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Papers by aditya kumar singh

The rare earth ions doped powdered ceramics and bulk glass ceramics are the subject of intense re... more The rare earth ions doped powdered ceramics and bulk glass ceramics are the subject of intense research for developing upconversion based optical devices. The fine powdered ceramic phosphors and transparent bulk glass ceramics have their own specificities and applications.
In the present talk upconversion emission results in various ceramic materials would be discussed. The ceramic upconversion phosphors such as La2O3:Er3+/Yb3+, LaF3:Er3+/Yb3+, CeO2:Er3+/Yb3+, and CeF3:Er3+/Yb3+ were prepared and their upconversion emission using 976 nm wavelength excitation are investigated deeply. The replacement of oxide by fluoride ion has increased the emission intensity due to the reduction in average lattice vibration. The LaF3:Er3+/Yb3+ phosphor is found best for achieving upconversion emission in visible region while the CeF3:Er3+/Yb3+ is best for infrared emission near 1550 nm wavelength. The temperature sensing property of the prepared ceramic phosphors has also been checked.

The europium and neodymium oxides doped nano-structured calcium aluminate phosphor samples have ... more The europium and neodymium oxides doped nano-structured calcium aluminate phosphor samples have
prepared through combustion technique and their luminescence properties are studied using laser excitations.
Samples prepared in open atmosphere showed the presence of both Eu3+ and Eu2+ states and their
ratio changes with calcination temperature. Single Eu3+/Eu2+ ions doped sample has found to give broad
emission at 450 nm without the persistence glow while the Eu3+ + Nd3+ ions codoped sample has shown
persistence glow at 450 nm (Eu2+) on 355 nm laser excitation. Wavelength selective excitations show
that 266 nm excitation gives the intense emissions from both Eu3+ and Eu2+ states with no afterglow
but 355 nm excitation gives negligible emission from Eu3+ ions and a strong afterglow at 450 nm wavelength.
The mechanism of wavelength dependent phosphorescence has been discussed. Studies on Stark
splittings and their relative intensities in emission spectra of Eu3+ ions have shown that Eu3+ ion can be
used as excellent probe of crystal structure.

Springer Netherlands, 2012

"Corrosion inhibition of mild steel (MS) by chloroquine (CQ) in 1 M HCl was investigated using w... more "Corrosion inhibition of mild steel (MS) by chloroquine (CQ) in 1 M
HCl was investigated using weight loss, polarization, electrochemical impedance
spectroscopy (EIS) and quantum chemical techniques. The inhibitor showed 99 %
inhibition efficiency at concentration of 3.1 9 10-4 M. Polarization studies showed
that CQ is a mixed-type inhibitor. Adsorption of inhibitor molecules on the MS
surface showed Langmuir adsorption isotherm. Thermodynamic parameters led to
the conclusion that adsorption is predominantly chemisorption. Quantum chemical
calculations were carried out to investigate the corrosion-inhibiting property of CQ.
Various parameters such as energy of the highest occupied molecular orbital
(HOMO) and lowest unoccupied molecular orbital (LUMO), softness of molecule,
Mullikan charges on various atoms and number of electrons transferred from
inhibitor molecule to metal were calculated and correlated with the inhibiting
property of CQ."

"Low-power-threshold cw laser-induced incandescence (CWLII) has been observed in La2O3:Er3-Yb3 ... more "Low-power-threshold cw laser-induced incandescence (CWLII) has been observed in La2O3:Er3-Yb3 phosphor on
excitation by a 976 nm IR laser. It is suggested that incandescence originates from the extensive heating induced by
the nonradiative processes taking place following the laser excitation. Other mechanisms for similar observations
have also been suggested in the literature and have been discussed with the present observations. The estimated
temperature for the CWLII approaches around 2650 K, and this seems to provide an effective way to rapidly attain
high temperature in nano/microvolumes of phosphor. The phosphor exhibited efficient upconversion, and the ratio
of the 2H11∕2 → 4I15∕2 and 4S3∕2 → 4I15∕2 band intensities of Er3 permits measurement of the temperature rise, from a
distance."

Multifunctional europium doped Li2O–Nb2O3–B2O2 glass has been prepared by melt-quench method. Th... more Multifunctional europium doped Li2O–Nb2O3–B2O2 glass has been prepared by melt-quench method.
Through subsequent heat treatments glass has then been transformed into glass ceramics containing ferroelectric
LiNbO3 phase. The glass ceramics have shown enhanced Eu3+ emission compared to parent
glass when excited by 266 nm radiation. The emission measurements of glass ceramics have also shown
the presence of Eu2+ state along with Eu3+ and Eu2+ state was found to increase when glass was heated in
inert atmosphere. Lifetime of the 5D0 level of the Eu3+ has been measured and a significant increase is
found in case of glass ceramic prepared around glass transition temperature. Glass ceramics have also
shown good second harmonic generation (SHG) with pulsed 1064 nm laser excitation.

Hexagonal LaF3:Er3+ /Yb3+ phosphor material has been synthesized by chemical precipitation meth... more Hexagonal LaF3:Er3+
/Yb3+ phosphor material
has been synthesized by chemical precipitation method to
obtain high near-infrared to green upconversion (UC) efficiency.
Its thermal, structural and fluorescence properties
have been studied. UC emission bands have been observed
up to 315 nm in UV region. The effect of input pump power
on the intensities of various emission bands has been studied
in detail and photon avalanche UC mechanism has been
identified. On increasing the excitation power, some bands
have shown saturation in intensity. Also, at higher pump intensities
two new UC bands were observed and their origin
has been discussed. The phosphor has also been tested for
possible UC-based fingerprint detection.

A nano-crystalline La2O3: Er3+ /Yb3+ phosphor sample has been synthesized through the solution ... more A nano-crystalline La2O3: Er3+
/Yb3+ phosphor
sample has been synthesized through the solution combustion
route using urea as a reducing agent. Thermal, structural
and optical characterizations have been carried out to
explore several of its properties. By thermal analysis one
concludes to the presence of moisture and hydroxide phases
[La(OH)3 and LaOOH] of lanthanum in the as-synthesized
sample, which further changes to La2O3 phase above 600°C
temperature. Up-conversion (UC) study shows the intense
emission bands in the UV, blue, green and red regions. This
paper also reports the first observation of UC emission bands
extending up to the UV (240 nm) region on excitation with
976 nm wavelength. Heat treatment of the samples shows a
change in the crystallite phase along with crystallite growth
and relative UC luminescence intensities. The input pump
power dependence shows the involvement of up to four photons.

Springer Netherlands, 2012