Alternative Energy Materials

Alternative Energy Materials Group (DP #4.03)

The Alternative Energy Materials group is actively engaged in the areas of (A) development of novel thermoelectric materials and devices for harnessing solar energy and other forms of waste heat, (B) advanced luminescent materials and (c) development of rare-earth free permanent magnet materials.

Activity A: Thermoelectric Materials and Devices

The main focus of the thermoelectric materials and devices are to develop novel thermoelectric materials and devices based on Si-Ge alloys, magnesium silicides and copper selenides for harnessing solar energy and other forms of waste heat. The other activities include process technology to produce p & n-type bulk materials, with high figure-of-merit, design & development of an efficient thermoelectric device (employing the developed thermoelectric materials) and its performance evaluation.

Current R & D highlights

Owing to its green technology, vigorous efforts are being made world-wide to realize thermoelectric waste-heat recovery devices for energy generation and this technology is rapidly emerging as a suitable alternative to other existing renewable sources of energy. However, despite decades of research, currently there are no thermoelectric devices available commercially for harnessing waste-heat in the high temperature range (> 300°C) due to several technological impediments. Even the existing commercial devices (< 300°C) have a limited efficiency ~ 5% and are made of elements which are both toxic (Pb) and expensive (Te, Ag, RE). Despite several n & p-type thermoelectric materials available with high figure-of-merit for higher temperature applications (Chalcogenides, Skuttrudites, Silicides with ZT as high as 1.5-2.6), most of these are either not stable at high-temperatures or are incompatible in terms of matching thermoelectric properties and coefficient of thermal expansion of their n & p-type counterparts at high operating temperatures.

In this group, the research was mainly focused on the development of novel thermoelectric materials with enhanced figure-of-merit and special emphasis on the design, synthesis, characterization and thermoelectric property evaluation of several novel nanostructured thermoelectric materials (Lead, Tellurium and Halfnium free), such as, Cu2Se, Mg2Si, MnSi, SiGe, Half-Heusler, Skutturudites and other novel thermoelectric materials. The focus of research was to develop compatible n & p-type thermoelectric elements for integration as a thermoelectric device. Also, peltier based refrigerator with a temperature of 7°C over a volume of 5 litres have been successfully developed. Cost effective silicide based materials for mid temperature range thermoelectric generators (TEG) development is under progress. Also, lanthanide doped multicolor emitting luminescent security inks, In the context of magnetic materials, process parameters have been established to synthesize rare-earth free (Hf-Co and Mn based) permanent magnets with 5 MGOe energy product.


The group is well equipped with several state-of-art facilities for materials synthesis, characterization and testing.

Figure 1: Spark plasma sintering technique used for sintering and consolidation of ball milled powders. Inset indicated the sample condition during sintering at high temperatures and (b) its basic configuration

Figure 2: X-Ray Diffractometer used for phase identification and purity of samples

Figure 3: Field emission scanning electron microscope with EBSD facility

Figure 4: Seebeck coefficient and electrical resistivity measurement facility used for electrical transport properties.

Figure 5: Laser flash thermal diffusivity measurement facility used for temperature dependent thermal diffusivity measurement

Figure 6: (a) Differential Scanning Calorimetry used for specific heat measurement

Figure 7: Melt spinning unit

Figure 8: Mini Arc melter (Single arc)

Figure 9: Vibrating Sample Magnetometer (3.1 T) with high temperature Oven (1273 K)

Figure 10: Pulse magnetizer and demagnetizer with Magnetizing coil of diameter 12 and 20mm suitable to generate flux density of 7 and 5 Tesla, respectively

Figure 11: Thermoelectric Conversion Efficiency Evaluation System for Small Modules Mini-PEM (up to 500°C)

Figure 12: Hall Effect Measurement System (HEMS) from temperature range 4K – 1000K.

Patents (Filed/Granted/Published)

Sl. No. Title Country Filed on (Date) Granted on (Date) Name of other inventors
01 An improved process for the synthesis of nanostructured copper-selenide (Cu 2 Se) as a p-type thermoelectric material with high thermoelectric figure-of-merit. USA, China, UK, Europe

   Dt: 19-03-2015

Application published Bhasker Gahtori, Bathula Sivaiah , Tyagi Kriti, Srivasatava Avanish Kumar,  Dhar Ajay,  Budhani Ramesh Chandra
02 An improved process for the synthesis of nanostructured copper-selenide (Cu 2 Se) as a p-type thermoelectric material with high thermoelectric figure-of-merit. India 2693/DEL/2013

Dt: 12-09-2013

Application published Bhasker Gahtori, Bathula Sivaiah , Tyagi Kriti, Srivasatava Avanish Kumar,  Dhar Ajay,  Budhani Ramesh Chandra

Recent High Impact Publications

  1. Giant Enhancement in Thermoelectric Performance of Copper Selenide by incorporation of different Nanoscale Dimensional Defect Features, B.Gahtori, Sivaiah, Kriti Tyagi, A. K. Srivastava and Ajay Dhar, Nano Energy , 13, p 36, (2015)

  2. Role of nanoscale defect features in enhancing the thermoelectric performance of p-type nanostructured SiGe alloys , S Bathula, BG Bhasker, AK Srivastava, A Dhar , Nanoscale, 7, p 12474, (2015)

  3. Thermoelectric properties of Cu 3 SbSe 3 with intrinsically ultralow lattice thermal conductivity, K Tyagi, B Gahtori, S Bathula, AK Srivastava, Ajay Dhar, Journal of Materials Chemistry A 2, p15829, (2014)

  4. Band structure and transport studies of copper selenide: An efficient thermoelectric material, K Tyagi, B Gahtori, S Bathula, S Auluck, Ajay Dhar, Applied Physics Letters, 17, p. 173905, (2014)

  5. Facile synthesis of higher manganese silicide employing spark plasma assisted reaction sintering with enhanced thermoelectric performance , S Muthiah, RC Singh, BD Pathak, A Dhar, Scripta Materialia 119, 60-64 (2016)

  6. Electrical transport and mechanical properties of thermoelectric tin selenide, K Tyagi, B Gahtori, S Bathula, NK Singh, S Bishnoi, S Auluck, Ajay Dhar   RSC Advances , 6 p 11562, (2016)

  7. Improving the thermoelectric performance of TiNiSn half-Heusler via incorporating submicron lamellae eutectic phase of Ti 70.5 Fe 29.5 : a new strategy for enhancing the power factor and reducing the thermal conductivity , A Bhardwaj, DK Misra, Journal of Materials Chemistry A 2, 48, p 20980,(2014)

  8. Enhanced thermoelectric figure-of-merit in spark plasma sintered nanostructure n-type SiGe alloys, Sivaiah Bathula, M. Jayasimhadri, Nidhi Singh, A. K. Srivastava, Jiji Pulikkotil, Ajay Dhar and R.C. Budhani, Applied Physics Letters 101, p 213902, (2012)

  9. Implications of nanostructuring on the thermoelectric properties in half-Heusler alloys, A.Bhardwaj, D. K. Misra, J. J. Pulikkotil, S. Auluck, Ajay Dhar, and R. C. Budhani, Applied Physics Letters 101, p.133103, (2012)

  10. Enhancing thermoelectric properties of a p-type Mg 3 Sb 2 -based Zintl phase compound by Pb substitution in the anionic framework, A Bhardwaj, DK Misra, RSC Advances , 4, p 34552, (2014)

On-going R&D Projects

Synthesis of high figure-of-merit thermoelectric materials for high temperature range (>650C) – GAP-161432 (BRNS sponsored)

Activity B: Luminescent Materials and Devices

Development of industrially important phosphors and nanophosphors by different synthesis routes for application in new generation lighting, displays and bio-medical applications. New down-conversion phosphors and nanophosphors are being developed for solid-state lighting in conjunction with blue/near-UV LEDs. Phosphors having high quantum efficiencies for their use in next generation Plasma Display Panel (PDP) panels, quantum cutting etc is also one of the key activities of our group. Development of energy efficient and low-power driven hybrid electroluminescent lamps, long decay materials for dark-vision displays, water-dispersible quantum dots, core-shell nanostructures, bio-compatible “Antibiotic Dots” for bio-medical applications etc. are major research areas of the group. R&D on up-conversion (anti-Stoke’s) phosphors in powder and colloidal forms that produce efficient luminescence when excited by IR radiations is another thrust area that the group is pursuing. These materials are extremely useful in improving the solar cell efficiency by spectral modification of solar IR radiation to visible light, bio-medical applications, IR detection and sensing etc.

Current R & D Highlights

Core-Shell upconversion nanophosphor for enhancement of solar cell efficiency

A novel approach for harnessing the hitherto unutilized part of solar IR radiation through spectrum modification by nanophosphor (NP) for enhancing solar cell efficiency is being carried out. Terrestrial solar energy encompasses the photon energy range of 4.24 - 0.41 eV, only a fraction of which can be utilized by existing solar cells for conversion into electrical energy. Up-conversion (UC) nanophosphor coupled to the solar cell can convert the long wavelength IR photons to visible radiation that can be gainfully absorbed by solar cell for photo voltage generation. Success of this process depends on development of highly efficient UC NP that is excitable by low intensity IR radiation. One of the most efficient NIR-Visible upconverting UC lattices is NaYF 4 . Synthesis of ultra small NaYF 4 particles require complicated process and high reaction temperature resulting in toxic fumes of harmful fluorides. Moreover, due to large number of incompletely bonded atoms on the surface of NP providing non radiative pathways, UC efficiency is usually low. A green chemistry approach has been taken to synthesize monodisperse monophasic core-shell nanoparticles with the core (~20 nm) and shell (~5 nm) [Fig.13a]. Hydrophobic core/shell nanoparticles have been further made hydrophilic by coating a transparent SHMP layer without affecting luminescence. A distinct enhancement of upconversion luminescence from core to core-shell (C/S)  structure under low flux NIR excitation at 976 nm has been achieved in Lanthanide (Er 3+ ,Yb 3+ ) doped NaYF 4 core with undoped NaYF 4 shell nanoparticles (NP) as shown in Fig.10b. Core shell (NaYF 4 :Er,Yb/NaYF 4 ) UCNP integrated dye sensitized solar cell (DSSC) indicated 11.9% enhancement in overall conversion efficiency under AM 1.5 conditions, due to NIR-Visible spectrum modification by fluorescent NPs [Fig.13c]. The results indicate the potential of such upconverting C/S nanophosphor in solar cell applications.

Fig. 13: (a) TEM image of NaYF 4 :Er 3+ ,Yb 3+ core and core/shell NPs showing uniformity in size and morphology of the particles. HRTEM image and lattice fringes of a single NaYF 4 :Er 3+ ,Yb 3+ core particle and NaYF 4 :Er 3+ ,Yb 3+ /NaYF 4 core/shell NPs clearly show core shell formation and shell thickness of 3.5 nm; (b) UC PL spectra of NaYF 4 : Er 3+ , Yb 3+ core (solid line), NaYF 4 : Er 3+ , Yb 3+ /NaYF 4 core/shell (dotted  line) and SHMP coated core /shell (dashed line) NPs under diode laser excitation at 976 nm.  Inset (a) Photograph showing green emitting NaYF 4 : Er 3+ , Yb 3+ /NaYF 4 core/shell nano powder under 976 nm laser excitation and inset (b) shows schematic drawing of NaYF 4 :Er,Yb/NaYF 4  core/shell structure and scatter free NIR to green UC luminescence in colloidal NPs; (c) I-V characteristic of DSSC coupled with upconverting core shell nanoparticles of NaYF 4 :Er 3+ ,Yb 3+ /NaYF 4 . The plot clearly depicts increase in V OC due to incorporation of NPs.

Tunable photoluminescence from hydrophobic silica gel nanoparticles for displays:

Luminescent materials have been utilized widely in applications involving lighting to sensing. The photoluminescence (PL) properties of silica have also been an important topic of research for a long time, but the difficulty in the incorporation of rare-earth (RE) ions attached covalently to the silica (SiO 2 ) network is still considered a great challenge. The weak PL bands with peak energies ~1.9-4.3 eV for both bulk and thin films of SiO 2 have been reported so far. It has been observed that monodisperse silica nanospheres formed by hydrolysis and condensation of alkoxides using Stober-Fink-Bohn (SFB) process gives negligible luminescence. Hence, we proposed a novel methodology to prepare alkoxide-based silica gel nanospheres doped with Eu 3+ ions that show enhanced PL brightness, uniform size distribution and improved quantum efficiencies. This is a process by which highly disordered but doped silica gels could be effectively made useful for practical applications involving luminescence. The tunable photoluminescence ranging from UV (373 nm) to deep-red (655 nm) colours has been achieved in SiO 2 :Eu 3+ gels with various Eu concentrations as shown in Fig. 14. Anomalous blue-green photoluminescence aroused from 4f 6 5d 1 –4f 7 transition of Eu 2+ and deep-red emission from 5 D 0 – 7 F 2 transition of Eu 3+ ions are attributed to the effective sensitizing action of the SiO 2 gel network.

Fig. 14: Tunable photoluminescence ranging from UV (373 nm) to deep-red (655 nm) colours exhibited by SiO 2 :Eu 3+ gels with Eu concentration of a) 0 mol-%, b) 0.02 mol-%, c) 0.04 mol-%, d) 0.06 mol-%, e) 0.08 mol-% and f) 0.1 mol-%. Anomalous blue-green photoluminescence aroused from 4f 6 5d 1 –4f 7 transition of Eu 2+ and deep-red emission from 5 D 0 – 7 F 2 transition of Eu 3+ ions. In both the cases, SiO 2 gel networks act as an effective sensitizer.

Probing a Bifunctional Luminomagnetic Nanophosphor for Biological Applications

In nature, materials that exhibit significant magnetism and efficient luminescence rarely exist. Such materials are highly desirable in a number of potential biological applications including drug and gene delivery, bio-sensing, and bioimaging with magnetic resonance imaging (MRI) contrast. LMD group has developed such a luminomagnetic material in the form of GdVO 4 :Eu nanoparticles used as nanoprobes for bioimaging applications. We have developed a simple and effective method for the high quality ultra-fine europium doped gadolinium vanadate (Gd 1-x Eu x VO 4, x=0.35) luminomagnetic nanophosphor, with a particle size measuring ~ 30 nm, by facile sol-gel method, which can be produced on a large-scale. Probing the luminomagnetic nanophosphor using photoluminescence, time-resolved spectroscopy, magnetization measurement and cytotoxicity assay reveal its suitability for biological applications. The photoluminescence emission (PL) spectrum recorded at 308 nm excitation shows a sharp intense hypertensive red emission peaking at ~618 nm at room temperature (Fig. 15a and c).

Fig. 15: Colloidal solution of luminomagnetic nanophosphor in de-ionized water(2µgmL -1 )(a)Transparency of suspended luminomagnetic nanophosphor, second photograph shows the magnetic tracking through permanent magnet (~ 2000 Oe)  as well as shows strong red emission under UV 254 nm wavelength(b) Room temperature M-H curves of as-synthesized Gd 0.65 Eu 0.35 VO 4 nanophosphor; Photographs of luminomagnetic nanophosphors in glass vials (i) without and (ii) with external permanent magnet (~ 1000 Oe) are shown in inset (c) Room temperature PL emission spectrum recorded at 308 nm excitation. The right inset shows the other emission spectra at 362, 382, 395, 416 and 465 nm excitation wavelengths and the left inset shows the color coordinates(d) High resolution digital micrographs of the Aphanothece sp cells treated with 2 µ g/mL Gd 0.65 Eu 0.35 VO 4 nanophosphor after 2days of incubation both under room light and UV light (254 nm).

We have carried out magnetization measurements using a super conducting quantum interference device (SQUID) magnetometer (see Fig. 15b). The synthesized luminomagnetic nanophosphor exhibits typical paramagnetic behavior with high magnetic moment. We have investigated the cell viability of GdVO 4 :Eu 3+ luminomagnetic nanoparticles using Prokaryotic algal ( Aphanothece sp in the class of cyanobacteria/blue-green algae) for biological applications (see Fig. 15d). We observed that the synthesized luminomagnetic nanophosphors were not only biocompatible with cells but also relatively nontoxic over reasonable concentrations, which is of significance for applications in biomedical diagnostics and analyses requiring luminescence and magnetic tracking.

Optical Bifunctionality of Europium-complexed Luminescent Graphene Nanosheets

LMD group in joint collaboration with Rice University, USA has successfully synthesized the luminescent graphene (LG) which offers a new paradigm shift in the engineering of graphene analogs for tuning optical and electronic properties. It has been demonstrated the dual functionality of graphene by the quenching of luminescence of Rhodamine-B while displaying its own red emission. A plausible structural model of europium-complexed graphene is shown in Fig.  16(a-b).

Fig. 16: a) Demonstration of dual functionality of graphene by the quenching of luminescence of Rhodamine-B while displaying its own red emission. b) Plausible structural model of europium-complexed graphene.

The SEM image of europium complexed-graphene, a TEM image of the LG, the arrows indicating the presence of mono or double layer   LG, carbon and europium elemental mapping of a selected region and atomic HRTEM Images of the LG are shown in Fig. 17(a-d). The inset of Fig. 17d shows the FFT pattern of the selected region.

Fig. 17: a) SEM image of europium complexed-graphene. b) TEM image of the LG. Arrows indicate the   presence of mono or double layer   LG. c) carbon and europium elemental mapping of a selected region. d) Atomic HRTEM Images of the LG. The inset is the FFT pattern of the selected region.

The synthesis of luminescent graphene or europium complexed-graphene nanosheets is achieved through a simple and efficient high temperature thermal dissociation and reduction process. The introduction of Eu(III) ions in the graphene lattice was proven by XPS analysis and EDS mapping. Spectroscopic results convincingly show the complexation of trivalent europium with graphene oxygen functionalities (Fig. 18).

Fig. 18: a) UV-visible spectrum of the LG. b) PL excitation of the LG (emission at 618 nm) exhibiting a strong peak at 314 nm. c) Photo-luminescence (PL) emission of the LG (excitation at 314 nm) exhibiting hypersensitive red emission at 614 and 618 nm. d) TRPL decay profile of the LG. The inset shows the lifetime data.

More specifically, a shift in the photoluminescence red emission of the starting material, europium oxide, from 611 nm to a hypersensitive red emission for the europium (III) complexed-graphene at 618 nm was observed(Fig.18 a-c). The luminescent graphene had a triple decay lifetime with an average value of 391.13 µ s, which contrasts with the single decay lifetime (65.68 µ s) of europium oxide as shown by time-resolved spectroscopy (Fig.  18d).

Fig. 19: a) PL spectrum of pristine Rhodamine-B, LG and GO in Rhodamine-B (excitation at 562 nm) exhibiting complete quenching. b)Self-luminescence of the LG / Rhodamine-B solution (excitation at 314 nm)exhibiting the hypersensitive red emission at 614 and 618 nm.

We have successfully demonstrated the concurrent fluorescence quenching of Rhodamine-B by the luminescent graphene as well as its self-luminescence (Fig. 19). The importance of such luminescent materials is in biological application where cells showing their own luminescence (e.g. MCF-7GFP, Human Breast Cancer Cell displays strong green luminescence) and are difficult to target/label those cells without quenching their luminescence. We envision that such accomplishments will be milestone in developing the much-awaited high-performance applications of graphene and its analogs in the fields of optoelectronics and nano-biotechnology.

Recent Achievements

Development of unclonable security codes designed from multicolour luminescent lanthanide doped Y 2 O 3 nanorods for anti-counterfeiting

The duplicity of important documents has emerged as a serious problem worldwide. Therefore, many efforts have been devoted to develop easy and fast anti-counterfeiting techniques with multicolour emission. CSIR-NPL has developed multicolour luminescent lanthanide doped Y 2 O 3 nanorods and their usability in designing of unclonable security codes for anti-counterfeiting applications. These nanorods of  Y 2 O 3 : Eu 3+ , Y 2 O 3 :Tb 3+ and Y 2 O 3 :Ce 3+ emit hypersensitive red (at 611 nm), strong green (at 541 nm) and bright blue (at 438 nm) emissions at 254 nm, 305 nm and 381 nm, respectively. The obtained results suggests that these multicolor nanorods provide futuristic approach to print multicolor security codes for anti-counterfeiting application which are hard to duplicate and easy to detect.

Figure 20: Schematic of unclonable security codes designed from multicolour luminescent nanorods for smart phone with a QR scanning application.

Figure 21: A novel electroluminescent device based on a reduced graphene oxide wrapped phosphor (ZnS:Cu,Al) and hexagonal-boron nitride for high-performance luminescence.

Figure 22: Experimental observation of spatially resolved photo-luminescence intensity distribution in dual mode upconverting nanorod bundles.

Figure 23: In vitro fluorescence microscopy images of T47D cells incubated with luminescent Gd1.85Eu0.15O3 nanorods (5µg mL-1) for 4 h. Sequential images of single cell (i-v) and cell cluster (vi-x) show: i) Phase contrast image. ii) Nuclear staining with DAPI. iii) Red fluorescence from Gd1.85Eu0.15O3 nanorods. iv) Overlapped images of blue DAPI and red Gd1.85Eu0.15O3 nanorods (ii and iii). v) Overlap of phase contrast, blue, and red, from(i–iii), respectively. A similar imaging pattern presented for cell cluster with vi) Phase contrast image. vii) Nuclear staining with DAPI. viii) Red fluorescence from Gd1.85Eu0.15O3 nanorods. ix) Overlapped images of blue DAPI and red Gd1.85Eu0.15O3 nanorods (vii and viii). x) Overlap of phase contrast, blue, and red, from (vi–viii), respectively.

Fast Track Translational Projects Current R & D highlights

  • CSIR-funded Fast Track Translational (FTT) project (2016-18) entitled “Sunlight sensitized long afterglow phosphor powder and paint ”

  • CSIR-NPL Fast Track Translational (FTT) mission project (2016-2017) entitled: “Development of single layer CVD grown graphene for quantum hall resistance metrology” .


Dr. Ajay Dhar, Chief Scientist

Dr. D. Haranath
Dr. D. K. Misra
Dr. Mahesh Kumar
Dr. Bathula Sivaiah
Mr. M. Saravanan
Dr. Bipin Kumar Gupta
Dr. Bhasker Gahtori

Technical support:
Mr. Radhey Shyam
Mr. Naval Kishor Upadhyay
Mr. Madan Pal