Co-doped Nanophosphors Research Articles

Eu+3 Ion as a Luminescent Probe in ZrO2: Gd+3 Co-Doped Nanophosphor

Eu+3 Ion as a Luminescent Probe in ZrO2: Gd+3 Co-Doped Nanophosphor

Surface analysis and enhanced photoluminescence via Bi3+ doping in a Tb3+ doped Y2O3 nano-phosphor under UV excitation

The Tb3+, Bi3+ co-doped Y2O3 nano-phosphor has been synthesized through solution combustion method for the first time. The surface analysis of the phosphor has been done using XRD and TEM measurement techniques, which reveal strong crystallinity and spherical particles agglomerated to each other. The EDS spectra of Tb3+, Bi3+ co-doped Y2O3 phosphor show the presence of Y, O, Tb and Bi elements. The Tb3+ doped Y2O3 phosphor emits intense green emission centered at 542 nm due to 5D4 → 7F5 transition along with other weak bands on excitation with 266 nm. The emission intensity is found to be optimum at 1 mol% concentration of Tb3+ ions. The sample annealed at higher temperature gives larger emission intensity due to reduction in the optical quenching centers. The presence of Bi3+ ions in the Tb3+ doped phosphor further enhances the emission intensity of Tb3+ up to two times. The enhancement in the emission intensity is due to energy transfer from Bi3+ to Tb3+ ions, which has been confirmed by lifetime measurements. Thus, the Tb3+, Bi3+ co-doped Y2O3 nano-phosphor may be a suitable candidate for solid state lighting.

Enhanced frequency upconversion in Ho3+/Yb3+/Li+:YMoO4 nanophosphors for photonic and security ink applications

The YMoO4 nanophosphors codoped with Ho3+/Yb3+/Li+ ions synthesized by the chemical coprecipitation method have been structurally characterized by using X-Ray Diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM), and Transmission Electron Microscopy (TEM) techniques. The TEM bright field imaging shows that the developed nanophosphors are crystalline in nature with particle size ∼45 nm. The upconversion (UC) emission spectra upon excitation at 980 nm of the nanophosphors at low pump power (<900 mW) show the emission peaks in the UV, green, and red regions, whereas at high pump power (≥900 mW) an intense broad band ranging from 400–900 nm along with a UV band has been observed. The enhancement of about ∼104 times corresponding to the green band in the Ho3+-Yb3+-Li+ codoped nanophosphors compared to that of the Ho3+ singly doped nanophosphors has been observed. This enhancement is caused by the energy transfer from the Yb3+ to Ho3+ ions and modified the local crystal field developed around the rare earth ions. A higher value of the slope (i.e., n ∼ 6.38) for broad band emission within the 944 mW-1200 mW pump power region in the Ho3+-Yb3+-Li+ codoped nanophosphors is found to be due to the involvement of the photon avalanche population process but it is not related to the black body radiation. The intense peak at ∼564 nm and ∼648 nm for the broad band emission is attributed to the charge transfer luminescence of codoped nanophosphors, which is related to the oxygen ion present in the MoO4 group and Yb3+ ion. The observations described in this paper may be of significant interest for developing the visible upconverters, security ink, and novel devices for displays in the low and high pump power region.

Near Infrared Quantum Cutting of Tb3+-Yb3+ Co-Doped CeF3 Nanophosphors.

In this paper, Tb3+-Yb3+ Co-doped CeF3 nanophosphors were synthesized using the microwave-assisted heating hydrothermal method (M-H). The excitation and emission spectra of the samples at room temperature show that the samples absorb ultraviolet light from 250 nm to 280 nm, and emit light at 300 nm. This corresponds to the transitions from 5D to 4F of Ce3+, 480 nm, 540 nm, 583 nm, 620 nm which correspond to the transitions from 5D4 to 7F6,5,4,3 of Tb3+, 973 nm which corresponds to the transitions from 2F5/2-2F7/2 of Yb3+. In the emission spectra, it is clear that the emission intensity of Ce3+ and Tb3+ decreases, and Yb3+ increases with increasing Yb3+. This suggests that energy transfer from Ce3+ to Yb3+, and Ce3+ to Tb3+ to Yb3+ may occur. In the near infrared emission area, it is noted that a distinct emission centered at 973 nm was observed under 260 nm excitation. This is due to transitions among the different Stark levels of 2FJ(J=5/2,7/2) Yb3+ ions. This also suggests an energy transfer from Ce3+ ions to Tb3+ and then to Yb3+. The energy transfers from Tb3+-Yb3+ Co-doped CeF3 nanophosphors, which lead to intense NIR emissions at 900-1050 nm, match the energy of Si band gaps of Si-based solar cells. Therefore, these kinds of materials are promising candidates for applications that require modifying if solar spectrums and enhancement of conversion efficiency of Si-based solar cells.

Upconversion Luminescence Properties of Er3+ Doped Yb2Ti20 Nanophosphor by Gd3+ Codoping.

Er3+ doped Yb2Ti207 nanophosphors by Gd3+ codoping with nominal composition of (Er0.05Yb0.95-xGd3+)2Ti2O7 (x = 0, 0.2, 0.4, 0.6, 0.8, and 0.95) have been prepared by sol-gel method. Er3+-Gd3+ codoped Yb2Ti2O7 was characteristic of a typical face-centered cubic crystal phase, and the unit cell parameter increased linearly with the increase of Gd3+ concentration. Under a 976 nm laser diode excitation, both green and red upconversion emissions were observed and the upconversion emissions were enhanced significantly by Gd3+ codoping, showing the strongest green and red emissions at 80 mol% Gd3+ codoping. The intensity ratio of green to red emissions (Igreen/Ired) increased monotonously with the increase of Gd3+ concentration. The energy transfer between Yb3+ and Er3+ and the variation of local crystal field symmetry of Er3+ by the substitution of Yb3+ by Gd3+ ions led to the improvement of upconversion properties of Er3+-Gd3+ codoped Yb2TiO7 nanophosphors.

Role of Li+ on white light emission from Sm3+ and Tb3+ co-doped Y2O3 nano-phosphor

This paper reports on white light emission from Sm3+ and Tb3+ co-doped Y2O3 nano-phosphor, synthesized through the solution combustion method. The XRD and TEM measurements of the nano-phosphors reveal a crystalline nature and spherical particle distribution. The Sm3+-doped nano-phosphor gives off an orange-red emission whereas the Tb3+-doped nano-phosphor gives off blue and green emissions individually on excitation with 380 nm radiation. When the Sm3+and Tb3+ ions are doped together, the co-doped nano-phosphor emits white light with the CIE coordinates 0.33 and 0.37, due to the combined emissions of these two ions on excitation with 380 nm radiation. The color of the emitted light is tunable with the concentration of Sm3+ ions, and it emits white light at the 2.0 mol% concentration of Sm3+ and 1.0 mol% concentration of Tb3+ ions. The nano-phosphor sample annealed at a higher temperature results in a greater emission intensity. The presence of Li+ ions in the co-doped sample enhances the emission intensity of white light up to three times. The enhancement in the emission intensity is discussed in terms of a reduction in the optical quenching centers and an increase in the crystallite size. The Sm3+ and Tb3+ co-doped Y2O3 nano-phosphor in the presence of Li+ is a suitable candidate for white light in a solid state display.

Synthesis and Upconversion Emission Study of Tm3+/Yb3+ Co-Doped CaMoO4 Nano-Phosphor

Synthesis and Upconversion Emission Study of Tm₃₊/Yb₃₊ Co-Doped CaMoO₄ Nano-Phosphor

Surface Characterization and Photoluminescence Properties of Ce3+,Eu Co-Doped SrF2 Nanophosphor

SrF2:Eu,Ce3+ nanophosphors were successfully synthesized by the hydrothermal method during down-shifting investigations for solar cell applications. The phosphors were characterized by X-ray diffraction (XRD), scanning Auger nanoprobe, time of flight-secondary ion mass spectrometry (TOF-SIMS), X-ray photoelectron spectroscopy (XPS) and photoluminescence (PL) spectroscopy. XRD showed that the crystallite size calculated with Scherrer’s equation was in the nanometre scale. XPS confirmed the formation of the matrix and the presence of the dopants in the SrF2 host. The PL of the nanophosphor samples were studied using different excitation sources. The phenomenon of energy transfer from Ce3+ to Eu2+ has been demonstrated.

Incorporation of Eu–Tb codoped nanophosphors in silica-based coatings assisted by atmospheric pressure plasma jet technology

Different deposition methods of nanocomposite silica films with embedded Y2O3:Eu3+, Tb3+ by atmospheric pressure plasma jet (APPJ) technology are presented. We found that a two-step strategy consisting in the APPJ deposition of a silica film on previously deposited nanophosphors is a very efficient method to obtain nanocomposite coatings with excellent adhesion to the substrate. Moreover the APPJ deposited silica film ensures protection of the luminescent nanoparticles and preserves the photoluminescence emission properties of the nanophosphors. Optically active coatings can be therefore deposited by using this technology.

Excitation Induced Tunable Emission in Ce3+/Eu3+Codoped BiPO4Nanophosphors

Ce3+, Eu3+ions singly doped, and Ce3+/Eu3+codoped bismuth phosphate (BiPO4) nanophosphors were synthesized by a simple precipitation method and their structural, morphological, and photoluminescence properties were investigated. The structural and morphological analysis confirms the pure hexagonal crystal structure of the synthesized nanophosphors. From the Fourier transform infrared (FTIR) spectra various absorption bands respective to functional groups such as PO4 and phonon vibrations including the bending modes of the PO4units are identified. The Ce3+doped nanophosphors show spectrally broad luminescence in the blue (centred at 459 nm) wavelength region under the direct optical excitation of Ce3+at 417 nm. For Eu3+doped nanophosphors, five emission bands have been observed with 394 nm excitation wavelength. Among them, 595 nm has shown bright yellowish-orange emission. These results demonstrate that by appropriately tuning the excitation wavelength of these codoped nanophosphors the emission color in the visible region (blue and orange) can be flexibly controlled in a single sample without varying its chemical composition and size. The mechanism for this excitation energy dependent tunable emission is explained on the basis of nonenergy transfer (ET) occurring among Ce3+/Eu3+dopant ions.

Structural characterizations and intense green upconversion emission in Yb3+, Pr3+ co-doped Y2O3 nano-phosphor

We report the structural and optical properties of Yb3+, Pr3+ co-doped Y2O3 nano-phosphor synthesized through solution combustion method. The structural studies reveal the nano-crystalline structure of the sample. The energy dispersive spectroscopy (EDS) measurements confirm the presence of Y, O, Pr and Yb elements in the sample. Fourier transform infrared studies show the vibrational features of the samples. The fluorescence spectra of the samples have been monitored on excitation with 976nm and the intense green upconversion emission observed at 552nm is due to 3P0→3H5 electronic transition. The concentration of Pr3+ ion in the sample is optimized and the fluorescence intensity is maximum at 0.08mol% of Pr3+. The power dependence studies reveal the involvement of two photons in the emission process. The possible mechanism of upconversion has been discussed on the basis of schematic energy level diagram. The sample annealed at higher temperature enhances the fluorescence intensity up to 8 times and this enhancement is discussed in terms of the removal of optical quenching centers. The nano-phosphor can be applicable in the field of display devices and green laser.

Effect of Yb3+ concentration on upconversion luminescence in Yb3+, Tm3+ co-doped Lu2O3 nanophosphors

Lutetium oxide nanophosphors codoped with Yb3+ and Tm3+ ions were successfully synthesized by the reverse-like co-precipitation method, using ammonium hydrogen carbonate as precipitants. Effect of the Yb3+ molar concentration on the structural and upconversion luminescent properties of the Lu2O3 nanophosphors has been investigated. The XRD results show that all the prepared nanophosphors can be readily indexed to pure cubic phase of Lu2O3 and exhibit good crystallinity. The experimental results show that the optimum Yb3+ doped concentration is 4 mol% at fixed Tm3+ concentration of 0.2 mol%. The strong blue, weak red and near infrared emissions from the prepared nanophosphors were observed under 980 nm laser excitation, which are attributed to the 1G4 → 3H6,1G4 → 3F4 and 3H4 → 3H6 transitions of Tm3+ ion, respectively. Under strong power density (50 W/cm2) excitation, the upconversion blue intensity ratio (477 nm/490 nm) was dependent on the Yb3+ concentration, which was resulted from the thermal effect induced by laser irradiation. The upconversion mechanism was also discussed in detail.

Intense white light emission in Tm3+/Er3+/Yb3+ co-doped Y2O3–ZnO nano-composite

The Tm3+/Er3+/Yb3+ co-doped Y2O3–ZnO nano-composite is synthesized using the solution combustion technique. The structural morphology is monitored using x-ray diffraction, transmission electron microscopy and scanning electron microscopy. The Yb3+/Tm3+ co-doped nano-phosphor emits intense blue as well as weak red emissions, while Yb3+/Er3+ co-doped nano-phosphor emits strong green along with red emissions on excitation with 976 nm laser. Joining these together (i.e. Tm3+/Er3+/Yb3+ co-doped phosphor) give very strong white light, which is further verified by CIE coordinates (0.32, 0.36). The addition of ZnO with Y2O3 phosphor gives further enhancement in the intensity of white light. The possible reason for this enhancement is the removal of optical quenching sites.

Influences of Doping and Annealing on the Structural and Photoluminescence Properties of Y2O3 Nanophosphors

This paper reports the structural and optical properties of rare earth doped and codoped yttrium oxide nanophosphors. Dysprosium (Dy(3+)) and Terbium (Tb(3+)) doped and codoped yttrium oxide (Y2O3) phosphors were prepared by combustion synthesis method and subsequently annealed to high temperature to eliminate the hydroxyl group (-OH) and to get more crystallinity. The formation of compounds was confirmed by the X-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR). The diffuse reflectance spectra (DRS) of doped and codoped Y2O3 powder phosphors were measured and it is observed that the absorption edge of the doped samples is shifted towards blue region with respect to undoped sample. The bandgap of the prepared samples were evaluated with the help of Kubelka-Munk function using Diffuse Reflectance Spectra (DRS) and an increase in bandgap was observed with the decrease in crystallite size. A strong characteristics emission from Tb(3+) and Dy(3+) ions was identified and the influence of doping concentration and annealing temperature on photoluminescence properties was systematically studied. Transfer of energy was observed in dysprosium-terbium codoped Y2O3 nanophosphor at room temperature from Dy(3+) ions to Tb(3+) ions.

Upconversion Luminescence of Tb3+ and Yb3+ Co-doped Hexagonal and Monoclinic GdPO4 Nanophosphors

Tb3+ and Yb3+ codoped hexagonal GdPO4 nanorods have been prepared by a hydrothermal method at 220°C for 12 h and monoclinic GdPO4 nanoparticles have been obtained by sintering the hydrothermal products at 900°C for 5 h. Green upconversion luminescence of Tb3+ has been observed when pumped by 980 nm diodes due to efficiently cooperative energy transfer from codopant Yb3+. The luminescence of Tb3+ in both hexagonal and monoclinic GdPO4 nanophosphors has been comparatively studied. The dependence of the upconversion luminescence intensity on pump laser power shows that two-phonon processes involved in upconversion luminescence of the emission level 5D4 of Tb3+ is populated via two-photon process. Upconversion luminescence emission intensity and the energy transfer efficiency ηT from Yb3+ to Tb3+ ions upon the concentration of Tb3+ have been investigated.

Enhanced blue luminescence in BaMgAl10O17:Eu, Er, Nd nanophosphor for PDPs and Mercury free fluorescent lamps

The Er3+/Nd3+ codoped BaMgAl10O17:Eu2+ phosphor nanoparticles have been synthesized through solution combustion method. Nanophosphor has shown intense broad blue photoluminescence (PL), corresponding to the 4f65d→4f7 electronic transition of Eu2+ ion under vacuum ultraviolet (147nm) as well as UV (355nm) excitations. An enhancement in blue emission of Eu2+ has been observed on the codoping of Er3+/Nd3+ ions and concentration of the doping ions have been optimized. Lifetime of the 4f65d→4f7 transition has been measured and discussed. The enhancement in emission intensity of codoped blue nanophosphor is explained by energy transfer from the Er3+/Nd3+ ions and created defect states to the Eu2+ in the BaMgAl10O17. This phosphor has also shown better emission intensity as compared to commercial blue phosphor under VUV excitation and thus making it attractive for the application in plasma display panels and mercury free-fluorescent lamps.

Energy transfer in Tb3+,Yb3+ codoped Lu2O3 near-infrared downconversion nanophosphors

Tb3+ and Yb3+ codoped Lu2O3 nanophosphors were synthesized by the reverse-strike co-precipitation method. The obtained Lu2O3:Tb3+,Yb3+ nanophosphors were characterized by X-ray diffraction (XRD) and photoluminescence (PL) spectra. The XRD results showed that all the prepared nanophosphors could be readily indexed to pure cubic phase of Lu2O3 and indicated good crystallinity. The Tb3+→Yb3+ energy transfer mechanisms in the UV-blue region in Lu2O3 nanophosphors were investigated. The experimental results showed that the strong visible emission around 543 nm from Tb3+ (5D4→7F5) and near-infrared (NIR) emission around 973 nm from Yb3+ (2F5/2→2F7/2) of Lu2O3:Tb3+,Yb3+ nanophosphors were observed under ultraviolet light excitation, respectively. Tb3+ could be effectively excited up to its 4f75d1 state and relaxed down to the 5D4 level, from which the energy was transferred cooperatively to two neighboring Yb3+. The Yb3+ concentration dependent luminescent properties and lifetimes of both the visible and NIR emissions were also studied. The lifetime of the visible emission decreased with the increase of Yb3+ concentration, verifying the efficient energy transfer from the Tb3+ to the Yb3+. Cooperative energy transfer (CET) from Tb3+ to Yb3+ was discussed as a possible mechanism for the near-infrared emission. When doped concentrations were 1 mol.% Tb3+ and 2 mol.% Yb3+, the intensity of NIR emission was the strongest.

Preparation and characterization of upconversion luminescent Tm3+/Yb3+ co-doped Y2O3 nanophosphor

Tm3+/Yb3+ co-doped Y2O3 nanophosphor has been synthesized by the solution combustion technique. Heat treatment of the phosphor materials at higher temperatures modifies the structural and optical properties. At low concentration of Yb3+, an intense upconversion emission is observed in blue region (478 nm) on excitation with 976 nm radiations. Emission has also been observed in the ultraviolet (UV) region viz. at 300 nm. The intensity of blue emission initially increases with dopant concentration as well as with the annealing temperature. However, for higher concentrations of Yb3+ (10 mol%), emission in the blue region is greatly suppressed and NIR emission at 813 nm appears with a large intensity. Intensity ratio of NIR and blue emission (I NIR/I B) reaches 74, resulting in almost monochromatic light at 813 nm. To check the suitability of blue emission for display devices, CIE color coordinates (x,y), color purity and the dominant wavelength (λ d) for the blue emission have been calculated and the resulting value is found to be close to the coordinates of available standard blue phosphors.

Facile Synthesis of Ce3+, Eu3+ Co-Doped YAG Nanophosphor for White Light-Emitting Diodes

Luminescent Ce3+, Eu3+ co-doped yttrium aluminum garnet (Y3Al5O12, YAG) nanophosphors were successfully synthesized by a facile hydrothermal-assistant combustion method without a reducing atmosphere. The photoluminescence (PL) spectrum of the as-prepared YAG:Ce3+, Eu3+ nanophosphors consisted of a typical broad yellow emission band attributed to the characteristic emission of Ce3+ and several sharp emission bands in red spectral region attributed to the characteristic emission of Eu3+ due to the successful co-doping of Eu3+ into YAG host lattice, and the intensities of these sharp red emission bands could be adjusted by varying the Eu3+ doping concentration. The energy transfer from Ce3+ to Eu3+ inside YAG was also investigated, and the results showed that both Ce3+ and Eu3+ could be efficiently excited by 465 nm blue light, which indicated the red emission of YAG:Ce3+, Eu3+ under 465 nm blue light excitation was not merely enhanced at the cost of emission intensity of Ce3+. Moreover, YAG: Ce3+, Eu3+ nanophosphors were combined with blue light-emitting diode (LED) chip to fabricate white LED, and the resulting white LED showed good performance with a luminous efficiency of 70.4 lm/W, Ra of 82, and Tc of 4964 K at 100 mA.

Anomalous Raman Scattering of Colloidal Yb3+,Er3+ Codoped NaYF4 Nanophosphors and Dynamic Probing of the Upconversion Luminescence

AbstractSize‐dependent Raman spectra of the hexagonal (β)‐phase Yb3+,Er3+ codoped NaYF4 nanophosphors and dynamic probing of the upconversion luminescence (UCL) are reported. Raman scattering results show the normal red shifts of Raman peaks but anomalous line narrowing with decreasing the particle sizes. The phonon confinement effects are believed to be dominated by the surface vibrational energies in affecting UCL. Dynamic decay data are then applied to quantitatively verify the surface effects and size‐dependent UCL. Dynamic probing is shown to be an efficient tool to both qualitatively and quantitatively characterize the upconversion nanophorphors (UCNPs) that have no “quantum efficiency.” The findings are relevant to the engineering of the nanostructures of the UCNPs for the applications of the bioimaging and photodynamic therapy.