Y. Dwivedi

Intense white upconversion emission in Pr/Er/Yb codoped tellurite glass

Near infrared sensitized white light emitting glass has been developed and demonstrated. The white light comes from a combination of radiations emitted from triple rare earth ions (Er, Pr, and Yb) doped in tellurite glass. White light emission is possible by suitably mixing the red-green-blue (RGB) intensities emitted from these rare earth ions. The 980 nm radiation sensitized Yb3+ ions transfer their excitation energy to the Er3+ and Pr3+ ions to promote them to the upper states. The green and red emissions come mainly from Er3+ ion whereas blue emission from Yb3+ and Pr3+ ions. The RGB intensities could be adjusted by tuning the rare earth ion concentration. The optical quality of white light was adjudged using the Commission Internationale de l’ Eclairage coordinates by the rare earth ion concentration and incident power density.

Optical avalanche in Ho:Yb:Gd2O3 nanocrystals

Intense green upconversion emission in Ho:Yb:Gd2O3 spherical nanoparticles is reported through hetrolooping enhanced energy transfer process. Different techniques used for structural characterization divulge the formation of spherical Ho:Yb:Gd2O3 crystals of diameter ∼100 nm. Efficient energy transfer from Yb3+ → Ho3+ ions set spherical nanocrystal to emit in the range of UV-NIR via three NIR photons absorption process. Power dependence and the temporal evolution of upconversion emission intensity suggest the occurrence of a photon avalanche process. The enhancement in emission intensity in nanophosphor sample has been explained and the photophysics involved is correlated with the unique structural properties of the crystallites formed and the time resolved spectroscopy.

Yb3+ sensitized Tm3+ upconversion in tellurite lead oxide glass.

Triply ionized thulium/thulium--ytterbium doped/codoped TeO2-Pb3O4 (TPO) glasses have been fabricated by classical quenching method. The upconversion emission spectra in the Tm3+/Tm3+-Yb3+ doped/codoped glasses upon excitation with a diode laser lasing at ∼980 nm has been studied. Effect of the addition of the Yb3+ on the upconversion emission intensity in the visible and near infrared regions of the Tm3+ doped in TPO glass has been studied and the processes involved explored.

Laser induced breakdown spectroscopy diagnosis of rare earth doped optical glasses

In the present work, rare earth (Nd, Eu, Er, Ho) doped oxyfluoroborate glasses were studied using laser induced breakdown spectroscopy (LIBS) technique. It has been observed that rare earth elements other than the doped one also reveal their presence in the spectrum. In addition the spectral lines of elements constituting the glass matrix have also been observed. Different plasma parameters such as plasma temperature and electron density have been estimated. It is concluded that the LIBS is a potential technique to identify simultaneously the light elements (B, O, F) as well as the heavy elements (Fe, Ba, Ca, Eu, Nd, Ho, Er) present in optical glasses.

Enhanced luminescence and energy transfer study in Tb:Sm codoped lead fluorotellurite glass

Spectroscopic properties of Sm(3+), Tb(3+) doped and Tb(3+):Sm(3+) co-doped lead fluorotellurite glasses have been studied in detail. On the excitation with 355 and 532 nm laser wavelengths, the luminescence properties of the singly and doubly doped glasses have been analyzed. Intensity of characteristic emission bands due to Sm(3+) ions is appreciably enhanced in the presence of Tb(3+) ions. This is due to the energy transfer from Tb(3+) to Sm(3+) ions. Different energy transfer parameters have also been calculated, which affirm an efficient energy transfer from Tb(3+) to Sm(3+) ions.

Spectroscopic study of Er:Sm doped barium fluorotellurite glass

In this paper, we report the physical and spectroscopic properties of Er(3+), Sm(3+) and Er(3+):Sm(3+) ions codoped barium fluorotellurite (BFT) glasses. Different Stokes and anti-Stokes emissions were observed under 532 nm and 976 nm laser excitations. Energy transfer from Er(3+) ion to Sm(3+) ion was confirmed on the basis of luminescence intensity variation and decay curve analysis in both the cases. Under green (532 nm) excitation emission intensity of Sm(3+) ion bands improves whereas on NIR (976 nm) excitation new emission bands of Sm(3+) ions were observed in Er:Sm codoped samples. Ion interactions and the different energy transfer parameters were also calculated.

Optical properties of cerium doped oxyfluoroborate glass.

Cerium doped oxyfluoroborate glasses have been prepared and its spectroscopic properties have been discussed. It is found that the absorption edge shifts towards the lower energy side for the higher concentration of cerium dopant. Optical band gap for these glasses have been calculated and it is found that the number of non-bridging oxygen increases with cerium content. The emission spectra of these glasses have been recorded using UV laser radiations (266 and 355 nm) and it is observed that these glasses show bright blue emission. On the basis of excitation and emission spectra we have reported the existence of at least two different emission centers of Ce(3+)ions.

Green and NIR sensitized luminescent nanophosphor: preparation, characterization and application.

Luminescent nanophosphor of Er, Yb: Gd(2)O(3) has been synthesized by well known combustion synthesis. Along with strong UV-Vis upconversion emission, sensor for temperature and magnetic field, nano-heater etc., it can also be used as luminescent ink by dispersing the nanophosphor in aqueous polyvinyl alcohol solution. The stability of the ink has been found to depend strongly on the mixing process of the phosphor powder in the polymer solution. The X-ray diffraction results and TEM images with diffraction pattern show that the particles are in cubic phase of Gd(2)O(3) with particles of average size <40 nm. SEM images show flaky structure which makes it suitable for dispersing in PVA and useful for luminescent ink purposes on NIR excitation. The FT-IR and the thermal analysis support the presence of PVA. Upconversion and downconversion luminescence has also been observed with 532 nm excitation and energy transfer mechanism has been explained. The NIR pumping gives strong UC emission bands in red and green regions extending up to extreme UV (240 nm) in this host.

Structural and spectroscopic diagnosis of Eu:ZnO and Eu:Yb:ZnO glass and ceramics

Eu and Eu:Yb codoped ZnO nanocrystals embedded in B(2)O(3) glass matrix were synthesized and their structural, optical properties were discussed. On excitation with 532 nm laser radiation intense orange/red emissions from Eu(3+) ions were observed. The fluorescence intensity was found to enhance on annealing. Frequency upconversion emissions from Eu(3+) ions were observed in presence of Yb(3+) ions on excitation with NIR (976 nm) laser. The enhancement in emission intensity was explained and the photo-physics involved is linked with the unique structural properties of the crystallites formed. Ion interactions and the different energy transfer parameters were also calculated.

Structural and optical characterization of nanosized La(OH)3:Sm3+ phosphor

In the present work, Sm(3+) doped La(OH)(3) nano-phosphor (~40 nm) has been synthesized using combustion synthesis method and detailed structural and spectroscopic characterizations are carried out. On excitation with 532 nm, several photoluminescence peaks extending over green to NIR regions have been observed and assigned to be due to 4f-4f transitions of Sm(3+) ions. A bright orange-red perception is observed in annealed sample, which is 10 times higher than as synthesized sample. Time resolved emission spectroscopy reveals pronounced effect of heating, which induce good crystalline in the host.