Luminescence centers in low-dimensional layered cadmium iodide crystals and nanostructures

It has been established that dominant luminescence centers both in layered CdJ
₂
crystals and related to them nanostructures are associated donor-acceptor complexes of intrinsic point defects within the cation vacancy and interstitial cadmium. Layered structure results in two different types of such intrinsic donor-acceptor pairs with different spatial orientation: “cation vacancy - interstitial cadmium in the structural layer” and “cation vacancy-interstitial cadmium between the layers”. The reasons of Cd
_i
^o
-V V
_cd
- - Cd
_i
⁺
complexes creation are discussed and the result of their existence are proved in the appearance of a selective band around 3.23 eV in the region of fundamental absorption edge at low temperatures. An increase of the width of forbidden gap width occurs in thin CdJ
₂
films and nanostructures related to them. In the spectra of luminescent emission for the states 5p
_z
J →5s Cd (maximum at 315 nm) and 5p
_x,y
→ 5s Cd (maximum at 325 nm) an indirect band transition of exciton mechanism changes to direct one and so a discrete transition takes place.