Browsing by Author "Ram Sagar Yadav"

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Concentration and pump power-mediated color tunability, optical heating and temperature sensing via TCLs of red emission in an Er3+/Yb3+/Li+ co-doped ZnGa2O4 phosphor
(Royal Society of Chemistry, 2019) Monika; Ram Sagar Yadav; Amresh Bahadur; Shyam Bahadur Rai
Intense red upconversion luminescence was observed in the Er3+/Yb3+/Li+ co-doped ZnGa2O4 phosphor synthesized through the solid state reaction method for the first time. The structural characterization showed a large crystalline nature and an increase in the particle size via Li+ doping. The absorption spectra showed a large number of peaks in the UV-vis-NIR regions due to the Er3+ and Yb3+ ions. The Er3+/Yb3+ co-doped ZnGa2O4 phosphor exhibited green, red and NIR upconversion emissions on excitation with 980 nm radiation. The intensity of the red emission was relatively larger than that of the other emissions. The luminescence intensity versus pump power measurements revealed the number of required photons for these emissions. The phosphor showed very interesting color tunability as a function of Er3+ ion concentration and incident pump power. The luminescence intensity of the Er3+/Yb3+ co-doped phosphor was enhanced more than two times via Li+ doping. The enhancement in the luminescence intensity was proposed to be due to the increase in the crystallinity and particle size of the phosphor. The lifetimes of the 4S3/2 and 4F9/2 levels also increased in the presence of Li+ ions. The variation in the fluorescence intensity ratio (FIR) of the thermally coupled levels (TCLs) of the red emission with incident pump power offered effective optical heating in the phosphor. The temperature-induced FIR using TCLs of red emission exhibited a larger value of temperature sensing sensitivity in the presence of Li+ ions, which was up to 14 × 10-4 K-1. Thus, the Er3+/Yb3+/Li+ co-doped ZnGa2O4 phosphor may be used in photonic, optical heating, and temperature sensing devices. © 2019 The Royal Society of Chemistry.
Concentration and wavelength dependent frequency downshifting photoluminescence from a Tb3+ doped yttria nano-phosphor: A photochromic phosphor
(Elsevier Ltd, 2018) Ram Sagar Yadav; Shyam Bahadur Rai
In this article, the Tb3+ doped Y2O3 nano-phosphor has been synthesized through solution combustion method. The structural measurements of the nano-phosphor have been carried out by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques, which reveal nano-crystalline nature. The Fourier transform infrared (FTIR) measurements reveal the presence of different molecular species in the nano-phosphor. The UV–Vis–NIR absorption spectrum of the nano-phosphor shows large number of bands due to charge transfer band (CTB) and 4f-4f electronic transitions of Tb3+ ion. The Tb3+ doped Y2O3 nano-phosphor emits intense green downshifting photoluminescence centered at 543 nm due to 5D4 → 7F5 transition on excitation with 350 nm. The emission intensity of the nano-phosphor is optimized at 1.0 mol% concentration of Tb3+ ion. When the as-synthesized nano-phosphor is annealed at higher temperature the emission intensity of the nano-phosphor enhances upto 5 times. The enhancement in the emission intensity is due to an increase in crystallinity of the nano-phosphor, reduction in surface defects and optical quenching centers. The CIE diagram reveals that the Tb3+ doped nano-phosphor samples show the photochromic nature (color tunability) with a change in the concentration of Tb3+ ion and excitation wavelength. The lifetime measurement indicates an increase in the lifetime for the annealed sample. Thus, the Tb3+ doped Y2O3 nano-phosphor may be used in photochromic displays and photonic devices. © 2017 Elsevier Ltd
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.
Effects of Yb3+ ion doping on lattice distortion, optical absorption and light upconversion in Er3+/Yb3+ co-doped SrMoO4 ceramics
(Elsevier Ltd, 2021) Ankur Shandilya; Ram Sagar Yadav; Ajai K. Gupta; K. Sreenivas
Sintered ceramic pellets of rare-earth ion doped strontium molybdate compositions Sr1-x-yErxYbyMoO4 (x = 1 mol%; y = 0–9 mol%) were prepared using solid-state reaction method. Rietveld refinement of HR-XRD data reveals a high degree of lattice distortion for y = 3 mol %, and correspondingly a maximum deviation in the O–Sr–O and Mo–O bonds. Raman spectroscopy indicates the substitution of Er3+ and Yb3+ at the SrO8 polyhedron clusters of the SrMoO4 unit cell, and infrared absorption shows changes in the molybdenum-oxygen (Mo–O) bond strength in the [MoO4]2⎻ cluster. Variations in the optical band gap are attributed to positional change of oxygen octahedra and local bond distortion in the unit cell. A selective enhancement in green up-conversion luminescence is seen at y = 3 mol %, and originates due to direct contribution from the [Yb3+⎼MoO4]2- dimer complex sensitization, and correlates with the presence of high lattice distortion. A progressive increase in lifetime of the 4S3/2 from 0.195 to 0.424 ms at y = 0.03 increase the radiative transition probability and UC emission. Luminescence quenching for Yb3+ ion content (y > 0.03) is due to the reduced asymmetrical arrangement around erbium ion and corresponding changes in the Sr–O and Mo–O bond lengths. These studies provide new insight into the quenching effect and formulate a new strategy to design ceramic compositions for better UC performance. © 2021 Elsevier B.V.
Energy transfer induced color tunable photoluminescence in Tb3+/Sm3+ co-doped Y2O3 nano-phosphor for warm white LEDs
(Elsevier Ltd, 2023) Ram Sagar Yadav
In this work, the Tb3+/Sm3+ doped and co-doped Y2O3 nano-phosphors have been prepared by solution combustion method. The structural and morphological analyses of Y2O3 nano-phosphors confirm its nano-crystalline structure. The EDS spectra reveal the evidence of Y, Sm, Tb and O elements in the co-doped phosphor. The excitation spectrum of the Tb3+/Sm3+ co-doped nano-phosphor contains the excitation bands due to Tb3+ and Sm3+ ions. The Tb3+ doped nano-phosphor gives intense green (541 nm) and slightly weak blue (483 nm) emissions upon 292 nm excitation. The critical distance and PL intensity per activator ion were calculated to identify the factor responsible for quenching the PL intensity. The PL intensity of green and blue emission bands decreases regularly via doping of Sm3+ ion. This occurs due to energy transfer from Tb3+ to Sm3+ ions. The energy transfer leads to improve the PL intensity of the orange red emission band of Sm3+ ion. The energy transfer has been verified by the lifetime measurements and the energy transfer efficiency is found to increase via doping of Sm3+ ion. The CIE diagrams show wide color tunability from the greenish yellow to reddish orange regions and the color purity of Tb3+ doped nano-phosphor also changes accordingly via Sm3+ doping. The CCT analysis of Tb3+/Sm3+ co-doped nano-phosphors indicates a warm nature of the emitted light. Therefore, the Tb3+/Sm3+ co-doped Y2O3 nano-phosphor may be applied in the field of display devices, color tunable devices and warm white LEDs. © 2022 Elsevier B.V.
Enhanced mechanical properties and hydrophilic behavior of magnesium oxide added hydroxyapatite nanocomposite: A bone substitute material for load bearing applications
(Elsevier Ltd, 2020) Sunil Kumar; Chandkiram Gautam; Brijesh Singh Chauhan; Saripella Srikrishna; Ram Sagar Yadav; Shyam Bahadur Rai
Hydroxyapatite is a multifunctional biomaterial that combines biocompatibility and bioactivity for various biomedical applications such as bone repairing and bioimaging. In the present study nano-hydroxyapatite (n-HAp) was synthesized using microwave irradiation technique. Subsequently, the MgO was introduced into the n-HAp matrix and various bioactive compositions of HAp-MgO nanocomposites were fabricated. The structural, mechanical, in vivo cell viability, and in vivo imaging properties of these nanocomposites were studied. The XRD results show that the composites sintered at 1200 °C, n-HAp partially decomposed into beta-tricalcium phosphate (β-TCP). The sintered density of the composites varying from 2.72 ± 0.066 to 3.03 ± 0.093 g cm−3 with the addition of 0.0–2.0 wt % of MgO. As increasing the amounts of MgO, a remarkable increase in the mechanical properties of the composite was achieved. The composite HAp-1.0MgO exhibited the highest mechanical properties with a compressive strength of 111.20 ± 5 MPa, fracture toughness 136.98 ± 5 MJ/m3 and revealed much amplification than pure n-HAp. Thus, the addition of MgO acting as an excellent mechanical reinforcing agent. The surface morphology of the composites revealed a significant change in the porous surface to denser. The low contact angle revealed the considerable hydrophilic nature of the composite surface. The biological study of these nano-composites with Drosophila third instar larvae indicated comparable or more favorable biocompatibility in terms of cell viability. Also internalized by Drosophila third instar larvae exhibited fluorescence under green and red filters using epifluorescence microscopy. Thus, the fabricated HAp-MgO nanocomposites with excellent biological properties are expected to be a multifunctional bioactive material for bone tissue regeneration and cell imaging applications. © 2020 Elsevier Ltd and Techna Group S.r.l.
Enhanced photoluminescence in a Eu3+ doped CaTiO3 perovskite phosphor via incorporation of alkali ions for white LEDs
(Elsevier Ltd, 2021) Priti Singh; Ram Sagar Yadav; Shyam Bahadur Rai
Intense red photoluminescence has been observed in Eu3+/Z+ (Z+ = Li+, Na+ & K+) co-doped CaTiO3 perovskite phosphor materials, synthesized through high temperature solid-state reaction technique. The phosphor materials are structurally characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. All the compounds are crystalline with the orthorhombic phase. The crystallite and particle size of phosphor increase via incorporation of alkali ions. The vibrational groups in phosphor materials are studied by Fourier transform infrared (FTIR) technique. The diffuse reflectance spectra showed a number of peaks in the UV–visible regions due to different transitions of Eu3+ ion. The band gap (Eg) of the phosphor decreases on incorporation of alkali ions. The phosphor materials emit intense red color at 613 nm due to 5D0 → 7F2 transition of Eu3+ ion upon 398 nm and 466 nm excitation wavelengths. The intensity of red emission increases upto 12 mol% concentration of Eu3+ ions. On incorporation of alkali ions in the 12 mol% Eu3+: CaTiO3 phosphor, the emission intensity increases further due to crystallinity, charge compensation and the asymmetry created around the Eu3+ ions in the phosphor. The emission intensity is largest for the 12Eu3+/10Na+ co-doped CaTiO3 phosphor. The asymmetric ratio is higher for the 12Eu3+/10Na+ co-doped CaTiO3 phosphor. The lifetime of 5D0 level is enhanced via incorporation of alkali ions and it is also larger for the 12Eu3+/10Na+ co-doped CaTiO3 phosphor. The CIE color coordinates, correlated color temperature (CCT), color purity and color rendering index (CRI) calculations of the phosphors have also been carried out, which show pure red color in warm light region. Therefore, these synthesized perovskite phosphor materials can be advantageous for display devices, NUV excited red phosphors for making the tricolor phosphor converted WLEDs and blue LED chip-based WLEDs for solid state lighting applications. © 2020 Elsevier Ltd
Enhanced photovoltaic performance of Y2O3:Ho3+/Yb3+ upconversion nanophosphor based DSSC and investigation of color tunability in Ho3+/Tm3+/Yb3+ tridoped Y2O3
(Elsevier Ltd, 2020) Prachi Tadge; Ram Sagar Yadav; Pradeep Kumar Vishwakarma; S.B. Rai; Teng-Ming Chen; Sameer Sapra; Sudeshna Ray
The present study reports the upconversion (UC) based color tuning in Y2O3:Ho3+/Yb3+, Y2O3:Tm3+/Yb3+ and Y2O3:Tm3+/Ho3+/Yb3+ phosphors synthesized through complex based precursor solution method. The Y2O3:Ho3+/Yb3+ phosphor emits intense green and weak red colors whereas the Y2O3:Tm3+/Yb3+ emits NIR and blue colors on excitation with 976 nm. The impact of the enhancement in the concentration of Yb3+ on the color point of codoped as well as tridoped phosphors has been studied in detail. When Y2O3:Tm3+/Ho3+/Yb3+ phosphor is excited by 976 nm laser, the phosphor emits dominant green color. This is due to energy transfer from Tm3+ to Ho3+ ions. The increase in the concentration of Yb3+ ion leads to a color tunability not only in the co-doped but also in the tridoped phosphors. Furthermore, we have incorporated Y2O3:Ho3+,Yb3+ UC phosphor into TiO2 electrode to form an UC based DSSC for converting near IR (NIR) light into visible where DSSCs typically have high sensitivity. The short-circuit current density (Jsc) as well as the open-circuit voltage (Voc) of the UC-TiO2 based cell was found to be 8.46% and 5.18% higher which in turn, resulted into a 10.33% enhancement in power conversion efficiency as compared to that of bare TiO2 based DSSC. Thus, the UC based Y2O3:Ho3+/Yb3+ may be useful in color tunability and DSSC applications. © 2019 Elsevier B.V.
Enhanced Quantum Cutting via Li+ Doping from a Bi3+/Yb3+-Codoped Gadolinium Tungstate Phosphor
(American Chemical Society, 2016) Ran Vijay Yadav; Ram Sagar Yadav; Amresh Bahadur; Akhilesh Kumar Singh; Shyam Bahadur Rai
The Bi3+/Yb3+-codoped gadolinium tungstate phosphor has been synthesized through a solid-state reaction method. The structural characterization reveals the crystalline nature of the phosphor. The Bi3+-doped phosphor emits visible radiation from the blue to red regions upon excitation with 330 and 355 nm. The addition of Yb3+ to the Bi3+-doped phosphor reduces the emission intensity in the visible region and emits an intense near-infrared (NIR) photon centered at 976 nm through a quantum-cutting (QC) phenomenon. This is due to cooperative energy transfer (CET) from the 3P1 level of Bi3+ to the 2F5/2 level of Yb3+. The presence of Li+ ions in the Bi3+/Yb3+-codoped phosphor enhances the emission intensity in the NIR region up to by 3 times, whereas the emission intensity in the visible region is significantly reduced. The energy transfer (ET) from the Bi3+ ions to the Yb3+ ions is confirmed by lifetime measurements, and the lifetime for the 3P1 level of Bi3+ decreases continuously with increasing Yb3+ concentration. The ET efficiency (ηETE) and corresponding QC efficiency (ηQE) are calculated and found to be 29% and 129%, respectively. The presence of Li+ enhances the QC efficiency of the phosphor up to 43%. Thus, the Bi3+/Yb3+/Li+-codoped phosphor is a promising candidate to enhance the efficiency of a crystalline-silicon-based solar cell through spectral conversion. © 2016 American Chemical Society.
Estimation of spectroscopic parameters and TL glow curve analysis of Eu3+-activated CaY2O4 phosphor
(Royal Society of Chemistry, 2023) Tirath Ram; Neeraj Verma; Jagjeet Kaur; Abhishek Kumar Misra; Vikas Dubey; Neha Dubey; Marta Michalska-Domańska; Janita Saji; Ram Sagar Yadav
The solid-state reaction method was utilised to create a down-conversion phosphor in an air environment in CaY2O4:Eu3+ nanocrystalline material. The calcination temperature was set at 1000 °C, and the sintering temperature was set at 1300 °C. Following annealing, confirmation of the crystallinity quality of the phosphor was accomplished by the use of X-ray diffraction analysis. The particle size was predicted to be 43.113 nm using Scherrer's formula. To produce down-conversion luminescence spectra, an excitation wavelength of 247 nm was applied with a fluorescence spectrophotometer. The PL got increasingly intense as the concentration of the dopant increased. The maximum intensity was measured at 2.0 mol% of Eu3+ ion, which gradually decreased as the concentration increased because of concentration quenching. To analyse spectrophotometric peak determinations, the approach developed by the Commission Internationale de l'Éclairage (CIE) was used. Thermoluminescence (TL) glow curve analysis of the CaY2O4:Eu3+-doped phosphor manufactured here revealed a wide TL centred at 225 °C, which comprised of so many peaks that may be extracted by the computerised glow curve deconvolution (CGCD) approach using glow-fit software. The associated kinetic parameters were then determined. The prepared phosphor may be useful for application in various display devices upon excitation by 247 nm; the prominent 613 nm peak of the Eu3+ ion (5D0 → 7F2) electric dipole transition features a red component. CaY2O4:Eu3+ phosphors show promise as materials for potential use in phosphor-converted white LEDs in the field of solid-state lighting technology. The linear connection that the TL glow curve has with UV dose provides evidence for its possible use in dosimetry. © 2023 The Royal Society of Chemistry.
Fabrication of Graphene Nanoplatelet-Incorporated Porous Hydroxyapatite Composites: Improved Mechanical and in Vivo Imaging Performances for Emerging Biomedical Applications
(American Chemical Society, 2019) Sunil Kumar; Chandkiram Gautam; Vijay Kumar Mishra; Brijesh Singh Chauhan; Saripella Srikrishna; Ram Sagar Yadav; Ritu Trivedi; Shyam Bahadur Rai
Three-dimensional nanocomposites exhibit unexpected mechanical and biological properties that are produced from two-dimensional graphene nanoplatelets and oxide materials. In the present study, various composites of microwave-synthesized nanohydroxyapatite (nHAp) and graphene nanoparticles (GNPs), (100 - x)HAp-xGNPs (x = 0, 0.1, 0.2, 0.3, and 0.5 wt %), were successfully synthesized using a scalable bottom-up approach, that is, a solid-state reaction method. The structural, morphological and mechanical properties were studied using various characterization techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and universal testing machine (UTM). XRD studies revealed that the prepared composites have high-order crystallinity. Addition of GNPs into nHAp significantly improved the mechanical properties. Three-dimensional nanocomposite 99.5HAp-0.5GNPs exhibited exceptionally high mechanical properties, for example, a fracture toughness of ∼116 MJ/m3, Young's modulus of ∼98 GPa, and compressive strength of 96.04 MPa, which were noticed to be much greater than in the pure nHAp. The MTT assay and cell imaging behaviors were carried out on the gut tissues of Drosophila third instars larvae and on primary rat osteoblast cells for the sample 99.5HAp-0.5GNPs that have achieved the highest mechanical properties. The treatment with lower concentrations of 10 μg/mL on the gut tissues of Drosophila and 1 and 5 μg/mL of this composite sample showed favorable cell viability. Therefore, owing to the excellent porous nature, interconnected surface morphology, and mechanical and biological properties, the prepared composite sample 99.5HAp-0.5GNPs stood as a promising biomaterial for bone implant applications. © 2019 American Chemical Society.
Highly selective ppm level LPG sensors based on SnO2-ZnO nanocomposites operable at low temperature
(Elsevier B.V., 2023) Snehal D. Patil; Harshal A. Nikam; Y.C. Sharma; Ram Sagar Yadav; Dinesh Kumar; Akhilesh Kumar Singh; D.R. Patil
The nanoscaled SnO2, ZnO and SnO2-ZnO nanocomposite powders were prepared by microwave aided ultrasonication technique by employing centrifuge for the collection of dried powder of the materials. The fabrication of thick films of the pure ZnO and SnO2-ZnO nanocomposite powders were made by simple screen printing technique. The crystallographic phases of the pure ZnO and SnO2 doped ZnO are hexagonal in nature. The average crystallite size of 0 (pure), 1, 3, 5, 7 and 9 wt% of SnO2 doped ZnO films was found to be 30.2, 30.3, 109.7, 37.9, 36.8 and 45.6 nm, respectively. The SEM micrographs depict the porous nature of the thick films. The EDS analysis reveals that the pure ZnO and SnO2 doped ZnO films are oxygen deficient and show a semiconducting nature. The symmetric I-V characteristics depict the ohmic and non-ohmic natures of the thick films. The electrical resistivity measurements indicate a negative temperature coefficient of resistance. The gravimetric analysis shows that the average thickness of the pure ZnO thick film is 28 µm. The LPG response versus doping concentration plot suggests that the (1 wt%) SnO2 doped ZnO thick film exhibits crucial response to 100 ppm LPG at 50 °C and 100 °C. Therefore, the SnO2 doped ZnO thick film can be applicable in the field of LPG sensing with rapid response and recovery. © 2022 Elsevier B.V.
Impact of Sr2+ doping on the structural, dielectric, ferroelectric and optical properties of YFeO3 perovskite phosphor
(Elsevier Ltd, 2023) Dinesh Kumar; Sadhana Yadav; Chandra Bhal Singh; Ram Sagar Yadav; Shyam Bahadur Rai; Akhilesh Kumar Singh
The single phase Y1−xSrxFeO3 perovskite phosphors with x = 0, 0.025 and 0.050 were synthesized by using the sol-gel combustion method followed by calcination at a low temperature. The structural characteristics of Y1−xSrxFeO3 perovskites have been investigated by Rietveld structure refinement using the X-ray diffraction data. The Rietveld refinement shows that the Y1−xSrxFeO3 perovskite crystallizes into an orthorhombic crystal structure with Pnma space group. The average value of crystallite size decreases with increasing concentration of Sr2+ ion at the Y-site; however, the lattice strain increases. The HRSEM images of the phosphors show that the particle size of phosphors decreases with increasing concentration of Sr2+ ion. At room temperature, the dielectric permittivity and the electric polarization of Y1−xSrxFeO3 phosphors increase via the doping of Sr2+ ions. The FTIR spectra confirm the low phonon frequency of Y1−xSrxFeO3 phosphors. The optical band gap of YFeO3 decreased as the doping concentrations of Sr2+ ions increased. The phosphor gives large number of absorption bands at 334, 350, 360, 388, 467 and 482 nm. The Y1−xSrxFeO3 phosphor emits blue, yellow and red emissions on excitations with 350 and 360 nm. The lifetime of excited levels of the phosphor decreases with the contents of Sr2+ ion. The CIE diagram reveals that the emitted color lies in the bluish-magenta visible spectrum region. Therefore, the Y1−xSrxFeO3 phosphors may be applicable in capacitors, display devices and solid-state lighting. © 2023 Elsevier B.V.
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.
Influence of La3+ doping on structural and optical properties of SrCeO3 perovskite
(Institute of Physics, 2024) Dharmendra Yadav; Pravin Kumar; Alok Kumar Tripathi; Ram Sagar Yadav; Gurudeo Nirala; Sushma Yadav; Ashish Kumar Yadav; Sandip Yadav
The SrCe1-xLaxO3 (x = 0.0, 0.02, 0.4, 0.6, and 0.10) perovskite materials have been successfully synthesized by auto-combustion method and calcined at 1100°C. The XRD patterns reveal a highly crystalline orthorhombic crystal structure with a Pnma space group in all samples. The TEM micrograph shows a spherical morphology of the 10 mol% La3+ doped SrCeO3 perovskite sample alongwith the SAED pattern confirming its highly crystalline nature. The incorporation of La3+ ion in the SrCeO3 perovskite has been confirmed by the Raman and Fourier transform infrared (FTIR) measurements. The UV-vis absorption spectra at room temperature show various bands, with a strong absorption band observed below 400 nm. The optical band gap of the undoped and La3+ doped samples have been calculated and it is smaller for the La3+ doped perovskite samples than that of the undoped perovskite sample. Therefore, the La3+ doped SrCeO3 perovskite may be applicable for optoelectronic applications. © 2024 IOP Publishing Ltd. All rights, including for text and data mining, AI training, and similar technologies, are reserved.
Influence of Yb3+/Mg2+ ions on photoluminescence intensity of Tm3+ doped ZnWO4 phosphor for photonic applications
(Elsevier B.V., 2025) Ram Sagar Yadav
In this work, the Tm3+/Yb3+/Mg2+ tri-doped ZnWO4 phosphors have been synthesized with different concentrations of Yb3+ and Mg2+ ions through solid-state reaction method. The Tm3+ doped ZnWO4 phosphor has strong excitation bands at 311 and 360 nm due to charge transfer band (CTB) and 4f-4f transition of Tm3+ ion, respectively. The Tm3+ doped ZnWO4 phosphor sample emits strong blue and weak red emissions at (458, 482) and 561 nm wavelengths on excitation with 360 nm, respectively. When the Yb3+ ion is incorporated in the Tm3+ doped phosphor; the photoluminescence intensity of blue band decreases regularly. This is due to downconversion cooperative energy transfer (CET) from 1G4 level of Tm3+ ion to 2F7/2 level Yb3+ ion. The photoluminescence intensity of the Tm3+/Yb3+ co-doped ZnWO4 phosphor also decreases in presence of Mg2+ ion, which is due to increase in local crystal structure of the ZnWO4 phosphor. The lifetime value of 1D2 level of the Tm3+ ion also decreases as a result of CET from Tm3+ to Yb3+ ions in the Tm3+/Yb3+/Mg2+ tri-doped ZnWO4 phosphor. Therefore, the Tm3+/Yb3+/Mg2+ tri-doped ZnWO4 phosphor may be applicable in photonic and display devices. © 2025 Elsevier B.V.
Introduction to the RSC Advances themed collection on the photoluminescence of lanthanide-doped phosphor materials
(Royal Society of Chemistry, 2025) Ram Sagar Yadav; Bryce S. Richards; Joanna Pisarska; Xinyu Ye
[No abstract available]
Near-Infrared Light Excited Highly Pure Green Upconversion Photoluminescence and Intrinsic Optical Bistability Sensing in a Ho3+/Yb3+ Co-Doped ZnGa2O4 Phosphor through Li+ Doping
(American Chemical Society, 2020) Monika; Ram Sagar Yadav; Amresh Bahadur; Shyam Bahadur Rai
We report on highly pure green upconversion (UC) photoluminescence in a Ho3+/Yb3+/Li+ co-doped ZnGa2O4 phosphor prepared by the solid-state reaction method for the first time. The crystallite size, dislocation density, and microstrain values show the crystalline nature of the phosphors. The scanning electron micrographs show shapes and sizes of the phosphor, and they change in the presence of Li+ ions. The energy-dispersive X-ray spectroscopic analysis reveals the presence of Ga, Zn, Ho, Yb, and O elements in the phosphor. Fourier transform infrared studies show vibrational bands because of Zn-O and Ga-O groups. The diffuse reflectance spectra contain large number of absorption bands of Ho3+ and Yb3+ ions. The optical band gap of the phosphor sample slightly decreases through Li+ doping. The Ho3+/Yb3+ co-doped phosphor shows intense green along with weak blue, red, and near-infrared UC emissions excited at 980 nm. The intensity of green UC emission at 537 nm is a dominant one. The emission intensity of the Ho3+-doped phosphor is enhanced upto 372 times via Yb3+ doping, which further enhanced upto 966 times via Li+ doping. It is because of the increase in the local crystal structure and particle size. The spectral color purity (Sgr) is achieved as 0.98 in the phosphor. The lifetimes of the 5F4 state of Ho3+ ions are increased in the presence of Li+ ions. Interestingly, the variation of pump power gives rise to intrinsic optical bistability sensing in the Ho3+/Yb3+/Li+ co-doped ZnGa2O4 phosphor, and it gives efficient sensing for the green emission. Thus, the Ho3+/Yb3+/Li+ co-doped ZnGa2O4 phosphor may be used in green-emitting sources, UC-based devices, optical memory devices, and optically bistable devices. © 2020 American Chemical Society.
NIR light guided enhanced photoluminescence and temperature sensing in Ho3+/Yb3+/Bi3+ co-doped ZnGa2O4 phosphor
(Nature Research, 2021) Monika; Ram Sagar Yadav; Anita Rai; Shyam Bahadur Rai
The conversion of NIR light into visible light has been studied in Ho3+/Yb3+/Bi3+ co-doped ZnGa2O4 phosphor for the first time. The crystallinity and particles size of the phosphor increase through Bi3+ doping. The absorption characteristics of Ho3+, Yb3+ and Bi3+ ions are identified by the UV–vis-NIR measurements. The Ho3+ doped phosphor produces intense green upconversion (UC) emission under 980 nm excitations. The emission intensity ~ excitation power density plots show contribution of two photons for the UC emissions. The UC intensity of green emission is weak in the Ho3+ doped phosphor, which enhances upto 128 and 228 times through co-doping of Yb3+ and Yb3+/Bi3+ ions, respectively. The relative and absolute temperature sensing sensitivities of Ho3+/Yb3+/5Bi3+ co-doped ZnGa2O4 phosphor are calculated to be 13.6 × 10−4 and 14.3 × 10−4 K−1, respectively. The variation in concentration of Bi3+ ion and power density produces excellent color tunability from green to red via yellow regions. The CCT also varies with concentration of Bi3+ ion and power density from cool to warm light. The color purity of phosphor is achieved to 98.6% through Bi3+ doping. Therefore, the Ho3+/Yb3+/Bi3+:ZnGa2O4 phosphors can be suitable for UC-based color tunable devices, green light emitting diodes and temperature sensing. © 2021, The Author(s).