In the present study, structural and photo-luminescence studies of Eu3+ and Tb3+ co-doped ZnMoO4 host matrix has been investigated in detail. ZnMoO4:Eu3+/Tb3+ have been synthesized via a simple and ...cost effective co-precipitation method. XRD, Raman and FTIR studies confirmed its triclinic structure of Eu3+/Tb3+ co-doped ZnMoO4 host. Emission spectra of the measured samples corroborate the dominant electric dipole transition emission (5D0-7F2) intensity over magnetic dipole transition emission (5D0-7F1) intensity. Moreover, the improvement in red emission (5D0-7F2) for Eu3+(3at%) and Tb3+(2at%) and high asymmetric ratio ∼10.4 is observed which dictates it as a highly red emitter. Additionally, commission international de-I′ Eclairage (CIE) values approaches to NSTC. Color purity of red emission improves after Tb3+ co-doping. Photoluminescence studies reveals that Tb3+ acts as a sensitizer for the Eu3+ activated ZnMoO4 host matrix. Study reveals that Eu3+/Tb3+ co-doped ZnMoO4 can be excited by near UV device, which is bottleneck in the advancement of LEDs technology.
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Schematic representation of enhancement in red emission intensity via cross relaxation process. Energy transfer mechanism from Tb3+ions to Eu3+ ion by cross relaxation.
Iron oxide nanoparticles such as magnetite (Fe3O4) and maghemite (γ-Fe2O3) have been used in biological applications due to their high biocompatibility, i.e., as a contrast agent in magnetic ...resonance imaging, a hyperthermia agent in cancer treatment, a drug carrier, etc. There are debates on the formation of Fe3O4 or γ-Fe2O3 from the different synthesis routes including the co-precipitation method as the bulk size of the particle decreases to nanometers. This study reports on the preparation of pure 10 nm sized Fe3O4 nanoparticles at room temperature so that this can be kept for a long time (a few years) in an inert environment; otherwise, the surface of the Fe3O4 particles gets oxidized and, partly, gets converted into undesirable compounds of iron oxides such as α-Fe2O3 and Fe(OH)3. The formation of Fe3O4 has been ascertained by thermogravimetric analysis, the color of the compound, x-ray photoelectron spectroscopy, and magnetic measurement. It shows the contribution of hysteresis loss, eddy current, and Néel’s and Brownian relaxations in heat-generation by applying different alternating current magnetic fields. Power loss follows H2 dependence. Heat generation of Fe3O4 magnetic nanoparticles in phosphate buffer saline will be the potential candidate of the therapy of cancer.
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•Confirmation of electric and magnetic dipole transitions of Eu3+in YPO4 host.•Observation of Stark splitting by decrease of excitation and emission slit widths.•Association of ...unwanted light (stray) with increase in slit width.•Requirement of proper slit widths to get reasonable signal to noise ratio.•Explanation of low value in asymmetric value of Eu3+ using polarizability factor.
An effect of variation of slit widths of excitation and emission monochromators on emission intensity, peak position and asymmetric ratio of Eu3+ has been observed in YPO4:Eu3+. Stark splitting is observed. Eu3+ ion occupies D2d site symmetry in crystal lattice. However, asymmetric ratio is observed to be lesser in value ∼≤1.5. The possible explanation for low value of asymmetric ratio is explained.
In this work, we report a polyol route for easy synthesis of upconversion (UC) phosphor nanoparticles, YVO4:Ho3+-Yb3+-K+, which enables large-scale production and enhancement of luminescence. Upon ...980 nm laser excitation, the UC emission spectrum shows a sharp bright peak at ∼650 nm of Ho3+ ion; and the luminescence intensity increases twofold upon K+ codoping. Upon 300 nm excitation, the downconversion emission spectrum shows a broad peak in the 400–500 nm range (related to the charge transfer band of V–O) along with Ho3+ peaks. In addition, the polyethylene glycol-coated UC nanoparticles are highly water-dispersible and their hybrid with Fe3O4 nanoparticles shows magnetic-luminescence properties. A hyperthermia temperature is achieved from this hybrid. Both UC and hybrid nanoparticles show interesting security ink properties upon excitation by a 980 nm laser. The particles are invisible in normal light but visible upon 980 nm excitation and are useful in display devices, advanced anticounterfeiting purposes, and therapy of cancer via hyperthermia and bioimaging (since it shows red emission at ∼650 nm). Using UC nanoparticles, detection of uranyl down to 20 ppm has been achieved.
In the present work, we describe the synthesis of (Ca0.99–x Ho0.01Yb x )TiO3 (x = 0.05, 0.10, and 0.15) perovskite nanoparticles with a cubic structure by using a sol–gel method. As-synthesized ...particles have been found to be spherical in shape, as analyzed by transmission electron microscopy and scanning electron microscopy. Fourier transform infrared spectra of the product perovskite consist of distinct featured vibrational modes of Ti–O. Upconversion as well as power-dependent (500–4000 mW) spectra have been investigated at 980 nm excitation. It exhibits emission peaks at 547, 655, and 759 nm owing to 5F4/5S2 → 5I8, 5F5 → 5I8, and 5F4/5S2 → 5I7 transitions of Ho3+ ions, respectively. Optical thermometry behavior has been evaluated using fluorescent intensity ratio (FIR) of thermally and electronically coupled levels of Ho3+ ions. It reports a good sensitivity with 0.0229 and 3 × 10–3 K–1 as estimated through thermally and electronically coupled FIR, respectively, at room temperature (303 K). Upconversion nanoparticles of (Ca0.89Ho0.01Yb0.1)TiO3 have further been coupled with Fe3O4 as hybrid magnetic nanoparticles for hyperthermia study. It attains hyperthermia temperature (42 °C) in 3 min under ac magnetic field, with a specific absorption rate of 35 W/g. Therefore, it could be interpreted that the present hybrid upconversion nanoparticles may be very useful and paves the path for cancer therapy (hyperthermia) and in likewise biomedical applications.
YVO4:Ho3+/Yb3+ nanophosphors prepared by an effective polyol-mediated route show dual-mode behavior in photoluminescence. Upon 980 nm excitation, the upconversion red emission spectrum exhibits a ...bright red peak at ∼650 nm, characteristic of the electronic transition of the Ho3+ ion via involvement of two-photon absorption, which has been confirmed by the power-dependent luminescence study. Moreover, at 300 nm excitation, downconversion emission peaks are observed at 550, 650, and ∼755 nm. The nonradiative resonant energy transfer occurs from the V–O charge transfer band to Ho3+ ions, resulting in an improved emission of Ho3+ ions. Moreover, polyethylene glycol-coated nanoparticles make it suitable for water dispersibility; and these particles are conjugated with Fe3O4 nanoparticles to form magnetic–luminescent hybrid nanoparticles. Highly water-dispersible magnetic–luminescent hybrid material attained the hyperthermia temperature (∼42 °C) under an applied AC magnetic field. The specific absorption rate value is found to be high (138 W/g), which is more than that of pure superparamagnetic Fe3O4 nanoparticles. At 300 nm excitation, the high quantum yield value of ∼27% is obtained from YVO4:Ho3+/Yb3+, which suggests that it is a good phosphor material. By employing the neutron activation analysis technique, it is shown that nanophosphor particles can absorb Au3+ up to the ppm level. Interestingly, such nanophosphor also shows the potentiality for anticounterfeiting applications.
Monodispersed polyvinylpyrrolidone (PVP) arrested ZnS quantum dots (QDs) having diameter in range ~2-5 nm are synthesized by a colloidal precipitation method using PVP as the stabilizing agent. X-ray ...diffraction (XRD), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), selective area electron diffraction (SAED) and Fourier transform infrared (FT-IR) spectroscopy are probed to investigate the structural information. The optical properties are studied using diffuse UV-visible reflectance and photoluminescence (PL) spectroscopy techniques. TEM images as well as XRD reflection peak broadening indicate the nanometer size particles formation with cubic (sphalerite) phase within the polymer matrix. Optical absorbance studies reveal an excitonic peak at around ~310 nm dictates the effect of quantum confinement effect in the ZnS QDs. PL emission spectra for ZnS QDs in PVP exhibit four emission peaks at ~382 nm, ~414 nm, ~480 nm and ~527 nm are observed. These excitonic emissions from ZnS QDs are caused by the interstitial sulfur/Zn vacancies and surface states.
Nanocrystals having single-band red emission under near-infrared (NIR) excitation through the upconversion process offer great advantages in terms of enhanced cellular imaging in in vitro and in vivo ...experiments in the biological window (600–900 nm), as a security ink, in photothermal therapy (PTT), in photodynamic therapy (PDT), and so forth but are challenging for materials scientists. In this work, we report for the first time the preparation of a super bright red emitter at 655 nm from monodispersed NaErF4:0.5%Tm@NaYF4:20%Yb nanocrystals (core@active shell). This phosphor exhibits 35 times stronger photoluminescence as compared to NaErF4:0.5%Tm@NaYF4 (core@inactive shell). Here, an Er3+-enriched host matrix works simultaneously as an activator and a sensitizer under NIR excitation. Upconversion red emission at 655 nm arises due to the electronic transition of Er3+ via the involvement of a three-photon absorption (expected to be a two-photon absorption), which has been confirmed via a power-dependent luminescence study. Tm3+ ions incorporated into the core with the active shell act as trapping centers, which promote the red band emission via the back-energy transfer process. Moreover, the active shell containing Yb3+ ions efficiently transfers the energy to the Er3+-enriched core, which suppresses the nonradiative channel rate, and Tm3+ ions act as trapping centers, which reduce the luminescence quenching via reduction of energy migration to the surface of the host lattice. Also, we have shown the potential applications of these nanocrystals: cellular imaging through downconversion and upconversion processes and security ink.
All‐inorganic CsPbX3 (X=I, Br, Cl) perovskite quantum dots (PQDs) have been investigated because of their optical properties, such as tunable wavelength, narrow band, and high quantum efficiency. ...These features have been used in light emitting diode (LED) devices. LED on‐chip fabrication uses mixed green and red quantum dots with silicone gel. However, the ion‐exchange effect widens the narrow emission spectrum. Quantum dots cannot be mixed because of anion exchange. We address this issue with a mesoporous PQD nanocomposite that can prevent ion exchange and increase stability. We mixed green quantum‐dot‐containing mesoporous silica nanocomposites with red PQDs, which can prevent the anion‐exchange effect and increase thermal and photo stability. We applied the new PQD‐based LEDs for backlight displays. We also used PQDs in an on‐chip LED device. Our white LED device for backlight display passed through a color filter with an NTSC value of 113 % and Rec. 2020 of 85 %.
Points of light: Green CsPbBr3 perovskite quantum dots (PQDs), embedded in mesoporous silica (MP), were mixed with red CsPb(Br0.4I0.6)3 quantum dots in a silicone resin and placed on an InGaN blue chip. The green and red QDs were excited by blue light with λ=450 nm. The resulting PQD white light emitting diode (LED) exhibits a wide color gamut because of its narrow emission wavelength.
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