Upconversion Emission Properties Research Articles

Preparation of Gd2O2S: Yb3+, Er3+, Tm3+ sub-micro phosphors by sulfurization of the oxides derived from sol-gel method and the upconversion luminescence properties

Yb3+, Er3+ and Tm3+ co-doped Gd2O2S sub-micro phosphors were synthesized by solid-state sulfurization of the oxide powders derived from sol-gel method. The crystal structure, morphology and upconversion luminescence properties of the phosphors were characterized by x-ray diffraction, scanning electron microscopic and fluorescence spectrum analysis methods. The phosphors exhibited typical hexagonal Gd2O2S phase when sulfurized at 800 °C for 2 h. Under the excitation of 980 nm laser diode, the Gd2O2S: Yb3+, Er3+, Tm3+ phosphors displayed distinct blue, green and red upconversion emissions centered at 481, 546 and 669 nm, respectively. The Gd2O2S phosphors using acetic acid as a chelating agent in the sol-gel process had the optimal upconversion emission property. The upconversion mechanism analysis revealed that the two-photon absorption was mainly responsible for the green and red upconversion emission of Er3+ ions, and the three-photon absorption was responsible for the blue upconversion emission of Tm3+ ions in the Gd2O2S: Yb3+, Er3+, Tm3+ phosphors.

Insights into Er3+↔Yb3+ energy transfer dynamics upon infrared ~1550 nm excitation in a low phonon fluoro-tellurite glass system

Highly upconverting, monolithic transparent inorganic glass co-doped with Er3+/Yb3+ ions have been explored in view of their easy integration with Si-PV cell. A ~4 fold enhancement in the photo-current of mc-Si-PV cell has been observed using a Er3+/Yb3+ co-doped sample compared to Er3+ ions singly doped glass. The role of Yb3+ ions on the enhancement of photo-current has been discussed in light of the Er3+↔Yb3+ energy transfer mechanism involved from IR to NIR and VIS upconversion process upon IR ~1550nm excitation. The influence of excitation pump power and donor Er3+ ion concentration on the energy transfer upconversion (ETU) as well as excited state absorption (ESA) energy transfer mechanisms and its effect on the upconversion emission properties have been described in detail. The prominence of ETU or ESA process were elaborated considering the decay dynamics of NIR upconversion emission upon ~1550nm excitation.

Optical properties of Mg2+, Yb3+, and Ho3+ tri-doped LiNbO3 crystals**Project supported by the National Natural Science Foundation of China (Grant No. 51301055), the Youth Science Fund of Heilongjiang Province, China (Grant No. QC2015061), the Special Funds of Harbin Innovation Talents in Science and Technology Research, China (Grant No. 2015RQQXJ045 ), and the Science Funds for the Young Innovative Talents of

A series of LiNbO3 crystals tri-doped with Mg, Yb, and Ho are grown by the conventional Czochraski technique. The concentrations of Mg, Yb, and Ho ions in Mg:Yb:Ho:LiNbO3 crystals are measured by using an inductively coupled plasma atomic emission spectrometry. The x-ray diffraction is proposed to determine the lattice constant and analyze the internal structure of the crystal. The light-induced scattering of Mg:Yb:Ho:LiNbO3 crystal is quantitatively described via the threshold effect of incident exposure energy flux. The exposure energy () is calculated to discuss the optical damage resistance ability. The exposure energy of Mg(7 mol):Yb:Ho:LiNbO3 crystal is 709.17 J/cm2, approximately 425 times higher than that of the Mg(1 mol):Yb:Ho:LiNbO3 crystal in magnitude. The blue, red, and very intense green bands of Mg:Yb:Ho:LiNbO3 crystal are observed under the 980-nm laser excitation to evaluate the up-conversion emission properties. The dependence of the emission intensity on pumping power indicates that the up-conversion emission is a two-photon process. The up-conversion emission mechanism is discussed in detail. This study indicates that Mg:Yb:Ho:LiNbO3 crystal can be applied to the fabrication of new multifunctional photoluminescence devices.

Luminescence, energy transfer, and up-conversion mechanisms of Yb3+ and Tb3+ co-doped LaNbO4

Novel green-emitting Yb3+ and Tb3+ co-doped LaNbO4 particles were prepared through a facile sol-gel and combustion method. X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), thermogravimetric and differential thermal analysis (TG-DTA), up-conversion luminescence (UCL) with different powers and varied concentrations, and luminescent lifetimes were employed to test the prepared samples. The XRD data exhibit that a sample with high crystallinity can be acquired at 1000 °C. FE-SEM images show homogeneous and spherical grains after Yb3+ and Tb3+ are co-doped in the LaNbO4 samples. TG-DTA reveals that the LaNbO4 synthetic process is accompanied by a temperature increase. In our work, we utilize a 980 nm laser to excite Yb3+ ions to achieve the 2F7/2 → 2F5/2 transition, and the LaNbO4:Yb3+, Tb3+ sample exhibits intense green emission. Luminescent spectra at different powers demonstrated the two-photon absorption process; meanwhile, the corresponding energy transfer mechanism from Yb3+ to Tb3+ and the emission of Tb3+ under 980 nm laser excitation was described via an energy level diagram. Moreover, concentration-dependent up-conversion luminescent properties were systematically explored, and it was confirmed that LaNbO4:0.15Yb3+,0.02Tb3+ exhibits the strongest luminescent properties. In particular, as the content of Yb3+ ions increases, the 5D4 → 7F6 transition quickly becomes stronger, resulting in the emitted color shifting from green to blue. Therefore, the emitted color can be tuned by adjusting the content of Yb3+ ions. The excellent up-conversion emission properties of the obtained samples allow for their potential application in the fields of 3D display technologies and solid-state lasers.

Up-conversion emission properties and unexpected white light emission from Er3+/Yb3+ doped Gd2O3 nanophosphors

Gd2O3 nanopowders doped with Er3+ and Yb3+ were synthesized using the combustion method. X-ray diffraction and scanning electron microscopy were used to estimate the crystallite size and the morphology of the materials. Scherrer and Warren–Averbach calculations were employed to estimate the mean crystallite size and size distribution of the powders. The crystallite size was found to be <100 nm. The down- and up-conversion emission properties of the materials were studied by laser spectroscopy. Results showed that the 1.5 μm emission of the Er3+ ions broadened with an increasing amount of Yb3+ ions. An n-shape pumping power dependence of the up-conversion emission intensity was observed. Formation of new emission bands and unexpected production of white light emission with increasing excitation power were also observed. The color quality parameters of the obtained visible emission were also measured.

Screening of Er3+/Yb3+Codoped RE–Ta–O and RE–Nb–O (RE = Y, La, or Gd) Upconversion Phosphors

Upconversion (UC) phosphors comprising Er3+/Yb3+ codoped rare-earth complex oxides, RExTayOz and RExNbyOz (RE = Y, La, or Gd), were synthesized via the gelable citrate complex method, and their UC emission properties were compared. This led to the discovery of an intense green-emitting UC phosphor, YTa7O19:Er3+/Yb3+, which is the first example of a YTa7O19 UC phosphor host material. Green UC emission obtained using optimum Er3+ and Yb3+ content was 20 times stronger than that obtained using a Y2O3 host.

Role of Gd3+ ion on downshifting and upconversion emission properties of Pr3+, Yb3+ co-doped YNbO4 phosphor and sensitization effect of Bi3+ ion

Dual-mode luminescence (downshifting-DS and upconversion-UC) properties of Pr3+/Yb3+ co-doped Y1−xGdxNbO4 (x = 0.0, 0.5, and 1.0) phosphors synthesized by solid state reaction technique have been explored with and without Gd3+ ion. The structural characterizations (XRD, SEM, and FTIR) confirm the pure phase of YNbO4 phosphor. Further, with the Gd3+ ion co-doping, the YNbO4 phosphors having a random shape and the large particle size are found to be transformed into nearly spherical shape particles with the reduced particle size. The optical band gaps (Eg) of Y1−xGdxNbO4 (x = 0.00, 0.25, 0.50, and 1.00) calculated from UV-Vis-NIR measurements are ∼3.69, 4.00, 4.38, and 4.44 eV, respectively. Moreover, YNbO4 phosphor is a promising blue emitting material, whereas Y1−x−y−zPryYbzGdxNbO4 phosphor gives intense green, blue, and red emissions via dual-mode optical processes. The broad blue emission arises due to (NbO4)3− group of the host with λex = 264 nm, whereas Pr3+ doped YNbO4 phosphor gives dominant red and blue emissions along with comparatively weak green emission on excitation with λex = 300 nm and 491 nm. The concentration dependent variation in emission intensity at 491 nm (3P0→3H4 transition) and 612 nm (1D2→3H4 transition); at 612 nm (1D2→3H4 transition) and 658 nm (3P0→3F2 transition) of Pr3+ ion in YNbO4 phosphor with λex = 300 nm and 491 nm excitations, respectively, has been thoroughly explored and explained by the cross-relaxation process through different channels. The sensitization effect of Bi3+ ion co-doping on DS properties of the phosphor has also been studied. The observed DS results have been optimized by varying the concentration of Pr3+ and Bi3+ ions, and the results are explained by the well-known simple band structure model. The study of Gd3+ co-doping reveals noticeable differences in DS characteristics of Y1−xPrxNbO4 phosphors: the overall decrement and increment (except for 612 nm emission) in intensity of DS emission on excitation with λex = 264 nm and 491 nm, respectively. These observations have been thoroughly explained, and the 1D2→3H4 transition (612 nm) of Pr3+ ion is found to be strongly dependent on surrounding environment of the host matrix. The UC properties of Y0.95−xPrxYb0.05NbO4 phosphors have been explored using Near Infra-Red (NIR) excitation. The material gives intense green and relatively weak blue and red UC emissions with λex = 980 nm. Interestingly, the UC emission intensity is further enhanced in the case of Y0.949−xPr0.001Yb0.05GdxNbO4 phosphors. In addition, the less explored laser induced heating effect with the pump power as well as the irradiation time on the UC emission has been explored in Y0.949−xPr0.001Yb0.05GdxNbO4 (x = 0, 0.5, and 0.949) phosphor samples, and subsequently, this feature has been found to be superior for Gd0.949Pr0.001Yb0.05NbO4 phosphor. The comparative study between the two hosts, viz., YNbO4 and GdNbO4 shows that GdNbO4 is better than YNbO4 for UC emission behavior; however, a reverse is observed as for as DS behavior is concerned only for the particular excitation wavelength (λex = 264 nm).

Synthesis and intense ultraviolet to visible upconversion luminescence of YF3:Ho3+ nanoparticles

Abstract Ho 3+ single-doped YF 3 nanoparticles were successfully synthesized by a hydrothermal method. Ultraviolet upconversion luminescence around 288 nm was observed clearly in YF 3 :Ho 3+ nanoparticles under excitation at 450 nm. The structure, composition and upconversion emission properties of the as-prepared products were characterized by X-ray crystallography, scanning electron spectrophotometry, energy-dispersive X-ray analysis, and fluorescence spectrophotometry. Hydrothermal temperature had a significant influence on the size and morphology of YF 3 :Ho 3+ nanoparticles, but the molar ratio of Y 3+ /Ho 3+ had little effect on these characteristics. Upconversion emission spectra demonstrated that the upconversion luminescence properties of the synthesized products were closely related to hydrothermal temperature and the molar ratio of Y 3+ /Ho 3+ . The YF 3 :Ho 3+ @TiO 2 photocatalyst was prepared via a sol-gel process and gave higher photocatalytic activity in degraded Rhodamine B (RhB) than did P25 under Xe lamp irradiation.

Spectroscopic investigation of zinc tellurite glasses doped with Yb3 + and Er3 + ions

This paper presents a detailed spectroscopic investigation of zinc tellurite glasses with the compositions (0.80−x−y) TeO2+(0.20) ZnO+xEr2O3+yYb2O3 (x=0, y=0; x=0.004, y=0; x=0, y=0.05 and x=0.004, y=0.05 per moles). The samples were synthesized by the conventional melt quenching method. The optical absorption and emission measurements were conducted at room temperature to determine the spectral properties of lanthanides doped zinc tellurite glasses and, to study the energy transfer processes between dopant lanthanide ions. The band gap energies for both direct and indirect possible transitions and the Urbach energies were measured from the absorption spectra. The absorption spectra of the samples were analyzed by using the Judd-Ofelt approach. The effect of the ytterbium ions on the emission properties of erbium ions was investigated and the energy transfer processes between dopant ions were studied by measuring the up-conversion emission properties of the materials. The color quality parameters of obtained visible up-conversion emission were also determined as well as possibility of using the Er3+ glasses as erbium doped fiber amplifiers at 1.55μm in infrared emission region.

One-Step Synthesis and Characterization of N-Doped Carbon Nanodots for Sensing in Organic Media.

Photoluminescent nitrogen-doped carbon nanodots (N-doped CNDs) soluble in organic media are synthesized in a one-step synthesis from a single-source precursor (an amphiphilic polymer), which exhibits a very high quantum yield (QY = 78%), excitation wavelength-dependent emission, and upconversion emission properties. The evolution of N-doped CND formation is studied via ultraviolet-visible and photoluminescence spectroscopy. Their analytical application as an effective sensor for the direct determination of nitroaromatic explosives and byproducts is shown based on their selective response via a fluorescence quenching mechanism. The proposed method is validated in soil samples by directly using the sensor in organic media without any further treatment or additional functionalization, which is an interesting aspect for practical applications.

Room‐Temperature Wavelength‐Tunable Single‐Band Upconversion Luminescence from Yb3+/Mn2+ Codoped Fluoride Perovskites ABF3

In contrast to well‐known multiple and fixed upconversion (UC) emission bands from lanthanide (Ln3+) ions activated luminescent materials, room temperature wavelength‐tunable single‐band UC emissions are designed and demonstrated in Ln3+ ions/transition metal Yb3+/Mn2+ codoped fluoride perovskites ABF3 (A = K+, Rb+, and Cs+; B = Mg2+, Zn2+, and Cd2+). Upon 976 nm laser excitation, the perovskites ABF3:Yb3+, Mn2+ exhibit intense single band UC emission centered at 550–610 nm depending on the substitution of the A+ and / or the B2+ species in ABF3. Crystal structure and luminescent properties analysis show that the UC emission should originate from the transitions of super‐exchange coupled Yb3+–Mn2+ pair. The Stokes and UC emission properties, UC luminescence decay behaviors, as well as temperature dependent UC emission properties of ABF3:Yb3+, Mn2+ are investigated and discussed in detail. The intense room (or high) temperature UC emission and ultralong UC decay lifetimes (≈25–45 ms) clearly reveal that the perovskites ABF3:Yb3+, Mn2+ can be potentially applied in the fields of time‐resolved luminescence imaging, lighting, and solid state lasers.

Upconversion emission and cathodoluminescence of Yb3+ ions activated BiOCl:Ho3+ phosphors

Upconversion (UC) emission and cathodoluminescence (CL) properties of Ho3+/Yb3+-codoped BiOCl phosphors were reported. Under 980nm light excitation, all the samples exhibited strong green and red UC emissions corresponding to the (5F4,5S2)→5I8 and 5F5→5I8 transitions of Ho3+ ions, respectively. Furthermore, the UC emission intensity as a function of Yb3+ ion concentration was investigated to determine an optimum doping concentration and the UC mechanism was found to be a two-photon process. Additionally, excellent CL properties were observed in Ho3+/Yb3+-codoped BiOCl phosphors and the CL emission intensity increased with increasing the accelerating voltage and filament current.

Molecular cocrystals of diphenyloxazole with tunable fluorescence, up-conversion emission and dielectric properties

The development of molecule-based solid-state materials with novel photofunctional and optoelectronic properties has received much attention recently. In this sense, the construction of two-component molecular systems (such as cocrystals) provides an effective way to adjust and optimize the molecular stacking, aggregation state and related performances. In this work, 2,5-diphenyloxazole (DPO) was chosen as a photoactive model system to study the structure–property relationship of its cocrystals. It was found that the as-prepared new cocrystals exhibited tunable fluorescence properties, up-conversion emission and thermal stability relative to the pure DPO solid. Moreover, the cocrystal based on DPO and hydroquinone has exhibited a pump-enhanced luminescence effect. The measurement of dielectric constants also suggests that the co-crystallization strategy can be applied in modulating the permittivity for the development of new materials in electro-optical applications. Therefore, this work provides a detailed picture on the relationship between the molecular stacking and optoelectronic properties of new DPO cocrystals and gives an alternative to achieve tunable fluorescence, up-conversion emission and dielectric properties.

Tuning Crystal Phase and Emission Properties of Upconversion Nanocrystals Through Lanthanide Doping.

Infrared-to-visible upconversion fluorescent nanocrystals of Yb³⁺/Er³⁺-codoped NaYF₄ and Yb³⁺/Er³⁺/Gd³⁺-tridoped NaYF₄ were synthesized using a modified coprecipitation process. X-ray diffraction and transmission electron diffraction scans of the nanocrystals confirmed that Gd³⁺ doping caused a phase transition to occur in the nanocrystals, changing them from a cubic to a hexagonal phase. Hexagonal phase Yb³⁺/Er³⁺/Gd³⁺-tridoped NaYF₄ nanocrystals displayed much stronger and sharper upconversion luminescence, and larger intensity ratios of red over green emissions relative to their cubic phase counterparts. The influence of the crystal phase on the upconversion emission properties was explored by use of excitation power dependence curves, dynamic fluorescence and Raman spectra. The results suggest that the cubic-to-hexagonal phase transition decreases the crystal field symmetry, and then enhances upconversion luminescence intensity by relaxing forbidden selection rules. The conversion into the hexagonal phase also increases the number of phonon modes, and consequently improves the phonon-assisted energy transfer efficiency from Yb³⁺ to Er³⁺, thus facilitating the output of red emissions.

Effect of Defect States on the Upconversion Emission Properties in KLu2F7 Nanocrystalline

The influence of the introduction of Li+ ions on the upconversion (UC) properties of KLu2F7:Yb3+, Er3+ nanocrystalline has been investigated in detail. It is found that the UC emission intensity of 10 mol% Li+ ions doped KLu2F7:Yb3+, Er3+ nanocrystalline is enhanced about 13 times in comparison with that of Li+-free sample. Under the excitation of 980 nm laser diode (LD), a significant improvement of the green to red emission ratio (GRR) in the 10 mol% Li+-doped sample is observed by increasing pump power density. Li+ ions could occupy the cationic sites or the interstitial sites in the KLu2F7 host matrix, which probably eliminate the defect states via the charge compensation and tailor of the crystal field, leading to the promotion of the UC emission efficiency. Thus, the introduction of Li+ ions provides new opportunities for enhancing the scope of applications of Yb3+, Er3+ doped KLu2F7 nanocrystalline ranging from infrared solar cells to volumetric multiplexed bio-probe.

Upconversion Emission Modification and White Light Generation in NaYF4:Yb3+, Er3+, Tm3+Nanocrystals/Opal Photonic Crystal Composites

In this paper, we fabricated NaYF 4:Yb 3+, Er 3+, Tm 3+ nanocrystal/opal photonic crystal composites by depositing NaYF 4:Yb 3+, Er 3+, Tm 3+ nanocrystals on the surface of opal photonic crystals, and we investigated the influence of photonic bandgaps on upconversion (UC) emission properties of NaYF 4:Yb 3+, Er 3+, Tm 3+ nanocrystals. When the photonic bandgaps overlapped with the UC emission bands of NaYF 4:Yb 3+, Er 3+, Tm 3+ nanocrystals on the opal photonic crystal surfaces, the suppression or enhancement of UC emissions was observed due to the Bragg reflection effect of photonic crystal, resulting in the modification of red, green, and blue UC emissions. Thus, white UC emission was realized.

Red to UV and blue up-conversion in alumina sol containing only Tm3+ or both Tm3+ and Yb3+ ions via low energy pumping

This paper reports the up-conversion emission properties of alumina sol containing only Tm3+ or both Tm3+ and Yb3+ ions under 650 nm pumping using a low power xenon lamp source. Two UV emission bands which centered at 349 nm for the 1I6 → 3F4 transition of Tm3+ ion and at 367 nm for the 1D2 → 3H6 transition of Tm3+ ion and two blue emission bands which centered at 457 nm for the 1D2 → 3H4 transition of Tm3+ ion and at 485 nm for the 1G4 → 3H6 transition of Tm3+ ion have been observed. The up-conversion emission follows a two-photon absorption process for both blue bands, and the UV band centered at 367 nm but follows a cross-relaxation process for the UV band centered at 349 nm. The concentration quenching effect is relatively low in this material under 650 nm pumping. Due to the back energy transfer from Yb3+ to Tm3+ ions, the intensity of UV emission corresponding to the 1I6 → 3F4 transition of Tm3+ ion is stronger in alumina sol samples containing both Tm3+ and Yb3+ ions than in which containing only Tm3+ ions.

Selectively enhanced up- and down-conversion emissions of Er3+ via Yb3+-Mn2+ dimer sensitizing in spinel MgGa2O4:Er3+,Yb3+,Mn2+

Selectively enhanced green upconversion (UC) and near-infrared (NIR) downconversion (DC) emissions of Er3+ by Yb3+-Mn2+ dimer sensitizing have been demonstrated in Er3+/Yb3+/Mn2+ tri-doped spinel MgGa2O4 upon excitation of 980nm laser diode (LD). By optimizing the doping rate of Mn2+, the intensity ratio of green to red UC emission intensities of Er3+ (G/R) could be enhanced about 10 times. Meanwhile, the 1.5μm NIR DC emission could also be increased about 3.6 times in this system. The DC and UC emission properties, UC mechanism, as well as the enhancing mechanism have been investigated and discussed in detail. A selectively enhancing mechanism based on Yb3+-Mn2+ dimer sensitizing is proposed to explain the selectively enhancing phenomena. This work could inspire the design of novel UC materials for various applications, such as temperature sensors and optical transmission, etc.

Green and Red Up-Conversion Luminescence of Er3+/Yb3+ Co-Doped 0.94Na0.5Bi0.5TiO3-0.06 BaTiO3 Ceramics

The Er3+/Yb3+ co-doped 0.94Na0.5Bi0.5TiO3-0.06BaTiO3 (NBT-BT:Er3+/Yb3+) cera-mics were synthesized by a traditional solid state reaction method. The XRD patterns show that all the ceramics are the single phase with perovskite structure. Under the excitation of 980 nm laser diode, the samples exhibit bright green up-conversion (UC) emission bands, which corresponds to the radiative transitions from (4S3/2,2H11/2) to 4I15/2, respectively. By tailoring the ratio of Er3+/Yb3+, the optimal UC emission properties were obtained in NBT-BT:0.01Er, 0.10Yb ceramics. The thermal behavior of UC emission in the ceramics was also investigated and the maximum sensitivity based on fluorescence intensity ratio (FIR) technology was approximately 0.0040K−1 at 502K. Moreover, ferroelectric and dielectric properties were enhanced with small amount of Er3+/Yb3+ co-doped. These ceramics, with excellent properties, may be a potential candidate in the application for electro-optical devices.

Enhanced up-conversion emissions in ZnO-LiYbO2:RE3+ (RE = Er or Ho) hybrid phosphors through surface modification

The ZnO-LiYbO2:RE3+ (RE = Er or Ho) hybrid phosphors were synthesized by a sol–gel method and then surface modified with ZnO via a seed deposition method. The structure, morphology and element distribution of the hybrid phosphors were studied by X-ray powder diffraction (XRD), field emission scanning electron microscope (FE-SEM) and energy dispersive X-ray spectroscopy (EDS), respectively. Under 980 nm excitation, the ZnO-LiYbO2:RE3+ (RE = Er or Ho) hybrid phosphors exhibited strong red or green dominated up-conversion (UC) emissions and the emission intensities were further dramatically enhanced after being surface modified with ZnO. The transform infrared (FT-IR) measurement indicated that surface states, including surface dangling bonds and surface defects, can greatly affect the UC emission properties. Further pump power dependence of UC emission intensity revealed that the two-photon processes were involved in the red and green emissions in both the ZnO-LiYbO2:Er3+ and the ZnO-LiYbO2:Ho3+ hybrid phosphors, and then the possible UC mechanisms were discussed.