Visible Upconversion Emission Research Articles

Exploring luminescence dynamics in Ce3+/Er3+ co-doped lithium zinc barium borate optical glasses: A study for advancing photonic technologies

Lithium zinc barium borate glasses were synthesized using the melt-quenching method and doped with Ce3+, Er3+, and their combination. The study examines the influence of Ce3+ on the photoluminescence of Er3+ in these glasses. X-ray diffraction confirmed the amorphous nature of both undoped and doped glasses, while Fourier-transform infrared spectroscopy showed the conversion of BO3 to BO4 units, and Raman spectroscopy indicated a phonon energy around 1136 cm−1. The Ce3+-doped glasses exhibited a blue emission at 447 nm due to the 5d→4f1 transition. Co-doping with Ce3+ and Er3+ led to decreased visible upconversion emissions but significantly enhanced near-infrared emissions at 1.53 μm. This enhancement is attributed to reduced non-radiative decay and improved energy transfer between Er3+ and Ce3+ ions, facilitated by the phonon energy of host glass. The 1.53 μm emission intensity in Ce3+/Er3+ co-doped glass was about 60% higher than in singly Er3+-doped samples, highlighting the potential of Ce3+ co-doping for broad amplification at 980 nm excitation.

Comparative upconversion emission studies in AF3: Tm3+/Yb3+ (A=La, Y and Gd) phosphor for latent fingermarks detection

In this work the effect of change of host lattice on upconversion emission properties of Tm3+/Yb3+ doped/codoped fluoride upconversion phosphor particle with host variations is discussed. Lanthanum (La), yttrium (Y) and gadolinium (Gd) based fluoride hosts are selected and Tm3+/Yb3+ ions combination is incorporated via chemical co-precipitation method. The structural and optical properties of developed systems is studied through FE-SEM, XRD, FTIR, Thermogravimetric analysis and visible upconversion emission. Further, these samples were utilised for latent fingermarks detection on different difficult surfaces. Results obtained are appreciable for security and forensic detection purposes.

Twofold increase in the sensitivity of Er3+/Yb3+ Boltzmann thermometer

Luminescence thermometry is the most versatile remote temperature sensing technique and can be employed from living cells to large surfaces and from cryogenic temperatures to the melting points of metals. Ongoing research aims to optimize the sensitivity of the ratio between the emission intensity from two coupled excited states. However, this approach is inherently limited to temperature-dependent processes involving only the excited states. Here, we develop a novel measurement technique, called luminescence intensity ratio squared (LIR2) for the Yb3+/Er3+ pair, that combines the temperature sensitivity of ground- and excited-state populations. We use Y3Al5O12:Er3+,Yb3+ nanoparticles as a promising model system with both visible and infrared emissions. To apply our method, we record two luminescence spectra at different excitation wavelengths and determine the LIR2 using one emission in each of the two spectra. The LIR2 testing with Y3Al5O12 nanoparticles showed a sensitivity increase of 70% in the visible region and an impressive 230% increase in the NIR region compared to the conventional LIR method. This enhances the measurement precision by a factor of 1.5–2.5. The LIR2 based on the visible upconversion emission is particularly useful for measurements of high temperatures, while the LIR2 based on the downshifted ∼1.5 μm emission may revolutionize temperature measurements of biological samples in the range of physiological temperatures.

Laser Pyrolysis Synthesis of Upconverting Lanthanide-Doped NaYF4 Nanocrystals for Anticounterfeiting Applications

Laser pyrolysis, an aerosol nanosynthesis technique, uses a 10.6 μm CO2 laser to rapidly heat precursors to induce decomposition and particle nucleation. A photosensitizing agent, usually SF6, absorbs the laser beam and transfers energy to the precursors. Here, we exploit the presence of SF6 in the system and use it as a safe source of fluorine to synthesize NaYF4 nanocrystals in a single-step process. NaYF4 is an excellent host for rare-earth ions to create upconverting nanocrystals (UCNCs) that absorb infrared photons and emit at shorter wavelength. We thus dope the NaYF4 nanocrystals during synthesis with ytterbium as a sensitizer and erbium, thulium, or holmium as an upconversion emitter. Each emitter produces upconversion emission at specific wavelengths in the visible spectral range after near-infrared light (∼980 nm peaked emission from laser diode) is absorbed by ytterbium followed by energy transfer to emitter. We then show that calcining these materials, in a simple second step, dramatically increases upconversion emission intensity. Finally, we optimize the laser pyrolysis process and postsynthesis calcination to produce the most intense emission at each emission color. We also show that these laser-synthesized UCNCs can be dispersed in a broad range of solvents and retain their visible upconversion emission. This dispersibility could be particularly valuable in creating inks for printing in anticounterfeiting applications. Proof-of-concept use of the synthesized UCNC for anticounterfeiting applications was demonstrated by drop-casting a dispersion of UCNC in stencils on paper, to create various luminescent patterns that were visible under irradiation by a 980 nm laser diode. Overall, this study demonstrates a promising vapor-phase route to rapid, single-step, continuous synthesis of lanthanide-doped fluoride nanomaterials for anticounterfeiting and related applications.

Perovskite-Sensitized Upconversion under Operando Conditions

Perovskite-sensitized upconversion (UC) has resulted in near-infrared-to-visible UC at solar-relevant fluxes. However, the successful implementation of UC devices into operating solar cells will result in exposure to similar environmental stressors as for the commercial photovoltaics (PVs), mainly elevated temperatures, and continuous irradiation. In this article, we investigated the effects of these two stressors, heat and light, on the triplet generation process at the perovskite/rubrene interface. Following exposure to both stressors, local discrepancies across the upconversion device were discovered. The first region showed changes to the morphology, and no detectable upconverted emission was observed. Through the combination of optical microscopy and spectroscopy, crystallization of the organic semiconductor layer, degradation of dibenzotetraphenylperiflanthene, and concurrent degradation of the perovskite sensitizer were found. These effects culminate in a reduction in both triplet generation and triplet–triplet annihilation. In the second region, no changes to the morphology were present and visible UC emission was observed following exposure to both stressors. To probe the triplet sensitization process at elevated temperatures, transient absorption spectroscopy was performed. The presence of the excited spin-triplet state of rubrene at 60 °C highlighted successful triplet generation even at elevated temperatures. This work emphasizes the challenges and continued potential for the integration of perovskite-sensitized UC into commercial photovoltaic devices.

Down conversion and efficient NIR to visible up-conversion emission analysis in Ho3+/Yb3+ co-doped tellurite glasses

A series of glasses with chemical composition (50−x−y) TeO2–30ZnO–10YF3–10NaF–xHo2O3–yYb2O3 (x=0.5 and y=0.5, 1.0, 3.0, 5.0mol%) were prepared by melt-quenching procedure. The absorption spectra, excitation, down conversion emission spectra, up-conversion (UC) emission spectra and decay time measurements were analyzed. In down conversion, the visible emission transition intensity associated with 5F4→5I8 (547nm), 5F5→5I8 (657nm), and 5F4→5I7 (755nm) of Ho3+ ions decreased with Yb3+ concentration due to the energy transfer (ET) process from Ho3+ to Yb3+ ions. In up-conversion, on exciting with 980nm diode laser beam, we observed a strong green (543nm) and red (657nm) UC emissions, that refers to the energy level transitions; 5F4 (5S2)→5I8 and 5F5→5I8 of Ho3+. The influence of excitation power on UC intensities studies revealed that the population at 5F4 (5S2) and 5F5 levels of Ho3+ ion occurs due to two-photon absorption process associated energy transfer from Yb3+ to Ho3+. The influence of Yb3+ doped concentration on UC was studied, and it is observed that both the green and red UC intensities improved significantly on increasing Yb3+ ions concentration.

Effect of silver nanoparticles on the visible upconversion emission of Er3+/Yb3+ co-doped SbPO4-GeO2 glasses

Rare earth-doped glasses are largely studied for developing new and efficient photonic devices. The influence of localized electric fields from the LSPR of metallic nanoparticles (MNP) on the rare-earth luminescent properties is a matter of study. This work describes the effect of Ag-MNP on the visible-upconversion emission of Er3+/Yb3+-co-doped SbPO4-GeO2 glass. Ag-MNP was obtained with an average size of ∼5 nm and a LSPR absorption band at 520 nm. A significant enhancement of the red emission (∼650 nm) of Er3+ as a function of Ag-MNPs content was observed. It showed silver nanocluster emission through excitation at infrared via energy transfer from Er3+ to the Ag nanoclusters. Photoluminescence spectroscopy revealed that longer heat treatment times increase the red emission and enhance the rapid depopulation of 4F9/2 level, reducing the lifetime by 57% due to the LSPR of Ag-MNPs in the vicinity of the Er3+ and Yb3+.

Novel insights on energy transfer processes in [Ce4+/Ce3+]-Er3+-doped tellurite glass

Previous works have been already reported on multiphonon-assisted non-resonant energy transfer in Ce3+-Er3+-doped tellurite glasses. However, it is not clear the mechanism of the radiative emission of Er3+ centered at 1530 nm. In this paper, we reported a better understanding of the mechanism of interactions between those two rare-earth ions via a systematic study. For that, we will explore the energy transitions between Ce4+/Ce3+ and Er3+ ions in a tungsten-tellurite glass to both emission (in the near infrared) and upconversion (in the visible) spectrum. Here, Ce4+ and Ce3+ were obtained in an Er3+-doped tellurite glasses via the addition of different concentrations of CeO2 as part of the composition of the samples. Emission spectrum, under a 980 nm excitation, giving rise to a series of interactions between Ce3+↔Er3+ resulting in: (i) a subtle increase of the Er3+ emission intensity in the near-infrared region for 0.1 mol% of CeO2, and then a decrease in the emission for higher CeO2 concentration in both cases without any significant increase in the bandwidth, and (ii) a decrease of the visible upconversion emission intensity with the addition of CeO2. Such interactions are achieved via a coupling yielding and energy transfer from both rare-earth ions.

Visible-near-Infrared Light-Driven Photocatalytic Characteristics of Er3+/Yb3+-Codoped BiOBr Upconverting Microparticles for Tetracycline Degradation.

To settle the unsatisfying efficiency and insufficient light harvesting ability of photocatalysts, we report on the development of Er3+/Yb3+-codoped BiOBr (BiOBr:Er3+/xYb3+) microparticles that were synthesized by a rational high-temperature solid-state reaction method. The prepared microcrystals exhibit high visible upconversion (UC) emissions with maximum intensities at x = 0.01 when excited by a 980 nm laser. Remarkably, the corresponding UC emission process is attributed to a two-photon absorption route. Furthermore, the photocatalytic activities of as-synthesized compounds were further evaluated through analyzing the visible-near-infrared light-triggered tetracycline degradation. Compared with BiOBr:Er3+ microparticles, BiOBr:Er3+/xYb3+ microparticles present superior photocatalytic properties and the optimal status is achieved when x = 0.05, in which h+, ·O2-, and ·OH active species contribute to the photocatalytic mechanism. Additionally, the designed microparticles exhibit better photocatalytic abilities than previously reported photocatalysts (i.e., TiO2, SnO2) upon full-spectrum light irradiation. These results reveal that Yb3+ codoping is able to not only enhance the UC emission properties of BiOBr:Er3+ microparticles but also reinforce their photocatalytic activities. Our findings may put forward a facile strategy to regulate the photodegradation capacity of photcatalysts.

Enhanced upconversion emission in Er3+/Yb3+-codoped Al2Mo3O12 microparticles via doping strategy: Towards multimode visual optical thermometer

To explore highly sensitive luminescent materials, a series of Er3+/Yb3+-codoped Al2Mo3O12 microparticles were prepared through a high-temperature solid-state reaction method. The phase structure, light harvest ability, morphology, and upconversion (UC) emission characteristics of these synthesized microparticles were investigated systematically. Excited at 980 nm, glaring visible UC emissions are gained in the developed specimens, in which the optimal doping content for Yb3+ is 7 mol% and the two-photon absorption process contributes to the UC emission mechanism. Based on the fluorescence intensity ratio technology, the thermometric properties of resultant microparticles are studied by analyzing the temperature-dependent green UC emissions of Er3+ arising from the thermal coupling energy levels. The maximum absolute and relative sensitivities of final products are 0.011 K-1 and 1.09% K−1, respectively, and they are barely influenced by Yb3+ contents. Besides, via exploring the lifetimes of 2H11/2 and 4S3/2 levels of Er3+ at various temperatures, the relative sensitivities of resultant microparticles are determined to be 0.27% and 0.26% K−1, respectively. Furthermore, the newly developed microparticles can be adopted to fabricate fluorescent ink to realize optical anti-counterfeiting and visual temperature monitoring. Our studies demonstrate that Er3+/Yb3+-codoped Al2Mo3O12 microparticles with strong UC emissions possess great potential for multimode visual optical thermometry applications.

Centimeter-Scale Curing Depths in Laser-Assisted 3D Printing of Photopolymers Enabled by Er3+ Upconversion and Green Light-Absorbing Photosensitizer

Photopolymer resins used in stereolithographic 3D printing are limited to penetration depths of less than 1 mm. Our approach explores the use of near-infrared (NIR) to visible upconversion (UC) emissions from lanthanide-based phosphors to initiate photopolymer crosslinking at a much higher depth. This concept relies on the use of invisibility windows and non-linear optical effects to achieve selective crosslinking in photopolymers. SLA resin formulation capable of absorbing light in the visible region (420–550 nm) was developed, in order to take advantage of efficient green-UC of Er3+/Yb3+ doped phosphor. NIR-green light UC shows versatility in enhancing curing depths in laser patterning. For instance, a structure with a curing depth of 11 ± 0.2 mm, cured width of 496 ± 5 µm and aspect ratios of over 22.2:1 in a single pass via NIR-green light UC. The penetration depth of the reported formulation approached 39 mm. Therefore, this technique would allow curing depths of up to 4 cm. Moreover, it was also demonstrated that this technique can initiate cross-linking directly at the focal point. This shows the potential of NIR-assisted UC as a low-cost method for direct laser writing in volume and 3D printing.

Eu3+ doped and Er3+/Yb3+ codoped glass ceramics containing NaLa(WO4)2 nanoparticles: Preparation, optical and temperature sensing properties

Eu3+ doped and Er3+/Yb3+ codoped glass ceramics containing NaLa(WO4)2 nanoparticles have been prepared and their optical and temperature sensing properties have been investigated. Strong diffraction peaks and elliptical NaLa(WO4)2 nanoparticles with well-defined lattice stripes are observed in the X-ray diffraction and transmission electronic microscope results, respectively. Great enhancement of the photoluminescence intensity of Eu3+ ions is observed owing to the selective entering of Eu3+ ions into the precipitated NaLa(WO4)2 nanoparticles. The improvement of visible upconversion emissions and near-infrared photoluminescence emissions of Er3+/Yb3+ ions are also attributable to the enrichment of Er3+/Yb3+ ions in the low phonon-energy NaLa(WO4)2 nanoparticles. The temperature dependence fluorescence intensity ratio was investigated and the temperature sensing characteristics was evaluated. The maximum temperature sensitivity Sa is 0.014K−1 at 476 K, which demonstrates Er3+/Yb3+ codoped NaLa(WO4)2:glass ceramic is one of the candidates for new optical temperature-sensing application.

Efficient near infrared to visible light upconversion from Er/Yb codoped PVDF fibrous mats synthesized using a direct polymer doping technique

Upconverting-materials are capable of converting near infra-red (NIR) excitation into lower wavelengths. These materials could have a myriad of promising potential applications. However, in some areas, its use has been hindered by its low upconversion luminescence (UCL) efficiency and processing/handling disadvantages from luminescent materials in powder form. This work presents a step towards overcoming this limitation, by developing polymer-based fiber membranes without adding external luminescent powders. Herein, we report on the synthesis of Yb3+ and Er3+ codoped polyvinylidene difluoride (PVDF) and its development into fiber membranes using the Forcespinning® technique. X-ray diffraction (XRD), Fourier transformed infrared (FTIR) spectroscopy were performed to confirm the phase formation, crystallinity and the presence of vibrational bands of the corresponding PVDF matrix. Scanning Electron microscopy (SEM) and thermogravimetric analysis were conducted to investigate the morphological and thermal properties of the codoped nanofibers while the X-ray photoelectron spectroscopy (XPS) showed efficient doping of the lanthanides in the PVDF fiber. Under exposure to 980 nm NIR illumination, the PVDF:Yb3+,Er3+ fibrous mats exhibited efficient UCL emission in the visible wavelength region (523, 540 and 656 nm). The observed results show a NIR to visible UCL process where the Yb3+ ions act as the sensitizer for the generation of visible upconversion emission from Er3+ ions through an excited state absorption (ESA) and two photon energy transfer (ET) mechanisms. The developed material further opens potential lighting and imaging related applications given the ease of preparation, handling, and flexibility of the developed membranes.

Visible and near infrared upconversion emission from Tm3+, Yb3+ ‎doped SrF2 nanoparticles

Tm3+, Yb3+-codoped SrF2 nanoparticles were synthesized through a facile hydrothermal ‎technique. Citrate ions were introduced as the capping agent into the reaction. Upconversion ‎nanoparticles were characterized by field emission scanning electron microscopy (FESEM), ‎Energy dispersive x-ray spectroscopy (EDS), x-ray diffraction (XRD), Dynamic light scattering ‎‎(DLS), Zeta potential, Fourier transform Infrared spectroscopy (Ft-IR), and the 980 nm laser induced ‎photoluminescence spectroscopy. Rare-earth ions (Na+), which are the cations of citrate salts, ‎are incorporated into the structure to act as charge compensators. Upconversion emission in the ‎visible and NIR region was observed by the 980 nm irradiation. Nanoparticles with a narrow size ‎distribution and a uniform morphology were directly dispersible in water, forming a quite transparent ‎suspension. Nanoparticles size was approximately 10 nm. High penetration of the Near-Infrared light into ‎the body tissue makes these nanoparticles appropriate for tumor targeting in the deeper tissues for ‎the purpose of bioimaging and photodynamic therapy‎.

Near-infrared responsive upconversion glass-ceramic@BiOBr heterojunction for enhanced photodegradation performances of norfloxacin

An efficient luminous and electronic energy transmission BiOBr based near-infrared (NIR) responsive heterojunction photocatalyst was successfully fabricated through growing BiOBr nanosheets on the superficial layer of the SrF2–Bi2O3–B2O3/Yb3+,Tb3+ (SBBF) upconversion glass-ceramic (GC) via a facile in-situ etching GC method (FIEG). A high norfloxacin (NOR) degradation rate of 56% was obtained under 180 min NIR light irradiation for the NIR GC photocatalyst (SBBF/BiOBr-10), and it possesses much enhanced photocatalytic activity compared with that of pure BiOBr under UV–vis–NIR light irradiation. Wherein six intermediate products were identified in the NOR photodegradation process and the possible degradation pathways were proposed. B3+, Yb3+ and Tb3+ ions in GC can be doped into BiOBr layer during the FIEG process. The core–shell structure of the GC@BiOBr heterojunction photocatalyst is in favor of increasing charge transport and reducing the recombination rate of excited carriers, and it efficiently harvests NIR photons to emit UV and visible light upconversion emissions, which can be utilized during the photocatalysis process. The photocatalyst can be facilely regenerated via HBr etching again, moreover, the low-cost and less time requirement promote the possibility of large-scale fabrication of the efficient photocatalysts.

Non-Linear Optical Properties of Er3+-Yb3+-Doped NaGdF4 Nanostructured Glass-Ceramics.

Transparent oxyfluoride glass–ceramics containing NaGdF4 nanocrystals were prepared by melt-quenching and doped with Er3+ (0.5 mol%) and different amounts of Yb3+ (0–2 mol%). The selected dopant concentration the crystallization thermal treatments were chosen to obtain the most efficient visible up-conversion emissions, together with near infrared emissions. The crystal size increased with dopant content and treatment time. NaGdF4 NCs with a size ranging 9–30 nm were obtained after heat treatments at Tg + 20–80 °C as confirmed by X-ray diffraction and high-resolution transmission electron microscopy. Energy dispersive X-ray analysis shows the incorporation of rare earth ions into the NaGdF4 nanocrystals. Near-infrared emission spectra, together with the up-conversion emissions were measured. The optical characterization of the glass–ceramics clearly shows that Er3+ and Yb3+ ions are incorporated in the crystalline phase. Moreover, visible up-conversion emissions could be tuned by controlling the nanocrystals size through appropriated heat treatment, making possible a correlation between structural and optical properties.

Temperature dependent fluorescence properties and mid-infrared random lasing emission in Ho3+ and Tm3+ co-doped lead lanthanum zirconate titanate ceramics

In this study, obvious up-conversion emission peaks centred at 553 nm and 696 nm were investigated in transparent Ho3+ and Tm3+ co-doped lead lanthanum zirconate titanate (PLZT) ceramics. Temperature dependent visible up-conversion emission and mid-infrared photoluminescence at approximately 2.0 μm were studied, and obvious luminous color modulation from yellow-green to red was observed. Energy transfer between Ho3+ and Tm3+ ions was studied by analyzing the suppression and enhancement of the emission peaks. Moreover, random lasing emission peaks at 1.95 μm were achieved with a full width at half maximum of 5 nm, which was desirable for developing mid-infrared lasers in ceramics materials.

Influence of transition metal ions: Broad band upconversion emission in thermally stable phosphors

Abstract Frequency upconversion (UC) study at different temperatures in Ho3+/Yb3+/Mn4+:SnO2 phosphors, prepared via solid state reaction method has been performed. The prepared phosphors have been characterized via XRD, Raman spectra, FESEM, EDAX, XPS and diffuse reflectance analysis. The decrease in bandgap has been reported due to codoping with Mn4+ ions in the developed phosphors. An enhancement of about 47 and 6 times in the green and red UC emission bands has been observed with the addition of Yb3+ ions. Moreover, incorporation of Mn4+ ions gives broad visible UC emission ranging from 400 nm to 900 nm. The mechanism responsible for the enhancement and broad band UC emission has been discussed on the basis of pump power dependence followed by the photon avalanche energy transfer process.

Near infrared to visible upconversion photoluminescence from Er/Yb co-doped MoS2 nanosheets with tunable thickness

Er/Yb co-doped MoS2 nanosheets exhibit efficient upconversion photoluminescence emission in the visible wavelength region at 524 nm, 541 nm, 650 nm and downconversion emission at 1124 nm under the excitation of 980 nm laser. These upconversion and downconversion emissions are proposed to be due to the 2H11/2 - 4I15/2 (524 nm), 4S3/2 - 4I15/2 (541 nm), 4F9/2 - 4I15/2 (650 nm) transitions of Er3+ and 2F5/2 → 2F7/2 (1124 nm) transition of Yb3+ ions respectively. It is also found that the Yb3+ ions play a significant role as a sensitizer for the generation of visible upconversion emission of Er3+ ions via excited state energy transfer mechanism. Further, the effects of the layer numbers in co-doped MoS2 on the upconversion photoluminescence properties are also evaluated. The MoS2 nanosheet possessing more number of layers fascinates stronger emission intensities due to the predominant crystal field effect.

Microwave hydrothermal synthesis and upconversion properties of BiVO4 nanoparticles

Nanomaterials are the subject of extensive investigations due to their applications in medicine, multimodal imaging, volumetric displays, and photonics. Here, lanthanide-doped bismuth vanadate (BiVO4) upconverting nanoparticles (UCNPs) have been reported. The nanoparticles have been synthesized by a microwave hydrothermal method. As-synthesized nanoparticles are highly crystalline in the tetragonal zircon phase with particles about 200 nm in size. Under 980 nm excitation, intense multicolor visible and near-infrared upconversion emissions are observed. Moreover, broadband infrared downshifting emissions are also observed. Time-resolved emission measurements have been carried out to investigate the involved upconversion and energy transfer mechanism. The BiVO4-based UCNPs may provide a new class of nanomaterials for multifunctional applications.