Engineering Spontaneous Emission in Hybrid Nanoscale Materials for

Optoelectronics and Bio-photonics

Arup Neogi

Department of Physics and Materials EngineeringUniversity of North Texas

Email: arup@unt.edu

Ultrafast and Nanoscale Photonics Group Arup Neogi, Department of Physics

Research AreasResearch Areas

1. Nanoscale Optoelectronic materials for efficient light emission2. Biophotonic materials; for hybrid molecular electronics and photonics

http://www.phys.unt.edu/research/photonic/website/

Funding:• National Science Foundation• US Department of Energy• Japan Soc. for Promotion of Sciences

Using subwavelength corrugated surface grating:• Momentum can be transferred to couple the light and plasmon modes• Directional Emission can be improved by using corrugated surfaces

Surface plasmons polariton coupling with directional emission

Change in radiative recombination lifetime in Qdots due to resonant exciton-surface plasmon coupling

Radiative recombination rate in strained quantum dots emission - observed above the SP emission energy

Energy Transfer in Quantum Dots entrapped in Hydrogel Microspheres

Arup Neogi, Zhibing Hu

Department of Physics

University of North Texas

Temperature induced changes in hydrogel

The NIPAM sample in water: Effect of temperature61

21 oC 35 oC1 cm 1 cm

The phase transition temperature (Tc) of PNIPAM is 34 °C.

below Tc, the hydrogel is hydrophilic and swells in water, while

above Tc it is hydrophobic and collapses into a small volume.

Change in scattering properties with particle size

200 250 300 350 4000.00

0.05

0.10

0.15

0.20

f(R

h)

Rh (nm)

Broken S-S bond PNIPAM microgels PNIPAM/ NCs microgels PNIPAM microgels

Variation of Particle size with chemistry Change in scattering properties with turbidity

Photoluminescence Spectrum of QDs embedded in GEL

UV

Sunlight

The image of PNIPAM/CdTe microgel

under sunlight

The PL image of PNIPAM/CdTe microgel

under UV lamp.

400 450 500 550 600 650 700 750 800

2000

4000

6000

8000

10000

Inte

nsi

ty

Wavelength (nm)

qd2 qd3 qd4

Electric Field Induced effects in PNIPA Gels

*Wu, J. et. al. Phys. Rev. Lett., 90, 48304 (2003) +Hu, Z. et. al. Advan. Mater. 13, 1708 (2001)

At room temperature

No electric field

3.5V/cm electric field

Hybrid Semiconductors for FRET based light emitters

Arup Neogi, Jianyou Li

University of North Texas, Denton, TX, USA

Terry Ishihara

Frontier Research Laboratory, RIKEN, Japan

Oligonucleotide based nanoscale photodetector

GaN

* MRS Best paper award 2005

SAGCs behave like wide-bandgap GaN semiconductors, with equivalent energy gap ~ 3.5 eV & electron e1ective mass ~ 2m* at 300 K; concentration ~ 3.33 x 10-2 M

280 300 320 340 360 380 400 420 440 4606.96

6.97

6.98

6.99

7.00

7.01

7.02

7.03

Ph

oto

cu

rre

nt

(a.u

.)

Wavelength (nm)

54 Device

Nanoscale Photodiode