Estimation of spectroscopic parameters and TL glow curve analysis of Eu3+-activated CaY2O4 phosphor.

The solid-state reaction method was utilised to create a down-conversion phosphor in an air environment in CaY2O4:Eu3+ nanocrystalline material. The calcination temperature was set at 1000 °C, and the sintering temperature was set at 1300 °C. Following annealing, confirmation of the crystallinity quality of the phosphor was accomplished by the use of X-ray diffraction analysis. The particle size was predicted to be 43.113 nm using Scherrer's formula. To produce down-conversion luminescence spectra, an excitation wavelength of 247 nm was applied with a fluorescence spectrophotometer. The PL got increasingly intense as the concentration of the dopant increased. The maximum intensity was measured at 2.0 mol% of Eu3+ ion, which gradually decreased as the concentration increased because of concentration quenching. To analyse spectrophotometric peak determinations, the approach developed by the Commission Internationale de l'Éclairage (CIE) was used. Thermoluminescence (TL) glow curve analysis of the CaY2O4:Eu3+-doped phosphor manufactured here revealed a wide TL centred at 225 °C, which comprised of so many peaks that may be extracted by the computerised glow curve deconvolution (CGCD) approach using glow-fit software. The associated kinetic parameters were then determined. The prepared phosphor may be useful for application in various display devices upon excitation by 247 nm; the prominent 613 nm peak of the Eu3+ ion (5D0 → 7F2) electric dipole transition features a red component. CaY2O4:Eu3+ phosphors show promise as materials for potential use in phosphor-converted white LEDs in the field of solid-state lighting technology. The linear connection that the TL glow curve has with UV dose provides evidence for its possible use in dosimetry.

Effect of Cr3+ doping on structural and optical properties of Eu3+ doped LaVO4 phosphor.

In this work, the Eu3+, Cr3+ doped and co-doped LaVO4 phosphors have been prepared through a high temperature solid-state reaction method. The powder XRD patterns of phosphors are very sharp and intense, which reflects a highly crystalline nature of phosphors. The XRD data were also refined by a Rietveld refinement method. The particle size of the phosphor samples lies in the sub-micron to micron range. The existence of La, Eu, Cr, V and O elements was verified by EDS spectra. The FTIR spectra show various absorption bands due to different vibrating groups. The optical band gap of the phosphor decreases on increasing concentration of Cr3+ ion. The photoluminescence excitation spectra of Eu3+, Cr3+ co-doped LaVO4 phosphor exhibit bands due to Eu3+ and Cr3+ ions. The Eu3+ doped LaVO4 phosphor exciting at 393 and 316 nm wavelengths gives intense red color at 614 nm due to the 5D0 → 7F2 transition of the Eu3+ ion. When the Cr3+ ion is co-doped in the Eu3+ doped LaVO4 phosphor the emission spectra contain emission bands due to Eu3+ and Cr3+ ions. The emission intensity of Eu3+ doped phosphor reduces due to energy transfer from Eu3+ to Cr3+ ions in presence of Cr3+ ions upon 393 and 386 nm excitations. The lifetime of the 5D0 level of Eu3+ ions decreases in the Eu3+, Cr3+ co-doped LaVO4 phosphor, which also reflects the energy transfer. The Eu3+, Cr3+ co-doped LaVO4 phosphor also produces a large amount of heat upon 980 nm excitation. Thus, the Eu3+, Cr3+ co-doped LaVO4 phosphors may be used for LEDs, solid state lighting and heat generating devices.

NIR light guided enhanced photoluminescence and temperature sensing in Ho3+/Yb3+/Bi3+ co-doped ZnGa2O4 phosphor.

The conversion of NIR light into visible light has been studied in Ho3+/Yb3+/Bi3+ co-doped ZnGa2O4 phosphor for the first time. The crystallinity and particles size of the phosphor increase through Bi3+ doping. The absorption characteristics of Ho3+, Yb3+ and Bi3+ ions are identified by the UV-vis-NIR measurements. The Ho3+ doped phosphor produces intense green upconversion (UC) emission under 980 nm excitations. The emission intensity ~ excitation power density plots show contribution of two photons for the UC emissions. The UC intensity of green emission is weak in the Ho3+ doped phosphor, which enhances upto 128 and 228 times through co-doping of Yb3+ and Yb3+/Bi3+ ions, respectively. The relative and absolute temperature sensing sensitivities of Ho3+/Yb3+/5Bi3+ co-doped ZnGa2O4 phosphor are calculated to be 13.6 × 10-4 and 14.3 × 10-4 K-1, respectively. The variation in concentration of Bi3+ ion and power density produces excellent color tunability from green to red via yellow regions. The CCT also varies with concentration of Bi3+ ion and power density from cool to warm light. The color purity of phosphor is achieved to 98.6% through Bi3+ doping. Therefore, the Ho3+/Yb3+/Bi3+:ZnGa2O4 phosphors can be suitable for UC-based color tunable devices, green light emitting diodes and temperature sensing.

Retraction of "Fabrication of Graphene Nanoplatelet-Incorporated Porous Hydroxyapatite Composites: Improved Mechanical and in Vivo Imaging Performances for Emerging Biomedical Applications".

[This retracts the article DOI: 10.1021/acsomega.8b03473.].

Influence of Bi3+ ion on structural, optical, dielectric and magnetic properties of Eu3+ doped LaVO4 phosphor.

In this paper, we have studied the structural, optical, dielectric and magnetic properties of Eu3+, Bi3+ co-doped LaVO4 phosphors prepared by solid state reaction method. Rietveld structural analysis of the samples confirms the monoclinic crystal structure with P21/n space group. The particles size of Eu3+ doped LaVO4 phosphor increased in presence of Bi3+ ion. The excitation spectrum of Eu3+, Bi3+ co-doped LaVO4 phosphor reveals bands due to charge transfer state (CTS) and electronic transitions of Eu3+ and Bi3+ ions. The Eu3+ doped LaVO4 phosphor gives intense red emission centred at 613 nm due to 5D0 â†’ 7F2 transition of Eu3+ ion excited at 266, 355 and 394 nm wavelengths. When Bi3+ and Eu3+ ions are co-doped in the LaVO4 phosphor the photoluminescence intensity is enhanced upto two times. The photoluminescence intensity is largest for the 266 nm excitation. This is due to energy transfer from CTS and (1P1, 3P1) levels of the Bi3+ ion to 5D4 level of the Eu3+ ion and increase in the particles size of phosphor. The Eu3+, Bi3+ co-doped LaVO4 phosphors also show excellent dielectric and magnetic properties with a variation in frequency and magnetic field, respectively. Thus, the Eu3+, Bi3+ co-doped LaVO4 phosphor may be useful in fabricating displays devices, red emitting phosphors, dielectric capacitors and magnetic devices.

Fabrication of Graphene Nanoplatelet-Incorporated Porous Hydroxyapatite Composites: Improved Mechanical and in Vivo Imaging Performances for Emerging Biomedical Applications.

Three-dimensional nanocomposites exhibit unexpected mechanical and biological properties that are produced from two-dimensional graphene nanoplatelets and oxide materials. In the present study, various composites of microwave-synthesized nanohydroxyapatite (nHAp) and graphene nanoparticles (GNPs), (100 - x)HAp-xGNPs (x = 0, 0.1, 0.2, 0.3, and 0.5 wt %), were successfully synthesized using a scalable bottom-up approach, that is, a solid-state reaction method. The structural, morphological and mechanical properties were studied using various characterization techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and universal testing machine (UTM). XRD studies revealed that the prepared composites have high-order crystallinity. Addition of GNPs into nHAp significantly improved the mechanical properties. Three-dimensional nanocomposite 99.5HAp-0.5GNPs exhibited exceptionally high mechanical properties, for example, a fracture toughness of ∼116 MJ/m3, Young's modulus of ∼98 GPa, and compressive strength of 96.04 MPa, which were noticed to be much greater than in the pure nHAp. The MTT assay and cell imaging behaviors were carried out on the gut tissues of Drosophila third instars larvae and on primary rat osteoblast cells for the sample 99.5HAp-0.5GNPs that have achieved the highest mechanical properties. The treatment with lower concentrations of 10 µg/mL on the gut tissues of Drosophila and 1 and 5 µg/mL of this composite sample showed favorable cell viability. Therefore, owing to the excellent porous nature, interconnected surface morphology, and mechanical and biological properties, the prepared composite sample 99.5HAp-0.5GNPs stood as a promising biomaterial for bone implant applications.

Concentration and pump power-mediated color tunability, optical heating and temperature sensing via TCLs of red emission in an Er3+/Yb3+/Li+ co-doped ZnGa2O4 phosphor.

Intense red upconversion luminescence was observed in the Er3+/Yb3+/Li+ co-doped ZnGa2O4 phosphor synthesized through the solid state reaction method for the first time. The structural characterization showed a large crystalline nature and an increase in the particle size via Li+ doping. The absorption spectra showed a large number of peaks in the UV-vis-NIR regions due to the Er3+ and Yb3+ ions. The Er3+/Yb3+ co-doped ZnGa2O4 phosphor exhibited green, red and NIR upconversion emissions on excitation with 980 nm radiation. The intensity of the red emission was relatively larger than that of the other emissions. The luminescence intensity versus pump power measurements revealed the number of required photons for these emissions. The phosphor showed very interesting color tunability as a function of Er3+ ion concentration and incident pump power. The luminescence intensity of the Er3+/Yb3+ co-doped phosphor was enhanced more than two times via Li+ doping. The enhancement in the luminescence intensity was proposed to be due to the increase in the crystallinity and particle size of the phosphor. The lifetimes of the 4S3/2 and 4F9/2 levels also increased in the presence of Li+ ions. The variation in the fluorescence intensity ratio (FIR) of the thermally coupled levels (TCLs) of the red emission with incident pump power offered effective optical heating in the phosphor. The temperature-induced FIR using TCLs of red emission exhibited a larger value of temperature sensing sensitivity in the presence of Li+ ions, which was up to 14 × 10-4 K-1. Thus, the Er3+/Yb3+/Li+ co-doped ZnGa2O4 phosphor may be used in photonic, optical heating, and temperature sensing devices.

Enhanced Quantum Cutting via Li+ Doping from a Bi3+/Yb3+-Codoped Gadolinium Tungstate Phosphor.

The Bi3+/Yb3+-codoped gadolinium tungstate phosphor has been synthesized through a solid-state reaction method. The structural characterization reveals the crystalline nature of the phosphor. The Bi3+-doped phosphor emits visible radiation from the blue to red regions upon excitation with 330 and 355 nm. The addition of Yb3+ to the Bi3+-doped phosphor reduces the emission intensity in the visible region and emits an intense near-infrared (NIR) photon centered at 976 nm through a quantum-cutting (QC) phenomenon. This is due to cooperative energy transfer (CET) from the 3P1 level of Bi3+ to the 2F5/2 level of Yb3+. The presence of Li+ ions in the Bi3+/Yb3+-codoped phosphor enhances the emission intensity in the NIR region up to by 3 times, whereas the emission intensity in the visible region is significantly reduced. The energy transfer (ET) from the Bi3+ ions to the Yb3+ ions is confirmed by lifetime measurements, and the lifetime for the 3P1 level of Bi3+ decreases continuously with increasing Yb3+ concentration. The ET efficiency (ηETE) and corresponding QC efficiency (ηQE) are calculated and found to be 29% and 129%, respectively. The presence of Li+ enhances the QC efficiency of the phosphor up to 43%. Thus, the Bi3+/Yb3+/Li+-codoped phosphor is a promising candidate to enhance the efficiency of a crystalline-silicon-based solar cell through spectral conversion.