Stokes Photoluminescence Research Articles

Improved sensing of metal ions via abnormal enhancement of the anti-stokes emission of the near-infrared fluorescent probe

Sensing of toxic and heavy metals is of great importance for protecting environment and health monitoring. Here we demonstrate an improved fluorescent probe operating in the near-infrared (NIR). The probe represents a NIR tricarbocyanine dye with 2,2′-dipicolylamine meso-group which is able to chelate zinc, cobalt and palladium ions. We show that the probe operation via monitoring of the anti-Stokes photoluminescence provides much better sensitivity of the probe compared to its Stokes photoluminescence. Particularly, it is shown that the anti-Stokes photoluminescence increases by more than an order of magnitude and can reveal additional features of the dye-metal complex not observed via the Stokes emission.

Enhancement of photoluminescence properties in Er3+-doped Gd3ScxGa5−xO12 garnet nanocrystals by Sc3+ co-doping

In this work, a series of novel garnet nanocrystals Gd3ScxGa5−xO12 (x = 0–2) doped with fixed Er3+ content were synthesized by a sol-gel combustion method. The structure, morphology, chemical composition, optical reflectance, and photoluminescence properties of the nanocrystals were investigated in detail. Following 980 nm laser excitation, steady-state and time-dependent Stokes Er3+: 4I13/2 → 4I15/2 emission spectra are investigated together with steady-state upconversion photoluminescence (UCPL) emission spectra. Although the activator content at the dodecahedral site is fixed, incorporation of Sc3+ into the octahedral site of the garnet host enhances the photoluminescence properties. The Stokes photoluminescence intensity keeps increasing with increasing Sc3+ content in the studied region. However, the intensity of UCPL is significantly increased in the Er3+-doped Gd3Sc2Ga3O12 sample. It is found that the substitution of Ga3+ by Sc3+ at the octahedral site of the studied garnet nanocrystals leads to a reduction of the maximum phonon energy and may affect the crystal field surrounding Er3+.

1.5 μm photoluminescence and upconversion photoluminescence in GeGaAsS:Er chalcogenide glass

Abstract The paper reports on ≈1.5 μm Stokes photoluminescence (PL) emission and upconversion photoluminescence (UCPL) emission in the visible and near-infrared spectral region in Er3+-doped Ge25Ga8As2S65 chalcogenide glasses at pumping wavelengths of 980 and 1550 nm. The ≈1.5 μm PL emission spectra are broadened with increasing concentration of Er ions which is discussed in terms of radiation trapping and UCPL dynamics affecting the Er3+: 4 I 13/2 level lifetime. The UCPL emission was observed at ≈530, ≈550, ≈660, ≈810 and ≈990 nm and its overall intensity as well as red-to-green UCPL emission intensity ratio increases with increasing Er concentration. To explore the UCPL dynamics we measured double logarithmic dependency of green (≈550 nm) and red (≈660 nm) UCPL emission versus pump power at pumping wavelength of 975 nm. Moreover, we measured quadrature frequency resolved spectroscopy (QFRS) on green UCPL emission (≈550 nm) using 975 nm pumping wavelength and various excitation powers. The QFRS spectra on green UCPL were analyzed in term of QFRS transfer function for three-level model from which we deduced energy transfer upconversion rate w 11 (s−1) originating from Er3+: 4 I 11/2, 4 I 11/2→4 F 7/2, 4 I 15/2 transitions.

Physico-chemical and optical properties of Er3+-doped and Er3+/Yb3+-co-doped Ge25Ga9.5Sb0.5S65 chalcogenide glass

Abstract We investigated the physicochemicаl properties, structure and optical properties of the Ge25Ga9.5Sb0.5S65: Er3+/Yb3+ glasses. The Judd-Ofelt theory was used to calculate the intensities of the intra-4f electronic transitions of Er3+ ions. We observed the upconversion photoluminescence (UCPL) at 530, 550, 660 and 810 nm under 980 nm excitation. In the Ge25Ga9.5Sb0.5S65: 0.1 at.% Er3+, we found that the Stokes photoluminescence (PL) at the green spectral region excited by the 490 and 532 nm laser is only ≈5 times higher than the UCPL emission under 810 or 980 nm excitation making these materials attractive for UCPL applications. The addition of 0.1–1 at.% of Yb3+ into Ge25Ga9.5Sb0.5S65: 0.1 at.% Er3+ glass reduces the UCPL as well as the Er3+ ≈1.5 μm emission intensity probably due to the reabsorption processes of the excitation light and concentration quenching. However, the observed Er3+: 4 S 3/2→4 I 13/2 (≈850 nm) emission in the Ge25Ga9.5Sb0.5S65: 0.1 at.% Er3+ sample populates the 4 I 13/2 level, which promises the using of this material for the 1.5 μm optical amplification.

Transformation of LaOF into LaF3owing to Al3+in luminescent Eu3+-doped crystalline powders

Conversion of LaF3 into LaOF has been demonstrated in the literature through heat treatment of the samples. In this work, we investigated the possibility of converting LaOF into LaF3 using Al3+ in a combustion synthesis technique. The conversion was proposed by taking advantage of the affinity that aluminium has for oxygen. The morphological study via scanning electron microscopy has shown an increase in the porosity of the samples with the inclusion of aluminium. X-ray powder diffraction data analysis demonstrated complete crystallization and conversion of LaOF into LaF3 due to the presence of aluminium. A small fraction of LaAlO3 has been detected and it confirms that aluminium bonds with oxygen, as expected. The samples were also doped with the rare-earth ion europium as a luminescence probe. Stokes photoluminescence was produced using UV light (λ = 355 nm) and the spectral analysis of Eu3+ 4f–4f electronic transitions has confirmed that LaOF is converted into LaF3. The measured luminescence lifetimes of reactant and product are characteristic of Eu3+ in the compounds LaOF and LaF3.

Erbium Doping Effects on the Structural and Infrared Luminescence Properties of Gd2Ti2O7 Nanocrystals

Er3+ (0.1, 1, 5, 10, 15, or 20 mol%)-doped Gd2Ti2O7 nanocrystals were fabricated by the sol-gel method. While annealing temperature reaches 800°C, amorphous phase transfers to well-crystallized ErxGd2-xTi2O7 pyrochlore nanocrystals. The average crystal size increases from ∼70 to ∼600 nm under 800 to 1200°C/1 h annealing. Because of the fast Er-Er energy transfer, all of the Stokes photoluminescence (PL) (4I13/2 → 4I15/2 transition, ∼1534 nm) decay curves are single-exponential for samples with 0.1–20 mol% Er3+ doping concentrations annealed at 1100°C/1 h. The Gd2Ti2O7 nanocrystals with 10 mol% Er3+ doping concentration (1.56 × 1021 ions/cm3) annealed at 1100°C/1 h possess the maximum PL intensity, 77 nm full width at half maximum (FWHM) of the PL spectrum, and longest lifetime (9.52 ms). However, Er3+ (20 mol%)-doped Gd2Ti2O7 nanocrystals annealed at 1100°C/1 h exhibit the weaker PL intensity, wider FWHM of the PL spectrum (109 nm), and shortest lifetime (2.46 ms) due to the concentration quenching effect.

Liquid-Crystalline Polymer Composites with CdS Nanorods: Structure and Optical Properties

We report on the structure, uniaxial orientation, and photoluminescent properties of CdS nanorods that form stable nanocomposites with smectic C hydrogen-bonded polymers from the family of poly(4-(n-acryloyloxyalkoxy)benzoic acids. TEM analysis of microtomed films of nanocomposites reveals that CdS nanorods form small domains that are homogeneously distributed in the LC polymer matrix. They undergo long-range orientation with the formation of one-dimensional aggregates of rods when the composite films are uniaxially deformed. The Stokes photoluminescence was observed from CdS NRs/LC polymer composites with emission peak located almost at the same wavelength as that of NRs solution in heptane. An anti-Stokes photoluminescence (ASPL) in polymer nanocomposites was found under the excitation below the nanoparticles ground state. The mechanism of ASPL was interpreted in terms of thermally populated states that are involved in the excitation process. These nanocomposites represent an unusual material in which the optical properties of anisotropic semiconductor nanostructures can be controlled by mechanical deformation of liquid-crystalline matrix.

Co-Doping Effects of Zn2+ on Upconversion Luminescence of Gd2O3:Er Nanophosphors

Zn2+ and Er3+ ions co-doped Gd2O3 nanophosphors were synthesized via a citric acid complexing method. The crystalline characterization shows that the Zn2+ doping induced a shrinking effect of the host cell by changing the lattice constant. Both Stokes photoluminescence and upconversion emission were significantly enhanced by the Zn2+ doping. The reason for emission enhancement was mainly ascribed to the lowered crystal symmetry of lattice by introducing oxygen vacancy.

Ultraviolet anti-Stokes photoluminescence in GaN single crystals

Ultraviolet anti-Stokes photoluminescence (ASPL) is observed under continuous visiblelight excitation in a GaN single crystal at 4 and 77 K. The ASPL spectra are almost thesame as the Stokes photoluminescence (SPL) spectra under band-to-band excitation.Namely, we observe ASPL due to bound and free excitons at 4 and 77 K, respectively.Based on the temporal decay, the excitation spectrum and the excitation intensitydependence of the ASPL intensity, we propose a two-step two-photon absorptionmechanism through an electron trapped at a deep ionized donor with a lifetime of 1.45 ms.

New phase transition of erbium-doped KNbO 3 polycrystalline

Raman scattering, Stokes photoluminescence (PL) spectroscopy and differential scanning calorimetry (DSC) measurements have been used to study the phase transition of 2 mol% erbium-doped potassium niobate (KNbO 3) polycrystalline. The low-temperature Raman scattering experiments showed that the phase transition occurred at around 200 and 300 K, and the DSC thermograms indicated that the phase transition occurred at 203, 290, 481 and 666 K, respectively. Comparing our results with Matthias's, we proposed that 2 mol% erbium-doped KNbO 3 polycrystalline exhibits a new phase transition at 203 K. The PL spectra intensity was also unusual during these temperatures; a strong non-exponential behavior was found. From these results of Raman scattering, DSC and PL, we concluded that the behavior of 2 mol% erbium-doped KNbO 3 polycrystalline at 203 K should be a new phase transition.

Polarization Dependence of the Luminescence Properties of the Erbium Doped KNbO3 Ferroelectric Ceramics

ABSTRACTThe polarization dependence of the Stokes photoluminescence (PL) spectra of erbium doped Potassium niobate (KNbO3) ceramics has been investigated by studying the relations between PL spectra with the poling electric field, poling time. All the Stark splitting components of 4S3/2→ 4I15/2 transition were evident after the poling process. The experiments also showed that the polarization enhances the fine structure and modifies the intensity ratio of the 4S3/2→ 4I15/2, 4F9/2 → 4I15/2 and the 4S3/2→4I13/2 transitions at different poling electric fields and poling times. From the similar tendency between the frequency shift of PL spectra Δv and the planar electromechanical coupling factor Kp demonstrate indirectly that the Stark splitting was produced by the dipole moment of erbium ions state interacting with the internal local electric field due to polarization.

Polarization tuning the Stokes photoluminescence spectra of erbium doped KNbO3 ceramics

The poling effect in Stokes photoluminescence (PL) spectroscopy of erbium doped potassium niobate (KNbO3) ceramics has been investigated by studying the relations between PL spectra with the poling electric field, poling time, and annealing conditions, respectively. All the Stark splitting components of S3∕24→I13∕24 transition were evident after the poling process. The experiments also showed that the polarization enhances the fine structure and modifies the intensity ratio of the S3∕24→I15∕24, F9∕24→I15∕24, and S3∕24→I15∕24 transitions at different poling electric fields and poling times for the samples doped with 5% of erbium. Comparing the poling spectra with annealing spectra, we can see that both polarization and annealing can modify the intensity of PL. However, the mechanisms of the two effects are different. The frequency shift Δν of the peaks depended on the wavelength after poling demonstrates that the Stark splitting was produced by the dipole moment of erbium ions interacting with the internal local electric field due to polarization.

The post-annealing effects on the Stokes photoluminescence spectra of erbium-doped KNbO 3 polycrystalline

The annealing effect on Stokes photoluminescence (PL) spectroscopy of erbium-doped potassium niobate (KNbO 3) ceramics has been investigated by studying the relations between room-temperature PL spectra with the annealing conditions. The experiments showed that the shape and intensity of the PL spectra is a function of the annealing temperature; the relative intensity of 4S 3/2→ 4I 15/2, 4F 9/2→ 4I 15/2 and the 4S 3/2→ 4I 13/2 transitions increased where the annealing temperature was increased. After annealing, the relative intensity ratio of the 541 and 526 nm peaks decreased gradually, indicating the decrease of the symmetry of ligand field and an increase of covalence. From the unusual phenomenon, in which the green and near-infrared transitions intensity change was different after annealing, the near-infrared emission may correspond to the 4I 9/2→ 4I 15/2 transition instead of 4S 3/2→ 4I 13/2 transition.

The stokes photoluminescence spectra of erbium-doped KNbO 3 polycrystalline

This paper reports the Stokes photoluminescence (PL) spectra of erbium-doped potassium niobate (KNbO 3), which are prepared by synthesized method. In this work, we research the relations between PL spectra with the sintering temperature and erbium concentration. The experiments showed that 2H 1/2→ 4I 15/2, 4S 3/2→ 4I 15/2 and the 4S 3/2→ 4I 13/2 emission peaks have maximum intensity at sintering temperature of 1060°C for the concentration of erbium ( C Er)=1% sample. The PL spectra is also a function of dopant concentration. It was found that the relative intensity of 2H 1/2→ 4I 15/2, 4S 3/2→ 4I 15/2 and the 4S 3/2→ 4I 13/2 transitions increased as the concentration of erbium dopants increased, but then it decreased. The material characteristics were studied using X-ray diffraction, scanning electron microscopy and Raman spectrometer.

Anti‐Stokes photoluminescence in CdSe self‐assembled quantum dots

Anti-Stokes photoluminescence (ASPL) as well as Stokes photoluminescence (SPL) were studied in CdSe self-assembled quantum dots using a micro-photoluminescence technique. A few ASPL peaks were observed, and they also appeared in the SPL spectra. Photoluminescence intensities of both ASPL and SPL increase linearly with the excitation intensity. The emission mechanism of the observed ASPL is discussed.

Efficient Photoluminescence Upconversion in Porous Si

Abstract : We report on a new phenomenon specific for a system of spatially interconnected nanocrystal assemblies: efficient low temperature photoluminescence (PL) conversion at resonant optical excitation of porous Si. The upconverted photoluminescence (anti-Stokes PL) is observed at intensities as low as 0.1 W/cm(exp 2) and its intensity is as large as that of the Stokes PL band. The confirmation of the essence of connectivity between nanocrystals comes from the same type of studies performed on systems containing Si nanocrystals surrounded by a thick SiO(2) shell where the anti-Stokes PL is completely absent for any excitation energy and intensity used while the properties of the Stokes PL are very similar to those of porous Si.

Anti-Stokes photoluminescence in colloidal semiconductor quantum dots

We report anti-Stokes photoluminescence (photon energy up-conversion) from size-quantized CdSe and InP nanocrystalline colloids. The observed up-conversion is highly efficient and occurs at very low excitation intensities. With low temperatures the intensity of the up-converted photoluminescence decreases while that of the usual Stokes photoluminescence increases; the up-converted photoluminescence is also restricted to energies corresponding to the band gaps of the quantum dots that are present in the colloid ensemble. The anti-Stokes photoluminescence is explained by a model that involves surface states.