Showing papers by "Chandran Sudakar published in 2016"

Synthesis of Cu-Deficient and Zn-Graded Cu–In–Zn–S Quantum Dots and Hybrid Inorganic–Organic Nanophosphor Composite for White Light Emission

Abstract: Cu-deficient graded-zinc Cu-In-Zn-S (CIZS) quantum dots (QDs) were synthesized by a two-step solvothermal method. These CIZS QDs exhibited size and composition tunable photoluminescence characteristics with emission color tunable from greenish-yellow to orange to red with a relatively high quantum yield between 45 and 60%. Novel white-light-emitting (WLE) hybrid composite is fabricated by integrating the blue-emissive 1,4-bis-2-(5-phenyl oxazolyl)-benzene (POPOP) organic fluorophore and quaternary CIZS inorganic QDs. Integrating CIZS QDs with POPOP fluorophore resulted in series of tunable emission colors with CIE coordinates lying in a straight line between the coordinates of the end member. WLE was shown for hybrid mixture comprising 0.5 nM of POPOP and 3 mg/mL of CIZS QDs with color coordinates (0.3312, 0.3324). Thin films of this hybrid mixture in PMMA matrix coated on UV-LED or on glass substrates with UV backlit light also showed broadband WLE with ideal CIE color coordinates of (0.34, 0.33), high color-rendering index value of 92, and correlated color temperature value of 5143 K. The hybrid composite exhibit Forster resonance energy transfer cascading from POPOP to CIZS which results in emission covering the entire visible spectral range. POPOP and CIZS QDs hybrid composite is a versatile material for WLED applications.

High-rate capability of bamboo-like single crystalline LiFePO4 nanotubes with an easy access to b-axis 1D channels of olivine structure

Abstract: Surfactant aided sol–gel method is used to fabricate highly crystalline carbon-coated LiFePO4 (LFP) in two contrasting microstructural forms: (i) nanoparticulate crystallites (LFP-NP), and (ii). bamboo-like single crystalline nanotubes (LFP-NT) obtained using template-assisted method. LFP-NT exhibit a high specific capacity (∼165 mA h g−1 at 1C-rate) and superior rate capability with reversible capacity of ∼100 mA h g−1 (∼60 mA h g−1) at a current rate of 10C (25C) with almost 100% capacity retention after 1000 cycles, whereas, LFP-NP exhibit poor capacity retention even at low C-rates (<10 mA h g−1 at 5C-rate). Although shortened pathways for Li transport exist in both the microstructures, the key point to achieve high-rate capability in LFP system is to facilitate easy access to the entry points of 1D channels running along b-axis of olivine structure. The curved cylindrical surfaces of bamboo-like nanotubes have a large proportion of these entry points. The nanoparticles have limited access to these entry points due to agglomeration, therefore exhibiting poor capacity retention at high C-rates. Fabricating LFP with microstructural-openness with a large number of accessible 1D-channel entry points on the surface of LFP is crucial for achieving high-rate capability cathode.