Weak Red Emission Research Articles

Effect of Synthesis Techniques on the Optical Properties of Ho3+/Yb3+ Co-doped YVO4 Phosphor: A Comparative Study.

The Ho3+/Yb3+-codoped YVO4 phosphors have been synthesized by three different techniques (viz., solution combustion, sol–gel, and solid-state reaction techniques). X-ray diffraction patterns confirm the formation of a pure phase in the samples synthesized by all of the three methods; however, the average crystallite sizes in the three cases are different. The crystallite size increases if they are heated to higher temperature. The particle sizes are measured by scanning electron microscopy, which shows an increase in particle size with increasing the calcination temperature. The vibrational behavior of all of the three synthesized phosphor samples is studied by the Fourier transform infrared (FTIR) technique. The UV–vis absorption measurements give a large number of bands in all of the three samples prepared by three different methods. The upconversion (UC) emissions in all three samples have been monitored using a 980 nm diode laser. It gives an intense red emission in all of the three samples. Upconversion emission intensity is more prominent in the phosphor sample synthesized by the sol–gel technique and heated at 1473 K. The enhancement in UC emission intensity is well understood by the shape and size of the particles and also confirmed by the FTIR and UV–vis measurements. It is interesting to note that whereas UC measurements give red and weak green emissions, downshifting (DS) measurements show intense green, weak red, and broad blue emissions on UV excitation (323 nm). The DS behavior shows the same characteristics of the enhancement in overall emission. Overall, the phosphor sample synthesized by the sol–gel method gives better results in upconversion and downshifting behaviors when heated at 1473 K.

Spectral behaviour of dysprosium doped zinc oxide nano particles

Nano structured, Dysprosium doped Zinc oxide were synthesized by coprecipitation method. X-ray diffraction (XRD), scanning electron microscopy (SEM) and photoluminescence (PL) were performed to characterize the morphology, growth and optical nature of the samples. Some rod and particle like morphology of zinc oxide has been observed by scanning electron microscopy. The particle size was found to vary from 8–25 nm. The room temperature PL spectra exhibits emission peak at 481 nm, 525 nm and weak red emission band around 622 nm.

Concentration effect on up-conversion luminescence and excitation path-dependent luminescence temperature quenching in YNbO4:Ho3+/Yb3+ phosphors.

Usually, the luminescence intensity and mechanism of rare-earth ions doped materials are dependent on both doping concentration and sample temperature. In this study, we attempt to explore the concentration effect on up-conversion (UC) luminescence and the dependence of luminescence temperature quenching on excitation wavelength in YNbO4: Ho3+/Yb3+ phosphors. The YNbO4: Ho3+/Yb3+ phosphors with various Ho3+ and Yb3+ concentrations were synthesized via a high-temperature solid-state reaction technique. Intense green UC emission peaked at 543 nm was observed, accompanying with weak red and near infrared (NIR) UC emissions centered at 659 and 745 nm. Based on the laser working current dependence of UC luminescence, two-photon processes were responsible for both the green and the red UC emissions under 980 nm excitation, which have no apparent dependence on both Ho3+ and Yb3+ concentrations. According to the Arrhenius model, crossover process was responsible for the temperature-dependent down-conversion (DC) luminescence quenching of Ho3+ under 452 nm excitation. However, the temperature quenching processes of the green and the red UC luminescence cannot be well explained by Arrhenius model. It was found that the UC luminescence intensity decayed with increasing sample temperature, which was caused by both the crossover and temperature-dependent energy transfer processes.

Quantitative Solvent-Free Thermal Synthesis of Luminescent Cu(I) Coordination Polymers.

The luminescent Cu(I) coordination polymers [Cu2I2( m, m'-bpy)] n (CuI- m; m, m'-bpy = m, m'-bipyridine; m = 3, 4) were successfully synthesized by the solvent-free thermal reaction of the metal salt CuI with the organic linkers m, m'-bpy. Powder X-ray diffraction analysis revealed that CuI-3 was immediately formed when a mixture of CuI and 3,3'-bpy was ground in a mortar at room temperature (20 °C). In contrast, a temperature >120 °C was required to synthesize the CuI-4 isomer, probably because of the higher melting point of the 4,4'-bpy linker. Although excess bpy linker was necessary to afford the CuI- m in high yield, the quantitative synthesis, without any purification processes, was successfully achieved by simple heating at 140 °C, whereby the excess bpy linker was thermally removed by evaporation. Single crystal X-ray structural analysis indicated that in CuI-3 the dinuclear {Cu2I2} rhombic cores were bridged by 3,3'-bpy linkers. A similar structure was observed for CuI-4; however, the intermolecular π-π stacking that was effective in CuI-4 was suppressed in CuI-3 because of the twisted configuration of the two pyridyl rings of the 3,3'-bpy linker. CuI-3 exhibited bright green emission with the maximum (λem) at 519 nm and a high emission quantum yield (Φ = 0.58) in the solid state at room temperature, in contrast to the weak red emission of CuI-4 (λem = 653 nm, Φ < 0.01). Emission decay analysis and density functional theory calculations suggested that the CuI- m emissions could be attributed to the delayed fluorescence from the metal-to-ligand charge-transfer excited state effectively mixed with the halide-to-ligand charge-transfer excited state.

Enhanced upconversion from Er3+/Yb3+ co-doped alkaline earth aluminates phosphor in presence Zn2+: A comparative study

Abstract In the present work, the upconversion emission spectra of Er3+/Yb3+co-doped CaAl2O4 (CAO), SrAl2O4 (SAO) and BaAl2O4 (BAO) phosphor samples have been studied in absence and presence of Zn2+. The samples were synthesized using high temperature solid state reaction technique at 1623 K. The X-ray diffraction (XRD) measurements have been carried out to verify the pure phase formation in all the three cases. Whereas the CAO and SAO samples show the monoclinic phase, the BAO sample shows hexagonal phase. The surface morphology of the three phosphor samples has been studied by scanning electron microscopy (SEM) technique. The Fourier-transform infrared (FTIR) and Raman measurements show the vibrational bands due to different groups present in the samples. The upconversion emission spectra of all the three samples show green and red emissions bands due to Er3+ ion on excitation with 980 nm laser. However, it is interesting to note that CAO phosphor emits very intense green and weak red emissions, the SAO and BAO phosphors give intense red and weak green emissions. However, the upconversion emission intensity (green as well as red both) in all the three samples is enhanced several times in presence of Zn2+ ions. The mechanism involved in UC emissions has been explained by partial energy level diagram.

Dependence of upconversion emission and optical temperature sensing behavior on excitation power in Er3+/Yb3+ co-doped BaMoO4 phosphors

BaMoO4: Er3+/Yb3+ phosphors with different concentrations have been fabricated by a facile hydrothermal method. The morphology observation shows that the shape and size of BaMoO4 powders change after Er3+/Yb3+ doping. The upconversion luminescence spectra consist of intense green bands centered at 536 and 558 nm and a weak red emission band peaked at 668 nm upon 980 nm excitation. The excitation power and doping concentration have little impacts on the color emitted from the samples. Applying the fluorescence intensity ratio (FIR) technique, the temperature sensing behaviors are investigated based on thermally coupled levels (2H11/2 and 4S3/2) and non-thermally coupled levels (4F9/2 and 4S3/2), respectively. The thermometry is sensitive to the excitation power for 4F9/2 and 4S3/2 levels, leading to large measurement errors caused by the power variation. Such a problem can be solved by using the power-insensitive FIR between 2H11/2 and 4S3/2 levels, which also shows the advantage of high absolute sensitivity with the maximum of 110.7 × 10−4 K−1. So, the developed BaMoO4:Er3+/Yb3+ phosphors can be applied in green light upconverters, display devices and temperature sensors.

High-purity green emission in Yb3+/Ho3+ Co-doped BaIn6Y2O13 up-conversion phosphor

Yb3+-Ho3+ pairs doped BaIn6Y2O13 (BIY) phosphors were successfully prepared through sol-gel process, and the crystal structure and optical properties were investigated in detail. As-prepared samples exhibited strong green and weak red emission peaked at 549 nm and 652 nm originated from Ho3+ transitions of 5S2, 5F4 → 5I8 and 5F5 → 5I8 with 980 nm excitation, respectively. The dopant contents, pumping power and pulse width of excitation laser dependent up-conversion luminescence (UCL) spectra of samples were modulated to acquire the intense and high-purity green emissions. Moreover, possible dynamic UCL process from non-steady-state to steady-state between Yb3+ and Ho3+ was schematically proposed in detail. These results indicate that BaIn6Y2O13: Yb3+/Ho3+ phosphors with strong and pure green UC emissions are potential candidates in display and lighting technology.

Engineering Atomically Precise Copper Nanoclusters with Aggregation Induced Emission

Controlled synthesis of atomically precise metal nanoclusters (MNCs) and fundamental understanding of their physical properties have emerged as an active area of research because of their potential applications in healthcare and energy-related materials. In the present study, atomically precise copper nanoclusters (Cu NCs) have been synthesized from nonluminescent plasmonic copper nanoparticles (Cu NPs) by core etching with excess reduced glutathione (GSH). Electrospray ionization (ESI) mass spectrometry confirms the formation of kinetically controlled, polydisperse Cu34–32(SG)16–13 NCs at room temperature and monodisperse Cu25(SG)20 NCs at elevated temperature (70 °C). Cu34–32(SG)16–13 NCs exhibit weak red emission (625 nm), while Cu25(SG)20 NCs emit intense blue luminescence at 442 nm with 9.7% quantum yield. Rational tuning of reaction temperature, pH, GSH concentration, and reaction time are crucial for the composition and emission band tuning of atomically precise Cu NCs. Interestingly, Cu34–32(SG)16...

Sol-Gel Synthesis and Optical Temperature Sensing Behavior of Double-Perovskite Gd2ZnTiO6:Yb3+/Er3+ Phosphors

The Gd2ZnTiO6:Yb3+/Er3+ phosphors (abbreviated as GZT:Yb3+/Er3+) have been successfully prepared by means of the sol-gel method. The GZT:Yb3+/Er3+ phosphor exhibits intense green upconversion (UC) emission bands near 525/547 nm (2H11/2/4S3/2→4I15/2) and weak red UC emission band near 663 nm (4F9/2→4I15/2) upon the 980 nm laser excitation. Furthermore, the sample simultaneously emits near-infrared centered at 1527 nm associated with 4I13/2→4I15/2 transition of Er3+ ions. The high thermal activation energy (0.34 eV) of the GZT:Yb3+/Er3+ phosphor is determined via the temperature dependent luminescence spectra upon the 980 nm laser excitation (low power density: 0.8W/cm2). Two thermally coupled levels (2H11/2/4S3/2) for Er3+ using the fluorescence intensity ratio (FIR) technology were studied in detail. The maximum absolute sensitivity (90.11 × 10−4 K−1 at 539 K) of the targeted phosphor is determined from the experimental results. All results demonstrate a potential of application of as-prepared GZT:Yb3+/Er3+ phosphors in optical thermometry.

Structural and photoluminescence properties of UV-excited Er3+ doped Ba2CaWO6 yellowish-green phosphors

Double perovskite Ba2CaWO6 phosphors doped with different concentrations of Er3+ have been synthesized by the conventional solid state reaction method in air at 1250 °C and are characterized by X-ray diffraction analysis (XRD), Energy Dispersive X-ray Spectrometer (EDS), Scanning electron microscope (SEM), Transmission electron microscope (TEM), Fourier transform infrared spectroscopy (FTIR) and Photoluminescence measurements. An intense green and weak red emissions are observed at 566 nm (4S3/2 → 4I15/2), 680 nm (4F9/2 → 4I15/2) under 314 nm, 378 nm corresponding to charge transfer band and rare earth excitations respectively. Under charge transfer excitation Ba2CaWO6:xEr3+ samples exhibit high intense emission peaks of Er3+ than the rare earth excitation. This is due to an efficient energy transfer from WO66- to Er3+. The maximum emission intensity was observed for 0.08 wt% concentration of Er3+ ions in Ba2CaWO6 phosphors. The critical energy transfer distance among Er3+ ions is calculated to be 15.18 Å and the quenching mechanism is due to dipole-dipole interaction. The energy transfer mechanism is discussed based on the energy level diagram of Er3+. The radiative lifetimes were determined from the fluorescence decay analysis. The CIE color coordinates were calculated from the emission spectra. The result shows that Ba2CaWO6: Er3+ phosphor can be considered as a potential candidate for UV excited yellowish-green phosphor for display applications.

Investigating efficient energy transfer in novel strategy-obtained Gd2O2S:Dy3+, Eu3+ nanofibers endowed with white emitting and magnetic dual-functionality

Gd2O2S:Dy3+, Eu3+ nanofibers were successfully prepared via electrospinning combined with dual-boat sulfurization approach. X-ray diffractometer analysis reveals that Gd2O2S:Dy3+, Eu3+ nanofibers possess hexagonal structure (space group: P3¯m1). The as-synthesized samples are apparently nanofibers in morphology with field emission scanning electron microscope investigation, and the average diameters of PVP/(Gd(NO3)3+Dy(NO3)3+Eu(NO3)3) electrospinning-produced nanofibers and Gd2O2S:Dy3+, Eu3+ nanofibers are 454.10 ± 4.97 nm and 162.93 ± 0.75 nm, respectively. Gd2O2S:Dy3+ nanofibers demonstrate the typical blue, yellow and weak red emission bands via the excitation of 268-nm ultraviolet. Resulted from the effective spectral overlap between Dy3+ and Eu3+, Dy3+ is proved to be the effective sensitizer for Eu3+, which leads to the energy transfer of Dy3+→Eu3+ in Gd2O2S host and improved red emission of Eu3+. Further, the mechanism of energy transfer between Dy3+ and Eu3+ is determined to be an electric doublet-electric doublet interaction. Additionally, variable fluorescent color, including blue, red and especially white, can be achieved by properly modulating the ratios between Dy3+ and Eu3+. The formation mechanism of Gd2O2S:Dy3+, Eu3+ nanofibers is also advanced. Besides, the Gd2O2S:Dy3+, Eu3+ nanofibers display paramagnetism at ambient temperature. The as-synthesized Gd2O2S:Dy3+, Eu3+ nanofibers have applicable prospects in anti-fake, lasers, modulator, liquid crystal display, drug delivery and light emitting diodes (LEDs) due to their magnetism-photoluminescence dual-functionality.

The α, β-unsaturated pyrazolone-based fluorescent sensor with red emission and its application for real-time monitoring hypochlorite in cancer cells and zebrafish

Fluorescent sensors have been the most commonly applied with drug discovery projects and delivery systems, as well as screening the chemical catalysts in synthetic chemistry. α, β-unsaturated pyrazolone and its derivatives have been widely developed in medicinal chemistry and in synthetic chemistry. Hence, a novel fluorescent sensor BODIPY-Pyra was explored based on α, β-unsaturated pyrazolone and BODIPY fluorophore. BODIPY-Pyra had a weak red emission (600 nm) because of rotation of CC bond. However, an enviromental restriction of TICT promoted the red fluorescence enhancement in glyceryl alcohol. Especially, α, β-unsaturated pyrazolone skeleton presented the good reactivity, which afforded the fluorescent change of BODIPY-Pyra through the chemical reaction. It's beneficial for monitoring drug delivery and chemical reaction based on CC associated and stimulated linker by fluorescence assay. To explore the potential application of BODIPY-Pyra, the response towards hypochlorite was studied as a model in cancer cells and zebra fish. The results showed that BODIPY-Pyra could respond selectively and sensitively (LOD = 172 nM) towards hypochlorite among ROS and RSS. A 320 folds fluorescent enhancement at 520 nm was observed within 60s. Moreover, it could detect the intracellular hypochlorite in cancer cells, even endogenous hypochlorite in living zebra fish without drug induction. Noteworthy, the fluorescent sensor BODIPY-Pyra might provide a potential platform by fluorescent assays to the HTS of prodrug and chemical catalyst by the chemical reaction of unsaturated pyrazolone skeleton.

Down-conversion PL characteristics of CaSrSiO4:Tb3+ nanophosphor and its application on optical low-temperature sensor

The CaSrSiO4 nanophosphor-doped 0.7 mol% Tb3+ ions have been prepared by the high-temperature sintering method. XRD pattern is consistent with the standard card of CaSrSiO4 host, and the average particle size of CaSrSiO4:0.7Tb is about 50 nm. There exist intense green (544, 552 nm) and weak blue (485, 488 nm), yellow (588 nm), and red (625 nm) emissions under the excitation of 325 nm He–Cd laser, corresponding, respectively, to the transitions of Tb3+ ions from 5D4 and its splitting to 7F5,4,6,3,2 energy levels. The low-temperature photoluminescence characteristics of the sample are measured in the range of 290–10 K. The relationship between fluorescence intensity ratio and temperature is FIR = 0.895 + 0.469exp(− 145.8/T) and the maximum value of sensitivity is 17.6 × 10− 4 K− 1 at 70 K, indicating that CaSrSiO4:Tb3+ nanophosphor is a promising sensing material for low-temperature measurement.

Dysprosium doped niobium zinc fluorosilicate glasses: Interesting materials for white light emitting devices

Trivalent dysprosium doped niobium zinc fluorosilicate glasses modified with different Nb2O5/ZnF2 molar (M) ratios have been fabricated by the traditional melt-quenching technique and derived their structural, photoluminescence and decay properties using spectroscopic techniques. Induced structural modifications have been observed upon increasing content of Nb2O5. Maximum phonon energy of the glass matrix is found to be 1010 cm−1 from the Raman spectrum. The emission spectra of these glasses exhibit two intense bands at 480 and 570 nm besides a weak red emission at 650 nm. The decay profiles of Dy3+ ion for the 4F9/2 level exhibit a non-exponential behavior for all the glasses. The intrinsic lifetimes for the 4F9/2 level of Dy3+ ion have been determined by using the Inokuti-Hirayama model and are found to be 409, 366 and 325μs for the glasses with Nb2O5/ZnF2:10/30, 20/20 and 30/10 M ratios, respectively. The color coordinates have been evaluated from the emission spectra of the glasses and found that the glass with Nb2O5/ZnF2:30/10 M ratio appears near to the equal energy point. The correlated color temperature matches well to the summer sunlight region (4900–5600 K), indicating that the glasses could be a potential candidate for white light emitting devices.

Structural and Photoluminescence Characteristics of Cu Doped CdS Nanoparticles

EDTA surfactant assisted bare and Cu doped CdS nanoparticles were prepared by simple chemical coprecipitation method. As the prepared samples were characterized by energy dispersive analysis of X-rays (EDAX), X-ray diffraction patterns (XRD), transmission electron microscopy (TEM), Raman spectroscopy and photoluminescence spectroscopy (PL). Existence of Cu in host lattice with near stoichiometric ratio was corroborated by EDAX spectra. X-ray diffraction patterns revealed that cubic structure as that of CdS host lattice. TEM images suggested that spherical nature of nanoparticles with a size ranging from 4–6 nm. Room temperature photoluminescence (PL) spectra revealed that pristine host lattice nanoparticles demonstrate a strong green emission peak located at 525 nm as well as weak red emission shoulder situated at 598 nm. Auxiliary in Cu doped CdS samples, the luminescence intensity was gradually reduced as well as the green emission peak was shifted to red region (660 nm). With increase of Cu content in host matrix a red shift is found in the PL emission peak.

Enhanced photoluminescence in Tm3+, Yb3+, Mg2+ tri-doped ZnWO4 phosphor: Three photon upconversion, laser induced optical heating and temperature sensing

Three photon upconversion photoluminescence has been observed in Tm3+, Yb3+ co-doped ZnWO4 phosphor synthesized through solid state reaction method. The structural measurements reveal an increase in crystallinity and particles size on Mg2+ incorporation. The EDS spectrum shows the presence of Zn, W, Tm, Yb, Mg and O elements in the phosphor. The UV–vis-NIR absorption spectra contain CTB and 4f-4f transitions due to Tm3+ and Yb3+ ions, respectively. The Tm3+, Yb3+ co-doped phosphor gives intense blue and NIR emissions alongwith a weak red emission due to 1G4→3H6, 3H4→3H6 and 1G4→3F4 transitions, respectively upon 976 nm excitation. The emission intensity of the phosphor is found optimum at 2 mol% concentration of Yb3+ ion. When the Mg2+ ion is incorporated in the co-doped phosphor, the emission intensity enhances upto two times. This may be due to improved crystal structure and an increase in the intensity of absorption bands. The FIR analysis in the Stark components of 1G4 level suggests an efficient optical heating and temperature sensing ability. The temperature sensing sensitivity is found to be 34 × 10−4 °K-1 at 300°K. Thus, the Tm3+, Yb3+, Mg2+ tri-doped ZnWO4 phosphor may be used in photonic devices, NIR source, as an optical heater and temperature sensor purposes.

Strong red emission and enhanced electrostrain in (Bi0.5Na0.5)0.935−xPrxBa0.065Ti1−xSbxO3 lead-free multifunctional ceramics

Lead-free perovskite (Bi0.5Na0.5)0.935−xPrxBa0.065Ti1−xSbxO3 (BNBT6.5–xPS) ceramics are prepared by ordinary sintering technique. The compositional dependence of phase structure, electrical and photoluminescence properties of the ceramics was systematically investigated. Results showed that all samples exhibit pure perovskite structure with dense microstructures. With the addition of PS, a strong red emission located at 610 nm and a weak red emission at 660 nm under a light 450 nm excitation was observed. The strong red emission band is ascribed to the inter-4f transition from the excited 1D2 to the ground state 3H4 and the weak red emission located at 660 nm is due to the 3P0 → 3F2 transition. And then the BNBT6.5–0.004PS ceramic exhibited the strongest photoluminescence property. Besides the excellent photoluminescence properties, PS modifications induced an enhanced filed-induced strain. At x = 0.001, a large strain of 0.31% was obtained at a driving field of 70 kV/cm. As a multifunctional material, it has potential application as a multifunctional device such as optical-electro integration and coupling device applications.

Spectroscopic investigation of Er3+ doped BaF2 single crystal

We report on the spectroscopic investigation of Er3+ doped BaF2 single crystals. High-quality crystals have been gown by the Bridgman-Stockbarger pulling technique. The room temperature absorption, excitation, emission and fluorescence decay spectra of the luminescent Er3+ ions inserted in BaF2 fluoride single crystals have been investigated. Using the Judd-Ofelt (JO) theory, the intensity parameters of Er3+ ions have been calculated to be Ω2 = 0.949 × 10−20 cm2, Ω4 = 0.975 × 10−20 cm2 and Ω6 = 1.258 × 10−20 cm2. These parameters were then used to calculate the radiative transition probabilities (AJJ′), branching ratios (βJJ′) and radiative lifetimes (τrad) of the main laser emitting levels of Er3+ ions. The obtained spectroscopic properties are compared to those of Er3+ transitions in other fluoride and oxide hosts. The excitation spectrum in the UV–Visible spectral range is very close to the absorption spectrum indicating that all observed absorption levels can excite the Erbium green emission. The emission spectrum is mainly dominated by the green emission alongside a weak red emission. For the main transitions, there is a good agreement between the emission spectrum and the spontaneous emission probabilities given by the JO analysis. Using the Fuchtbauer–Ladenburg method, the emission cross-section of the three main visible emission were determined in addition to other important laser parameters such radiative quantum efficiency and optical gain.

Elucidating the Structure-Reactivity Correlations of Phenothiazine-Based Fluorescent Probes toward ClO.

In this work, with the aim of developing effective molecular probes and investigating the structure-reactivity correlation, a short series of phenothiazine-based fluorescent probes are designed for the detection of ClO- with differing electron push-pull groups. Sensing experiment results and single-crystal X-ray analysis with the aid of time-dependent DFT (TD-DFT) calculations reveal that substituting groups with increasing electron-withdrawing ability can increase the dihedral angle of the phenothiazine moiety and reduce the gap energy of the probes, leading to enhanced reactivity toward ClO- . Both PT1 and PT2 show two-color switching upon detection of ClO- . PT1, with the strong electron-donating group thiophene, shows a fluorescence color switch from salmon to blue. PT2, with a medium electron-donating/accepting group benzothiazole, shows a fluorescence color switch from red to green. However, both PT1 and PT2 show almost no response to ONOO- . Through the introduction of strong electron-withdrawing ketone combined with a cyano group, PT3 shows a cyan emission upon detection of ClO- and weak red emission upon detection of ONOO- . HRMS and 1 H NMR results confirm that PT1 and PT2 have the same sensing mode, in which the divalent sulfur of phenothiazine can be oxidized to sulfoxide by ClO- . Upon reaction with ClO- , PT3 experiences two-step reactions. It is first oxidized into the sulfone structure by ClO- , and then transformed into sulfoxide phenothiazine aldehyde. Upon encountering ONOO- , PT3 changes into an aldehyde structure and some nonfluorescent byproducts. Owing to their special selectivity and high sensitivity, PT1 and PT2 are applied to image the endogenous ClO- in macrophage cells and zebrafish larvae. This study is expected to provide useful guidelines for probe design for various applications.

Alkali ions effect on optical properties of Tm3+, Yb3+ co-doped gadolinium tungstate phosphor

The Tm3+, Yb3+ co-doped gadolinium tungstate phosphor in presence and absence of alkali ions (i.e. Li+, Na+ and K+) has been synthesized through solid state reaction method. The structural characterization confirms the crystalline nature with coexistence of the two monoclinic phases. The phase fraction varies on addition of alkali ions. The Tm3+, Yb3+ co-doped phosphor emits intense blue and near infrared emissions centered at 472 and 793 nm due to 1G4 → 3H6 and 1G4 → 3H5 transitions, respectively and a weak red emission at 655 nm due to 1G4 → 3F4 transition of Tm3+ on excitation with 976 nm. The emission intensity of near infrared band dominates over the blue and red bands. When the alkali ions are added in the Tm3+, Yb3+ co-doped phosphor, the emission intensity of the bands is enhanced significantly due to modification in the local crystal field. The emission intensity is highest for K+ incorporation compared to Li+ and Na+ due to its occupancy at the interstitial sites. The lifetime measurement reveals an enhancement in the emission intensity. The pump power dependent emission intensity plots confirm the involvement of three photons for blue and two photons for red and NIR emissions. Thus, the Li+, Na+ and K+ incorporated Tm3+, Yb3+ co-doped gadolinium tungstate phosphor emitting intense blue and NIR radiations may be useful for photonic devices, bio-imaging and solar converters.