) PEROVSKITE LAYER WITH CU2- STUDY OF THE CL--]CU2+ CHARGE-TRANSFER INTENSITY ENHANCEMENT ALONG THE SERIES( )

The polarized optical absorption spectra of the 2-D A(2)Cd(1-x)Mn(x)Cl (4) (x = 0-1; A = CH3NH3) crystals doped with Cu2+ investigated. The a nalysis of both the charge transfer and crystal field spectra indicate s that the copper impurities form CuCl64- complexes with an elongated D-2h (nearly D-4h) symmetry. A salient feature is the enhancement of c harge transfer band intensity as well as the presence of new intense b ands at 21000 and 25000 cm(-1) observed on passing from x = 0 to x = 1 along the series. These bands are associated with Mn-Cu aggregates wh ose superexchange pathways involve the short (equatorial) Cu-Cl bond ( 25000 cm(-1)) and the long (axial) Cu-Cl bond (21000 cm(-1)) of the Cu Cl64- complex. A noteworthy fact of these exchange coupled Mn-Cu syste ms is that the transition energy of the first Mn2+ excitations are res onant with the Cl- --> Cu2+ charge transfer transitions. This effect s eems to play a fundamental role in the enhancement of intensity. The t emperature dependence of the oscillator strength allowed us to estimat e a ground state exchange constant J approximate to 70 cm(-1) for the Mn-Cu pair. The results are compared with those obtained in Mn-Cu aggr egates in fluorides.