Upconversion Luminescence Spectra Research Articles

Study on optical temperature sensing properties of YVO4:Er3+, Yb3+ nanocrystals

The YVO4: Er3+, Yb3+ phosphors with various particle sizes were prepared by a precipitation method and the crystal structure and microscopic image were characterized by means of X-ray Diffraction (XRD) and field emission scanning electron microscopy (FE-SEM). The up-conversion luminescent spectra of Er3+, Yb3+ co-doped YVO4 nanocrystals with different particle sizes have been measured. It can be found that the red-green upconversion emission intensity ratio increases with the decrease of the particle size. Furthermore, the temperature sensing properties of YVO4: Er3+, Yb3+ phosphors with different particle sizes were studied based on the change of emission intensities from two thermally coupled 2H11/2 and 4S3/2 levels of Er3+. It shows that in a relatively wide range of sensing temperature (293–603K), the temperature sensing sensitivity of nanosized materials is somewhat higher than that of bulk material. The sensing sensitivity of the sample increases with decreasing particle size, and a relative high sensitivity of 1.112×10−2K−1 was obtained for the sample with a particle size of 20nm, which is about 17.3% higher than the bulk sample. Finally, physical mechanism for the size-dependence of temperature sensing sensitivity was explained and predicted.

A facile one-pot method to synthesize ultrasmall core-shell superparamagnetic and upconversion nanoparticles

Ultrasmall core-shell Fe3O4@NaYF4:Yb3+/Er3+ nanoparticles with bifunctional properties have been successfully synthesized via one pot thermolysis method using oleylamine as both solvent and stabilizer. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), upconversion (UC) luminescence spectra and the physical properties measurement system (PPMS) were used to characterize the resulting samples. The synthesized samples have uniform morphology with a mean size of 14.5nm and excellent dispersibility. Moreover, these nanoparticles exhibit superparamagnetic behaviour with saturation magnetization of 8.45emμ/g and efficient up-conversion emission with a two-photon induced process when excited by a 980nm laser. These results suggest that the synthesized ultrasmall bifunctional nanoparticles may find many biomedical applications, such as clinical diagnosis and treatment of cancers.

Effect of Yb3+ concentration on upconversion luminescence and temperature sensing behavior in Yb3+/Er3+ co-doped YNbO4 nanoparticles prepared via molten salt route

Yb3+/Er3+ co-doped YNbO4 nanoparticles (NPs) with an average size of 35nm were prepared via modified molten salt method for the first time. The phase purity, crystal structure, morphologies, and upconversion luminescence (UCL) properties as well as quantum yield and temperature sensing behavior of the as-prepared samples were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM) and upconversion luminescence (UCL) spectra, respectively. The XRD Rietveld refinements based on the XRD data were employed to reveal the phase purity and structure of the as-prepared samples. It was confirmed that the optimal doping concentration of Yb3+ ions in YNbO4:Yb3+, Er3+ NPs is around 10mol%, which has a maximal quantum yield of 0.1%. The temperature sensing behavior of the as-prepared YNbO4:Yb3+, Er3+ NPs was studied based on the fluorescent intensity ratio (FIR) technique from two thermal coupled 2H11/2 and 4S3/2 levels. It was found that the temperature sensitivity was sensitive to the doping concentration of Yb3+ ions. In addition, the dependence of UCL colors on temperature was observed and the corresponding mechanism was proposed. Therefore, the as-prepared Yb3+/Er3+ co-doped YNbO4 NPs have double function of optical thermometer and safety sign for the high temperature environment.

Uniform Cerium-Based Coordination Polymer Microsnheres: Preoaration and Upconversion Emission.

Homogeneously doped Yb3+ and Er3+ cerium-based coordination polymer (CP) microspheres have been successfully synthesized on a large scale through a simple solvothermal route with 2,5-pyridinedicarboxylic acid (2,5-H2PDC) as the organic linker. CeO2: Yb3+, Er3+ porous microspheres were obtained by annealing the corresponding CP microspheres at 600 °C for 4 h under atmospheric pressure. These as-prepared products were characterized by Powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), energy-dispersion X-ray (EDX) spectroscopy, Thermogravimetric (TG) and derivative thermogravimetric (DTG) analysis. The room temperature upconversion luminescent spectra of the as-prepared microspheres were carried out by 980 nm NIR light excitation. Interestingly, Yb3+ and Er3+ codoped CP microspheres give a single-band emission centered at 673 nm, while the CeO2: Yb3+, Er3+ microspheres give emission in green and red region, with red being the dominant emission. The emission intensity of the CeO2: Yb3+, Er3+ microspheres were much stronger than that of the Yb3+ and Er3+ codoped CP microspheres.

Sensitive optical temperature sensor based on up-conversion luminescence spectra of Er3+ ions in PbO–Ga2O3–XO2 (X = Ge, Si) glasses

Up-conversion luminescence spectra of Er3+ ions in PbO–Ga2O3–GeO2 and PbO–Ga2O3–SiO2 glasses have been examined as a function of temperature in the 298–650K range. The relative emission intensities of green bands corresponding to 2H11/2→4I15/2 and 4S3/2→4I15/2 transitions of Er3+ were determined with temperature. Based on up-conversion luminescence spectra of Er3+, the fluorescence intensity ratio and temperature sensitivity for glasses based on PbO–Ga2O3–XO2 (X=Ge, Si) were calculated. The maximum sensitivity is equal to 20.4×10−4K−1 at T=620K (X=Ge) and 26.4×10−4K−1 at T=590K (X=Si) suggesting potential application in optical sensor thermometry.

Broadband Near-Infrared Photoluminescence and Strong Visible Up-Conversion Emission in BaTiO3-(Na0.5Er0.5)TiO3 Lead-Free Piezoelectric Ceramics

For checking photoluminescence properties of BaTiO3-(Na0.5Er0.5)TiO3 lead-free piezoelectric ceramics, optical diffuse reflection spectra, visible up-conversion luminescence spectra, 1.55 μm near-infrared photoluminescence spectra, and optical temperature sensing performances under the excitation of 980 nm laser were investigated systematically. Broadband near-infrared (˜1.55 μm, FWHM˜90 nm) emission and strong visible up-conversion (˜550 nm) emission were observed under the 980 nm excitation in the ceramics at room temperature. Near-infrared emission and visible up-conversion emission became stronger with increasing (Na0.5Er0.5)TiO3 concentration below quenching point above which it will degrade. The optimal emission intensity was obtained when (Na0.5Er0.5)TiO3 content was 7 mol%. These ceramics with excellent ferro-/piezoelectric and photoluminescence properties may be useful for ultrasonic transducer, optical temperature sensor, optical amplifier, and other relative applications.

Anomalous Temperature-Dependent Upconversion Luminescence of α-NaYF4:Yb3+/Er3+ Nanocrystals Synthesized by a Microwave-Assisted Hydrothermal Method

Yb³⁺/Er³⁺co-doped cubic-(α-) phase NaYF₄ nanocrystals were prepared through a microwave- assisted hydrothermal method. Temperature-dependent upconversion luminescence (UCL) and sensing properties were systematically studied. It is interesting that anomalous temperature- dependent UCL behavior is observed. With increasing temperature (303-573 K), the UCL intensity of Er³⁺ does not quench monotonously but reaches a minimum around 483 K and then increases. However, it was found that the UCL spectra change in a different way with decreasing temperature (573-303 K) from the one measured with increasing temperature. The fluorescence intensity ratio of ²H₁₁/₂ --> ⁴I₁₅/₂ to ⁴S₃/₂ --> ⁴I₁₅/₂ at any measured temperature point remains almost constant in all measurement processes, indicating the consistency of temperature in each spectrum measurement at all temperature points regardless of the heating or the cooling process in our experiments. The results demonstrate that NaYF₄:Yb³⁺/Er³⁺ UC nanocrystal has good sensing stability and may have potential application in the nanoscale thermal sensor.

Gel combustion synthesis of La x Gd14–x B6Ge2O34 (x = 3 and 4) codoped with Yb3+–Er3+ and Yb3+–Tm3+ active ions

This paper reports the gel combustion synthesis of La x Gd14–x Ge2B6O34 (x = 3 and 4) germanate borates codoped with Yb3+–Er3+ and Yb3+–Tm3+ active ions. The synthesized compounds are isostructural with Gd14Ge2B6O34 and crystallize in trigonal symmetry (sp. gr. P31). We have determined the unit-cell parameters of the synthesized mixed-cation germanate borates La3Gd9.74Yb0.84Tm0.42Ge2B6O34 (a = b = 9.794 A, c = 25.7913 A, V = 2143 A3) and La3.16Gd10Yb0.7Er0.14Ge2B6O34 (a = b = 9.746 A, c = 25.7450 A, V = 2118 A3) and assessed their thermal stability. The results demonstrate that the La x Gd14–x Ge2B6O34 (x = 3 and 4) germanate borates codoped with Yb3+–Tm3+ and Yb3+–Er3+ active ions melt congruently at T = 1660 and 1700 K and crystallize with undercooling at T = 1620 and 1660 K, respectively. We have obtained an upconversion luminescence spectrum of the La3.16Gd10Yb0.7Er0.14Ge2B6O34 germanate borate. The spectrum shows two bands. The stronger band (in the green region) corresponds to two transitions: 2 H 11/2 → 4 I 15/2 (λ = 525 nm) and 4 S 3/2→ 4 I 15/2 (λ = 550 nm). The weaker band (in the red region) corresponds to the Er3+ 4 F 9/2→ 4 I 15/2 transition.

α-NaYb(Mn)F4:Er(3+)/Tm(3+)@NaYF4 UCNPs as "Band-Shape" Luminescent Nanothermometers over a Wide Temperature Range.

Novel flower-like α-NaYb(Mn)F4:Er(3+)/Tm(3+)@NaYF4 upconversion nanoparticles (UCNPs) as luminescent nanothermometers have been developed by combining liquid-solid solution hydrothermal strategy with thermal decomposition strategy. Under 980 nm excitation, they exhibit intense upconversion luminescence and temperature-dependent upconversion luminescence over a wide temperature range. The influence of temperature on "band-shape" upconversion luminescence (UCL) spectra and the intensity of emission bands are analyzed and discussed in detail. We further successfully test and verify that intensity ratios REr of (2)H11/2 → (4)I15/2 and (4)S3/2 → (4)I15/2 and RTm of (1)G4 → (3)H5 and (3)H4 → (3)H6 are sensitive to temperature, and the population of active ions follows Boltzmann-type population distribution very well. These luminescent nanothermometers could be applied over a wide temperature range from 123 to 423 K with high sensitivity, which enable them to be excellent candidates for temperature sensors.

Synthesis of Er3+:Lu2O3 nanopowders by carbonate co-precipitation process and fabrication of transparent ceramics

Er3+ ions-doped Lu2O3 nanopowders were synthesized by co-precipitation method using NH4HCO3 as a precipitant, then Er3+:Lu2O3 transparent ceramics were fabricated by vacuum sintering using the as-prepared powder. The structure, crystallite size and upconversion luminescence (UCL) spectra of the as synthesized powders were characterized. The results indicated that the UCL properties of the powders varied with the calcination temperature and the Er3+ doping concentrations. Under the excitation of 980 nm laser diode, the ceramic sample showed a visually dominant green emission. Power studies revealed that the green (4S3/2 → 4I15/2) and red (4F9/2 → 4I15/2) upconversion emission of the sample occurred via a two-photon process.

Solvothermal synthesis and upconversion properties of about 10 nm orthorhombic LuF3: Yb3+, Er3+ rectangular nanocrystals

The Yb3+ and Er3+ codoped orthorhombic LuF3 rectangular nanocrystals (NCs) with the size of about 10nm were synthesized by a facile and effective solvothermal process. X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), upconversion (UC) luminescence spectra and decay curves were used to characterize the resulting samples. Compared with YF3 and α-NaYF4 NCs, owning the similar size and the same doping levels of Yb3+ ions and Er3+ ions as LuF3 NCs, the green UC emission of LuF3 NCs is 18.7 times and 5.1 times stronger than that of YF3 and α-NaYF4 NCs respectively; the red UC emission of LuF3 NCs is 13.2 times and 0.6 times stronger than that of YF3 and α-NaYF4 NCs respectively. Under 980nm wavelength excitation, the decay curves of both 4S3/2→4I15/2 transition and 4F9/2→4I15/2 transition exhibit a single exponential function, resulting from the fast energy migrations among Yb3+ ions caused by the high concentration of Yb3+ ions (20mol%). Meanwhile, at relatively low power density, the slopes of the linear plots between log(I) and log(P) for green UC and red UC are 1.7 and 1.9 respectively, which are less than 2 due to the quenching of the thermal effect, indicating a two-photon process for them. At high power density, the slopes are decreased caused by the saturation effect. In addition, we proved the existence of the thermal effect by the pump power dependence of the intensity ratio of 2H11/2→4I15/2 transition to 4S3/2→4I15/2 transition.

Enhanced high-order upconversion luminescence of hexagonal phase NaYF 4 :Yb 3+ ,Tm 3+ crystals coated with homogeneous shell

Abstract High-order upconversion luminescence (ultraviolet (UV), violet and blue emissions) of rare earth nanocrystals is quite desirable for photodynamic therapy and near-infrared photocatalysis applications. The hexagonal phase NaYF4:Yb3+,Tm3+/x mmol NaYF4 (x = 0, 0.1, 0.5, and 1) crystals were prepared by a hydrothermal method. With the amount of the shell precursor increasing, the crystals shape changed from hexagonal plate to hexagonal prism gradually, with the particles size increased. After coating a homogeneous inert NaYF4 shell, the high-order upconversion luminescence (1I6 and 1D2 radiative transitions) of all core–shell crystals were enhanced by several times compared with core-only crystals. Impressively, when the amount of the shell precursor was 0.1 mmol, the increased ratio of the emissions from 1I6 and 1D2 were 7.44 and 5.63 times, respectively. With further increasing the amount of the shell precursor, the increased ratio displayed a slight decline. The further photoluminescence decay results were consistent with the upconversion luminescence spectra. We demonstrated that the enhancement of high-order upconversion luminescence was attributed to the well-known surface passivation effect of the homogeneous shell.

Upconversion Luminescence Properties of NaYF4:Yb:Er Nanoparticles Codoped with Gd3+

The temperature-dependent upconversion luminescence of NaYF4:Yb:Er nanoparticles (UCNP) containing different contents of Gd3+ as additional dopant was characterized. The UCNP were synthesized in a hydrothermal synthesis and stabilized with citrate in order to transfer them to the water phase. Basic characterization was carried out using TEM and DLS to determine the average size of the UCNP. The XRD technique was used to investigate the crystal lattice of the UCNP. It was found that due to the presence of Gd3+, an alteration of the lattice phase from α to β was induced which was also reflected in the observed upconversion luminescence properties of the UCNP. A detailed analysis of the upconversion luminescence spectra—especially at ultralow temperatures—revealed the different effects of phonon coupling between the host lattice and the sensitizer (Yb3+) as well as the activator (Er3+). Furthermore, the upconversion luminescence intensity reached a maximum between 15 and 250 K depending on Gd3+ content. In c...

Preparation, Structure, and Up‐Conversion Luminescence of Yb3+/Er3+ Codoped SrIn2O4 Phosphors

SrIn2O4, which shows lower phonon energy than CaIn2O4, is not only a good photocatalyst but also can be an excellent up‐conversion (UC) host to exhibits UC luminescence. In this work, Yb3+ and/or Er3+ doped SrIn2O4 phosphors were synthesized, and their UC luminescence properties were studied and compared with those in the CaIn2O4 host. The structure of SrIn2O4: 0.01Er3+ and SrIn2O4: 0.1Yb3+/0.01Er3+ samples were refined by the Rietveld method and found to that SrIn2O4: 0.1Yb3+/0.01Er3+ showed increasing unit cell parameters and cell volume, indicating In3+ sites were substituted successfully by Yb3+ and/or Er3+ ions. From the UC luminescence spectra and diffuse reflection spectra, Er3+‐doped SrIn2O4 showed very weak luminescence due to ground state absorption of Er3+; Yb3+/Er3+ codoped SrIn2O4 presented strong green (550 nm) and red (663 nm) UC emissions which were assigned to energy transfer from Yb3+ transition 2F7/2→2F5/2 to the Er3+ transition 4S3/2 → 4I15/2 and 4F9/2 → 4I15/2. Comparing with CaIn2O4, Yb3+/Er3+ codoped SrIn2O4 showed obvious advantages with higher UC luminescent intensity. The pumping powers study showed that UC emissions in Yb3+/Er3+ codoped SrIn2O4 were attributed to energy transfer of Yb3+→Er3+ with a two‐photon process. The possible UC luminescent mechanism of Yb3+/Er3+‐doped SrIn2O4 was discussed.

Decrease in particle size and enhancement of upconversion emission through Y3+ions doping in hexagonal NaLuF4:Yb3+/Er3+nanocrystals

The upconversion (UC) enhancement with size decrease has been realized through Y3+ ions doping in β-NaLuF4:Yb3+/Er3+ nanocrystals (NCs) by a solvothermal process. X-Ray diffraction (XRD), scanning electron microscopy (SEM) and UC luminescence spectra were used to characterize the resulting samples. With an increase of the Y3+ doping concentration, the NCs size is continuously decreased with no phase transition. Meanwhile, the UC intensity is firstly increased and then it decreases when the Y3+ ions concentration is over 30 mol%. The NCs (β-NaLu0.48Y0.3Yb0.2Er0.02F4) with the optimum Y3+ ions doping concentration (30 mol%) for UC emission have a diameter of about 80 nm. Compared with β-NaLu0.78Yb0.2Er0.02F4 and β-NaY0.78Yb0.2Er0.02F4 prepared under the same conditions, the green UC emission is enhanced by a factor of 1.8 and 16, respectively, for β-NaLu0.48Y0.3Yb0.2Er0.02F4. The variation of the UC intensity with the increasing Y3+ ions concentration is attributed to the changing of the symmetry of the local crystal field induced by Y3+ ions doping, which has been proved by the structural probe Eu3+ ions. For β-NaLu0.78Yb0.2Er0.02F4 and β-NaLu0.48Y0.3Yb0.2Er0.02F4, a three-photon green UC process and a three-photon red UC process occur simultaneously at high pump power density, which can be described as 4G11/2 (Er3+) + 4I15/2 (Er3+) → 2H11/2/4S3/2 (Er3+) + 4I13/2 (Er3+) and 4G11/2 (Er3+) + 2F7/2 (Yb3+) → 4F9/2 (Er3+) + 2F5/2 (Yb3+), respectively.

In vivo targeted magnetic resonance imaging and visualized photodynamic therapy in deep-tissue cancers using folic acid-functionalized superparamagnetic-upconversion nanocomposites.

Multifunctional nanoprobes used in magnetic resonance imaging (MRI) and photodynamic therapy (PDT) also have potential applications in diagnosis and visualized therapy of cancers, and hence it is important to investigate the active-targeting ability and in vivo reliability of these nanoprobes. In this work, folic acid (FA)-targeted, photosensitizer (PS)-loaded Fe3O4@NaYF4:Yb/Er (FA-NPs-PS) nanocomposites were synthesized for in vivo T2-weighted MRI and visualized PDT of cancers by modeling MCF-7 tumor-bearing nude mice. By measuring the upconversion luminescence (UCL) and fluorescence emission spectra, the as-prepared FA-NPs-PS nanocomposites showed near-infrared (NIR)-triggered PDT performance due to the production of a singlet oxygen species. Moreover, by tracing PS fluorescence in MCF-7, HeLa cells and in MCF-7 tumors, the FA-targeted nanocomposites demonstrated good targeting ability both in vitro and in vivo. Under the irradiation of a 980 nm laser, the viabilities of MCF-7 and HeLa cells incubated with FA-NPs-PS nanocomposites could decrease to about 18.4% and 30.7%, respectively, and the inhibition of MCF-7 tumors could reach about 94.9%. The transverse MR relaxivity of 63.79 mM(-1) s(-1) (r2 value) and in vivo MR imaging of MCF-7 tumors indicated an excellent T2-weighted MR performance. This work demonstrated that FA-targeted MRI/PDT nanoprobes are effective for in vivo diagnosis and visualized therapy of breast cancers.

Fabrication and upconversion emission processes in nanoluminophores NaYF<SUB align="right">4: Er, Yb and NaYF<SUB align="right">4: Tm, Yb

In this paper we present the new results of fabrication, characterisation and upconversion emission process of NaYF4 nanoparticles doped with Er3+ or Tm3+and Yb3+ as sensitiser. In order to fabricate α–, β–NaYF4:2%Er3+, 19%Yb3+and α–, β–NaYF4:2%Tm3+, 19%Yb3+ nanoparticles the soft template method in isopropylamine at 140C and diethylene glycol (DEG) at 180C has been used. The morphology, structures and emission properties were studied by X–ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and luminescence spectroscopy. The upconversion luminescence (UCL) spectra of α and β crystalline forms of NaYF4:2%Er3+, 19%Yb3+and NaYF4:2%Tm3+, 19%Yb3+ nanoparticles were investigated upon diode laser excitation at 976 nm. The strong emissions in the green and red spectral regions were observed upon this excitation. The spectral lines of the UCL could be assigned to the upconversion radiative transitions of the Er3+ or Tm3+ ions with Yb3+ sensitiser. The upconversion emission spectra dependent on laser excitation powers have been investigated in order to elucidate the upconversion emission paths which could take place. We found the significant influence of the type of nanocrystalline structure on the upconverting radiative transition mechanisms in NaYF4:2%Er3+, 19%Yb3+and NaYF4:2%Tm3+, 19%Yb3+ nanoparticles.

Experimental optimal design of the Er3+/Yb3+ codoped BaGd2ZnO5 phosphor and its upconversion luminescence properties

In order to obtain the Er3+/Yb3+ co-doped BaGd2ZnO5 up-conversion phosphor which has the maximum green and red emission intensity, firstly, the method of homogeneous design rooted in the experimental optimal design is employed to search optimum Er3+/Yb3+doping concentration preliminarily. Next, the quadratic general rotary unitized design is adopted to further optimize the experiment, and the regression equation in green and red emission intensity is established as a function of the doping concentration of Er3+/Yb3+. Finally, the optimal solution, that is, the doping concentration of Er3+/Yb3+ corresponding to the maximum emission intensity, is calculated by genetic algorithm. The optimal Er3+/Yb3+co-doped BaGd2ZnO5 phosphor is synthesized by the conventional high temperature solid state method. The crystal structure of as-prepared products is characterized by X-ray diffraction (XRD), and the results show that all the Er3+/Yb3+co-doped BaGd2ZnO5 phosphors we synthesized are of pure phase. The steady-state up-conversion (UC) emission spectra of products are measured under the excitation of a continuous 980 nm laser diode at different working currents. From the UC luminescent spectra of Er3+/Yb3+co-doped BaGd2ZnO5 phosphor, we can see a red emission centered at 662 nm, two green emissions centered at 551 nm and 527 nm, which are assigned to 4F9/2→4I15/2, 4S3/2→4I15/2 and 2H11/2→$4I15/2 transitions of Er3+ ion, respectively. The dependences of green and red UC emission intensities of optimal samples on working current are investigated, indicating that the red emission and green emission of optimal samples both originate from two-photon process. From the normalized green UC emission spectra, it can be concluded that the experimental laser working current induced temperature variation of samples can be omitted. According to Boltzmann distribution law and the thermal equilibrium existing between the levels of 2H11/2 and 4S3/2, the relationship between green emission and temperature in the optimal green UC emission sample is discussed in depth, and the energy level gap between 2H11/2 level and 4S3/2 level is calculated to be 926.11 cm-1. Through the study of the temperature effect on the optimal green UC emission sample, we find that the emission intensity decreases with the increasing of the temperature, owing to the thermal quenching effect. Furthermore, we calculate the activation energies of the samples, the activation energies of the green emission, red emission, and the overall emission are deduced to be 0.45, 0.46, and 0.45 eV, respectively.

Luminescence Enhancement Mechanism of Lanthanide-Doped Hybrid Nanostructures Decorated by Silver Nanocrystals

Hybrid nanostructures composed of rare earth ion-doped lanthanum trifluoride nanocrystals deposited on silica nanospheres (LaF3:Yb3+, Er3+@SiO2) and decorated with varying quantities of silver nanoparticles (Ag NPs) were synthesized using a simple strategy. Down and upconversion luminescence spectra were recorded. The luminescence dynamics were also recorded following excitation with a 532-nm pulse. Silver loading was found to have a significant effect both on the luminescence intensity and the luminescence decay rate, with the samples with the lowest silver content showing reduced luminescence intensity over silver-free samples, while the samples with large levels of silver loading showed significant luminescence enhancement. The results were successfully (and quantitatively) interpreted in terms of the competition between surface plasmon-induced field enhancement mediated by the Ag nanoparticles and nonradiative energy transfer from the luminescent ions to Ag nanoparticles. By combining the measured luminescence intensity with the luminescence decay rate determined from the dynamics measurements, and with the measured surface plasmon absorption spectra, one could obtain a quantitative and self-consistent understanding of the observed dependence of the green 4S3/2→4I15/2 (~540 nm) and red 4F9/2→4I15/2 (~650) emission bands on the Ag NP metal loading.

Effect of Yb3+ concentration on photoluminescence properties of cubic Gd2O3 phosphor

Yb3+ doped phosphor of Gd2O3 (Gd2O3:Yb3+) have been prepared by solid state reaction method. The structure and the particle size have been determined by X-ray powder diffraction measurements. The average particle size of the phosphor is in between 35 and 50nm. The particle size and structure of the phosphor was further confirmed by TEM analysis. The visible and NIR luminescence spectra were recorded under the 980nm laser excitation. The visible upconversion luminescence of Yb3+ ion was due to cooperative luminescence and the presence of rare earth impurity ions. The cooperative upconversion and NIR luminescence spectra as a function of Yb3+ ion concentration were measured and the emission intensity variation with Yb3+ ion concentration was discussed. Yb3+ energy migration quenched the cooperative luminescence of Gd2O3:Yb3+ phosphor with doping level over 5%, while the NIR emission luminescence continuously increases with increasing Yb3+ ion concentration.