Energy Transfer Upconversion Processes Research Articles

Full-Spectrum Utilization of ZIF-67/Ag NPs/NaYF4:Yb,Er Photocatalysts for Efficient Degradation of Sulfadiazine: Upconversion Mechanism and DFT Calculation.

In this work, novel ternary composite ZIF-67/Ag NPs/NaYF4:Yb,Er is synthesized by solvothermal method. The photocatalytic activity of the composite is evaluated by sulfadiazine (SDZ) degradation under simulated sunlight. High elimination efficiency of the composite is 95.4% in 180min with good reusability and stability. The active species (h+, ·O2 - and ·OH) are identified. The attack sites and degradation process of SDZ are deeply investigated based on theoretical calculation and liquid chromatography-mass spectrometry analysis. The upconversion mechanism study shows that favorable photocatalytic effectiveness is attributed to the full utilization of sunlight through the energy transfer upconversion process and fluorescence resonance energy transfer. Additionally, the composite is endowed with outstanding light-absorbing qualities and effective photogenerated electron-hole pair separation thanks to the localized surface plasmon resonance effect of Ag nanoparticles. This work can motivate further design of novel photocatalysts with upconversion luminescence performance, which are applied to the removal of sulphonamide antibiotics in the environment.

Beam-profile compensation for quantum yield characterisation of Yb-Tm codoped upconverting nanoparticles emitting at 474 nm, 650 nm and 804 nm.

Upconverting nanoparticles (UCNPs) have found widespread applications in biophotonics and energy harvesting due to their unique non-linear optical properties arising from energy transfer upconversion (ETU) mechanisms. However, accurately characterising the power density-dependent efficiency of UCNPs using the internal quantum yield (iQY) is challenging due to the lack of methods that account for excitation beam-profile distortions. This limitation hinders the engineering of optimal UCNPs for diverse applications. To address this, this work present a novel beam profile compensation strategy based on a general analytical rate-equations model, enabling the evaluation of iQY for ETU processes of arbitrary order, such as ETU2, ETU3, and beyond. The method was applied to characterise the ETU2 and ETU3 processes corresponding to the main emission peaks (474 nm, 650 nm, and 804 nm) of a Yb-Tm codoped core-shell β-UCNP. Through this approach, the transition power density points (which delimit the distinct non-linear regimes of the upconversion luminescence (UCL)), and the saturation iQY values (which are reached at high excitation power densities above the transition points) were determined. The ETU2 process exhibits a single transition power density point, denoted as ρ2, while the ETU3 processes involve two transition points, ρ2 and ρ3. By compensating for the beam profile, we evaluate the iQY of individual lines across a wide dynamic range of excitation power densities (up to 105 W cm-2), encompassing both non-linear and linear regimes of UCL. This study introduces a valuable approach for accurately characterising the iQY of UCNPs, facilitating a deeper understanding of the upconversion and its performance. By addressing excitation beam-profile distortions, this method provides a comprehensive and reliable assessment of the power density-dependent iQY. The results highlight the applicability and effectiveness of this beam profile compensation strategy, which can be employed for a wide range of UCNPs. This advancement opens new avenues for the tailored design and application of UCNPs in various fields, especially for biophotonics.

Precise determination of energy transfer upconversion coefficient for the erbium and ytterbium codoped laser crystals.

Energy transfer upconversion (ETU) coefficient plays a crucial role in investigating complex laser systems as it greatly influences both the laser output behavior and heat generation. For some quasi-three-energy-level lasers based on Er3+ doped, Ho3+ doped and codoped gain media, the available theoretical studies relied on some unreasonable approximations due to the lack of spectroscopic data, notably the ETU coefficient. We put forward what we believe is a novel approach to overcome the difficulties caused by wavelength jump occurred in aforementioned laser systems. Based on net gain cross-section analysis and rate equations modelling, the functional relationship between the ETU coefficient, the laser power and pump power at the jumping wavelength are established. ETU coefficients and their temperature dependences of Er,Yb:YAB crystals with different crystal doped concentrations are experimentally determined for the first time. The results reveal that the ETU process in Er,Yb:YAB laser system is 5∼35 times stronger than that in Er3+ and Yb3+ codoped phosphate glass. The determination of these spectroscopic data paves the way for precise modelling of laser system based on Er,Yb:YAB or similar gain media.

Near-infrared to visible up-conversion in Er3+ doped LaAlO3 phosphors and their assessment as an optical temperature sensor

The present work studies the optical temperature sensing in micro and nanospheres of LaAlO3, synthesized by a Pechini sol-gel method. The optical properties focus on the up-conversion emission and optical temperature sensing properties of thermally and non-thermally coupled levels. Exciting at 975 nm, the up-conversion produces three emissions bands centered at 533, 545, and 670 nm. When the concentration of Er ion increases, the intensity of emission increases up to 5 %. The mechanism shows the absorption of two photons and the energy transfer up-conversion process. Optical temperature sensing is studied in the range of 299–327 K based on thermal coupled and non-thermal coupled levels by the luminescence intensity ratio technique. The absolute sensitivity, relative sensitivity, and uncertainty temperature values were obtained to study the material's performance and applicability. The maximum absolute and relative sensitivity values are 5.21 × 10−3 K−1 at 327 K for I670/I545 and 0.87 % at 299 K for I533/545. On the other hand, the temperature uncertainty is 0.2 K, indicating that the present material may be used as an effective temperature-sensing device using thermal coupled and non-thermal coupled levels.

33.8 W Mid-infrared 2.8 μm Er-doped fiber laser with high optical efficiency

We demonstrate an efficient, high-power single-end-pumped Er-doped ZBLAN (Er:ZBLAN) fiber laser operating at 2.8 μm. A maximum laser power of 33.8 W at a wavelength of 2.87 μm was achieved with an optical efficiency of 26.4 %. A maximum slope efficiency of 32.8 % was obtained, which approaches the Stokes efficiency of the intrinsic Er3+ energy transfer up-conversion process. We examine both experimentally and theoretically, the change in optical efficiency in relation to output coupling ratios, laser wavelength, and pump power. Simulations demonstrate that the Er:ZBLAN fiber laser system exhibits high gain at 2.8 μm, and red-shifting of the laser wavelength results in reduced laser field reabsorption and increased laser efficiency. To the best of our knowledge, this work demonstrates the highest output power generated from a single-end-pumped Er-doped fluoride fiber laser.

Influence of the laser crystal temperature on the intensity noise performance of solid-state lasers

The influence of the laser crystal boundary temperature on the intensity noise performance of solid-state lasers is theoretically investigated in this paper. The intensity noise spectra of a Nd:YVO4 laser with various laser crystal boundary temperatures are numerically simulated. The simulation results are qualitatively analyzed by normalizing the intensity noise spectra to the output powers of the laser upon considering the influence of the laser crystal temperature on the laser parameters. It is found that the intensity noise spectra of the laser below shot noise limit (SNL) moves to low frequency range and the resonant relation oscillation (RRO) frequency of the laser decreases from 765.93 to 524.61 kHz when tuning the laser crystal boundary temperature from 20 to 80 °C with a step of 10 °C. However, the amplitude of the RRO peak increases from 43.08 to 51.69 dB/Hz above the SNL, which can be ascribed to an enhanced non-radiation transition induced by the decreased stimulated radiation rate and the increased energy transfer upconversion process of the laser.

Frequency-Domain Method for Characterization of Upconversion Luminescence Kinetics.

The frequency-domain (FD) method provides an alternative to the commonly used time-domain (TD) approach in characterizing the luminescence kinetics of luminophores, with its own strengths, e.g., the capability to decouple multiple lifetime components with higher reliability and accuracy. While extensively explored for characterizing luminophores with down-shifted emission, this method has not been investigated for studying nonlinear luminescent materials such as lanthanide-doped upconversion nanoparticles (UCNPs), featuring more complicated kinetics. In this work, employing a simplified rate-equation model representing a standard two-photon energy-transfer upconversion process, we thoroughly analyzed the response of the luminescence of UCNPs in the FD method. We found that the FD method can potentially obtain from a single experiment the effective decay rates of three critical energy states of the sensitizer/activator ions involved in the upconversion process. The validity of the FD method is demonstrated by experimental data, agreeing reasonably well with the results obtained by TD methods.

Boosting Photo Upconversion in Electropolymerised Thin Film with Yb/Er Complexes

AbstractUpconversion luminescence (UCL) in organometallic complexes has attracted great interest in photovoltaics and biological applications due to their fascinating energy transfer mechanism from low‐energy photon to high‐energy photon. However, photon‐upconversion operating in a single discrete entity remains a challenge caused by low‐absorption cross section of the luminescent lanthanide element. Here, a novel upconversion system is reported combining Yb (Ytterbium) sensitizers and Er (Erbium) activators in the film by electropolymerization, which leads to excited‐state absorption (ESA) and energy transfer upconversion (ETU) processes. For the first time, the UCL has been achieved in the thin films upon near‐infrared laser irradiation, and the upconversion intensity exhibits up to 30‐fold enhancement with the variation of Yb/Er ratio.

Generalised analytical model of the transition power densities of the upconversion luminescence and quantum yield.

The quantum yield (QY) evaluation of upconverting nanoparticles (UCNPs) is an essential step in the characterisation of such materials. The QY of UCNPs is governed by competing mechanisms of populating and depopulating the electronic energy levels involved in the upconversion (UC), namely linear decay rates and energy transfer rates. As a consequence, at low excitation, the QY excitation power density (ρ) dependence obeys the power law ρn-1, where n represents the number of absorbed photons required for the emission of a single upconverted photon and determines the order of the energy transfer upconversion (ETU) process. At high power densities, the QY transits to a saturation level independent of the ETU process and the number of excitation photons, as a result of an anomalous power density dependence present in UCNPs. Despite the importance of this non-linear process for several applications (e.g., living tissue imaging and super-resolution-microscopy), little has been reported in the literature regarding theoretical studies to describe the UC QY, especially for ETUs with order higher than two. Therefore, this work presents a simple general analytical model, which introduces the concept of the transition power density points and QY saturation to characterise the QY of an arbitrary ETU process. The transition power density points determine where the power density dependence of the QY and the UC luminescence changes. The results provided in this paper from fitting the model to experimental QY data of a Yb-Tm codoped β-UCNP for 804 nm and 474 nm emissions (ETU2 and ETU3 processes, respectively) exemplify the application of the model. The common transition points found for both processes were compared to each other showing strong agreement with theory, as well as, compared to previous reports when possible.

Upconversion Yb3+/Er3+:La2Ti2O7 phosphors for solid-state lighting and optical thermometry

The solid-state reaction was employed as a suitable method to produce orthorhombic Yb3+/Er3+ co-doped La2Ti2O7 phosphors. The pump power and temperature dependencies of spectra of the Yb3+/Er3+ co-doped La2Ti2O7 were studied for color tunability and optical thermometry.The pump power significantly affected the color coordinates of the phosphors. The upconversion green light transformed to the broad white light at higher pump power. A two-photon transition was proposed to explain the upconversion energy transfer process. The fluorescence intensity ratio technique was used to calculate the optical temperature sensor sensitivities. The ΔE energy difference obtained from the intensity ratios of the thermally coupled 2H11/2 and 4I15/2 energy levels of Er3+ are 763.64 ± 76.62 cm−1, 777.77 ± 44.62 cm−1, 640.71 ± 137.39 cm−1 for La1.95Yb0.04Er0.01Ti2O7, La1.94Yb0.04Er0.02Ti2O7, and La1.93Yb0.04Er0.03Ti2O7, respectively. Absolute temperature sensitivities of the phosphors decreased with increasing Er3+ concentration. The maximum absolute sensitivity was determined to be 0.51x10-2 K−1 at 553 K for La1.95Yb0.04Er0.01Ti2O7, 0.64x10-2 K−1 at 571 K for La1.94Yb0.04Er0.02Ti2O7, and 0.38x10-2 K−1 at 457 K for La1.93Yb0.04Er0.03Ti2O7.

Role of energy transfer in concentrated Dy3+-doped fibers

Using high power quasi-cw pulse pumping, we show that energy transfer upconversion (ETU) processes in highly doped Dy3+ double clad ZBLAN fibers creates a pathway for significant excitation loss that clamps the gain. For a 4 mol.% Dy3+-doped fiber, we establish that the pump absorption is non-saturable up to a maximum launched (peak) pump power of 100 W. We propose that this arises from a co-operative three-ion ETU process. Additionally, the high power pulsed pumping of Tm3+, Dy3+-co-doped fiber produces laser relaxation spikes that appear after the pump pulse, suggesting that ETU dominates all other process during pumping.

Spectroscopy and Near-Infrared to Visible Upconversion of Er3+ Ions in Aluminosilicate Glasses Manufactured with Controlled Optical Transmission

In this work we report on the spectroscopic properties and the near-infrared to visible upconversion of Er3+ ions in aluminosilicate glasses manufactured by directionally solidification with the laser floating zone technique. Glasses were manufactured in a controlled oxidizing atmosphere to provide them with high optical transmission in the visible spectral range. Absorption and emission spectra, and lifetimes were assessed in both the visible and the near infrared spectral range. Green upconversion emissions of the 2H11/2→4I15/2 and 4S3/2→4I15/2 transitions at 525 nm and 550 nm attributed to a two-photon process were observed under excitation at 800 nm. Mechanisms responsible for the upconversion luminescence were discussed in terms of excited state absorption and energy transfer upconversion processes. Excitation spectra of the upconverted emission suggest that energy transfer upconversion processes are responsible for the green upconversion luminescence.

Influence of upconversion transition process on the performance of inband pumped holmium-doped silica fiber amplifiers

In this report, a theoretical model of in-band pumped holmium-doped silica fiber amplifiers (HDFAs) is presented. This model is developed to consider the influence of energy transfer up-conversion (ETU) on the HDFAs performance. The advantage of this model is to investigate the properties of HDFAs as a function of holmium-doped fiber length and doping concentration. A good agreement is observed between the simulation results and the previous experimental findings. Our simulation results show the negative impact of ETU process to deteriorate the HDFAs performance and this process may have bigger effect at high holmium doped concentration. This is the first time to our knowledge that the influence of upconversion process is theoretically investigated on the performance of in-band pumped HDFAs.

Near-infrared light-mediated Er3+ and Yb3+ co-doped CaTi4O9 for optical temperature sensing behavior

In present report, CaTi4O9: 1 at% Er3+, 1 at% Yb3+ phosphors have been synthesized via sol-gel method and reported herein for its temperature sensing performance. XRD spectra confirms high crystallinity and successful inclusion of rare earth (RE) ions into CaTi4O9 as the dopant ions do no induce any change in the peak position. The X-ray diffraction analysis indicates that the host calcium titanate exhibits hexagonal crystal structure. The green up-conversion (UC) emission observed using 980 nm diode laser excitation. Since, Er3+ ion has ladder type energy levels, thereby it receives energy from Yb3+ ion by excited state absorption and energy-transfer up-conversion processes. Furthermore, the Er3+ ion has two temperature sensing levels 4S3/2→4I15/2 (550 nm) and 2H11/2→4I15/2 (525 nm). Therefore, temperature dependent up-conversion spectra illustrate good temperature sensitivity for present phosphor. The sensitivity of above mentioned phosphor has been evaluated with temperature from 300K to 500K, which shows the suitability of the phosphor for developments in temperature thermometry.

Experimental investigation of mid-infrared Er:ZBLAN fiber laser

In this contribution the diode pumped high-power Er:ZBLAN laser operating at around 2.8 µm is reported. The laser produces 2 W output power with the slope efficiency of 24 % measured with respect to the incident pump power. Full Text: PDF ReferencesS. D. Jackson, "Towards high-power mid-infrared emission from a fibre laser", Nature Photonics 6, 423 (2012). CrossRef V. Portosi, D. Laneve, C. M. Falconi, and F. Prudenzano, "Advances on Photonic Crystal Fiber Sensors and Applications", Sensors 19, (2019). CrossRef M. C. Falconi, D. Laneve, and F. Prudenzano, "Advances in Mid-IR Fiber Lasers: Tellurite, Fluoride and Chalcogenide", Fibers 5, 23 (2017). CrossRef M. Michalska, P. Grześ, J. Świderski, "High power, 100 W-class, thulium-doped all-fiber lasers", Phot. Lett. Poland, 11, 109 (2019). CrossRef Y. O. Aydin, V. Fortin, R. Vallée, and M. Bernier, "Towards power scaling of 2.8 μm fiber lasers", Opt. Lett. 43, 4542 (2018). CrossRef S. Crawford, D. D. Hudson, and S. D. Jackson, "High-Power Broadly Tunable 3- μm Fiber Laser for the Measurement of Optical Fiber Loss", IEEE Photonics Journal 7, 1 (2015). CrossRef V. Fortin, F. Jobin, M. Larose, M. Bernier, and R. Vallée, "10-W-level monolithic dysprosium-doped fiber laser at 3.24 μm", Opt. Lett. 44, 491 (2019). CrossRef L. Sójka, et al., "Experimental Investigation of Mid-Infrared Laser Action From Dy3+ Doped Fluorozirconate Fiber", IEEE Photon. Technol. Lett. 30, 1083 (2018). CrossRef M. Pollnan and S. D. Jackson, "Erbium 3 /spl mu/m fiber lasers", IEEE J. Sel. Top. in Quantum Electron., 7, 30 (2001). CrossRef Y. O. Aydin, F. Maes, V. Fortin, S. T. Bah, R. Vallée, and M. Bernier, "Endcapping of high-power 3 µm fiber lasers", Opt. Express 27, 20659 (2019). CrossRef C. A. Schäfer, "Fluoride-fiber-based side-pump coupler for high-power fiber lasers at 2.8 μm", et al., Opt. Lett. 43, 2340 (2018). CrossRef O. Henderson-Sapir, J. Munch, and D. J. Ottaway, "New energy-transfer upconversion process in Er3+:ZBLAN mid-infrared fiber lasers", Opt. Express 24, 6869 (2016). CrossRef F. Maes, V. Fortin, S. Poulain, M. Poulain, J.-Y. Carrée, M. Bernier, and R. Vallée, "Room-temperature fiber laser at 3.92 μm", Optica 5, 761 (2018). CrossRef R. I. Woodward, M. R. Majewski, D. D. Hudson, and S. D. Jackson, "Swept-wavelength mid-infrared fiber laser for real-time ammonia gas sensing", APL Photonics 4, 020801 (2019). CrossRef M. Kochanowicz, et al., "Near-IR and mid-IR luminescence and energy transfer in fluoroindate glasses co-doped with Er3+/Tm3+", Opt. Mater. Express 9, 4772 (2019). CrossRef M. Kochanowicz, et al., "Sensitization of Ho3+ - doped fluoroindate glasses for near and mid-infrared emission", Optical Materials 101, 109707 (2020). CrossRef J. Wang, X. Zhu, M. Mollaee, J. Zong, and N. Peyhambarian, "Efficient energy transfer from Er3+ to Ho3+ and Dy3+ in ZBLAN glass", Opt. Express 28, 5189 (2020). CrossRef M. C. Falconi, D. Laneve, V. Portosi, S. Taccheo, and F. Prudenzano, "Design of a Multi-Wavelength Fiber Laser Based on Tm:Er:Yb:Ho Co-Doped Germanate Glass", J Lightwave Technol 1 (2020). CrossRef K. Anders, A. Jusza, P. Komorowski, P. Andrejuk, and R. Piramidowicz, "Short wavelength up-converted emission studies in Er3+ and Yb3+ doped ZBLAN glasses", J. Lumin. 201, 427 (2018). CrossRef P. Komorowski ,K. Anders ,U. Zdulska,R. Piramidowicz R. "Erbium doped ZBLAN fiber laser operating in the visible - feasibility study", Photonics Lett Pol 9, 85 (2017). CrossRef J. Swiderski, M. Michalska, and P. Grzes, "Broadband and top-flat mid-infrared supercontinuum generation with 3.52 W time-averaged power in a ZBLAN fiber directly pumped by a 2-µm mode-locked fiber laser and amplifier", Applied Physics B 124, 152 (2018). CrossRef V. Fortin, M. Bernier, S. T. Bah, and R. Vallée, "30 W fluoride glass all-fiber laser at 2.94 μm", Opt. Lett. 40, 2882 (2015). CrossRef

Revisiting the Luminescence Decay Kinetics of Energy Transfer Upconversion.

Energy transfer upconversion (ETU) can efficiently upconvert near-infrared photons into higher-energy photons. Although a comprehensive understanding of ETU is fundamental to the design of ETU materials, the basic excited-state decay kinetics of ETU remains a complicated problem. Here we unravel the mechanism underlying ETU decay in benchmark β-NaYF4:Er3+ and β-NaYF4:Ln3+/Yb3+ (Ln = Er, Ho, Tm) ETU microcrystals by combining rate equation analyses with ETU decay measurements. The results show that all of the excited states of one ETU system decay concordantly, with the ETU decay of the emitting state determined by only its intrinsic decay and the product of the ETU decays of the two intermediate states directly responsible for the emitting-state photon upconversion. This general mechanism may serve as a basic rule for excited-state kinetics in upconversion microparticles and nanoparticles, which could provide detailed insight into ETU processes and guide the design of efficient ETU materials.

High power, 100 W-class, thulium-doped all-fiber lasers

In this work, sub-kilowatt, compact thulium-doped fiber laser systems, operating at a wavelength of 1940 nm, have been presented. The continuous-wave laser power generated out of a single oscillator was 90 W with a slope efficiency of 56.7%. Applying a master oscillator – power amplifier configuration, an output power of 120.5 W with a slope efficiency of 58.2% was demonstrated. These are the first results of the works aimed at developing kW-class “eye-safe” laser systems in Poland. Full Text: PDF ReferencesZ. Liu, et al., "Implementing termination analysis on quantum programming", Sci. China Inf. Sci. 62, 41301 (2019) CrossRef S. D. Jackson, A. Sabella, D.G Lancaster, "Application and Development of High-Power and Highly Efficient Silica-Based Fiber Lasers Operating at 2 μm", IEEE J. Sel. Top. Quantum Electron. 13, 567, (2007). CrossRef E. Russell, N. Kavanagh, K. Shortiss, and F. C. G. Gunning, "Development of thulium-doped fibre amplifiers for the 2μm waveband", Proc. SPIE 10683, 106832Q (2018) CrossRef P. Peterka, B. Faure, W. Blanc, M. Karásek, and B. Dussardier, "Theoretical modelling of S-band thulium-doped silica fibre amplifiers", Opt. Quantum Electron. 36, 201 (2004) CrossRef M. Eichhorn, "Pulsed 2 μm fiber lasers for direct and pumping applications in defence and security", Proc. SPIE 7836, 78360B (2010). CrossRef O. Traxer and E. X. Keller, "Thulium fiber laser: the new player for kidney stone treatment? A comparison with Holmium:YAG laser", World J. Urol. 2019 Feb 6. doi: 10.1007/s00345-019-02654-5 CrossRef S. Das, "Optical parametric oscillator: status of tunable radiation in mid-IR to IR spectral range based on ZnGeP2 crystal pumped by solid state lasers", Opt. Quant. Electron. 51, 70 (2019) CrossRef M. Michalska, P. Hlubina, and J. Swiderski, "Mid-infrared Supercontinuum Generation to ∼4.7 μm in a ZBLAN Fiber Pumped by an Optical Parametric Generator", IEEE Photon. J 9, 3200207 (2017) CrossRef https://www.ipgphotonics.com DirectLink M.D. Burns, P. C. Shardlow, P. Barua, T. L. Jefferson-Brain, J. K. Sahu, and W. A.Clarkson, "47 W continuous-wave 1726 nm thulium fiber laser core-pumped by an erbium fiber laser", Opt. Lett. 44, 5230 (2019) CrossRef S.D. Jackson, "Cross relaxation and energy transfer upconversion processes relevant to the functioning of 2 μm Tm3+-doped silica fibre lasers", Opt. Commun. 230, 197 (2004). CrossRef X. Wang, P. Zhou, X. Wang, H. Xiao, and L. Si, "102 W monolithic single frequency Tm-doped fiber MOPA", Opt. Express 21, 32386 (2013) CrossRef K. Yin, R. Zhu, B. Zhang, G. Liu, P. Zhou, and J. Hou, "300 W-level, wavelength-widely-tunable, all-fiber integrated thulium-doped fiber laser", Opt. Express 24, 11085 (2016) CrossRef G. D. Goodno, L. D. Book, and J. E. Rothenberg, "600-W, single-mode, single-frequency thulium fibre laser amplifier", Proc. SPIE 7195, 71950Y (2009). CrossRef T. Ehrenreich, R. Leveille, I. Majid, K. Tankala, G. Rines, and P. Moulton, "1-kW, all-glass Tm: fiber laser", Proc. SPIE 7580, 1 (2010) DirectLink M. Michalska et al., "Highly stable, efficient Tm-doped fiber laser—a potential scalpel for low invasive surgery", Laser Phys. Lett. 13, 115101 (2016). CrossRef

Directly diode-pumped mid-infrared dysprosium fiber laser.

We report the demonstration of a Dy3+-doped ZBLAN fiber laser directly diode-pumped at 800nm utilizing a codoping scheme with Tm3+ serving as the donor ion. In this initial demonstration, a modest output power of 12mW is generated with a slope efficiency of 0.3% at an emission wavelength of 3.23μm. Energy transfer dynamics are investigated through excited state lifetime analysis and comparison to resonant pumping of the Dy3+ upper state. The likely presence of an energy transfer upconversion process is identified, which has an undesirable effect on 3μm class lasers but may be of significant benefit for future 4μm systems.

Super-quadratic upconversion luminescence among lanthanide ions.

We explore the arguably most fundamental aspect of energy-transfer upconversion (ETU), namely the dependence of upconversion luminescence from a higher-energy level, following ETU excitation from a metastable lower-energy level, on direct luminescence from that metastable level. We investigate ETU among neighboring Nd3+ ions in single crystals of GdVO4 and LaSc3(BO3)4 with different doping concentrations by measuring, after short-pulse laser excitation with different pump energies, the infrared luminescence decay from the metastable 4F3/2 level and the yellow upconversion luminescence decay from the 4G7/2 level. We observe a highly super-quadratic dependence of upconversion on direct luminescence intensity. We conclude that the commonly assumed quadratic law of ETU, as proposed by Grant's model and frequently employed in rate-equation simulations, is inadequate to the description of ETU processes. Whereas Zubenko's model, which considers a finite migration rate, provides significantly better fits to the experimental luminescence-decay curves, also this model cannot accurately reproduce the measured decay curves, partly because it does not take the non-homogeneous distribution of active ions into account.

Improved Red Emission and Short-Wavelength Infrared Luminescence under 808 nm Laser for Tumor Theranostics.

In this research, a multimodal imaging platform guided photodynamic theranostics under 808 nm was designed using a NaErF4:Tm@NaYF4:Yb@NaLuF4:Nd,Yb-ZnPc structure. Unlike conventional codoped Yb3+/Er3+ system, Er3+ ions as activator and sensitizer were used to improve the up-conversion energy transfer processes. Furthermore, higher energy transfer processes between Er3+ ions could be obtained through doped 1% Tm3+ ions as an energy trapping center in the NaErF4. This platform could emit much brighter upconversion luminescence (UCL) (124-fold enhancement for red emission) and short wavelength infrared (SWIR) emission under single 808 nm laser excitation. Importantly, the SWIR imaging with higher resolution and better signal-to-noise ratio can pass the blood-brain barrier to see the brain vessels. Because of the enhanced red emission, the UCL nanoparticles were combined with ZnPc agent to exhibit photodynamic therapy (PDT) effect, and its distribution and excretion could be detected by the photoacoustic (PA) imaging under single near-infrared (NIR) laser. Thus, this platform could be used as multimodal imaging (SWIR, PA, CT, and UCL) guided PDT agent under single 808 nm laser.