• S K OMANWAR

      Articles written in Bulletin of Materials Science

    • Slow evaporation method and enhancement in photoluminescence properties of YPO$_4$ : Eu$^{3+}$ co-doped with Bi$_{3+}$ ions

      K A KOPARKAR S K OMANWAR

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      The series of Bi$^{3+}$ co-doped YPO$_{4}:Eu$^{3+}$ nanophosphors were successfully synthesized by the slow evaporation method. Bi$^{3+}$-doped and un-doped YPO$_4$:Eu$^{3+}$ phosphors were characterized by using powder X-ray diffraction, Fourier transform infrared spectroscopy and field emission scanning electron microscopy. Photoluminescence (PL) properties and decay time of phosphors were studied at room temperature. The YPO$_4$:Eu$^{3+}$ and Bi$^{3+}$ exhibit enhancement in PL intensity and quenched at 0.5 mol% of Bi$^{3+}$ ions.

    • Synthesis and luminescence properties of Tb$^{3+}-doped LiMgPO$_4$ phosphor

      C B PALAN N S BAJAJ A SONI S K OMANWAR

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      Polycrystalline sample LiMg$_{(1.x)}$PO$_4$:$x$Tb$^{3+}$ ($x = 0.001, 0.002, 0.005, 0.01, 0.02$) phosphor was synthesized via modified solid state method (MSSM). The prepared sample was characterized through XRD pattern (X-ray diffraction) and SEM (scanning electron microscope). Additionally, photoluminescence (PL), optically stimulated luminescence (OSL), thermoluminescence (TL) and other dosimetric properties including dose linearity, reusability and fading were studied. In OSL mode, sensitivity of prepared phosphor was found to be 2.7 times that of LiMgPO$_4$:Tb$^{3+}, B (BARC) phosphor and 4.3 times that of $\alpha$-Al$_2$O$_3$:C (BARC) phosphor. The TL glow consists of overlapping peaks in temperature range of 50-400$^{\circ}$C and first peak (P$_1$) was observed at 150$^{\circ}$C, second peak (P$_2$) at 238$^{\circ}$C, third peak (P$_3$) at 291$^{\circ}$C and fourth peak (P$_4$) at 356$^{\circ}$C. The TL sensitivity of second peak (P$_2$) of LiMgPO$_4$:Tb$^{3+}$ phosphor was compared with $\alpha$-Al$_2$O$_3$:C (BARC) phosphor and found to be 100 times that of the $\alpha$-Al$_2$O$_3$:C (BARC) phosphor. The minimum detectable dose (MDD) was found to be 5.6 $\mu$Gy. Moreover, photoionization cross-sections, linearity, reusability, fading and kinetic parameters were calculated. Also, photoluminescence spectra of LiMgPO$_4$:Tb$^{3+}$ shows characteristic green.yellow emission exciting at 224nm UV source.

    • Luminescence properties of terbium-doped Li$_3$PO$_4$ phosphor for radiation dosimetry

      C B PALAN N S BAJAJ S K OMANWAR

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      A polycrystalline sample of Li$_3$PO$_4$:Tb$^{3+}$ phosphor was successfully synthesized using solid-state diffusion method. This synthesis method is of low cost, low temperature and does not require any other atmospheres for the synthesis. The powder X-ray diffraction (PXRD), photoluminescence (PL) emission and excitation spectra, thermoluminescence (TL) and optically stimulated luminescence (OSL) were measured. The particle size was calculated using the Debye Scherrer formula and found to be 79.42 nm. PL emission spectra of Li$_3$PO$_4$:Tb$^{3+}$ phosphor show the strong prominent peak at 544 nm corresponding to ${}^{5}$D$_4$ to ${}^{7}$F$_5$ transitions of Tb$^{3+}$. The OSL sensitivity of prepared Li$_3$PO$_4$:Tb$^{3+}$ phosphor was 50% of that of $\alpha$-Al$_2$O$_3$:C. Its decay curve consists of three components withphotoionization cross-sections $0.44\times 10^{−17}$, $3.09\times 10^{−17}$ and $23\times 10^{−17}$ cm$^{2}$. The TL glow curve of the prepared sampleconsists of two characteristic peaks, which were deconvoluted using the peak fit software, and kinetic parameters were determined using the peak shape method. TL intensity was compared with that of the commercially availableTLD-500 phosphor. OSL dose response was linear in the measured range and the minimum detectable dose (MDD) was found to be 67.42 $\mu$Gy, while fading of the OSL signal was found to be about 27% in 4200 min after which theOSL signal stabilizes.

    • Near-infrared spectral downshifting in Sr$_{(3−x)}$(VO$_4$)$_2$:${}_x$Nd$^{3+}$ phosphor

      N S SAWALA K A KOPARKAR N S BAJAJ S K OMANWAR

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      In this study, the spectral downshifting (DS) from ultraviolet (UV) light to near-infrared (NIR) radiation in Sr$_3$(VO$_4$)$_2$:Nd$^{3+}$ phosphor is reported. The prepared materials were characterized by X-ray powder diffraction(XRD) and photoluminescence (PL) properties along with steady state luminescence time decay curves were studied, which confirmed the energy transfer (ET) from VO$_4^{3−}$ ions to Nd$^{3+}$ ions. The DS phenomenon by phosphor was observed, which involved emission of NIR photons (1075 and 1064 nm) and visible photons (506 nm) from absorbed UV photons at 349 nm. The theoretical energy transfer efficiency (ETE) was calculated with the help of steady state luminescence time decay curves and the maximum ET efficiency approached up to 41.33%. The crystalline silicon (c-Si) cell has maximum efficiency in NIR region of solar spectrum due to an energy band gap of 1.12 eV.Sr$_3$(VO$_4$)$_2$:Nd$^{3+}$ can be potentially used as a NIR DC phosphor for c-Si solar cells.

    • Synthesis and photoluminescence study of narrow-band UVB-emitting LiSr$_4$(BO$_3$)$_3$:Gd$^{3+}$, Pr$^{3+}$ phosphor

      A O CHAUHAN N S BAJAJ S K OMANWAR

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      A series of Pr$^{3+}$, Gd$^{3+}$ and Pr$^{3+}$–Gd$^{3+}$-doped inorganic borate phosphors LiSr$_4$(BO$_3$)$_3$ were successfully synthesized by a modified solid-state diffusion method. The crystal structures and the phase purities of samples were characterized by powder X-ray diffraction. Surface morphology of the sample was studied by scanning electronic microscopy (SEM). The optimal concentrations of dopant Gd$^{3+}$ ions in compound LiSr$_4$(BO$_3$)$_3$ were determined through the measurements of photoluminescence (PL) spectra of phosphors. Gd$^{3+}$-doped phosphorsLiSr$_4$(BO$_3$)$_3$ show strong band absorption in UV spectral region and narrow-band UVB emission under the excitation of 276 nm was only due to ${}^{6}$P$_J$ $\to$ ${}^{8}$S$_{7/2}$ transition of Gd$^{3+}$ ions. The effect of Pr$^{3+}$ ion on excitation of LiSr$_4$(BO$_3$)$_3$:Gd$^{3+}$ was also studied. The excitation of LiSr$_4$(BO$_3$)$_3$:Gd$^{3+}$, Pr$^{3+}$ gives a broad-band spectra, which show very good overlap with the Hg 253.7 nm line. The photoluminescence spectra of LiSr$_4$(BO$_3$)$_3$ with differentdoping concentrations Pr$^{3+}$ and keeping the concentration of Gd$^{3+}$ constant at 0.03 mol have also been studied. The emission intensity of LiSr$_4$(BO$_3$)$_3$:Pr$^{3+}$–Gd$^{3+}$ phosphors increases with increasing Pr$^{3+}$ doping concentration and reaches a maximum at 0.01 mol. From the photoluminescence study of LiSr$_4$(BO$_3$)$_3$:Gd$^{3+}$, Pr$^{3+}$ we conclude that there was efficient energy transfer from Pr$^{3+} $\to$ Gd$^{3+}$ ions in LiSr$_{4−x−y}$Pr$_x$Gd$_y$(BO$_3$)$_3$ phosphors.

    • Microwave-assisted synthesis and photoluminescence properties of ZnS:Pb$^{2+}$ nanophosphor for solid-state lighting

      D N GAME C B PALAN N B INGALE S K OMANWAR

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      Nanocrystalline ZnS:Pb$^{2+}$ phosphor was synthesized by microwave-assisted co-precipitation method. Thephase purity and surface morphology of prepared material were investigated using an X-ray diffractometer (XRD) anda scanning electron microscope. The photoluminescence property was studied by near-UV (nUV) excitation. The XRDpattern of prepared phosphor matches well with that of an ICDD (International Center for Diffraction Data) file. Surfacemorphology of prepared phosphor was found to be in submicron range. As-prepared ZnS:Pb$^{2+}$ phosphor shows a greenemission under nUV excitation. As Pb$^{2+}$ ions are located on a regular Zn$^{2+}$ site they produce a green emission band inthe range of 400–650 nm, centred at 500 nm, under excitation wavelength of 357 nm, exhibiting luminescence propertiestypically observed for Pb$^{2+}$. Effect of concentration of Pb$^{2+}$ ions on emission intensity was studied. The colour co-ordinates of prepared phosphor were calculated and found to lie in the green region of Commission Internationale de l’Eclairagediagram.

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