Nanocrystalline Phosphors Research Articles

Spectroscopic properties of red-emitting Sr0.9Na0.2ZrO3:Eu3+ phosphors with potential applications in lasers and LEDs

A range of Sr0.9-yNa0.2ZrO3: Eu3+ (SNEZ) nanocrystalline phosphors with high color purity and exceptional laser properties were synthesized using sol-gel technique. The samples were characterized for structural and spectroscopic properties using methods including X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), diffuse reflectance spectroscopy, and photoluminescence (PL) spectroscopy. Structural analysis revealed orthorhombic phase with average crystallite size 28-19 nm, decreasing with increasing Eu3+ concentration. A low phonon energy of 455–495 cm−1 and wide (expanding) band gaps (5.0–5.3 eV) were obtained for the SNEZ phosphors. Under the excitation of 300 nm, the SNEZ phosphor emits strong red light at 614 nm, attributed to the 5D0 → 7F2 transition of the Eu3+ ion. Both XRD and Judd-Ofelt analysis revealed two sites for the Eu3+ ions. Additionally, the optimized SNEZ-7 phosphor achieves a PL internal quantum efficiency of 96 % under UV light at 300 nm excitation. Laser properties such as stimulated emission cross-section, gain bandwidth, branching ratio of the SNEZ phosphor is comparable to those of glasses, fluorides and other oxides for red light emitting laser applications. The CIE coordinate values of the synthesized red phosphor closely match those of commercially available red light-emitting phosphors, with a purity level of about 95 %. This suggests its suitability for various device applications, particularly in high-power white LEDs and lasers, as a red emitter.

Reactive spark plasma sintering and luminescence properties of Gd2O2S:Tb nanocrystalline phosphor

Gd2O2S:Tb is promising for energy-efficient lighting and display applications. This work explores the use of reactive spark plasma sintering (SPS) to synthesis Gd2O2S:Tb nanocrystalline phosphor. It allows to significantly simplify the technological process in comparison with traditional multi-stage liquid-phase synthesis. As-sintered Gd2O2S:Tb demonstrated average crystallite size of 26 nm and secondary particle size of 26 μm. Bright green emission occurs at 545 nm under UV excitation of 245 nm. Average fluorescence lifetime was 0.656 ms. Further consolidation of the Gd2O2S:Tb prepared via reactive SPS can also be expected to yield highly dense ceramics. The innovative reactive synthesis strategies provide valuable insights into the design and development of high-performance luminescent ceramics.

Synthesis and Characterization of Color Tunable Europium(III) and Terbium(III) Co-Doped LaSrAl3O7 Nanocrystalline Phosphors: A Photoluminescent Synergy

Synthesis and Characterization of Color Tunable Europium(III) and Terbium(III) Co-Doped LaSrAl3O7 Nanocrystalline Phosphors: A Photoluminescent Synergy

Cool green-emissive Y2Si2O7:Tb3+ nanophosphor: auto-combustion synthesis and structural and photoluminescence characteristics with good thermal stability for lighting applications.

A cheap, versatile, sustainable and energy-efficient gel-combustion method was applied to develop a series of green-emitting down-converted Y2Si2O7:Tb3+ (YPS:Tb3+) nanophosphors. Employing XRD-based Rietveld refinement approach, the phase purity and crystallographic evaluation of the produced phosphor were conducted, revealing a triclinic crystal with P1̄ space group. EDX and TEM analyses were performed on the synthesized samples to determine their elemental composition and morphological properties. Diffuse reflectance spectra yielded 5.61 eV and 5.79 eV optical energy band gaps for the host and the optimized (0.04 mole of Tb3+) sample, respectively. UV light has the ability to excite the nanocrystalline phosphor in an efficient manner, leading to significant luminosity qualities attributed to the radiative relaxation of 5D4 → 7FJ (J = 6, 5, 4, 3). The bi-exponential decay function was derived by the PL decay curves. With an activation energy of 0.2206 eV, the Y1.96Si2O7:0.04Tb3+ phosphor exhibits good thermal quenching capabilities. Improved photometric attributes including CIE coordinates, CCT and color purity confirmed the green glow, indicating a strong competitor for cool-green emission in lighting applications.

Synthesis and Structural Features of Tunable Emitting Single- Phased Eu3+/ Tb3+ Co- Doped LaAlO3 Nanophosphors

In the prevailing study, single- phased color- tunable La1-x-yEuxTbyAlO3 co- doped nanocrystalline phosphors have been synthesized via the most simplistic and low cost urea- aided solution combustion synthetic route. This was done by adjusting the doping concentration of Eu3+ (x = 0.01, 0.03, 0.05, 0.07 mol) and Tb3+ (y = 0.03 mol) ions in the LaAlO3 host lattice. The X- ray powder diffraction (XRD) and Rietveld refinement analysis confirmed the formation of single- phased La0.97-xAlO3: xEu3+/ 0.03Tb3+ (x = 0.07), co- doped nanophosphor at 800°C. The synthesized nanophosphors were crystallized in cubic crystal system having Pm3̄m space group with 221 space group number. The morphological studies i.e., field emission scanning electron microscopy (FE- SEM), and transmission electron microscope (TEM) images depicted the agglomerated clusters of distinct spherical shaped particles of La0.97-xAlO3: xEu3+/ 0.03Tb3+ in nano- regime. Energy dispersive X- ray analysis (EDAX) was employed to ascertain the real elemental mapping of the fabricated phosphors. Through diffuse reflectance (DR) spectroscopy measurements, the optical band gap value for La0.92Eu0.05Tb0.03AlO3 nanocrystalline phosphor was determined to be 5.26 eV. The photoluminescent excitation (PLE) and photoluminescent emission (PL) spectra were studied in detail as a function of Eu3+ ion contents and La1-x-0.03AlO3: xEu3+/ 0.03Tb3+ (x = 0.05 mol) co- doped sample exhibits strongest emission and over the 0.05 Eu3+ ions doping concentration, the emission intensity falls as a consequence of the quenching phenomenon. The concentration quenching in directed co- doped nanophosphors was attributed to the dipole - dipole interactions. With the exploitation of photoluminescent data, Commission International de I'Eclairage 1931 (CIE) color coordinates (x, y) of co- doped samples have been calculated from the emission spectra, which revealed the color could be tuned i.e., from orange to red region in La0.97-xAlO3: xEu3+/ 0.03Tb3+ samples with divergences in the Eu3+ and other significant photometric assets viz. correlated color temperature (CCT), color purity (CP) of the synthesized La1-x-yAlO3: xEu3+, yTb3+ co- doped nanocrystalline photoluminescent materials were also determined. The studies outcomes suggested that Eu3+/ Tb3+ co- doped LaAlO3 phosphors have great potential as color- tunable luminescent material in solid- state lighting and display technologies.

Morphology and luminescent properties of nanocrystalline NaGdF4 phosphors doped with neodymium(III) ions

Nanocrystalline phosphors NaGd1- x Nd x F4 ( x = 0-1) were synthesized by hydrothermal synthesis for the first time. All the synthesized compounds have hexagonal β-NaYF4 crystalline phase. Neodymium(III) ions isomorphically replace gadolinium ions. NaGd0.96Nd0.04F4 compound has the largest photoemission intensity in NIR range upon 808 nm excitation; further doping with Nd3+ results in concentration quenching.

Structural, luminescence and thermometric properties of LaVO4:Ln3+ nanopowders (Ln = Dy and Sm)

Lanthanide-doped materials have been intensively studied for optical thermometry due to their unique luminescence properties. However, the engineering of high-resolution multimode nanopowders for high-sensitivity thermometry is still a big challenge. Here, we study the structural and luminescence properties of Dy3+- and Sm3+-doped LaVO4 concentration series to find the suitable candidates for possible application as a temperature sensor. The synthesized nanocrystalline phosphors have successfully demonstrated multimode thermal sensing in the wide temperature range based on the temperature-induced red shift of the charge transfer band. The proposed sensing strategies were compared in terms of thermal sensitivity and temperature resolution. The best thermometric performances of Sr = 2.07 % K−1 and ΔT = 0.2 K at room temperature were found for LaVO4:Sm3+ 2 at% sample. The studies testify that Ln3+-doped LaVO4 materials are promising in multimode high-sensitivity optical thermometry.

Ab-initio DFT calculations and experimental investigations into optoelectronic and structural properties of Ca9Al(PO4)7:Sm3+ orange phosphor

Nanocrystalline phosphors of composition Ca9Al(PO4)7:xSm3+ (x = 0.01–0.16) were successfully synthesized using a urea-assisted highly efficient solution combustion technique. The structural, morphological, and photoluminescence features of the series of white powdered samples were studied using powder X-ray diffraction, energy-dispersive X-ray spectroscopy, transmission electron microscopy, and photoluminescence characterization techniques. The structural framework and crystal phase purity of Ca9Al0.90Sm0.10(PO4)7 phosphor were investigated by Rietveld refinement analysis. The results showed that the replacement of Al3+ ions with Sm3+ ions in Ca9Al0.90Sm0.10(PO4)7 nanophosphor didn't alter the host lattice crystal structure and a trigonal lattice having R3c(161) space group was established. Meanwhile, the average particle size evaluated from the Scherrer equation was further confirmed by transmission electron microscopic studies revealing a size domain ranging from 35-60 nm. Structural optimization of the pure host via first-principle routing disclosed the density of states and electronic band structure having a band gap of 4.738 eV, which was found to be quite comparable to the experimentally observed value (4.37 eV) from the diffuse reflectance spectra. Many key optical properties, such as optical conductivity, extinction coefficient, loss function, and refractive index were determined by using a calculated dielectric function. Furthermore, photoluminescence studies inferred that 10 mol% of Sm3+ ion in Ca9Al(PO4)7 host matrix gave the best luminescence emission intensity. Detailed photoluminescent analysis of Ca9Al(PO4)7:xSm3+ phosphors demonstrated that on excitation at 401 nm, an intense reddish-orange emission was received at 600 nm (4G5/2 → 6H7/2 transition). The critical distance for energy migration came out to be 22 Å which strongly favors the mechanism behind luminescence quenching as dipole-quadrupole interactions resulting from the over-doping of activator ions. The chromaticity coordinates (0.5216, 0.3630) were obtained using MATLAB computations. These results favor the applicability of Sm3+ doped Ca9Al(PO4)7 phosphors as the reddish-orange emitter in near-ultraviolet excited white light-emitting diodes.

Photoluminescent Properties of Phosphor Based on Perovskite CsPbBr3 Nanocrystals Combined with Violet Leds.

The characteristics of an LED lighting system consisting of a commercial violet LED and a green phosphor based on CsPbBr3 nanocrystals are studied in the context of development of LED illumination sources with antibacterial effects but without harmful effects on human health. The internal efficiency of the nanocrystalline phosphor in a silicone compound was found to exceed 40%, dropping noticeably because of heating for an electric current of ~0.1 A (phosphor excitation intensity ~0.1 W/mm2). This undesirable feature can be diminished by using a remote phosphor design for the illuminators and by using chemical techniques to improve the thermal stability of the nanocrystals.

PHOTOLUMINESCENT PROPERTIES OF THE PEROVSKITE CsPbBr3 NANOCRYSTALS BASED PHOSPHOR COMBINED WITH VIOLET LEDS

In the context of development of LED luminaries with antibacterial effect but without harmful effects on human health, the characteristics of an LED lighting system consisting of a commercial violet LED and a green phosphor based on CsPbBr3 nanocrystals are studied. Internal efficiency of the nanocrystalline phosphor in a silicone compound was found to exceed 40% falling down noticeably because of heating for electric current of the order of 0.1 A (excitation intensity of the order of 0.1 W/mm2). This nondesirable feature can be diminished using remote phosphor design of luminaries as well as by rising thermal stability of nanocrystals with chemical techniques.

Investigation on the effects of Ce3+:Lu2SiO5 nanocrystalline phosphors in reducing environment

Lutetium oxyorthosilicate doped with cerium (Ce3+:Lu2SiO5) is a high resolution and highly responsive detector used in medical imaging frequently in the form of single crystals. Fabrication of ceramic polycrystalline lutetium oxyorthosilicate (LSO) doped with cerium is an upcoming alternative that requires high temperatures and a non-oxidising atmosphere for sintering. However, the stability of the nano phosphor itself under the sintering conditions is inconsistent and has stumped many investigators. This paper presents a systematic study of the formation of lutetium oxyorthosilicate from its respective constituents (lutetia and silica) and of the behavior of LSO under sintering conditions. The study shows a breakdown of the compound in highly reducing atmospheres to form lutetium oxide, as confirmed by x-ray diffraction studies. The decomposition of hot pressed Ce:LSO in a reducing environment studied by scanning electron micrography, Raman spectroscopy, shows the correlation of its structure and defects with its radioluminescence.

Non-cytotoxic Dy3+ activated La10W22O81 nanophosphors for UV based cool white LEDs and anticancer applications

White-light-emitting La10W22O81 (LWO): xDy3+ (0.5 ≤ x ≤ 10 mol%) nanocrystalline phosphors were developed by a facile hydrothermal assisted solid-state reaction. X-ray diffraction (XRD) pattern indicated that the prepared samples adopted orthorhombic crystal structures. The agglomeration of uniform nanorods was identified from the FE-SEM analysis of the optimized LWO: 1.5 mol% Dy3+ nanocrystalline phosphors. Additionally, transmission electron microscope, scanning transmission electron microscopy, selected area electron diffraction, and X-ray photoelectron spectroscopy were employed to explore the surface morphology, size, interplanar distance, and chemical composition with valence states of the LWO: 1.5 mol% Dy3+ phosphors, respectively. By exciting with 387 nm, the LWO: Dy3+ emission spectra showed two intense peaks at 476 nm (4F9/2→6H15/2) and 571 nm (4F9/2→6H13/2) and a shoulder peak at 659 nm (4F9/2→6H11/2). Optimum emission intensity was achieved for 1.5 mol% Dy3+ in the LWO host lattice. The luminescence quenching beyond 1.5 mol% Dy3+ is attributed to the dipole–dipole interactions when the Dy3+ (donor) and Dy3+ (acceptor) ions are at a critical distance of 58.53 Å. Photometric studies were conducted to evaluate the performance and practical applicability of the phosphors. The CIE chromaticity diagram suggests that the LWO: 1.5 mol% Dy3+ nanophosphor conspicuously exhibits cool white light. Therefore, this material could be a promising and potential white light-emitting nanocrystalline phosphor material for white light emitting diodes (LEDs) under near-UV excitation. In addition, the toxicity of the optimized nanophosphor in normal WI-38 lung fibroblast cells and MCF-7 breast cancer cells was examined. Surprisingly, LWO: 1.5 mol% Dy3+ nanophosphor was found to be non-cytotoxic to normal cells, but extremely toxic to cancer cells. Therefore, the nanophosphor materials can be considered potential candidates for biomedical applications, particularly for cancer treatment.

Crystal chemistry and photoluminescent aspects of down-converted Tb3+ activated SrGdAlO4 nanophosphors for multifunctional applications

A series of green radiating terbium (Tb3+) activated SrGdAlO4, i.e., SGAO:xTb3+ (0.01≤ x ​≥ ​0.05) nanocrystalline phosphors has been manufactured with insignificant expenses via a facile and ecological, urea-based solution combustion approach. Crystallographic analysis facilitated by diffraction data and Rietveld refinement revealed pure tetragonal phase with space group 14/mmm (139) for designated nanomaterials. Morphological attributes investigated using scanning and transmission electron micrographs reported weakly agglomerated particles with sizes in the range of 40–60 ​nm. HRTEM micrograph revealed separation between fringes as 0.27 ​nm for miller plane (013), while EDS (energy dispersive X-ray spectrometer) indicated requisite elements of synthesized materials. The lifetime of Tb3+ characterized greenish emission is found in order of 1.39 ​ms. Photoluminescent emission spectra displayed vivid green emission for prepared nanophosphors attributed to 5D4 → 7F5 transition of Tb3+ ions, centered at 549 ​nm. Band-gap studies postulated a wide band-gap value (5.01 ​eV) for optimum SrGd0.97Tb0.03AlO4 nanocrystalline phosphor. Maximum luminescence efficiency was attained at 3 ​mol % doping of Tb3+ ions i.e., for SGAO:0.03 ​Tb3+ nanophosphor with CIE chromaticity coordinates (0.339, 0.579), correlated color temperature (5389 ​K) and color purity (76.4%). The present findings envisaged the utility of designated nanomaterials as promising green emanating specialists for down-conversion white light-emitting diodes.

Structural and luminescence properties of SrGd2O4 nanocrystalline phosphor doped with Dy3+ and Sm3+

In this manuscript, down-conversion nanopowders of SrGd2O4 doped with different concentrations of either Dy3+ or Sm3+ ions were examined in detail. All samples were prepared via glycine-assisted combustion method, primarily burned at 500?C for 1.5 h and additionally calcined at 1000?C for 2 h, at ambient room temperature. The XRD analysis showed that all samples crystallize as single phase and the orthorhombic lattice SrGd2O4. TEM analysis determined high degree of crystallinity of samples with grain size of approximately 200 nm for Dy3+ doped and 150 nm for Sm3+ doped SrGd2O4. For both samples SAED confirmed that diffraction rings correspond to the hkl plane indices of SrGd2O4, while EDS confirmed presence of Dy in crystal structure. Results of luminescent characterization demonstrated all appropriate emission peaks related to either Dy3+ or Sm3+ dopant ions. Investigation of dopant concentration revealed that the lowest values of both dopants have the most prominent emission peaks, while coordinates obtained from the CIE diagram showed emission shifting with the change of concentration.

Luminescence and Vacuum Ultraviolet Excitation Spectroscopy of Nanophosphors under Synchrotron Irradiation

Vacuum ultraviolet (VUV) excitation spectroscopy under synchrotron irradiation is a powerful tool for the investigation of luminescence properties of wide bandgap nanocrystalline phosphor materials. The advantages of selective excitation in a wide spectral range present the possibility to explore the different aspects of luminescence processes in nanophosphors separately. It is shown that direct excitations of emission centers in wide bandgap materials need excitations in VUV spectral range and such excitations provide valuable information about f–f, f–d transitions, defects, and excitonic transitions in wide bandgap nanophosphors. It is also demonstrated that size‐dependent luminescence properties of nanophosphors are significant if the electron thermalization length becomes larger than the size of the nanoparticles. In this case, multiplication of electronic excitations processes well‐known in bulk materials are suppressed strongly in nanophosphors.

Finite-Size Effects on Energy Transfer between Dopants in Nanocrystals.

Many phosphor materials rely on energy transfer (ET) between optically active dopant ions. Typically, a donor species absorbs light of one color and transfers the energy to an acceptor species that emits light of a different color. For many applications, it is beneficial, or even crucial, that the phosphor is of nanocrystalline nature. Much unlike the widely recognized finite-size effects on the optical properties of quantum dots, the behavior of optically active ions is generally assumed to be independent of the size or shape of the optically inactive host material. Here, we demonstrate that ET between optically active dopants is also impacted by finite-size effects: Donor ions close to the surface of a nanocrystal (NC) are likely to have fewer acceptors in proximity compared to donors in a bulk-like coordination. As such, the rate and efficiency of ET in nanocrystalline phosphors are low in comparison to that of their bulk counterparts. Surprisingly, these undesired finite-size effects should be considered already for NCs with diameters as large as 12 nm. If we suppress radiative decay of the donor by embedding the NCs in media with low refractive indices, we can compensate for finite-size effects on the ET rate. Experimentally, we demonstrate these finite-size effects and how to compensate for them in YPO4 NCs co-doped with Tb3+ and Yb3+.

Down-conversion and structural characterizations of trivalent terbium-doped garnet nanocrystalline phosphors for lighting applications

Down-conversion and structural characterizations of trivalent terbium-doped garnet nanocrystalline phosphors for lighting applications

Augmenting the photoluminescence efficiency via enhanced energy-relocation of new white-emanating BaYAlZn3O7:Dy3+ nano-crystalline phosphors for WLEDs

Ongoing progress of solid-state illumination technology necessitates the compelling need for energy-efficient nanophosphors with superfine luminance. The present paper reports the synthesis and characterization of nano-crystalline phosphors by incursion of Dy3+ ions into BaYAlZn3O7 matrix. Rietveld-refinement of XRPD profiles revealed the hexagonal structure of as synthesized nano-crystalline phosphors. Non-uniform agglomerated particles with size ranging between 44 and 65 nm have been observed from morphological investigation. The observed white light in the studied nanophosphors is due to emissions lying in blue and yellow domains radiated from 4F9/2 to 6H15/2, 13/2 states of Dy3+ respectively. Inokuti-Hirayama (I-H) and Dexter’s models have been employed to understand the phenomenon of Photoluminescence. It has been observed that d-d (dipole-dipole) inter-linkages chiefly command the luminance-quenching for nanophosphor with Dy3+ content (x) equal to 0.05. Various radiative-possessions reflecting better luminance-potentiality of presently studied nanophosphor like decay-time, intrinsic life-time, quantum-efficiency and relaxation-rate have also been evaluated. White light parameters viz. CP and CCT values of BaY0.95Dy0.05AlZn3O7phosphors are 19.84 × 10−2 and 8088.31 K, respectively along with CIE-1931 coordinates (x = 0.2588, y = 0.3306), imply the studied nanophosphor to be a new superfine cool-white-emanating material for nUV-activated WLEDs (white-light-emanating diodes), portable-electronics, signage, aircraft-cabins, digital communication, sensors, horticulture, solar-cells and advanced lasers. The reported outcomes will certainly open an avenue for researchers to design more BaYAlZn3O7-like materials.

Photoluminescence, Synthesis,Characterization of MgO Nanophosphors Influenced by Dy3+ Ions Concentrations

The present paper reports the synthesis, characterization and photoluminescence (PL) studies of MgO:Dy3+ nanoparticles. In this work, MgO:Dy3+ nanophosphors were prepared through solution combustion synthesis method using magnesium nitrate as oxidizer and urea as a fuel. The as-obtained MgO:Dy3+ nanomaterials were characterized by powder X-ray diffraction (XRD), energy-dispersive X-ray (EDX) analysis, Fourier transformation infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), high resolution transmission electron microscope (HRTEM), photoluminescence (PL) spectra and afterglow curve analysis. The cubic structure of the MgO phosphors is confrmed by XRD analysis and crystalline size calculated by Scherer’s formula using XRD data shows the nanocrystalline nature of the phosphor. No phase change is observed with increasing concentrations of Dy3+ ions. The surface morphology of the prepared phosphors is determined by SEM, which shows a sphere-like structure and good connectivity of the grains. The confrmation of the nanocrystalline phosphors is examined by HRTEM analysis.The photoluminescence studies revealed that the emission spectra of the prepared phosphors shows the broad emission centered at 435 nm and 480 nm due to the transition arises from the 4f→5d defect band transition of Dy3+ ions. The afterglow decay characteristics of different as synthesized MgO:Dy3+ nanophosphors are conceptually described. This is the first reported that on the synthesis of nanocrystalline MgO:Dy3+ materials by combustion method using urea as a fuel.

Photoluminescence and Thermoluminescence Properties of Nanophosphors, YVO4:Eu3+ and YVO4:Eu3+:Dy3+

The as-synthesized, europium-doped, yttrium orthovanadate nanostructures exhibited photoluminescence properties that can vary based on the preparation conditions. All the samples exhibit red emissions, and the strongest emission band was observed at 620 nm and assigned to the 5D0 → 7F2 transition of Eu3+. The high intensity of the band is a consequence of the lack of inversion symmetry at the Eu3+ site (D2d symmetry) in the host lattice. The optimal europium doping concentration was 6 mol% for both preparation methods. These samples were annealed to obtain micro and nanoscale crystallite sizes in a range of 7.56 nm to 132.65 nm, and the emission spectra were obtained. The results revealed that the photoluminescence (PL) properties were dependent on crystallite size, the PL quantum yield measurements increased with increasing crystallite size. The introduction of the dopant ions induced changes in the TL glow curve structure and the kinetic properties, modifying the radiative recombination efficiency. The TL results suggest that both europium and europium-dysprosium doped YVO4 nanocrystalline phosphor present good potential for β-irradiation dosimeter applications.