FTIR Spectra of Ni (H-dmg)2 Hydrogen Bonded With Six Dyes

Here the one-dimensional semiconductor namely bis (dimethyiglyoximato) Ni is hydrogen bonded with 6 highly polarizable dyes which are Para red, Congo red, Direct red, Bismark brown, Evans blue and Trypan blue. The hydrogen bonding was verified with FTIR spectroscopy. FTIR specra also reveal modification of absorption edges by exciton-phonon coupling there are threshold energies for the formation of free excitons and electron-hole pairs with phonon emissions in the intrinsic absorption edge spectrum. The remainder absorption at the value of the band gap is proportional to the exciton ionization energy in both direct and indirect excitons. This remainder absorption increases with the increase in the number of phonon bands in the absorption edge.


EXPERIMENTAL DETAILS :
Ni(Hdmg) 2 was prepared by standard method using NiCl 2 -6H 2 O and dimethylglyoxime (6) as red precipitates. 6 dyes which are Congo red, Para red, Bismark brown, Direct red, Trypan blue and Evans blue were obtained from Aldrich chemical in pure forms. Ni(Hdmg) 2 and dyes were mixed in 1:4 proportions and grinded in agate mortar with pastle till color changed and till fine homogeneous poweders were formed. The mixture were again grinded after mixing them firther with dry spectrograde KBr powder. Round palates were prepared by compressing the powders in a die with manually operated compressing machine.
The semitransparent palates were placed in spectrophotometer's dark chamber.
The spectra in the range 400-4000 cm -1 were recorded using a GXFTIR single beam spectrophotometer manufactured by Perkin Elmer company in USA. It was having a resolution of 0.15 cm -1 , a scan range of 15600-30 cm -1 , a scan time of 20 scan sec -1 , and OPD velocity of 0-20 cm sec -1 . MIRTGS and FIRTGS detectors were used. A beam splitter of opt KBr type was used IJTSRD | Jan-Feb 2017 Available Online@www.ijtsrd.com having a range of 7800-370 cm -1 .The spectra were recorded in purge mode.

RESULTS AND DISCUSSION :
The molecular structures of Ni(Hdmg) 2  The intrinsic absorption edge spectrum above 1700 cm -1 is analyzed by plotting (αhν) 2 , (αhν) 1/2 , (αhν) 1/3 , (αhν) 2/3 vs hν and finding the best fit. (αhν) 1/3 vs hν was found to be the best fit indicating (αhν)=A(hν-E g ) 3 corresponding to forbidden indirect transition in all complexes except the Trypan blue complexes. In Ni(Hdmg) 2 -Trypan blue, (αhν)=A(hν-E g ) 1/2 an allowed direct transition was found to be the best fit. These best fits are shown The excitonic threshold energies are observed in GaP (4,6), SiC (7) and CdTe (8) and absorption edges were found to be modified by exciton-phonon coupling. This coupling for direct excitons is discussed (8). Every atomic system has an infinite set of discrete energy levels corresponding to finite motion of the electron. When the potential energy of the ineraction is normalized to be zero at infinity, the total energy of the electron is negative. For positive values of energy the electron is not bound to the ion and is moving freely. The energy spectrum of free motion is continuous. Overlapping transitions into discrete and continuous regions of the energy spectrum prevent the absorption coefficient from turning zero when ћω=∆E 0 (E g ).The absorption spectrum of direct allowed interband transition is givern by For ћw→∆E 0 we obtain i.e. the greater the exciton ionization energy E 1 e* the greater is α at ∆E 0 (E g ) . For  (1) and (2)  Where ћw is the photon energy and E G and E 0 are temperaturedependent fitting parameters. E 0 is the width of the tail. E G is comparable to the band gap energy. E 0 is given by and it is in the range 10-100 meV for amorphous semiconductors. E G and E 0 scales almost linearly. E G dereases as E 0 increases. There is a linear scaling relation ( Figure 6). This is also supported by theory (10).
The theory for indirect excitons coupled with phonons is also developed. The remainder absorption coefficient at E=E G IJTSRD | Jan-Feb 2017 Available Online@www.ijtsrd.com remains finite and is proportional to the ionization energy of the exciton. Here the remainder absorption in percerntage is plotted vs no. of phonon bands and vs band gap in eV ( Figure 7).
As band gap increases, the remainder absorption at hν=E g decreases. When exciton-phonon coupling is strong, the remainder absorption at E g is more. Since the remainder absorption at E g is proportional to the ionization energy of exciton, this shows that the excitons with more ionization energy are strongly bound to phonons. Band gap is less when the exciton ionization energy is more.