Browsing by Author "S.J. Dhoble"

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Effect of singly, doubly and triply ionized ions on downconversion photoluminescence in Eu3+ doped Na2Sr2Al2PO4Cl9 phosphor: A comparative study
(Elsevier Ltd, 2020) A.R. Kadam; R.S. Yadav; Girish C. Mishra; S.J. Dhoble
We report a change in the red photoluminescence of the Eu3+ doped Na2Sr2Al2PO4Cl9 phosphor via doping of singly, doubly and triply ionized ions. The synthesized phosphors show good crystalline nature. The EDS analysis confirms the presence of desired elements in the phosphor samples. The vibrational feature of the phosphor was confirmed by FTIR analysis. The photoluminescence excitation spectra of the phosphor show three peaks at 317, 395 and 467 nm. The Eu3+ doped Na2Sr2Al2PO4Cl9 phosphor emits intense red color on excitations with 395 and 467 nm wavelengths. However, the photoluminescence intensity of the phosphor is larger for 395 nm excitation. When the singly, doubly and triply ionized ions are co-doped in the Eu3+ doped Na2Sr2Al2PO4Cl9 phosphor (i.e. F−, WO4 2−, MoO4 2−, VO4 3−, La3+, and Y3+) the photoluminescence intensity of the phosphor is decreased significantly. The decrease in photoluminescence intensity is due to change in local crystal structure created by these ions. Interestingly, the photoluminescence intensity of phosphor increases many times when the (Y3+) ion incorporated phosphor is excited with 317 nm wavelength. The CIE diagram shows color emitted in the red region of visible spectrum and the color purity is larger for triply ionized (Y3+) ion. Thus, the singly, doubly and triply ionized ions activated Na2Sr2Al2PO4Cl9: Eu3+ phosphor may be used in displays devices, photonic devices, solid state lighting and white LEDs. © 2019 Elsevier Ltd and Techna Group S.r.l.
Enhanced photoluminescence in Tm3+, Yb3+, Mg2+ tri-doped ZnWO4 phosphor: Three photon upconversion, laser induced optical heating and temperature sensing
(Elsevier B.V., 2018) R.S. Yadav; S.J. Dhoble; S.B. Rai
Three photon upconversion photoluminescence has been observed in Tm3+, Yb3+ co-doped ZnWO4 phosphor synthesized through solid state reaction method. The structural measurements reveal an increase in crystallinity and particles size on Mg2+ incorporation. The EDS spectrum shows the presence of Zn, W, Tm, Yb, Mg and O elements in the phosphor. The UV–vis-NIR absorption spectra contain CTB and 4f-4f transitions due to Tm3+ and Yb3+ ions, respectively. The Tm3+, Yb3+ co-doped phosphor gives intense blue and NIR emissions alongwith a weak red emission due to 1G4→3H6, 3H4→3H6 and 1G4→3F4 transitions, respectively upon 976 nm excitation. The emission intensity of the phosphor is found optimum at 2 mol% concentration of Yb3+ ion. When the Mg2+ ion is incorporated in the co-doped phosphor, the emission intensity enhances upto two times. This may be due to improved crystal structure and an increase in the intensity of absorption bands. The FIR analysis in the Stark components of 1G4 level suggests an efficient optical heating and temperature sensing ability. The temperature sensing sensitivity is found to be 34 × 10−4 °K-1 at 300°K. Thus, the Tm3+, Yb3+, Mg2+ tri-doped ZnWO4 phosphor may be used in photonic devices, NIR source, as an optical heater and temperature sensor purposes. © 2018 Elsevier B.V.
Enhanced photoluminescence via doping of phosphate, sulphate and vanadate ions in Eu3+ doped La2(MoO4)3 downconversion phosphors for white LEDs
(Elsevier Ltd, 2020) Yatish R. Parauha; R.S. Yadav; S.J. Dhoble
In this study, the Eu3+ doped La2(MoO4)3 phosphor has been successfully prepared by solid state reaction method. The prepared phosphors are crystalline and the particle size increases in the presence of phosphate, sulphate and vanadate ions. The photoluminescence excitation (PLE) spectrum of the Eu3+ doped La2(MoO4)3 phosphor shows an intense peak centered at 467 nm due to absorption by Eu3+ ions. On the excitation at 467 nm, the Eu3+ doped La2(MoO4)3 phosphor emits strong red emission centered at 614 nm, which is attributed to the 5D0 → 7F2 transition of Eu3+ ions. The emission intensity of the phosphors has been optimized by appropriate selection of the concentration of Eu3+ ions. When the phosphate, sulphate and vanadate ions are incorporated in the thermally stable Eu3+ doped La2(MoO4)3 phosphor the emission intensity of Eu3+ion is enhanced significantly. This occurs due to modification in the local crystal structure and the particle size increase. The CIE diagram shows the presence of emission bands in the visible spectrum. It also shows color tunability with a high color purity of the phosphor. The phosphate, sulphate and vanadate doped La2(MoO4)3: Eu3+ phosphors may act as good candidates for the phosphor converted white LEDs in solid state lighting technology. © 2019 Elsevier Ltd
Improved photon upconversion photoluminescence and intrinsic optical bistability from a rare earth co-doped lanthanum oxide phosphor: Via Bi3+ doping
(Royal Society of Chemistry, 2018) R.S. Yadav; S.J. Dhoble; S.B. Rai
In this paper, an Er3+, Yb3+ co-doped La2O3 phosphor has been synthesized through a solid state reaction method. Structural analysis reveals the strong crystalline nature of samples. EDS measurements confirm the presence of La, O, Er, Yb and Bi elements in the sample. FTIR measurements of samples show bands due to La-O stretching vibrations. UV-vis-NIR spectra of samples show a large number of absorption bands due to different transitions of Bi3+, Er3+ and Yb3+ ions. The intensities of the absorption bands increase over the entire region due to Bi3+ doping. The phosphor sample emits intense green and weak red upconverted photoluminescence centered at 523 and 671 nm, respectively, upon excitation at 976 nm. The emission intensity of the phosphor is optimum for a 0.7 mol% Er3+ ion concentrations. Pump power versus emission intensity studies shows the absorption of two photons for this upconverted emission and color tunability. The emission intensity of the Er3+, Yb3+ co-doped La2O3 phosphor is enhanced up to ∼65 times as a result of Bi3+ doping. The enhancement in emission intensity is observed due to an increase in crystallinity and the intensity of the absorption bands. The Er3+, Yb3+ co-doped La2O3 phosphor also shows intrinsic optical bistability (IOB) and the area of the IOB curves increases significantly following Bi3+ doping. Thus, the Er3+, Yb3+, Bi3+ co-doped La2O3 phosphor may be used in photonic and optically bistable devices. © 2018 The Royal Society of Chemistry and the Centre National de la Recherche Scientifique.
Near UV excited multi-color photoluminescence in RE3+ (RE=Tb, Sm, Dy and Eu) doped Ca2Pb3(PO4)3Cl phosphors
(Elsevier B.V., 2019) Nahida Baig; R.S. Yadav; N.S. Dhoble; Vijay L. Barai; S.J. Dhoble
The Ca2Pb3(PO4)3Cl: RE3+ (RE = Tb, Sm, Dy and Eu) phosphor materials were prepared by wet chemical method. The synthesized phosphors were analyzed by using XRD, SEM and photoluminescence (PL) characterization techniques. The excitation spectrum of the Ca2Pb3(PO4)3Cl:Tb3+ phosphor consists of several bands in the 300–400 nm region by monitoring emission at 545 nm, which are assigned due to electronic transitions from 7F6 to the upper levels of Tb3+ ion. The Ca2Pb3(PO4)3Cl:Tb3+ phosphor emits efficient narrow green emission at 545 nm due to 5D4 → 7F5 transition upon 371 nm excitation. The PL excitation spectrum of the Ca2Pb3(PO4)3Cl:Sm3+ phosphor exhibits narrow bands in the near ultraviolet (NUV) region due to Sm3+ ion. The Ca2Pb3(PO4)3Cl: Sm3+ phosphor shows orange red emission centered at 598 nm, which is attributed to the 4G5/2 → 6H7/2 transition of Sm3+ ion. The concentration quenching has been studied in both the cases and the critical distance was calculated as 38.5 Å. The blue (482 nm) and yellow (576 nm) emissions are obtained in the Ca2Pb3(PO4)3Cl:Dy3+ phosphor under 352 nm and 455 nm excitations, which are attributed to the 4F9/2 → 6H15/2 and 4F9/2 → 6H13/2 transitions of Dy3+ ion, respectively. However, the Ca2Pb3(PO4)3Cl:Eu3+ phosphor emits strong orangish red emission centered at 594 nm, which is attributed to the 5D0 → 7F1 transition of Eu3+ ion on excitation with 396 nm. The CIE diagram shows green and orange red photoluminescence for the Ca2Pb3(PO4)3Cl:Tb3+ and Ca2Pb3(PO4)3Cl:Sm3+ phosphors, respectively whereas the bluish-yellow and orangish red photoluminescence for the Ca2Pb3(PO4)3Cl:Dy3+ and Ca2Pb3(PO4)3Cl:Eu3+ phosphors, respectively. The CIE coordinates indicate that the present phosphors have high color purity. These phosphors may act as good candidates for phosphor converted LEDs for solid state lighting technology. © 2019 Elsevier B.V.
Optical properties of lanthanide-based pyrophosphate phosphor materials
(Nova Science Publishers, Inc., 2020) R.S. Yadav; X. Monika; S.J. Dhoble; S.B. Rai
This chapter covers the synthesis, compositional effect and optical properties of lanthanide-based pyrophosphate phosphor materials. The general properties of the pyrophosphate materials have been discussed. The structural parameters of pyrophosphate phosphor materials have approved that these materials are very promising and thermally stable. Additionally, the energy transfer between the lanthanide ions has been discussed by taking some examples. Basically, the two ions are involved in the energy transfer in which former one is called as donor ion whereas latter one is the accepter ion. The energy transfer takes place from donor to acceptor ions. This leads to an enhancement in the photoluminescence intensity of different phosphor materials. The addition of some surface modifiers also enhances the photoluminescence intensity of the phosphor materials. The applications of lanthanide-based pyrophosphate phosphor materials have been also incorporated in this chapter. © 2020 Nova Science Publishers, Inc.
Optical transitions and radiative properties of green emitting Ho3+:YVO4 phosphor
(Royal Society of Chemistry, 2023) Vijay Singh; M. Seshadri; Deepak Taikar; S.J. Dhoble; R.S. Yadav
The Ho3+-doped YVO4 phosphors were successfully prepared via a sol-gel process in which citric acid was used as a chelating agent. X-ray diffraction (XRD) confirmed the effective inclusion of Ho3+ ions into the host matrix with the formation of single phase YVO4. The surface morphology was observed using SEM, the results of which showed a grain growth propensity and the agglomeration of prepared phosphors. The V-O (VO43−) vibration mode was analyzed through Fourier transform infrared (FTIR) spectra. The spectroscopic properties were reported through UV-vis-NIR diffuse reflectance and photoluminescence (PL) spectra. The Judd-Ofelt (J-O) intensity parameters Ω2 = 0.03 × 10−20 cm2, Ω4 = 0.22 × 10−20 cm2, and Ω6 = 0.23 × 10−20 cm2 obtained for the Y0.97VO4:0.03Ho3+ phosphors were used to obtain the total transition probabilities (AT), radiative lifetimes (τrad) and branching ratios (β) for the certain transitions of Ho3+ ions. Under 310 nm UV excitation, the visible emission spectra were measured, and an intense emission was observed around 541 nm (green region) for all the samples. The emission cross-section σP(λ) was 3.22 × 10−21 cm2 and the branching ratio (β) was 0.816; these were investigated to capture the optimal concentration of the Y0.97VO4:0.03Ho3+ phosphor. The estimated color coordinates were observed in the green region of CIE diagram. Ultimately, the superior properties (σP(λ), β, and color purity) of Y0.97VO4:0.03Ho3+ phosphor may make it suitable for green emitting devices. © 2023 The Royal Society of Chemistry.
Proposing a novel graphical method to determine effective bremsstrahlung focal spot size and shape of the therapeutic beam from a linear accelerator in radiation therapy
(Elsevier B.V., 2021) Ravindra Shende; Gourav Gupta; S.J. Dhoble; Ganeshkumar Patel; Ashutosh Dassharma
The purpose of this study is to introduce and demonstrate a novel graphical method to determine effective bremsstrahlung focal spot size and shape of the therapeutic beam from a linear accelerator. The energy distribution within the beam spot allows in determining effective bremsstrahlung size and shape of beam spot. The transverse and radial dose profiles were measured for a range of field sizes in an isocentric setup. The Length of direct focal region (LDFR) on either side of profiles were determined through the de-convolution of dose profile. The graph plotted for LDFR versus field size helps in determining properties of beam spot. The dimensions of FWHM of effective bremsstrahlung focal spot were found elliptical in nature close to the order of 1 mm. This method allows determination of FWHM of the effective bremsstrahlung focal spot that fairly falls within the range of dimension of FWHM of beamspot published in literature. © 2021 Elsevier B.V.
Recent advances on morphological changes in chemically engineered rare earth doped phosphor materials
(Elsevier Ltd, 2020) R.S. Yadav; Monika; S.B. Rai; S.J. Dhoble
The photoluminescent phosphor materials nowadays are extremely important source of light to fulfill the technological demand over the conventional light source for eco-friendly environment. This review brings the morphological and optical properties of the chemically engineered rare earth doped photoluminescent materials at one platform. The recent developments have been incorporated and different processes involved in the morphological changes of these materials are discussed. The optical properties of different mono-, di- and tri-rare earth doped phosphors have been analyzed and evaluated using various sensitizers and surface modifiers. The photoluminescence intensity of the materials is greatly affected by changing the morphology of the phosphors via some sensitizers and surface modifiers. The large photoluminescence intensity thus obtained has been summarized due to change in the morphology. The future aspects of change in the morphological properties of the chemically engineered rare earth doped phosphors have been also proposed. © 2019 Elsevier Ltd
Structural and spectroscopic characterizations of a new near-UV-converting cyan-emitting RbBaScSi3O9:Eu2+ phosphor with robust thermal performance
(Elsevier Ltd, 2017) Sudeshna Ray; Prachi Tadge; S.J. Dhoble; Govind B. Nair; Akash Singh; Abhishek Kumar Singh; Monika Rai; Teng Ming Chen; Vinita Rajput
To facilitate the next generation of White Light Emitting Diodes (WLEDs) with higher color rendering and warm lighting, the development of inorganic phosphor for efficient conversion of photons from blue/near-UV light to other visible wavelengths is essential. In this regard, we demonstrate a systematic, cost effective, solution-processable, easily scalable and fully controllable synthesis of a series of RbBaScSi3O9:xEu2+ (x = 0.2, 0.5, 2, 5, 7), a new cyan emitting scandium silicate based phosphor with 79% internal quantum efficiency under n-UV excitation with robust thermal performance. The concept as well as the methodology of using a “Mineral Inspired Approach” emerges as a new blueprint for the rational design of novel phosphor for phosphor converted WLEDs. The structural refinement, electronic structural calculation using “Density Functional Theory”, characteristic photoluminescence study, lifetime measurement as well as the thermal quenching properties of the phosphor has been investigated in detail. Owing to the highly efficient cyan emission at λmax ∼492 nm a full-width at half-maximum of 63 cm−1 that shows only very low thermal quenching (89.28% relative to the PL intensity at 150 °C with respect to that of measured at room temperature), reflects the great potential for the industrial application of this particular phosphor. © 2017 Elsevier B.V.