Browsing by Author "Ekta Rai"

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Effect of Bi3+ ion on upconversion-based induced optical heating and temperature sensing characteristics in the Er3+/Yb3+ co-doped La2O3 nano-phosphor
(Royal Society of Chemistry, 2018) R.S. Yadav; Dinesh Kumar; A.K. Singh; Ekta Rai; S.B. Rai
The upconversion-based optical heating and temperature sensing characteristics are investigated in the Er3+/Yb3+/Bi3+ tri-doped La2O3 nano-phosphor synthesized through a solution combustion method. The structural measurements reveal an increase in lattice parameters and particles size of the phosphor on increasing the concentrations of Bi3+ ions. The energy dispersive spectroscopic (EDS) measurements confirm the presence of La, Er, Yb, Bi and O elements in the tri-doped phosphor. The absorption spectra show the large number of bands due to Er3+, Yb3+ and Bi3+ ions. The Er3+/Yb3+ co-doped phosphor gives strong green emission bands at 523 and 548 nm upon 976 nm excitation due to 2H11/2 → 4I15/2 and 4S3/2 → 4I15/2 transitions of Er3+ ion, respectively. The emission intensity of these bands is enhanced upto 15 times in the presence of Bi3+ ions. The emission intensities of the 523 and 548 nm bands vary non-linearly with the pump power. The fluorescence intensity ratio (FIR) of the thermally coupled 523 and 548 nm emission bands shows efficient optical heating in the tri-doped phosphor. The FIR of the 523 and 548 nm emission bands further varies with the increase in temperature of the phosphor. The relative temperature sensing sensitivity has been calculated to be 71 × 10−4 K−1 at 450 K for the tri-doped phosphor. Thus, the Er3+/Yb3+/Bi3+ tri-doped La2O3 nano-phosphor may provide a platform to use it in the photonic devices, as an optical heater and temperature sensor. © The Royal Society of Chemistry.
Effect of Cr3+ doping on structural and optical properties of Eu3+ doped LaVO4 phosphor
(Royal Society of Chemistry, 2023) Ekta Rai; Ram Sagar Yadav; Dinesh Kumar; Akhilesh Kumar Singh; Vijay Janardhan Fulari; Shyam Bahadur Rai
In this work, the Eu3+, Cr3+ doped and co-doped LaVO4 phosphors have been prepared through a high temperature solid-state reaction method. The powder XRD patterns of phosphors are very sharp and intense, which reflects a highly crystalline nature of phosphors. The XRD data were also refined by a Rietveld refinement method. The particle size of the phosphor samples lies in the sub-micron to micron range. The existence of La, Eu, Cr, V and O elements was verified by EDS spectra. The FTIR spectra show various absorption bands due to different vibrating groups. The optical band gap of the phosphor decreases on increasing concentration of Cr3+ ion. The photoluminescence excitation spectra of Eu3+, Cr3+ co-doped LaVO4 phosphor exhibit bands due to Eu3+ and Cr3+ ions. The Eu3+ doped LaVO4 phosphor exciting at 393 and 316 nm wavelengths gives intense red color at 614 nm due to the 5D0 → 7F2 transition of the Eu3+ ion. When the Cr3+ ion is co-doped in the Eu3+ doped LaVO4 phosphor the emission spectra contain emission bands due to Eu3+ and Cr3+ ions. The emission intensity of Eu3+ doped phosphor reduces due to energy transfer from Eu3+ to Cr3+ ions in presence of Cr3+ ions upon 393 and 386 nm excitations. The lifetime of the 5D0 level of Eu3+ ions decreases in the Eu3+, Cr3+ co-doped LaVO4 phosphor, which also reflects the energy transfer. The Eu3+, Cr3+ co-doped LaVO4 phosphor also produces a large amount of heat upon 980 nm excitation. Thus, the Eu3+, Cr3+ co-doped LaVO4 phosphors may be used for LEDs, solid state lighting and heat generating devices. © 2023 The Royal Society of Chemistry.
Effect of Synthesis Techniques on the Optical Properties of Ho 3+ /Yb 3+ Co-doped YVO 4 Phosphor: A Comparative Study
(American Chemical Society, 2019) Abhishek Dwivedi; Ekta Rai; Devendra Kumar; Shyam B. Rai
The Ho 3+ /Yb 3+ -codoped YVO 4 phosphors have been synthesized by three different techniques (viz., solution combustion, sol-gel, and solid-state reaction techniques). X-ray diffraction patterns confirm the formation of a pure phase in the samples synthesized by all of the three methods; however, the average crystallite sizes in the three cases are different. The crystallite size increases if they are heated to higher temperature. The particle sizes are measured by scanning electron microscopy, which shows an increase in particle size with increasing the calcination temperature. The vibrational behavior of all of the three synthesized phosphor samples is studied by the Fourier transform infrared (FTIR) technique. The UV-vis absorption measurements give a large number of bands in all of the three samples prepared by three different methods. The upconversion (UC) emissions in all three samples have been monitored using a 980 nm diode laser. It gives an intense red emission in all of the three samples. Upconversion emission intensity is more prominent in the phosphor sample synthesized by the sol-gel technique and heated at 1473 K. The enhancement in UC emission intensity is well understood by the shape and size of the particles and also confirmed by the FTIR and UV-vis measurements. It is interesting to note that whereas UC measurements give red and weak green emissions, downshifting (DS) measurements show intense green, weak red, and broad blue emissions on UV excitation (323 nm). The DS behavior shows the same characteristics of the enhancement in overall emission. Overall, the phosphor sample synthesized by the sol-gel method gives better results in upconversion and downshifting behaviors when heated at 1473 K. © 2019 American Chemical Society.
Improved photoluminescence in Eu3+ doped LaVO4 phosphor via co-doping of Li+/Ca2+ ions
(Elsevier B.V., 2022) Ekta Rai; Ram Sagar Yadav; Dinesh Kumar; Akhilesh Kumar Singh; Vijay Janardhan Fulari; Shyam Bahadur Rai
This paper investigates the structural and optical properties of Eu3+ doped LaVO4 phosphor via co-doping of Li+ and Ca2+ ions. The unit cell volume and particles size vary with Li+ and Ca2+ ions. The Eu3+ doped phosphor emits intense red color at 613 nm due to Eu3+ ion on excitation with 266, 355 and 394 nm. The photoluminescence intensity of Eu3+ doped phosphor is enhanced up to 2.1 and 4.5 times via co-doping of Li+ and Ca2+ ions, respectively. Therefore, the Eu3+, Li+, Ca2+ co-doped LaVO4 phosphor may be suitable candidate for the development of display devices and white light emitting diodes. © 2021 Elsevier B.V.
Influence of Bi3+ ion on structural, optical, dielectric and magnetic properties of Eu3+ doped LaVO4 phosphor
(Elsevier B.V., 2020) Ekta Rai; Ram Sagar Yadav; Dinesh Kumar; Akhilesh Kumar Singh; Vijay Janardhan Fulari; Shyam Bahadur Rai
In this paper, we have studied the structural, optical, dielectric and magnetic properties of Eu3+, Bi3+ co-doped LaVO4 phosphors prepared by solid state reaction method. Rietveld structural analysis of the samples confirms the monoclinic crystal structure with P21/n space group. The particles size of Eu3+ doped LaVO4 phosphor increased in presence of Bi3+ ion. The excitation spectrum of Eu3+, Bi3+ co-doped LaVO4 phosphor reveals bands due to charge transfer state (CTS) and electronic transitions of Eu3+ and Bi3+ ions. The Eu3+ doped LaVO4 phosphor gives intense red emission centred at 613 nm due to 5D0 → 7F2 transition of Eu3+ ion excited at 266, 355 and 394 nm wavelengths. When Bi3+ and Eu3+ ions are co-doped in the LaVO4 phosphor the photoluminescence intensity is enhanced upto two times. The photoluminescence intensity is largest for the 266 nm excitation. This is due to energy transfer from CTS and (1P1, 3P1) levels of the Bi3+ ion to 5D4 level of the Eu3+ ion and increase in the particles size of phosphor. The Eu3+, Bi3+ co-doped LaVO4 phosphors also show excellent dielectric and magnetic properties with a variation in frequency and magnetic field, respectively. Thus, the Eu3+, Bi3+ co-doped LaVO4 phosphor may be useful in fabricating displays devices, red emitting phosphors, dielectric capacitors and magnetic devices. © 2020 Elsevier B.V.
Realizing enhanced downconversion photoluminescence and high color purity in Dy3+ doped MgTiO3 phosphor in presence of Li+ ion
(Elsevier B.V., 2020) Ram Sagar Yadav; Monika; Ekta Rai; L.P. Purohit; Shyam Bahadur Rai
The Dy3+, Li+ co-doped MgTiO3 phosphor has been successfully synthesized through a high temperature solid state reaction method. The structural measurement suggests that the doping of Li+ ion improves the crystallinity and particles size of the phosphor. The EDS measurement approves the presence of Mg, Ti, O and Dy elements in the phosphor. The FTIR measurement reveals the presence of different vibrating molecules in the phosphor. The optical band gap of the phosphor slightly decreases in presence of Li+ ion. The photoluminescence excitation spectrum of Dy3+ doped phosphor shows a strong band centered at 355 nm alongwith other weak bands. The Dy3+ doped phosphor gives intense yellow photoluminescence centered at 579 nm due to 4F9/2 → 6H13/2 transition on excitations with 327, 355, 367 and 385 nm wavelengths. However, the emission intensity is relatively larger for 355 nm excitation. The emission intensity of phosphor varies on increasing concentrations of Dy3+ ions and it is optimum at 2 mol%. Interestingly, the emission intensity of the phosphor is enhanced up to 3 times in presence of Li+ ion. This is due to an increase in crystallinity, particles size and charge compensation induced by the Li+ ion. The CIE coordinates show the presence of emitted light with high color purity in the yellow region of visible spectrum. The lifetime of Dy3+ level in the phosphor is found to increase via doping of Li+ ion. Thus, the Dy3+, Li+ co-doped MgTiO3 phosphor may be a useful candidate in displays devices and white light emitting devices (WLEDs). © 2019 Elsevier B.V.
Structural and luminescent properties and energy transfer from Tb3+ to Eu3+ in LaVO4:xTb3+/ yEu3+ phosphors
(Elsevier Ltd, 2023) Ekta Rai; Abhishek Roy; Anita Rai; Vijay Janardhan Fulari; S.B. Rai
The structural and optical properties of Eu3+, Tb3+ doped and Eu3+/Tb3+ codoped LaVO4 a self-activated host have been studied in detail. The XRD patterns of phosphor samples show that the LaVO4 crystallizes in monoclinic phase with the P21/n space group. The average crystallite size is ∼ 60 nm which decreases on doping of Eu3+, Tb3+ ions. The SEM patterns show particles of nearly spherical shape whose average size (∼ 5.64 µm) decrease on doping. The UV-Vis absorption and FTIR spectra of the samples were also studied. The excitation spectra of Eu3+, Tb3+ doped and Eu3+/Tb3+ codoped LaVO4 samples show intense charge transfer band (CTB) at 323 nm due to [VO4]3- group of host material. Eu3+ doped /codoped phosphor samples, also show large number of sharp bands due to Eu3+ ion alongwith CTB. On the other hand, Tb3+ doped LaVO4 show broad band near 375 nm. Photoluminescence could be observed from 5D0, 5D1 to different levels of ground state (7FJ) in Eu3+ in which the 5D0-7F2 at 614 nm is very intense. Similarly, in case of Tb3+, bands could be observed from 5D4-7FJ in which the bands in green and blue at 543, 489 nm due to 5D4-5F5 and 5D4-7F6 transitions respectively are very intense. Thus, samples containing Eu3+/Tb3+ together emit blue, green and red colors on 323 nm excitation. The phosphor samples containing LaVO4:Tb3+/Eu3+ also show energy transfer from Tb3+ to Eu3+ ion on excitation with CTB wavelength. The energy transfer efficiency has also been calculated by considering the changes in emission intensity of 543 nm (5D4-7F5) band and the lifetime of 5D4 level of Tb3+ ion for different concentrations of Eu3+ and fixed concentration of Tb3+ ion in LaVO4:1Tb3+/yEu3+ phosphor samples. The interaction of two ions was found dipole-dipole. © 2022 Elsevier B.V.
Structural and photoluminescence properties of Cr3+ doped LaVO4 phosphor
(Elsevier Masson s.r.l., 2022) Ekta Rai; Ram Sagar Yadav; Dinesh Kumar; Akhilesh Kumar Singh; Vijay Janardhan Fulari; Shyam Bahadur Rai
In this work, we have studied the structural and photoluminescence properties of Cr3+ doped LaVO4 phosphor prepared by solid state reaction method. The XRD patterns of phosphors give an idea about the unit cell volume, crystallite size and crystalline nature. The SEM images provide the morphological features of the phosphor samples. The unit cell volume and the particles size of the Cr3+ doped LaVO4 phosphors decrease on increasing concentration of Cr3+ ion. The elements present in the Cr3+ doped phosphors have been analyzed using EDS and color mapping techniques. The FTIR spectra of Cr3+ doped LaVO4 phosphors specify the vibrational bands present in the samples. The UV–vis absorption and PL excitation spectra of the phosphor samples give information about the excitation wavelengths. The optical band gap of LaVO4 phosphor is 3.56 eV, which decreases on increasing concentration of Cr3+ ion. The Cr3+ doped LaVO4 phosphor gives yellow (581 nm), red (634 nm) and NIR (700 and 765 nm) emissions upon 428 and 467 nm excitations, respectively. The lifetime of Cr3+ doped LaVO4 phosphor decreases on increasing concentration of Cr3+ ion. The Cr3+ doped phosphor also shows heat generation capacity upon 980 nm excitation. Therefore, the Cr3+ doped LaVO4 phosphor may be used for solid state lighting, NIR sources and heat generating devices. © 2022 Elsevier Masson SAS