RAJKUMAR

EDUCATION

Ph. D. Physics Madurai Kamaraj university, Madurai - 2011

M. Sc. Physics Madurai Kamaraj university, Madurai - 2006

B. Sc. Physics Vivekananda College, Madurai - 2004

RESEARCH INTERESTS

Synthesis and Characterization of Metal Oxide Semiconductor
Nanomaterials, Mataloxide, Raman Spectroscopy, Diluted Magnetic Semiconductors (DMS),
Gas Sensors, and Dye-Sensitized Solar Cells (DSSC)

Scopus Publications

Correction to: Room temperature ammonia gas sensor using Nd-doped SnO2 thin films and its characterization (Journal of Materials Science: Materials in Electronics, (2020), 31, 15, (12586-12594), 10.1007/s10854-020-03809-6)
S. Maheswari, M. Karunakaran, L. Bruno Chandrasekar, K. Kasirajan, N. Rajkumar
Journal of Materials Science Materials in Electronics, 2020
The original version of the article (https://doi.org/10.1007/s10854-020-03809-6) was unfortunately published with errors in Table 2 and Fig. 9a. These errors are corrected in this article. The corrected table and figure are given below.
Room temperature ammonia gas sensor using Nd-doped SnO2 thin films and its characterization
S. Maheswari, M. Karunakaran, L. Bruno Chandrasekar, K. Kasirajan, N. Rajkumar
Journal of Materials Science Materials in Electronics, 2020
Nd-doped SnO2 thin films are prepared by the nebulizer spray pyrolysis method. The compositional and morphological studies are discussed. The X-ray diffraction reveals that the films are polycrystalline in nature. The grain size increases as the doping concentration of Nd increases. The x-axis orientation of the films is enhanced by Nd doping. The intensity of the miller indices (200) is enhanced due to doping. In the Raman spectrum, the doping concentration-dependent intensity is observed. The quenching is observed in the photoluminescence spectrum. The transmittance and the band gap of films have been decreased due to doping. The 5 wt% Nd-doped film shows the maximum response to ammonia.
Direct Observation of Thermal Equilibrium of Excited Triplet States of 9,10-Phenanthrenequinone. A Time-Resolved Resonance Raman Study
Venkatraman Ravi Kumar, Nagappan Rajkumar, Freek Ariese, Siva Umapathy
Journal of Physical Chemistry A, 2015
The photochemistry of aromatic ketones plays a key role in various physicochemical and biological processes, and solvent polarity can be used to tune their triplet state properties. Therefore, a comprehensive analysis of the conformational structure and the solvent polarity induced energy level reordering of the two lowest triplet states of 9,10-phenanthrenequinone (PQ) was carried out using nanosecond-time-resolved absorption (ns-TRA), time-resolved resonance Raman (TR(3)) spectroscopy, and time dependent-density functional theory (TD-DFT) studies. The ns-TRA of PQ in acetonitrile displays two bands in the visible range, and these two bands decay with similar lifetime at least at longer time scales (μs). Interestingly, TR(3) spectra of these two bands indicate that the kinetics are different at shorter time scales (ns), while at longer time scales they followed the kinetics of ns-TRA spectra. Therefore, we report a real-time observation of the thermal equilibrium between the two lowest triplet excited states of PQ, assigned to nπ* and ππ* of which the ππ* triplet state is formed first through intersystem crossing. Despite the fact that these two states are energetically close and have a similar conformational structure supported by TD-DFT studies, the slow internal conversion (∼2 ns) between the T(2)(1(3)nπ*) and T(1)(1(3)ππ*) triplet states indicates a barrier. Insights from the singlet excited states of PQ in protic solvents [ J. Chem. Phys. 2015 , 142 , 24305 ] suggest that the lowest nπ* and ππ* triplet states should undergo hydrogen bond weakening and strengthening, respectively, relative to the ground state, and these mechanisms are substantiated by TD-DFT calculations. We also hypothesize that the different hydrogen bonding mechanisms exhibited by the two lowest singlet and triplet excited states of PQ could influence its ISC mechanism.
Solvatochromism of 9,10-phenanthrenequinone: An electronic and resonance Raman spectroscopic study
Venkatraman Ravi Kumar, Nagappan Rajkumar, Siva Umapathy
Journal of Chemical Physics, 2015
Solvent effects play a vital role in various chemical, physical, and biological processes. To gain a fundamental understanding of the solute-solvent interactions and their implications on the energy level re-ordering and structure, UV-VIS absorption, resonance Raman spectroscopic, and density functional theory calculation studies on 9,10-phenanthrenequinone (PQ) in different solvents of diverse solvent polarity has been carried out. The solvatochromic analysis of the absorption spectra of PQ in protic dipolar solvents suggests that the longest (1n-π(1)*; S1 state) and the shorter (1π-π(1)*; S2 state) wavelength band undergoes a hypsochromic and bathochromic shift due to intermolecular hydrogen bond weakening and strengthening, respectively. It also indicates that hydrogen bonding plays a major role in the differential solvation of the S2 state relative to the ground state. Raman excitation profiles of PQ (400-1800 cm(-1)) in various solvents followed their corresponding absorption spectra therefore the enhancements on resonant excitation are from single-state rather than mixed states. The hyperchromism of the longer wavelength band is attributed to intensity borrowing from the nearby allowed electronic transition through vibronic coupling. Computational calculation with C2ν symmetry constraint on the S2 state resulted in an imaginary frequency along the low-frequency out-of-plane torsional modes involving the C=O site and therefore, we hypothesize that this mode could be involved in the vibronic coupling.
Effect of chlorine substitution on triplet state structure of thioxanthone: A time-resolved resonance Raman study
Rishikesh Pandey, Nagappan Rajkumar, Siva Umapathy
Journal of Raman Spectroscopy, 2013
Substitution plays an important role in determining the triplet state reactivity. In this paper, we have studied the effect of chlorine substitution on the triplet state structure and the reactivity of thioxanthone (TX). We have employed time-resolved resonance Raman technique to understand the structure of the lowest triplet excited state of 2-chlorothioxanthone (CTX). The experimental findings have been corroborated with the computational results using density functional theory. Akin to the parent compound (TX), coexistence of two lowest triplet states has been observed in case of CTX, which has been substantiated using resonant probe wavelength dependence study. The relative contribution of 3n–π* to 3π–π* to the equilibrated triplet state has been found to be more for CTX compared to TX suggesting increase in the triplet state reactivity after the substitution. The above observation has been further supported by the flash photolysis experiments. Copyright © 2013 John Wiley & Sons, Ltd.
Structural, optical, and magnetic properties of zn 1-Xmn XS (x = 0.00, 0.01, and 0.03) nanoparticles
Journal of Nano and Electronic Physics, 2011
Magnetism in Zn1-2xMnxCoxO (x=0.00, 0.01, 0.02, and 0.03) nanostructures
N. Rajkumar, K. Ramachandran, Alka B. Garg, R. Mittal, R. Mukhopadhyay
Aip Conference Proceedings, 2011
In this work, we report the structural, optical, and magnetic properties of Zn1−2xMnxCoxO (x = 0.00, 0.01, 0.02, and 0.03) nanostructures which were synthesized by seed based chemical method under ambient conditions. The X‐Ray diffraction analysis reveals the wurtzite structure of ZnO nanostructures with no secondary crystalline phase due to doping. The morphologies of samples were examined using scanning electron microscopy and transmission electron microscopy, which indicate the formation of ZnO nanorods (diameter∼150 nm and length∼10 μm) for undoped sample and the growth of nanorods were affected with the increase of dopant concentration. The elemental compositions were analyzed by energy dispersive spectroscopy and X‐Ray photoelectron spectroscopy (XPS), which infers the presence of oxygen deficiency due to rapid growth of nanostructures. From XPS analysis, the presence of Co and Mn in divalent form was confirmed and no metallic clusters in the semiconducting matrix. The absorption measurement shows t...
Ethanol sensor using undoped and Mn-doped CoFe2O4 nanoparticles
P. Indra Devi, N. Rajkumar, K. Ramachandran, Alka B. Garg, R. Mittal, R. Mukhopadhyay
Aip Conference Proceedings, 2011
Room temperature ferromagnetism and an increase in saturation magnetization due to Mn‐doping are observed in CoFe 2 O 4 nanoparticles. The ethanol sensitivity of undoped and Mn‐doped (3 at.%) CoFe 2 O 4 nanoparticles were experimented at ambient temperature using optical fiber based on evanescent wave adsorption phenomenon. By modifying the clad exposure to gas vapor, the sensitivities were calculated to be 0.07 and 0.12 counts/ppm for undoped and Mn‐doped CoFe 2 O 4 nanoparticles respectively, showing significant enhancement in ethanol sensitivity for Mn‐doped sample.
Ethanol gas sensing of Mn-doped CoFe2O4 nanoparticles
P. Indra Devi, N. Rajkumar, B. Renganathan, D. Sastikumar, K. Ramachandran
IEEE Sensors Journal, 2011
Undoped and Mn-doped cobalt ferrite (CoFe2O4) nanoparticles were synthesized and characterized for thermal conductivity and magnetic properties. Room temperature ferromagnetism and an increase in saturation magnetization due to Mn doping (65.4 emu/g for 3 at.% of Mn and 20.8 emu/g for undoped CoFe2O4 nanoparticles) are observed. The ethanol gas sensitivity of undoped and Mn-doped (3 at.%) CoFe2O4 nanoparticles were experimented at ambient temperature using optical fiber based on clad-modified method. By modifying the clad exposure to gas vapor, the sensitivities were estimated to be 7 and 12 counts/100 ppm for undoped and Mn-doped CoFe2O4 nanoparticles, respectively, showing significant enhancement in ethanol gas sensitivity.
Oxygen deficiency and room temperature ferromagnetism in undoped and cobalt-doped TiO\bm 2 nanoparticles
N. Rajkumar, K. Ramachandran
IEEE Transactions on Nanotechnology, 2011
The compositional analysis done on the synthesized undoped and cobalt (Co)-doped titanium dioxide ( TiO2) nanoparticles by X-ray photoelectron spectroscopy and energy dispersive X-ray analysis suggests oxygen deficiency in undoped and Co-doped TiO2 samples. Magnetic investigations by vibrating sample magnetometer (VSM) indicate that undoped TiO2 nanoparticles possess ferromagnetic ordering at room temperature due to the oxygen deficiency and in Co-doped TiO2, the enhancement in magnetic moment is due to Co doping.
Dumbbell-shaped ZnO nanorods: Growth and characterization
N. RAJKUMAR, M. PRABHU, K. RAMACHANDRAN
International Journal of Nanoscience, 2011
Performance of dye-sensitized solar cell based on TiO2:ZnO nanocomposites
N. Rajkumar, S. S. Kanmani, K. Ramachandran
Advanced Science Letters, 2011
On the phonon confinement and particle size in TiO2:ZnO nanocomposite
S. S. KANMANI, N. RAJKUMAR, K. RAMACHANDRAN
International Journal of Nanoscience, 2011
On the possibility of ferromagnetism in CdO:Mn at room temperature
N. Rajkumar, V.M. Susila, K. Ramachandran
Journal of Experimental Nanoscience, 2011
Structural, optical and magnetic investigations on undoped and Mn-Doped ZnO nanoparticles
N. RAJKUMAR, K. RAMACHANDRAN
International Journal of Nanoscience, 2010
Photoacoustics and magnetic studies of Fe3O4 nanoparticles
N. RAJKUMAR, D. UMAMAHAESWARI, K. RAMACHANDRAN
International Journal of Nanoscience, 2010
Synthesis and characterization of dye (phenosafranine) sensitized flower-type zno nanorods
N. RAJKUMAR, R. N. MARIAMMAL, K. RAMACHANDRAN
International Journal of Modern Physics B, 2010
Observation of ferromagnetism in Mn-doped NANO ZnO
N. RAJKUMAR, K. RAMACHANDRAN
International Journal of Modern Physics B, 2009
On the ferromagnetic phase transition in nano Zno:Mn by electron paramagnetic resonance
P. VINOTHA BOORANA LAKSHMI, B. RANGANATHAN, N. RAJKUMAR, K. RAMACHANDRAN
International Journal of Modern Physics B, 2009
On the heat transfer of the anatase titanium dioxide nanocrystals
P. Vinotha Boorana Lakshmi, N. Rajkumar, B. Ranganathan, K. Ramachandran
International Journal of Nanomanufacturing, 2008

RECENT SCHOLAR PUBLICATIONS

pH-Driven Modulation of Size, Morphology, and Electrochemical Performance in Copper Sulfide Nanostructures for High-Performance Supercapacitors
N Rajkumar, A Suganya
Journal of the Indian Chemical Society, 102594 , 2026
2026
Importance of Artificial Intelligence and Machine Learning in Disaster Detection
MI Kwari, N Rajkumar, V Kumar
AI and ML in Early Warning Systems for Natural Disasters, 1-28 , 2025
2025
Comparative Analysis of Deep Learning and Machine Learning Models for DDoS Attack Detection
K Jayasakthi, S Maheswari, N Rajkumar, VS Patil, A Pawar
2025 4th OPJU International Technology Conference (OTCON) on Smart Computing … , 2025
2025
Citations: 1
AI-Enhanced Anomaly Detection in Software-Defined Networks
JS Prasath, SJ Parvez, A Govindaram, T Anuradha, N Rajkumar
2025 International Conference on Advanced Computing Technologies (ICoACT), 1-7 , 2025
2025
Citations: 2
Non-Intrusive Load Monitoring Techniques for Intelligent Energy Management: A Comparative Study of FHMM and LSTM Approach
N Rajkumar, A Govindaram, R Geetha, S ASF
2025 International Conference on Visual Analytics and Data Visualization … , 2025
2025
Citations: 2
A comparative analysis of IoT platform tools: Security and scalability Preferences in Device Management using AHP
S Maheswari, N Rajkumar, R Geetha, K Theja, M Malleswari
2025 International Conference on Visual Analytics and Data Visualization … , 2025
2025
Citations: 7
Federated learning in big data with IoT for intrusion detection
A Govindaram, JS Prasath, A Suganya, K Jayasakthi, N Rajkumar
2025 6th International Conference on Mobile Computing and Sustainable … , 2025
2025
Citations: 22
Structured process on FL for big data analysis
A Govindaram, JS Prasath, K Jayasakthi, N Rajkumar, G Porkodi
2025 6th International Conference on Mobile Computing and Sustainable … , 2025
2025
Citations: 18
Emotional intelligence and aggression in adolescents: A review
R Jintu, SM Mubeez, V Naveen, K Vinod, N Rajkumar
J. Ecophysiol. Occup. Health 23 (10.18311) , 2023
2023
Citations: 4
Room temperature ammonia gas sensor using Nd-doped SnO2 thin films and its characterization (Jun, 10.1007/s10854-020-03809-6, 2020)
S Maheswari, M Karunakaran, LB Chandrasekar, K Kasirajan, ...
JOURNAL OF MATERIALS SCIENCE-MATERIALS IN ELECTRONICS 31 (16), 14000-14001 , 2020
2020
Room temperature ammonia gas sensor using Nd-doped SnO 2 thin films and its characterization
S Maheswari, M Karunakaran, LB Chandrasekar, K Kasirajan, ...
Journal of Materials Science: Materials in Electronics 31 (15), 12586-12594 , 2020
2020
Citations: 22
Solvatochromism of 9, 10-phenanthrenequinone: An electronic and resonance Raman spectroscopic study
V Ravi Kumar, N Rajkumar, S Umapathy
The Journal of Chemical Physics 142 (2) , 2015
2015
Citations: 21
Direct Observation of Thermal Equilibrium of Excited Triplet States of 9,10-Phenanthrenequinone. A Time-Resolved Resonance Raman Study.
SU Venkatraman Ravi Kumar, Nagappan Rajkumar, Freek Ariese
J. Phys. Chem. A, DOI: 10.1021/acs.jpca.5b07972 , 2015
2015
Citations: 33
Effect of chlorine substitution on triplet state structure of thioxanthone: A time‐resolved resonance Raman study
R Pandey, N Rajkumar, S Umapathy
Journal of Raman Spectroscopy 44 (2), 270-276 , 2013
2013
Citations: 10
On the possibility of ferromagnetism in CdO: Mn at room temperature
N Rajkumar, VM Susila, K Ramachandran
Journal of Experimental Nanoscience 6 (4), 389-398 , 2011
2011
Citations: 22
Ethanol Sensor Using Undoped And Mn‐Doped Nanoparticles
PI Devi, N Rajkumar, K Ramachandran
AIP Conference Proceedings 1349 (1), 307-308 , 2011
2011
Magnetism in ( 0.01, 0.02, and 0.03) Nanostructures
N Rajkumar, K Ramachandran
AIP Conference Proceedings 1349 (1), 1177-1178 , 2011
2011
ON THE PHONON CONFINEMENT AND PARTICLE SIZE IN TiO 2 :ZnO NANOCOMPOSITE
SS Kanmani, N Rajkumar, K Ramachandran
International Journal of Nanoscience 10 (01n02), 227-231 , 2011
2011
Citations: 4
Dumbbell-shaped ZnO nanorods: growth and characterization
N Rajkumar, M Prabhu, K Ramachandran
International Journal of Nanoscience 10 (01n02), 87-92 , 2011
2011
Citations: 12
Performance of dye-sensitized solar cell based on TiO2: ZnO nanocomposites
N Rajkumar, SS Kanmani, K Ramachandran
Advanced Science Letters 4 (2), 627-633 , 2011
2011
Citations: 32

MOST CITED SCHOLAR PUBLICATIONS

Ethanol Gas Sensing of Mn-Doped CoFe O Nanoparticles
PI Devi, N Rajkumar, B Renganathan, D Sastikumar, K Ramachandran
IEEE Sensors Journal 11 (6), 1395-1402 , 2010
2010
Citations: 39
Oxygen Deficiency and Room Temperature Ferromagnetism in Undoped and Cobalt-Doped $\hbox {TiO} _ {\bm 2} $ Nanoparticles
N Rajkumar, K Ramachandran
IEEE transactions on nanotechnology 10 (3), 513-519 , 2010
2010
Citations: 35
Direct Observation of Thermal Equilibrium of Excited Triplet States of 9,10-Phenanthrenequinone. A Time-Resolved Resonance Raman Study.
SU Venkatraman Ravi Kumar, Nagappan Rajkumar, Freek Ariese
J. Phys. Chem. A, DOI: 10.1021/acs.jpca.5b07972 , 2015
2015
Citations: 33
Performance of dye-sensitized solar cell based on TiO2: ZnO nanocomposites
N Rajkumar, SS Kanmani, K Ramachandran
Advanced Science Letters 4 (2), 627-633 , 2011
2011
Citations: 32
Federated learning in big data with IoT for intrusion detection
A Govindaram, JS Prasath, A Suganya, K Jayasakthi, N Rajkumar
2025 6th International Conference on Mobile Computing and Sustainable … , 2025
2025
Citations: 22
Room temperature ammonia gas sensor using Nd-doped SnO 2 thin films and its characterization
S Maheswari, M Karunakaran, LB Chandrasekar, K Kasirajan, ...
Journal of Materials Science: Materials in Electronics 31 (15), 12586-12594 , 2020
2020
Citations: 22
On the possibility of ferromagnetism in CdO: Mn at room temperature
N Rajkumar, VM Susila, K Ramachandran
Journal of Experimental Nanoscience 6 (4), 389-398 , 2011
2011
Citations: 22
Solvatochromism of 9, 10-phenanthrenequinone: An electronic and resonance Raman spectroscopic study
V Ravi Kumar, N Rajkumar, S Umapathy
The Journal of Chemical Physics 142 (2) , 2015
2015
Citations: 21
PHOTOACOUSTICS AND MAGNETIC STUDIES OF Fe 3 O 4 NANOPARTICLES
N Rajkumar, D Umamahaeswari, K Ramachandran
International Journal of Nanoscience 9 (03), 243-250 , 2010
2010
Citations: 21
Structured process on FL for big data analysis
A Govindaram, JS Prasath, K Jayasakthi, N Rajkumar, G Porkodi
2025 6th International Conference on Mobile Computing and Sustainable … , 2025
2025
Citations: 18
Dumbbell-shaped ZnO nanorods: growth and characterization
N Rajkumar, M Prabhu, K Ramachandran
International Journal of Nanoscience 10 (01n02), 87-92 , 2011
2011
Citations: 12
Effect of chlorine substitution on triplet state structure of thioxanthone: A time‐resolved resonance Raman study
R Pandey, N Rajkumar, S Umapathy
Journal of Raman Spectroscopy 44 (2), 270-276 , 2013
2013
Citations: 10
A comparative analysis of IoT platform tools: Security and scalability Preferences in Device Management using AHP
S Maheswari, N Rajkumar, R Geetha, K Theja, M Malleswari
2025 International Conference on Visual Analytics and Data Visualization … , 2025
2025
Citations: 7
Synthesis and characterization of dye (Phenosafranine) sensitized flower-type ZnO nanorods
N Rajkumar, RN Mariammal, K Ramachandran
International Journal of Modern Physics B 24 (10), 1289-1298 , 2010
2010
Citations: 6
On the heat transfer of the anatase titanium dioxide nanocrystals
PVB Lakshmi, N Rajkumar, B Ranganathan, K Ramachandran
International Journal of Nanomanufacturing 2 (3), 181-191 , 2008
2008
Citations: 6
Structural, optical and magnetic investigations on undoped and Mn-doped ZnO nanoparticles
N Rajkumar, K Ramachandran
International Journal of Nanoscience 9 (05), 495-502 , 2010
2010
Citations: 5
On the ferromagnetic phase transition in nano ZnO: Mn by electron paramagnetic resonance
PVB Lakshmi, B Ranganathan, N Rajkumar, K Ramachandran
International Journal of Modern Physics B 23 (15), 3221-3229 , 2009
2009
Citations: 5
Emotional intelligence and aggression in adolescents: A review
R Jintu, SM Mubeez, V Naveen, K Vinod, N Rajkumar
J. Ecophysiol. Occup. Health 23 (10.18311) , 2023
2023
Citations: 4
ON THE PHONON CONFINEMENT AND PARTICLE SIZE IN TiO 2 :ZnO NANOCOMPOSITE
SS Kanmani, N Rajkumar, K Ramachandran
International Journal of Nanoscience 10 (01n02), 227-231 , 2011
2011
Citations: 4
Structural, optical, and magnetic properties of Zn1-xMnxs (x= 0.00, 0.01, and 0.03) nanoparticles
SS Kanmani, N Rajkumar, K Ramachandran
Видавництво СумДУ , 2011
2011
Citations: 4

Publications

Articles Published in International Journals:
17. Room temperature ammonia gas sensor using Nd-doped SnO2 thin films and itscharacterization, S. Maheswari, M. Karunakaran, L. Bruno Chandrasekar, K. Kasirajan and N.Rajkumar,Journal of Materials Science: Materials in Electronics, 31, 12586 (2020)
16. Direct Observation of Thermal Equilibrium of Excited Triplet States of 9,10,Phenanthrenequinone. A Time-Resolved Resonance Raman Study
V. Ravikumar, N. Rajkumar, F. Ariese, and S. Umapathy,Journal of Physical Chemistry A, 119, 10147 (2015)
15. Solvatochromism of 9,10- phenanthrenequinone: An electronic and resonance Raman spectroscopic study,V. Ravikumar, N. Rajkumar, and S. Umapathy
The Journal of Chemical Physics, 142, 24305 (2015)
14. Effect of chlorine substitution on triplet state structure of thioxanthone: A time-resolved resonance Raman study, R. Pandey, N. Rajkumar and S. Umapathy,J. Raman Spectroscopy, 44, 270–276 (2013)
13. Oxygen deficiency and room temperature ferromagnetism in undoped and cobalt
doped TiO 2 nanoparticles
N. Rajkumar and K. Ramachandran
IEEE Trans. Nanotechnol., 10, 513-519 (2011)
12. Ethanol gas sensing of Mn-doped CoFe 2 O 4 nanoparticles
P. Indra Devi, N. Rajkumar, B. Renganathan, D. Sastikumar, and K. Ramachandran
IEEE Sensors J., 11, 1395-1402 (2011)
11. On the possibility of ferromagnetism in CdO:Mn at room temperature
N. Rajkumar, V.M. Susila, and K. Ramachandran
J. Exp. Nanosci., 6, 389-398 (2011)
10. Dumbbell shaped ZnO nanorods: Growth and Ch