Nanophosphor Powders Research Articles

Hexagonal rod-like Eu3+doped CaMoO4 phosphors: Structural, photoluminescence and photometric properties for display device applications

A multicolored LED illumination device is a compact, durable, easy to obtain color-adjustable output illumination source. It is frequently utilized in the domains of room illumination and exterior displays. However, the advancement of multicolor LEDs has been hampered by the rise in price and the fall in luminous efficacy while changing illumination colors. In the present investigation we have prepared intense red emitting Eu3+ doped CaMoO4 phosphor nanopowders via simple solid-state reaction technique. The powder X-ray diffraction (PXRD) studies reveal the crystalline nature of the samples with scheelite–type mono phase tetragonal structure with I41/a space group. The band gap (Eg) energy values were estimated and found to range between 4.63–5.32 eV. Scanning electron microscopy (SEM) studies reveled the hexagonal rod-like structures with different Aloe Vera gel concentrations. The particle size was found to be around 40 nm. The vibrational modes of the prepared powders were evaluated by using Fourier Transform Infrared Spectroscopy (FTIR) and Raman spectroscopy. It was observed from the results that, there were 26 vibrational modes of CaMoO4 (Γ=3Ag + 5Au + 5Bg + 3Bu + 5Eg + 5Eu) 8 of which (4Au and 4Eu) were infrared active and 13 (Ag, Bg, and Eg) are Raman active. Photoluminescence (PL) emission intensity increases up to 5 mol% of Eu3+ ions load and subsequently it declines due to the concentration quenching phenomenon and effective energy transfer from Mo-O charge transfer band (CTB) to 5D0 levels of Eu3+. It was noticed from PL emission spectra that, four intense peaks located at 5D0 → 7F1 (590 nm), 5D0 → 7F2 (613 nm), 5D0 → 7F3 (654 nm), 5D0 → 7F4 (702 nm) of Eu3+ respectively. The Commission International de I'Eclairage (CIE) diagram indicates the red color emission and average correlated color temperature (CCT) value was found to be 2050 K. Further, the external quantum efficiency (QE) and color purity (CP) were calculated to check the phosphor efficiency and found to be 92% and 72% respectively. The present investigation opens up a new avenue in the fabrication of low-cost display devices with high color purity and luminous efficacy.

Potential of Y2Sn2O7:Eu3+, Dy3+ Inorganic Nanophosphors in Latent Fingermark Detection

In this work, we investigated the potential of Eu3+/Dy3+-codoped Y2Sn2O7 fluorescent nanophosphors to visualize latent fingermarks. We prepared these nanophosphors with various doping concentrations by the conventional coprecipitation reaction. The crystal structure, morphology, luminescence properties, and energy transfer mechanisms were studied. The crystalline phase was characterized by X-ray diffraction and crystal structure refinement using the Rietveld method. XRD measurements showed that the samples crystallized in the pure single pyrochlore phase with few more peaks originated from secondary phases and impurities generated during phosphor production, and that Eu3+ ions occupied D3d symmetry sites. The average crystallite size after mechanical grinding was less than 100 nm for all compositions. The optical characterization showed that, when excited under 532 nm, the Eu3+/Dy3+-codoped Y2Sn2O7 samples’ main intense emission peaks were located at 580–707 nm, corresponding to the 5D0→7Fj (j = l, 2, 3, and 4) transitions of europium. In fact, the 5D0→7F2 hypersensitive transition is strongly dependent on the local environment and was quite weak in Eu3+:Y2Sn2O7 at low Eu3+ doping levels. We found that the presence of Dy3+ as a codopant permitted enhancing the emission from this transition. The calculated PL CIE coordinates for the synthesized nanophosphors were very close to those of the reddish-orange region and only slightly dependent on the doping level. Various surfaces, including difficult ones (wood and ceramic), were successfully tested for latent fingerprint development with the prepared Eu3+/Dy3+-codoped Y2Sn2O7 fluorescent nanophosphor powder. Thanks to the high contrast obtained, fingerprint ridge patterns at all three levels were highlighted: core (level 1) islands, bifurcation, and enclosure (level 2), and even sweat pores (level 3).

A highly efficient deep red-emitting Mn4+-powered oxyfluoride nanophosphor developed for plant growth and optical thermometric applications.

This research mainly highlighted an intense deep red-emitting and Mn4+-powered oxyfluoride nanophosphor, Mg14Ge4.99O16F8:0.01Mn4+ (MGOF:Mn), which was synthesized via adopting a scalable synthesis route for commercial temperature sensing and artificial plant growth applications. The electron microscopic analysis confirmed the formation of nanosized particles without any defined shape or size distribution. The obtained nanophosphor exhibited sharp emission peaks at 659 nm and 631 nm under UV (317 nm) and blue excitation (417 nm) owing to Mn4+:2Eg → 4A2g and Mn4+:2T1g → 4A2g transitions, respectively. The emission spectrum is situated in the deep red region of the CIE color diagram where the red color purity approached 100% under both the excitations. The absorption efficiency and the internal and external quantum efficiencies of this red-emitting system were calculated to be 53%, ∼77%, and ∼41%, respectively, under blue excitation of 417 nm, which indicated its potential for indoor plant cultivation. A prototype red LED was fabricated by pasting the red-emitting MGOF:Mn4+ nanophosphor powder on a 410 nm blue LED chip. The resulting electroluminescence spectrum overlapped with those of the important organic pigments of normal plants. Importantly, the thermometric properties of the nanophosphor were evaluated in detail for FIR and lifetime-based thermometry applications. The examined nanophosphor showed an extreme absolute sensitivity of 0.00326 K-1 at 373 K with excellent reproducibility and temperature resolution. Because of the small particle size and high luminescence efficiency, the nanophosphor could be implemented in various nano-devices where non-contact optical thermometry is necessary for high performance.

Characterization of the incorporated SiO2 co-doped with Sr2+ and Tb3+ phosphors into PLA polymer matrix

SiO2 :0.4% Sr2+, x% Tb3+ (0 ≤ x ≤ 0.5) nanophosphor powders were prepared by sol-gel method. The powder samples were dispersed into the PLA polymer matrix through melt mixing method and compression molding to prepare the nanophosphor polymer composite. X-ray diffraction (XRD) patterns showed broad peaks with the position of the peaks shifting and more separating with an increase in Tb3+ concentration. The transmission electron microscope (TEM) images showed darker patches with the introduction of the nanophosphor, which indicates the incorporation of phosphor particles into PLA polymer. Differential scanning calorimeter (DSC) results revealed that the composites show an increase in the cold crystallization temperature (Tcc) and slight decrease in the glass transition temperature (Tg) as compared to the PLA. Thermogravimetric analysis (TGA) results showed that the thermal stability of the composites show an initial decrease with the incorporation of the fillers, but they become more thermally stable with higher Tb concentration in the fillers. Ultraviolet visible spectroscopy (UV–vis) results showed the decrease in transmittance for the composite compared to the PLA polymer. The photoluminescence (PL) results showed that the incorporation of the Sr2+doped SiO2 only affected the luminescence intensity, while co-doping with the incorporation of the Sr2+ and Tb3+ ions induced the emissions peaks at 487, 543, 582 and 621 nm, which could be attributed to the 5D4 → 7F3, 7F4, 7F5, and 7F6 transitions of Tb3+, respectively. The main aim of this study was to fabricate the light emitting polymer-based material.

The blue-green emission color of Ag+, Gd3+ co-activated CdWO4 phosphor via energy transfer for luminescence applications

Ag+, Gd+3-doped CdWO4 (co-doped CWO) phosphor nanopowders were synthesized by an eco-friendly method and then embedded into the polymer matrix to produce a flexible and transparent thin film. A novel phosphor for the excitation by an ultraviolet source, 980 nm diode laser, and proton radiation was reported at room temperature and crystal structure, luminescent properties, and energy transfer between Ag+ and Gd+3 ions were thoroughly investigated. Elemental composition and chemical state analyses were measured using X-ray photoelectron spectroscopy and energy dispersive X-ray spectroscopy studies. Crystal structure and phase identification were confirmed using powder X-ray diffraction measurement. Based on all results, the flexible phosphor film prepared has good thermal stability and efficient blue-green emission under UV light, laser, and proton excitation used in emissive displays applications.

Sulfidization-free synthesis of well dispersed (Gd,La)2O2S:Pr3+ nanopowders and the effect of La3+ on structure and luminescence

Pr3+ activated Gd2O2S and La2O2S are finding a wide range of luminescence applications but their solid-solution form has rarely been reported in the literature. A series of [(Gd1.0-xLax)0.99Pr0.01]2O2S (x = 0.0–1.0, GLOS:Pr3+) solid-solution phosphor nanopowders were directly produced in this work by calcining their sulfated hydroxide type precursors in flowing hydrogen at 900 °C, without using any of the harmful sulfidization reagents indispensable to other technical routes. The synthesis method also has the significant advantages of fine crystallites (∼20–35 nm), high specific surface area (∼16–21 m2/g) and unimodal particle size distribution (average particle size ∼120–140 nm) of the product. Photoluminescence study indicated that La3+ doping may remarkably enhance Pr3+ luminescence under 263 nm excitation, though tends to lower the thermal stability and elongate the lifetime of the emission. Aside from phosphor application, the thus-synthesized GLOS:Pr3+ powders would be well suited for the sintering of high-quality ceramic scintillators because of their fine particle/crystallite size and unimodal/narrow size distribution.

Facile synthesis of Gd2O2SO4:Tb and Gd2O2S:Tb green phosphor nanopowders of unimodal size distribution and photoluminescence

Suppressing the crystallization and plate-like crystallite growth of RE2(OH)4SO4·2H2O compound by low-temperature (~4 °C) precipitation produced an amorphous RE2(OH)3.3(CO3)0.35SO4·2H2O precursor (RE = Gd1-xTbx) that can be decomposed to Gd2O2SO4:Tb and Gd2O2S:Tb green phosphor nanopowders of unimodal size distributions upon calcination in air at 1000 °C (average particle size ~156.9 nm) and in hydrogen at 800 °C (average particle size ~130.2 nm), respectively. The optimal RE3+ concentration for precursor synthesis was determined to be ~0.10 mol/L. Through detailed characterization by XRD, FTIR, DTA/TG, FE-SEM, TEM and particle sizing, the courses of phase/morphology evolution were clarified. Photoluminescence study found that the (Gd0.99Tb0.01)2O2SO4 and (Gd0.98Tb0.02)2O2S representative phosphors have quantum efficiencies of ~16.8% (λex = 275 nm) and 38.5% (λex = 286 nm), fluorescence lifetimes of ~3.70 and 1.75 ms and activation energies for thermal quenching of ~0.552 and 0.385 eV, respectively. The values are remarkably larger than those reported for Gd2O2S:Tb, which are considered to be due to higher purity, better crystallization and fewer luminescence-quenching defects of the product. Particularly, the (Gd0.99Tb0.01)2O2SO4 phosphor has negative thermal quenching up to ~150 °C and can retain over 85% of its room temperature emission intensity at 250 °C, which may enlighten its application in high-power LEDs.

Spectroscopic and microscopic properties of KSrVO4: Mn2+ synthesized by low-cost combustion method

This paper reports the systematic study of Mn2+ doped KSrVO4 nanophosphors synthesized by low-cost combustion method. X-Ray Diffraction, UV–Vis spectroscopy, Photoluminescence (PL) spectroscopy, Scanning Electron Microscopy (SEM), Energy Dispersive Analysis of X-rays (EDAX) and Transmission Electron Microscopy (TEM) revealed the structural and spectral properties of synthesized powders. By doping Mn2+ into the host, it is observed that for small concentration of Mn2+ the band gap decreases initially showing the red shift followed by increase in band gap for higher concentration of Mn2+. PL spectra exhibits two prominent emission peaks at 436 nm and 511 nm under 373 nm excitation. The synthesized nanophosphor powders may perhaps be thought of as new phosphor materials excited by UVA emitting InGaN LEDs.

Gd2O3:Er3+ embedded PMMA/PC nanocomposites: A luminescent nanocomposite

Gd2O3:Er3+ nanophosphor powders were synthesized by the solution combustion method and then embedded into neat Poly(methyl methacrylate) (PMMA) polymer solution and Poly carbonate (PC) polymer solution via the solvent casting method to obtain Polymer-Phosphor nanocomposites. This method is widely used due to certain advantages like uniform dispersion of the filler being added and ease of the preparation procedure. Different samples (0.5–2.0 wt %) of Er3+ doped Gd2O3 nanophosphors were prepared by the combustion method. The samples were then characterized by FTIR, XRD, SEM techniques. The particle size was evaluated by Debye Scherrer's formula and was found to be 12 nm using urea as fuel. XRD analysis revealed crystalline nature and monoclinic phase of the synthesized phosphor. On incorporation of the synthesized nanophosphor into the neat polymer solution, neat dispersion of the powder in the film was observed and also at higher phosphor loading (2 wt %), agglomeration was observed. XRD diffractogram of the nanocomposite films confirmed the incorporation of the nanophosphor into the polymer matrix. The emission spectra monitored at 275 nm excitation wavelength, similar emission bands as that of the nanophosphor at 552, 590 and 605 cm−1 were observed with slight shifts. TGA analysis revealed the thermal stability of the polymer. The CIE chromaticity diagram confirmed the emission color of the nanocomposite films, and the tuning of color by changing Er3+ concentration was also studied.

Characterization of the incorporated ZnO doped and co-doped with Ce3+ and Eu3+ nanophosphor powders into PVC polymer matrix

Abstract Zinc oxide (ZnO) undoped, doped and co-doped with Ce3+ and Eu3+ were synthesized by the chemical bath deposition method. The nanopowders were spread through a polyvinyl chloride (PVC) polymer matrix via the solution casting method to prepare nanocomposite films. The X-ray diffraction patterns showed crystalline peaks corresponding to a hexagonal wurtzite ZnO structure. Scanning electron microscope showed aggregated structures. Energy dispersive X-ray spectrometer and Fourier-transform infrared spectroscopy respectively revealed the existence of the expected elemental composition and functional groups. Differential scanning calorimetry showed nanoparticles as the starting point for particle growth. Thermogravimetric analysis showed lowering in thermal stability of the nanocomposites. In the UV–vis study, PVC had the highest energy band gap than all powder and composite systems. The PVC nanocomposites showed an emission peak at around 444 nm, which differed from that of the nanopowders. The chromaticity diagram showed emission colours changed to the blue vertex regions for nanocomposite.

Modifications in the Structural and Optical Properties of ZnO Nanophosphor on Doping with Tb

Background:The characteristic visible emission from ZnO being attributed to the defect energy states can be tailored by doping as well as by synthesis techniques. Rare-earth elements, among various dopants, are interesting because of their unique emission properties in the visible region. Terbium (Tb), in particular, is reported to contribute significantly to the creation of the defect energy states when doped in ZnO. This study investigated the Tb concentration dependent modifications in the structural and optical properties of ZnO nanophosphor.Methods:Tb (0.1, 0.5, 01.0 mol%) doped nanophosphor powder samples prepared by low temperature precipitation method, were sintered in air at 700oC using a home-built temperature controlled (±1oC) muffle furnace. Powder XRD and EDX spectra at room temperature were recorded using Philips X perts x-ray spectrometer while Jeol JSM-7600F was used to record SEM images. Photoluminescence spectra excited by the 280, 300, 380 and 460nm radiation from a Xe lamp were recorded using Carry 8000 spectrophotometer. Raman spectra excited by 514.5nm radiation from an Ar-ion laser, was investigated using Morrison microscope Olympus Bx 41 while UV-VIS absorption spectra were recorded on UV- 1800 UV-VIS Spectrophotometer.Results:FTIR and XRD spectra showed that the basic ZnO wurtzite crystal structure remained unchanged on doping. However, XRD data analysis indicated that the 0.1 mol% Tb might be incorporated in ZnO unit cell at an interstitial and / or substitutional site(s) while at 0.5 and 1.0 mol% doping levels migration of Tb to the surface could be the dominant process. This was further confirmed by Raman and photoluminescence studies. Broad emission (122nm FWHM) peaking around 510nm was observed when the doped samples were excited with 280 and 300nm radiation while characteristic ZnO emission was observed with 380 and 460nm radiation. The calculated chromaticity color coordinates (x,y) of the emission excited by 280nm in 0.5 mol% doped ZnO were: x=0.29 and y=0.31, which are very close to those of the daylight at noon.Conclusion:Concentration dependent lattice distortions were observed; it was concluded that at 0.1mol% concentration level Tb was incorporated in ZnO lattice resulting in interstitial or substitutional defects. On the other hand, at 0.5 and 1.0 mol% doping levels diffusion of Tb to the surface producing strain due to "hydrostatic like pressure" seemed to be the dominating process; maximum strain was observed at 0.5mol% doping. The calculated chromaticity color coordinates of the 280nm excited emission from ZnO:Tb (0.5mol%) were found to be very close to those of the "day light at noon” indicating the suitability of the material for the realization of white light sources.

Effects of Cr-doping on the morphology and optical properties in Zn2GeO4 (ZGO) nanorods prepared by hydrothermal method

The undoped Zn2GeO4 nanorods and the Cr-doped Zn2GeO4 nanorods were successfully prepared by the hydrothermal method. The structure, the optical characteristics properties of nano phosphor powders were studied by X-ray diffraction, ultraviolet-visible diffuse reflectance spectroscopy, photoluminescence spectroscopy, FESEM. The results indicated that Cr ions substituted for Ge ions and the Cr doping expanded for the unit cell of the crystal lattice. The band gap energy found to be decreased with increasing Cr doping concentration. At a wavelength of 250–320 nm excitation, Cr3+ doped Zn2GeO4 phosphors showed bluishwhite emission at 510 nm. The concentration of Cr3+ ions in Zn2GeO4:Cr3+ played important roles in the evolution of the length of nanorods, photoluminescence intensity and quality of nano crystal. This result contributed optimization of Cr3+ doped nano phosphors with 5% mol. The possible mechanism of substitution of ion Cr in Zn2GeO4 nano crystalline has also been discussed.

Novel bifunctional lanthanide‐centered nanophosphors for latent fingerprint detection and anti‐counterfeiting applications

Production of hybrid organic/inorganic complexes such as lanthanide phosphors in the nanodomain for human fingerprint visualization and anti‐counterfeiting ink under biocompatible UVA and blue light has not yet been studied that thoroughly. This paper presents the preparation of novel, bifunctional, green and red nanophosphors based on Eu3+ and Tb3+ complexes with quinolinone ligand (H2L). They have been prepared and characterized for latent fingerprint detection and anti‐counterfeiting ink applications. The analytical data confirm that the ligand acts in a monoanionic bidentate manner through OO donor sites, forming mononuclear complexes, formulated as [Ln(HL)3(C2H5OH)3] (Ln = Eu3+ or Tb3+; L = 1‐ethyl‐4‐hydroxy‐3‐(nitroacetyl)quinolin‐2‐(1H)‐one). The Eu3+ and Tb3+ complexes have nanospherical morphologies with average particle sizes of 17 and 5 nm, respectively. Pure red and green photoluminescence with long lifetime values has been obtained from the Eu3+ and Tb3+ complexes, respectively, under non‐harmful UVA and blue illumination. Latent fingerprint details, including their characteristic three levels, have been clearly identified from various forensic (non‐porous, semi‐porous, highly fluorescent porous) substrates using red (Eu3+) and green (Tb3+) nanophosphors. The green nanophosphor powder has a greater capability for visualizing latent fingerprints from highly fluorescent porous surfaces as compared to the red one. Both nanophosphor complexes have been used to develop luminescent ink for anti‐counterfeiting applications.

Effects of annealing period on the structure and photoluminescence of the mixed phases ZnAl2O4 /ZnO/SrAl2O4/Sr3Al2O6:0.025% Tb3+ nanophosphor synthesized by sol-gel technique

Nanophosphor powders of the mixed phases of ZnAl2O4/ZnO/SrAl2O4/Sr3Al2O6 (ZZSS) doped with Tb3+ (ZZSS:0.025%Tb3+) were successfully prepared by sol-gel technique. The effect of the annealing period at a fixed annealing temperature (1000 °C) and dopant concentration (0.025% Tb3+) on the structure and photoluminescence properties was investigated. X-ray diffraction results revealed that the crystallite size was influenced by the annealing period. Scanning electron microscopy showed that varying the annealing period influenced the particle morphology of the prepared nanophosphor material. High resolution transmission electron microscopy confirmed that the prepared material is on the nanoscale. The photoluminescence results showed that the ZZSS emits at 585 nm when excited at 374 nm, which is attributed to the defects centres within the ZnO phase. The Tb3+ doped samples showed emissions peaks at 545, 590 and 623 nm which were attributed to the 4f transitions of Tb3+, specifically 5D4 → 7FJ (J = 5, 4, 3). Increasing the annealing period up to 5.4 h led to luminescence enhancements, while a further increase led to quenching. The Commision Internationale de l’Eclairage coordinates showed that the greenish emission colour could be tuned by varying the annealing period.

YAG:Ce3+ phosphor nanopowders and thin textured coatings prepared by polymer-salt method

Ceramic YAG : Ce3 + powders and thin transparent coatings consisting of small (<70 nm) nanocrystals were prepared by polymer-salt method. The characterization of obtained materials was conducted by XRD, SEM, and luminescent analysis. The materials calcined at 900°C to 1250°C consist of small (30 to 70 nm) YAG : Ce3 + nanocrystals. The highest quantum yield of 41% was obtained for powders containing cerium doping 0.2 wt.% and consisting of nanocrystals having size about 70 nm.

Photoluminescence Property of Eu3+ doped CaSiO3 Nano-phosphor with Controlled Grain Size

A series of Eu3+ doped CaSiO3/SiO2 nano-phosphor powder of controlled grain size, crystalline structure, and chemical composition were synthesized using the microemulsion technique. The morphology, size, and shape of the synthesized nanophosphorous powder were investigated using transmission electron microscopy and X-ray diffraction (XRD) analysis. XRD profiles of samples sintered over 600 °C, suggested phase shift from amorphous powder grain to more ordered polycrystalline powder of triclinic type wollastonite, CaSiO3, with preferred crystal phase orientation of (112) and tetragonal type cristobalites of SiO2. The grain size, crystallinity, and chemical composition of the host matrix, activator and sensitizer strongly affected both the absorption and emission bands of these samples. The amplitude of both the orange and red emission bands significantly increased with sintering temperature. The emission band is red-shifted with decreasing grain sizes. These bands displayed good sensitivity to ionic concentration of the Si4+, Ca2+, and Eu3+. With increasing Ca2+ ion concentration both the intensity of the red photoluminescence (PL) band increased and a concentration quenching observed. Increase in Si4+ ion concentration led to quenching in PL intensity of both the orange and red bands, whereas the amplitude of the blue-band slightly increased. With increasing Eu3+ ion concentration the red-band initially increased whereas it started decreasing at higher sample concentration. In the presence of Ca2+ ion as a sensitizer, the sample showed a remarkable PL property-including–about 100% photon conversion efficiency and a two-fold increase in excitation and emission photons.

Energy transfer and photoluminescent analysis of a novel color-tunable Ba2Y1-xV3O11:xSm3+ nanophosphor for single-phased phosphor-converted white LEDs

Metal nitrates are used to synthesize a series of novel Ba2Y1-xV3O11:xSm3+ nanophosphors via urea-assisted solution combustion route. X-ray diffraction (XRD), diffuse reflectance (DR), transmission electron microscopy (TEM) and photoluminescence (PL) spectroscopy were employed to analyse the structure, morphology, photoluminescent behaviour and energy transfer mechanism. Rietveld analysis over Ba2Y0.98Sm0.02V3O11 showed that Y3+ ions can be well-replaced by trivalent samarium ions without resulting any major alteration in the crystal structure of host lattice. Furthermore, the lattice parameters were determined for both the host as well as the doped composition. The Scherrer equation yielded an average particle size of 44 nm, which in turn was further confirmed by TEM micrographs. The optical band-gap of the host (3.92 eV) was calculated from the diffuse reflectance spectra. Moreover, the photoluminescence spectral studies showed that under near ultra-violet (NUV) excitation of 340 nm, our nanophosphor powder exhibits the characteristic emission peaks of trivalent samarium along with the emission of VO43− (501 nm) group. The excitation energy transfer from vanadate group to Sm3+ produced a systematic color tunablity in white region itself. The optimum Sm3+ concentration for better luminescence was found to be 2 mol%. The critical distance for energy transfer was calculated to be 29.02 Å, which in turn assisted to shortlist the mechanism responsible for luminescence-quenching (dipole-dipole) arising from the over-doping of the activator. The photoluminescence decay curves revealed the decay kinetics of 4G5/2 electronic state. Finally, the calculation of CIE color coordinates from emission spectra in MATLAB program unveiled a somewhat white-light emitter which may find potential applications in phosphor-converted white light emitting diodes (PC-WLED) under near-ultraviolet (NUV) excitation.

Combustion synthesis of Ce2LuO5.5:Eu phosphor nanopowders: structure, surface and luminescence investigations

The spherical shape, uniform size and small degree of agglomeration of the particles play crucial roles in promoting the practical applications of the phosphor powders. In this paper, the novel Eu3+ -doped cerium lutetium Ce2LuO5.5 composite nanopowders with a cubic fluorite structure were prepared via a typical solution combustion route, and their internal structure, surface morphology as well as luminescence properties were investigated. The Eu3+ could substitute in either Lu3+ or Ce4+ sites and the existence of oxygen vacancy was confirmed in the composite by X-ray diffraction and Raman spectra techniques. Without the addition of surfactant, most of the as-prepared particles were bound together, and the luminescence was very weak even after a sintering process. Assisted with appropriate polyvinyl alcohol (PVA) surfactant in the combustion reaction and a subsequent heat-treatment process, the bound-particles were evidently separated and seemed to be nearly spherical shape. The particle size could be controlled to 30–120 nm and the luminescence was enhanced by adjusting the subsequent sintering temperature. Excited with 466 nm blue light, the nanopowders exhibited characteristic 5D0 → 7FJ (J = 0–4) emission transition of Eu3+ and showed enhanced red luminescence as Eu3+ occupied Ce4+ site rather than Lu3+ site. The maximum emission was obtained as 40 mol% Eu substitutes Ce in the composite. Due to the coincidence of 466 nm excitation light with the emission of InGaN chips in white light-emitting diodes, the surface-morphology improved Eu-doped Ce2LuO5.5 phosphor nanopowders have a potential application in solid state lighting fields.

Synthesis and luminescent properties of Tb3+ doped BaLa2ZnO5 nanoparticles

Nanophosphor powders of composition BaLa2ZnO5:Tb3+ have been synthesized via using urea assisted solution combustion method using metal nitrates as the precursor materials. The structural, morphological and luminescent properties have been investigated by powder X-ray diffraction (XRD) and photoluminescence (PL) spectroscopy. The Rietveld analysis showed that these nanophosphors crystallize in the tetrahedral phase with the 14/mcm (140) space group. The crystallite size was determined by Scherer formula and was found to be 70 nm. The photoluminescent excitation of these nanocrystals at 278nm yielded the characteristic emission peaks at 545nm and 489nm due to 5D4→7F5 (magnetic-dipole) and 5D4→7F6 (electric-dipole) transitions, respectively. The optimum activator concentration was found to be 3 mol% and the concentration quenching arising from the over-doping was attributed to the quadrupole–quadrupole interactions. The excellent luminescent profile of these nano-scaled particles suggests their auspicious applications in the solid-state lighting and display technology.

Rare Earth Doped Zinc Oxide Nanophosphor Powder: A Future Material for Solid State Lighting and Solar Cells

A comprehensive review of up-conversion (UP) and down-conversion (DC) or down shifting of rare earth (RE) doped zinc oxide (ZnO) nanophosphors is presented. Research interest in the development of RE3+ doped ZnO for UP and DC nanophosphors has been encouraged by the potential application of these materials in light emitting diodes and different types of photovoltaic cells. A range of remarkable characteristics, which are organized into different sections describing the structure, optical, and luminescence properties of these materials, are discussed in detail. Undoped ZnO has two characteristic emissions in the ultraviolet and visible regions related, respectively, to excitonic recombination and intrinsic defects. X-ray photoelectron spectroscopy (XPS) data demonstrated a correlation between the visible emission and intrinsic defects. In the case of the DC or shifting process, there was simultaneous emissions related to f → f transitions of RE ions and defects in ZnO host. These emissions were dependent o...