Abstract :
Summary form only given. The optical and related properties (i.e. luminescence, photoluminescence excitation, resonance Raman excitation profiles etc) of some natural three- and lower-dimensional semiconductor Systems are briefly reviewed and some new results are reported. The following kinds of systems are investigated. 1) 3-D systems: Compounds of the formula (CH/sub 3/NH/sub 3/)MX/sub 3/ (where M=Pb, Sn, Ge; X=Cl, Br, I). These have a cubic perovskite structure and some of them are 3-D semiconductors. 2) 2-D systems: Compounds of the formula (C/sub n//H/sub 2n+1/NH/sub 3/)/sub 2/MX/su 4/ and compounds of the formula (CH/su 3/NH/sub 3/) (C/sub n/H/sub 2n+1/NH/sub 3/)M/sub 2/X/sub 7/ have a perovskite structure and are 2-D semiconductors. 3) I-D systems: Compounds of the formula M(L-L)/sub 2/M(L-L) )/sub 2/X)/sub 2/(C1O)/sub 4/))/sub 2/ (where M=Pt, Pd, Ni; L-L=di-amine; X=Cl, Br, 1) show I-D semiconductor behaviour. 0-D systems: Small particles of CdS and similar compounds as well as compounds of the formula (NMe)/sub 4/))/sub 8/M)/sub 20/X)/sub 13/(Spli)/sub 22/ (M=Cd, Zn; X=S and /or Se) show 0-D semiconductor behaviour (quantum dots). In all cases, the excitonic or charge transfer (absorption) and luminescence) bands in the visible-near infrared is the common feature of these systems. In some cases, a blue shift of the bands has been observed by decreasing the dimensionality.
