Enhanced photoluminescence of Gd2O3:Eu3+ nanophosphors with alkali (M=Li+, Na+, K+) metal ion co-doping.
N Dhananjaya, H Nagabhushana, B M Nagabhushana, B Rudraswamy, C Shivakumara, K Narahari, R P S Chakradhar
Department of Physics, J.B. Campus, Bangalore University, Bangalore 560 056, India.
Gd(1.95)Eu(0.04)M(0.01)O(3)(M=Li(+), Na(+), K(+)) nanophosphors have been synthesized by a low temperature solution combustion (LSC) method. Powder X-ray diffraction pattern (PXRD), scanning electron microscopy (SEM), UV-vis and photoluminescence (PL) measurements were carried out to characterize their structural and luminescent properties. The excitation and emission spectra indicated that the phosphor could be well excited by UV light (243 nm) and emit red light about 612 nm. The effect of alkali co-dopant on PL properties has been examined. The results showed that incorporation of Li(+), Na(+) and K(+) in to Gd(2)O(3):Eu(3+) phosphor would lead to a remarkable increase of photoluminescence. The PL intensity of Gd(2)O(3):Eu(3+) phosphor was improved evidently by co-doping with Li(+) ions whose radius is less than that of Gd(3+) and hardly with Na(+), K(+) whose radius is larger than that of Gd(3+). The effect of co-dopants on enhanced luminescence was mainly regarded as the result of a suitable local distortion of crystal field surrounding the Eu(3+) activator. These results will play an important role in seeking some more effective co-dopants.
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Effect of different fuels on structural, thermo and photoluminescent properties of Gd(2)O(3) nanoparticles.
N Dhananjaya, H Nagabhushana, B M Nagabhushana, B Rudraswamy, S C Sharma, D V Sunitha, C Shivakumara, R P S Chakradhar
Department of Physics, J.B. Campus, Bangalore University, Bangalore 560 056, India; Department of Physics, B.M.S. Institute of Technology, Bangalore 560 064, India.
Gd(2)O(3) nanoparticles (27-60nm) have been synthesized by the low temperature solution combustion method using citric acid, urea, glycine and oxalyl dihydrazide (ODH) as fuels in a short time. The structural and luminescence properties have been carried out using powder X-ray diffraction (PXRD), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), Raman, UV-Vis, photoluminescence (PL) and thermoluminescence (TL) techniques. The optical band gap values were estimated for as formed and 800°C calcined samples. The band gap values in as-formed and calcined samples were found to be in the range 4.89-5.59eV. It is observed that, the band gap values are lower for as-formed products and it has been attributed to high degree of structural defects. However, in calcined samples, structure becomes more order with reduced structure defects. Upon 270nm excitation, deep blue UV-band at ∼390nm along with blue (420-482nm), green (532nm) and red emission (612nm) was observed. The 390nm emission peak may be attributed to recombination of delocalized electron close to the conduction band with a single charged state of surface oxygen vacancy. TL measurements were carried out on Gd(2)O(3) prepared by different fuels by irradiating with γ-rays (1kGy). A well resolved glow peak at 230°C was observed for all the samples. It is observed that TL intensity is found to be higher in for urea fuel when compared to others. From TL glow curves the kinetic parameters were estimated using Chen's peak shape method and results are discussed in detail.
D V Sunitha, C Manjunatha, C J Shilpa, H Nagabhushana, S C Sharma, B M Nagabhushana, N Dhananjaya, C Shivakumara, R P S Chakradhar
Professor C.N.R. Rao Centre for Advanced Materials Research, Tumkur University, Tumkur 572 103, India.
A series of Pr(3+)(1-9mol%) doped CdSiO(3) nanophosphors have been prepared for the first time by a low temperature solution combustion method using oxalyldihydrizide (ODH) as a fuel. The final product was characterized by Powder X-ray diffraction (PXRD), Fourier Transform Infrared Spectroscopy (FTIR), scanning electron microscopy (SEM), and UV-Vis spectroscopy. The average crystallite size was calculated using Debye-Scherrer's formula and Williamson-Hall (W-H) plots and found to be in the range 31-37nm. The optical energy band gap (E(g)) of undoped for Pr(3+) doped samples were estimated from Tauc relation which varies from 5.15-5.36eV. Thermoluminescence (TL) properties of Pr(3+) doped CdSiO(3) nanophosphor has been investigated using γ-irradiation in the dose range 1-6kGy at a heating rate of 5°Cs(-1). The phosphor shows a well resolved glow peak at ∼171°C along with shouldered peak at 223°C in the higher temperature side. It is observed that TL intensity increase with increase of Pr(3+) concentration. Further, the TL intensity at 171°C is found to be increase linearly with increase in γ-dose which is highly useful in radiation dosimetry. The kinetic parameters such as activation energy (E), frequency factor (s) and order of kinetics was estimated by Luschiks method and the results are discussed.
Swift heavy ion induced structural, iono and photoluminescence properties of β-CaSiO₃:Dy³⁺ nanophosphor.
D V Sunitha, H Nagabhushana, Fouran Singh, N Dhananjaya, S C Sharma, B M Nagabhushana, C Shivakumara, R P S Chakradhar
Prof C.N.R. Rao Centre for Nano Research (CNR), Tumkur University, Tumkur 572 103, India.
CaSiO(3):Dy(3+)(1-5 mol%) nanophosphors have been prepared by a low temperature solution combustion method. The structural and luminescence (ionoluminescence; IL and photoluminescence; PL) studies have been carried out for pristine and ion irradiated samples. The XRD patterns of pristine sample show a prominent peak at (320) for the monoclinic structure of β-CaSiO(3). Upon ion irradiation, the intensity of the prominent peak is decreased at the fluence of 7.81 × 10(12)ions cm(-2) and at higher fluence of 15.62 × 10(12)ions cm(-2), the prominent peak completely vanishes. The decrease in peak intensity might be due to the stress induced point defects. On-line IL and in situ PL studies have been carried out on pelletized samples bombarded with 100 MeV Si(7+) ions with fluences in the range (7.81-15.62)×10(12)ions cm(-2). The characteristic emission peaks at 481,574, 664 and 754 nm recorded in both IL and PL are attributed to the luminescence centers activated by Dy(3+) ions. It is found that IL and PL emissions intensity decreases with increase in Si(7+) ion fluence. The decrease in intensity can be due to the destruction of Si-O-Si and O-Si-O type species present on the surface of the sample. FTIR studies also confirm the Si-O-Si and O-Si-O type species observed to be sensitive for swift heavy ion (SHI) irradiated samples.
B Umesh, B Eraiah, H Nagabhushana, S C Sharma, B M Nagabhushana, C Shivakumara, J L Rao, R P S Chakradhar
Department of Humanities, PVP Polytechnic, Dr. AIT Campus, Bangalore 560 056, India.
Nanocrystalline Nd(2)O(3):Cu(2+)(2mol %) phosphors have been prepared by a low temperature solution combustion technique. Powder X-ray diffraction (PXRD) results confirm that hexagonal A-type Nd(2)O(3)(900°C, 3h) and the lattice parameters have been evaluated by Rietveld refinement. Surface morphology of as-formed and Cu(2+) doped Nd(2)O(3) phosphors show that the particles are irregular in shape and porous in nature. TEM results also confirm the nature and size of the particles. The EPR spectrum exhibits two resonance signals with effective g values at g(ǀǀ)≈2.12 and g(⊥)≈2.04. The g values indicate that the site symmetry of Cu(2+) ions is octahedral symmetry with elongated tetragonal distortion. Raman studies show major peaks, which are assigned, to F(g) and combination of A(g)+E(g) modes. It is observed that the Raman peaks and intensity have been reduced in Cu(2+) doped samples. UV-Visible absorption spectra exhibit a strong and broad absorption band at ∼240nm. Further, the absorption peak shifts to ∼14nm in Cu(2+) doped samples. The optical band gap is estimated to be 5.28eV for Cu doped Nd(2)O(3) nanoparticles which are higher than the bulk Nd(2)O(3)(4.7eV). This can be attributed to the quantum confinement effect of the nanoparticles.
B Umesh, B Eraiah, H Nagabhushana, S C Sharma, D V Sunitha, B M Nagabhushana, C Shivakumara, J L Rao, R P S Chakradhar
Department of Humanities, PVP Polytechnic, Dr. AIT Campus, Bangalore 560056, India.
Nanocrystalline Nd(2)O(3):Ni(2+)(2 mol%) phosphor has been prepared by a low temperature (∼400°C) solution combustion method, in a very short time (<5 min). Powder X-ray diffraction results confirm the single hexagonal phase of nanopowders. Scanning electron micrographs show that nanophosphor has porous nature and the particles are agglomerated. Transmission electron microscopy confirms the nanosize (20-25 nm) of the crystallites. The electron paramagnetic resonance (EPR) spectrum exhibits a symmetric absorption at g≈2.77 which suggests that the site symmetry around Ni(2+) ions is predominantly octahedral. The number of spins participating in resonance (N) and the paramagnetic susceptibility (χ) has been evaluated. Raman study show major peaks, which are assigned to F(g) and combination of A(g)+E(g) modes. Thermoluminescence (TL) studies reveal well resolved glow peaks at 169°C along with shoulder peak at around 236°C. The activation energy (E in eV), order of kinetics (b) and frequency factor (s) were estimated using glow peak shape method. It is observed that the glow peak intensity at 169°C increases linearly with γ-dose which suggest that Nd(2)O(3):Ni(2+) is suitable for radiation dosimetry applications.
D V Sunitha, H Nagabhushana, Fouran Singh, S C Sharma, N Dhananjaya, B M Nagabhushana, R P S Chakradhar
Prof. CNR Rao Centre for Nano Research, Tumkur University, Tumkur, India.
This paper reports on the ionoluminescence (IL) of Zn(2)SiO(4):Eu(3+) nanophosphors bombarded with 100 MeV Si(7+) ions with fluences in the range (3.91-21.48)×10(12) ions cm(-2). The prominent IL emission peaks recorded at 580, 590, 612, 650 and 705 nm are attributed to the luminescence centers activated by Eu(3+) ions. It is observed that IL intensity decreases and saturates with increase of Si(7+) ion fluence. Fourier transform infrared (FT-IR) studies confirm surface/bulk amorphization for a fluence of (3.91-21.48)×10(13) ions cm(-2). These results show degradation of SiO (2ν(3)) bonds present on the surface of the sample and/or due to lattice disorder produced by dense electronic excitation under heavy ion irradiation. These results are discussed in detail.
A Jagannatha Reddy, M K Kokila, H Nagabhushana, J L Rao, C Shivakumara, B M Nagabhushana, R P S Chakradhar
Department of Physics, M.S. Ramaiah Institute of Technology, Bangalore 560 054, India.
Nanocrystalline ZnO powders have been synthesized by a low temperature solution combustion method. The photoluminescence (PL) spectrum of as-formed and heat treated ZnO shows strong violet (402, 421, 437, 485 nm) and weak green (520 nm) emission peaks respectively. The PL intensities of defect related emission bands decrease with calcinations temperature indicating the decrease of Zn(i) and V(o)(+) caused by the chemisorptions of oxygen. The results are correlated with the electron paramagnetic resonance (EPR) studies. Thermoluminescence (TL) glow curves of gamma irradiated ZnO nanoparticles exhibit a single broad glow peak at ∼343°C. This can be attributed to the recombination of charge carriers released from the surface states associated with oxygen defects, mainly interstitial oxygen ion centers. The trapping parameters of ZnO irradiated with various γ-doses are calculated using peak shape method. It is observed that the glow peak intensity increases with increase of gamma dose without changing glow curve shape. These two characteristic properties such as TL intensity increases with gamma dose and simple glow curve structure is an indication that the synthesized ZnO nanoparticles might be used as good TL dosimeter for high temperature application.
A Jagannatha Reddy, M K Kokila, H Nagabhushana, J L Rao, C Shivakumara, B M Nagabhushana, R P S Chakradhar
Department of Physics, M. S. Ramaiah Institute of Technology, Bangalore 560054, India.
Spherical shaped ZnO nanopowders (14-50 nm) were synthesized by a low temperature solution combustion method in a short time <5 min. Rietveld analysis show that ZnO has hexagonal wurtzite structure with lattice constants a=3.2511(1) Å, c=5.2076(2) Å, unit cell volume (V)=47.66(5)(Å)(3) and belongs to space group P63mc. SEM micrographs reveal that the particles are spherical in shape and the powders contained several voids and pores. TEM results also confirm spherical shape, with average particle size of 14-50 nm. The values are consistent with the grain sizes measured from Scherrer's method and Williamson-Hall (W-H) plots. A broad UV-vis absorption spectrum was observed at ∼375 nm which is a characteristic band for the wurtzite hexagonal pure ZnO. The optical energy band gap of 3.24 eV was observed for nanopowder which is slightly lower than that of the bulk ZnO (3.37 eV). The observed Raman peaks at 438 and 588 cm(-1) were attributed to the E(2)(high) and E(1)(LO) modes respectively. The broad band at 564 cm(-1) is due to disorder-activated Raman scattering for the A(1) mode. These bands are associated with the first-order Raman active modes of the ZnO phase. The weak bands observed in the range 750-1000 cm(-1) are due to small defects.
A Jagannatha Reddy, M K Kokila, H Nagabhushana, J L Rao, B M Nagabhushana, C Shivakumara, R P S Chakradhar
Department of Physics, M. S. Ramaiah Institute of Technology, Bangalore 560 054, India.
Nanocrystalline ZnO:Mn (0.1 mol%) phosphors have been successfully prepared by self propagating, gas producing solution combustion method. The powder X-ray diffraction of as-formed ZnO:Mn sample shows, hexagonal wurtzite phase with particle size of ∼40 nm. For Mn doped ZnO, the lattice parameters and volume of unit cell (a=3.23065 Å, c=5.27563 Å and V=47.684 (Å)(3)) are found to be greater than that of undoped ZnO (a=3.19993 Å, c=5.22546 Å and V=46.336 (Å)(3)). The SEM micrographs reveal that besides the spherical crystals, the powders also contained several voids and pores. The TEM photograph also shows the particles are approximately spherical in nature. The FTIR spectrum shows two peaks at ∼3428 and 1598 cm(-1) which are attributed to O-H stretching and H-O-H bending vibration. The PL spectra of ZnO:Mn indicate a strong green emission peak at 526 nm and a weak red emission at 636 nm corresponding to (4)T(1)→(6)A(1) transition of Mn(2+) ions. The EPR spectrum exhibits fine structure transition which will be split into six hyperfine components due to (55)Mn hyperfine coupling giving rise to all 30 allowed transitions. From EPR spectra the spin-Hamiltonian parameters have been evaluated and discussed. The magnitude of the hyperfine splitting (A) constant indicates that there exists a moderately covalent bonding between the Mn(2+) ions and the surrounding ligands. The number of spins participating in resonance (N), its paramagnetic susceptibility (χ) have been evaluated.
H B Premkumar, D V Sunitha, H Nagabhushana, S C Sharma, B M Nagabhushana, J L Rao, Kinshuk Gupta, R P S Chakradhar
Prof. C.N.R. Rao Centre for Nano Research, Tumkur University, Tumkur 572 103, India.
YAlO(3):Cr(3+)(0.1mol%) nanophosphor has been synthesized by low temperature solution combustion method. The X-ray diffraction studies reveal an orthorhombic structure. Transmission electron microscopy reveals that the particles are spherical in shape with nano-size ∼40-65nm. Electron paramagnetic resonance (EPR) spectrum shows a resonance signal with effective g value at g=1.978 which can be attributed to the exchange coupled Cr(3+) ion pairs in weakly distorted sites. The photoluminescence spectrum shows an intense doublet at 677nm and 694nm (R lines) assigned to spin-forbidden (2)E(g)→(4)A(2)(g) transition of Cr(3+) ions. EPR and PL studies reveal that the Cr(3+) ions occupy Al(3+) sites in YAlO(3). The interesting feature reported in this work concerns the linearity with gamma dose in the wide range (0.1-6kGy). Prominent TL glow peaks at 226°C and 346°C were observed for both γ and UV-rays respectively. It is observed that the peaks at 226°C and 346°C eventually show a linear response up to 5kGy which makes them a candidate for high dose dosimetry of ionizing radiation. The kinetic parameters namely activation energy (E), order of kinetics (b), frequency factor (s) of undoped and Cr doped samples were determined using Chens glow peak shape method and the results are discussed in detail.
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ABSTRACT: Rare-earth phosphors are commonly used in display panels, security printing, and fluorescent lamps, and have potential applications in lasers and bioimaging. In the present study, Eu3+- and Dy3+-codoped uniform-shaped Y2O3 submicron particles were prepared using the urea homogeneous precipitation method. The structure and morphology of the resulting particles were characterized by X-ray diffraction, field emission scanning electron microscope, and field emission transmission electron microscope, whereas their optical properties were monitored by photoluminescence spectroscopy. The room-temperature luminescence color emission of the synthesized particles can be tuned from red to yellow by switching the excitation wavelength from 254 to 350 nm. The luminescence intensities of red and yellow emissions could be altered by varying the dopant concentration. Strong quenching was observed at high Eu3+ and Dy3+ concentrations in the Y2O3 host lattice.
Luminescence. 2012 Sep 27;: 23019178
Faculty of Nanotechnology and Advanced Materials Engineering, Sejong University, Seoul, 143-747, Korea. firstname.lastname@example.org.
A series of efficient Li(3) Al(2)(PO(4))(3):Eu(2+) novel phosphors were synthesized by the facile combustion method. The effects of dopant on the luminescence behavior of Li(3) Al(2)(PO(4))(3) phosphor were also investigated. The phosphors were characterized by X-ray diffraction, field emission scanning electron microscope and photoluminescence techniques. The result shows that all samples can be excited efficiently by near-ultraviolet excitation under 310 nm. The emission was observed for Li(3) Al(2)(PO(4))(3):Eu(2+) phosphor at 425 nm, which corresponded to the d → f transition. The concentration quenching of Eu(2+) was observed in Li(3) Al(2)(PO(4))(3):Eu(2+) when the Eu concentration was at 0.5 mol%. The prepared powders exhibited intense blue emission at the 425 nm owing to the Eu(2+) ion by Hg-free excitation at 310 nm (i.e., solid-state lighting excitation). Consequently, the availability of such a phosphor will significantly help in the development of blue-emitting solid-state lighting applications. Copyright © 2012 John Wiley & Sons, Ltd.
Luminescence. 2012 Sep 24;: 23001910
Department of Physics, R.T.M. Nagpur University, Nagpur,-440033, India.
A series of Eu(2+) activated SrCaP(2) O(7) pyrophosphate phosphors were synthesized by the modified solid-state reaction method. The X-ray diffraction (XRD) and photoluminescence (PL) properties of these phosphors were investigated at room temperature. The excitation spectra indicate that these phosphors can be effectively excited by Hg-free excitation. The emission spectra exhibit strong blue performance, which is due to the 4f(6) 5d(1) →4f(7) transition of Eu(2+). The Fourier transform infrared spectrum at room temperature was investigated and surface morphology has been studied by scanning electron microscope. The prepared phosphor exhibited intense blue emission at the 427 nm owing to Eu(2+) ion by Hg-free excitation at 330 nm, that is, solid-state lighting excitation. Hence, the availability of such a phosphor will significantly help in the growth of blue-emitting solid-state lighting applications. Copyright © 2012 John Wiley & Sons, Ltd.
Magnesium content ratio effects of MgxZn1-xO seed layers on structural and optical properties of ZnO nanorods.
Min Su Kim, Do Yeob Kim, Soaram Kim, Giwoong Nam, Sung-O Kim, Dong-Yul Lee, Jin Soo Kim, Jong Su Kim, Jae-Young Leem
Department of Nano Systems Engineering, Center for Nano Manufacturing, Inje University, Gimhae, Gyungnam 621-749, Republic of Korea.
ZnO nanorods were grown on MgxZn1-xO seed layers with different content ratio ranging from 0 to 0.3 by hydrothermal method. Scanning electron microscopy (SEM), X-ray diffraction (XRD), and photoluminescence (PL) were carried out to investigate the effects of Mg content ratio for the MgxZn1-xO seed layers on the structural and optical properties of the ZnO nanorods. The surface morphology and structural properties of the MgxZn1-xO seed layers were changed by the Mg incorporation. However, the appearance, such as density, diameter, and shape, of the ZnO nanorods grown on the MgxZn1-xO seed layers was not changed significantly. The highest intensity ratio of the near-band-edge emission (NBE) to deep-level emission (DLE) and the narrowest full width at half maximum (FWHM) of the NBE peaks, indicating improvement in the crystallinity and luminescent properties of the ZnO crystals, were observed in the ZnO nanorods grown on the MgxZn1_xO seed layers with the content ratio of the 0.05.
Luminescence. 2012 Sep 4;: 22949386
School of Chemistry and Chemical Engineering, Jinggangshan University, Ji'an, Jiangxi, 343009, China. email@example.com.
A facile chemical method was employed to prepare fine BiPO(4):Eu(3+) phosphor particles calcined at the same temperature. Introducing lithium greatly affected the morphology of the samples and further affected the luminescence intensity. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and photoluminescence (PL) spectroscopy. The XRD patterns of BiPO(4):Eu(3+) indicated a monoclinic phase. From the fluorescence spectra, the emission transition (5) D(0) → (7) F(1) is more prominent than the normal red emission transition (5) D(0) → (7) F(2). Based on the intensity ratios of (5) D(0) → (7) F(2) to (5) D(0) → (7) F(1) in the emission spectra, it can be concluded that introducing Li(+) can improve the symmetry of the crystal lattice and modify the emission intensity. Sharp lines at 395 nm are the strongest of the f-f transitions and match well with near-UV LED chips. Copyright © 2012 John Wiley & Sons, Ltd.
Department of Chemistry, Annamalai University, Annamalainagar 608 002, India.
The influence of strontium doping on the properties of bis(thiourea)zinc(II) chloride (BTZC) crystals has been described. The reduction in the intensity observed in powder X-ray diffraction of doped specimen and slight shifts in vibrational frequencies confirm the lattice stress as a result of doping. The incorporation of Sr(II) into the crystal lattice was confirmed by energy dispersive X-ray spectroscopy (EDS). Surface morphological changes due to doping of the alkaline earth metal are observed by scanning electron microscopy (SEM). The crystal is transparent in the entire visible region having a lower optical cut-off at ∼308nm with a band gap energy of 4.06eV. The DSC studies reveal the purity of the materials and no decomposition is observed up to the melting point. Dielectric studies show that the isovalent ion Sr(II)-doping altered the dielectric properties of the host crystal.
Luminescence properties of Mn(2+)-doped Li2ZnGeO4 as an efficient green phosphor for field-emission displays with high color purity.
State Key Laboratory of Rare Earth Resource Utilization, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun, 130022, PR China.
Green emitting Li(2)ZnGeO(4):Mn(2+) phosphors were synthesized through a high temperature solid-state reaction process. X-Ray diffraction, field emission scanning electron microscopy, photoluminescence (PL) and cathodoluminescence (CL) spectra were utilized to characterize the synthesized samples. Under UV and electron-beam excitation, the pure Li(2)ZnGeO(4) sample shows a blue emission due to defects, while the Li(2)ZnGeO(4):Mn(2+) sample exhibits a green emission corresponding to the characteristic transition of Mn(2+)((4)T(1)→(6)A(1)). In particular, the CL intensity (brightness) of Li(2)ZnGeO(4):Mn(2+) is higher than that of commercial green phosphor ZnO:Zn. In addition, the CL properties of Li(2)ZnGeO(4):Mn(2+) phosphor, the dependence of CL intensity on accelerating voltage and filament current, the decay behavior of CL intensity under electron bombardment, and the stability of CIE chromaticity coordinates, have been investigated in detail. The results indicate that the as-prepared Li(2)ZnGeO(4):Mn(2+) phosphor has a good CL intensity and CIE coordinate stability with green emission under low-voltage electron beam excitation. Therefore, Li(2)ZnGeO(4):Mn(2+) is a promising green phosphor for application in full-color field-emission displays.
Effects of the mixing ratio of the CaAl12O19:mn and Zn2SiO4:mn color-conversion layer on the color tunable emissions of white organic light-emitting devices.
Department of Electronics and Computer Engineering, Hanyang University, Seoul 133-791, Korea.
The optical properties of white organic light-emitting devices (WOLEDs) fabricated utilizing a CaAl12O19:Mn and Zn2SiO4:Mn phosphor layer were investigated. X-ray diffraction patterns for CaAl12O19:Mn and Zn2SiO4:Mn phosphors showed that Mn ions in the CaAl12O19:Mn phosphors were completely substituted into Ca ions and that Mn ions in the Zn2SiO4:Mn phosphors were completely substituted into Zn ions. Field emission scanning electron microscopy images showed that the size of the CaAl12O19:Mn phosphor was approximately between 0.1 and 3 microm, and that the size of the Zn2SiO4:Mn phosphor was smaller than 7 microm. The color coordinates of the electroluminescence spectra for WOLEDs with phosphor thicknesses of 0.25 and 0.35 mm shifted to the white emission side because the generated blue light from the blue OLEDs combined with the red and green lights was converted by the CaAl12O19:Mn and the Zn2SiO4:Mn phosphor down-conversion layers.
Laser and Spectroscopy Laboratory, Department of Physics, Banaras Hindu University, Varanasi 221005, India.
Luminescent nanophosphor of Er, Yb: Gd(2)O(3) has been synthesized by well known combustion synthesis. Along with strong UV-Vis upconversion emission, sensor for temperature and magnetic field, nano-heater etc., it can also be used as luminescent ink by dispersing the nanophosphor in aqueous polyvinyl alcohol solution. The stability of the ink has been found to depend strongly on the mixing process of the phosphor powder in the polymer solution. The X-ray diffraction results and TEM images with diffraction pattern show that the particles are in cubic phase of Gd(2)O(3) with particles of average size <40nm. SEM images show flaky structure which makes it suitable for dispersing in PVA and useful for luminescent ink purposes on NIR excitation. The FT-IR and the thermal analysis support the presence of PVA. Upconversion and downconversion luminescence has also been observed with 532nm excitation and energy transfer mechanism has been explained. The NIR pumping gives strong UC emission bands in red and green regions extending up to extreme UV (240nm) in this host.
Fengzhen Liu, Xin Shao, Yibin Yin, Limin Zhao, Zhengfeng Jia, Qiaozhen Sun, Zhuwei Shao, Xuehua Liu, Xianhua Meng
College of Materials Science and Engineering, Liaocheng University, Liaocheng 252059, China.
Eu3+-doped REVO4 nanphosphors were controllably synthesized by an EDTA-mediated hydrothermal method at 180 degrees C using RE(NO3)3 and Na3VO4 as precursors. The obtained products were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectrometry (FTIR), X-ray photoelectron spectra (XPS), and photoluminescence spectroscopy (PL). The XRD results showed that the products were pure tetragonal structure and no other impurity phase appeared. The PL studies demonstrated Eu3+ ions doping effectively enhanced luminescent properties of LaxRE(1-x)VO4 and YxRE(1-x)VO4 nanoparticles, but EU3+ ions doping did not enhance luminescent properties of CexRE(1-x)VO4 (x not equal 0) nanoparticles. The prepared phosphors showed well-defined red luminescence due to radiative transitions from 5D0 to 7F(J)(J = 1,2) levels of Eu3+ ions, respectively. Furthermore, we reported Eu3+-doped CexRE(1-x)VO4 (x not equal 0) phases represented a new class of optically inactive materials.