Pradeesh Kannan

Surface plasmon coupled emission molds the flow of optical energy and, hence, it is feasible to alter the spatial distribution of emission and customize the optical ambience around fluorophores by integrating them into plasmonic or photonic structures. Our current study examines such spatial distribution of emission from metal–dielectric–metal planar cavities. In addition to photonic emission and enhanced plasmonic emission, we observed photon–plasmon hybrid emission from these structures. With this hybrid emission, angular emission patterns specific to particular applications can be achieved by flexibly altering the design parameters of the plasmonic or photonic substrates. We envision that being able to regulate and tune the emitted light at the nanoscale will facilitate the advancement of a new generation of fluorescence-based sensors, instruments, and other emission-based devices.

The potential advantages of wavelength scanned surface Plasmon resonance (WS-SPR) technique over angle scanned surface plasmon resonance (AS-SPR) was investigated in Kretschmann-Raether (KR) configuration. While AS-SPR technique employs angular interrogation mode for resonance detection, WS-SPR is based on wavelength interrogation mode. Wavelength scanning can very well be performed using compact spectrometer without any mechanical movement making this method more convenient and error free for real time sensing. SPR sensitivities were compared by employing a simulated salt solution environment to the metal surface with a refractive index variation from 1.350 to 1.355. One to two orders of sensitivity enhancement could be obtained using motionless WS-SPR as compared to AS-SPR.

Emission of fluorescein dye is directionally controlled and enhanced by combining it with surface plasmons of silver films. Emission directionality will boost the sensitivity of fluorescence-based technology especially in optical biosensing.

Cu₂ZnSnS₄ (CZTS) with its high absorption coefficient, optimal band gap, and non-toxic, earth-abundant elemental constituents is a promising absorber material for low cost and high-performance photovoltaics. CZTS nanocrystals were prepared by microwave-assisted thermolysis method using ethylene glycol solvent in a rapid and energy efficient process with and without oleylamine as additional capping agent. X-ray diffraction data indicated crystallite sizes of 5 and 12 nm respectively. Raman spectra showed the formation of pure Cu₂ZnSnS₄ phase in both cases. With pure ethylene glycol solvent, field emission scanning electron microscopy images showed particle sizes around 250 nm, ultraviolet-visible absorption data gave optical band gap of 1.52 eV and Hall measurements yielded electrical resistivity ~70 Ωcm, carrier density ~2.7 × 10¹⁶/cm³, and hole mobility ~3.24 cm²/Vs. Adding optimum amount of oleylamine reduced the particle size to 100 nm and lower. The optical band gap reduced to 1.48 eV and electrical resistivity, carrier concentration, and Hall mobility changed to ~5.9 × 10⁴ Ωcm, 2.57 × 10¹²/cm³, and 4.1 cm²/Vs respectively. A knee voltage of ~0.8 V shown by CZTS/CdS p-n junction indicated that a good V_oc can be expected from a solar cell constructed with the CZTS nanocrystals as absorber layer.