Infrared Upconversion Research Articles

(Invited) Surface State Modulation of Colloidal Quantum Dots and Construction of Quantum Dot Based Infrared Detectors

Near-infrared photodetection and imaging devices play an important role in fields such as biological detection, information communication, military meteorology, etc. Traditional imaging devices require integration with readout circuits, and the complex integration process limits the development of infrared imaging systems. Lead sulfide colloidal quantum dots have excellent photoelectric properties in the infrared region, with a tunable bandgap width ranging from 0.4 to 1.5 eV, and spectral response covering below 2400 nm. Lead sulfide quantum dot films exhibit high absorption coefficients in the infrared region and excellent carrier mobility. In recent years, the performance of infrared detectors based on quantum dot systems has rapidly improved, and they are expected to develop into a new type of infrared detection and imaging technology. The speaker's team has combined infrared quantum dots with visible light quantum dots to prepare a simple, low-cost, and efficient infrared upconversion imaging device. By using the method of inducing band bending through interface electron storage, the efficiency of carrier tunneling and photon conversion has been improved, and the application of this technology in biological imaging has been preliminarily demonstrated. This report will introduce the development of quantum dot infrared detection materials and devices in recent years, as well as the research progress of the speaker's team in this area.

Dual Emission Bands of a 2D Perovskite Single Crystal with Charge Transfer State Characteristics.

Several hybrid halide 2D-perovskite species emit light with an emergent and controversial broadband emission Stokes-shifted down from the narrow band emission. This paper uncovers the sub- and above-bandgap emission and absorption characteristics of PEA2PbI4 prepared with gap states introduced during single crystal growth. Here, gap states led to coexistent intrinsic and heterostructured electronic frameworks that are selectively accessible with ultraviolet (UV) and infrared (IR) light, respectively, resulting in the phenomenon of photoluminescence (PL) switching from narrowband green to broadband red. Electron-energy dependent cathodoluminescence shows a relative increase in the broadband red PL intensity as the electron penetration depth increases from 30 nm to 2 μm, confirming the heterostructured framework is formed in the bulk of the crystal. Excitation-emission power slope of 2.5 and up-conversion pump transient absorption (TA) spectra suggest that the IR up-conversion excitation with red photoluminescence, peaked at 655 nm, is a multiphoton process occurring in the heterostructured framework through a nonlinear optical response. The energetic pathways toward the dual emission bands are revealed by pump-probe transient absorption spectroscopy, showing energetically broad gap states with high sensitivity to an IR pump are upconverted and subsequently quickly relax from high to low energy levels within 4 ps. Furthermore, the up-conversion red PL demonstrates a linear polarization with magnetic field effects, thus affirming that the band-like heterostructured framework is crystallographically aligned with characteristics of spatially extended charge-transfer states.

Highly Efficient Sum‐Frequency Generation in Niobium Oxydichloride NbOCl2 Nanosheets

AbstractParametric infrared (IR) upconversion is a process in which low‐frequency IR photons are upconverted into high‐frequency ultraviolet/visible photons through a nonlinear optical process. It is of paramount importance for a wide range of security, material science, and healthcare applications. However, in general, the efficiencies of upconversion processes are typically extremely low for nanometer‐scale materials due to the short penetration depth of the excitation fields. Here, parametric IR upconversion processes, including frequency doubling and sum‐frequency generation, are studied in layered van der Waals NbOCl2. An upconversion efficiency of up to 0.004% is attained for the NbOCl2 nanosheets, orders of magnitude higher than previously reported values for nonlinear layered materials. The upconverted signal is sensitive to layer numbers, crystal orientation, excitation wavelength, and temperature, and it can be utilized as an optical cross‐correlator for ultrashort pulse characterization.

Electronic transition pathways in energy transfer processes for upconversion photoluminescence of Yb3+/Ho3+ co-doped NaLa(MoO4)2 microcrystals

In recent years, upconversion photoluminescent micro/nanocrystals with unique anti-Stokes luminescence properties have shown high application value in many relevant fields. In this work, pure tetragonal phase NaLa(MoO4)2:Yb3+/Ho3+ microspheres have been synthesized by a solvothermal method in the presence of oleic acid and 1-octadecene. Under the excitation of 980 nm laser, NaLa(MoO4)2:Yb3+/Ho3+ microcrystals emit red, green and near infrared upconversion luminescence with peak wavelengths at 660/643 nm, 541 nm, and 756 nm. Based on the analysis of excitation power-dependent upconversion luminescence intensities and energy level diagram of Yb3+/Ho3+, electronic transition pathways in the energy transfer processes for upconversion luminescence of NaLa(MoO4)2:Yb3+/Ho3+ microcrystals are studied. For red upconversion luminescence at 660/643 nm, the predominant population pathway to state 5F5 (Ho3+) is “Yb3+ (2F5/2) + Ho3+ (5I7) → Yb3+ (2F7/2) + Ho3+ (5F5)”. While, “Yb3+ (2F5/2) + Ho3+ (5I6) → Yb3+ (2F7/2) + Ho3+ (5F4/5S2)” process accounts for the population of state 5F4/5S2 (Ho3+) for radiative transitions of upconversion luminescence at 541 and 756 nm. Energy back transfer contributes to the intense red upconversion luminescence at 660/643 nm. These electronic transition pathways in energy transfer processes are further confirmed by the analyses based on energy level mismatch and luminescent lifetimes.

Upconversion luminescence and non-contact optical temperature sensing in Ho3+-doped 0.94Na0.5Bi0.5TiO3-0.06BaTiO3 lead-free ceramics

A series of Ho3+-doped 0.94Na0.5Bi0.5TiO3-0.06BaTiO3 lead-free piezoelectric ceramics (NBT-0.06BT: xHo3+, 0.0025≤x ≤ 0.03) are prepared by a conventional solid-state reaction method. Under the excitation of 980 nm, all the samples exhibit strong green, red and near infrared upconversion emissions, which are ascribed to the 5F4/5S2→5I8 (∼547 nm), 5F5→5I8 (∼656 nm), 5F4/5S2→5I7 (∼756 nm) transitions of Ho3+ ions, respectively. The NBT-0.06BT: 0.015Ho3+ ceramic displays the optimal emission among these Ho3+-doped NBT-0.06BT solid solutions. Optical thermometry behavior is evaluated via fluorescent intensity ratio (FIR) of green to red emissions of Ho3+ ions. The temperature sensing performances is investigated in the temperature range of 293–473 K based on non-thermally coupled levels (NTCL). The maximum relative sensitivity is found to be 0.35% K−1 at 293 K. The present investigation results imply the promising application of NBT-0.06BT: Ho3+ in non-contact optical thermometers.

A novel upconversion luminescence temperature sensing material: Negative thermal expansion Y2Mo3O12:Yb3+, Er3+ and positive thermal expansion Y2Ti2O7:Yb3+, Er3+ mixed phosphor

Thermal enhancement and quenching of upconversion luminescence of rare earth ions can be realized in the negative expansion and positive expansion hosts, respectively, which is advantage of temperature sensing applications. In this work, the negative expansion Y2Mo3O12:Yb3+, Er3+ and positive thermal expansion Y2Ti2O7:Yb3+, Er3+ phosphors were prepared, respectively. The temperature dependence of upconversion luminescence demonstrated that the green, red and near infrared upconversion luminescence of Y2Mo3O12:Yb3+, Er3+ phosphor increases with the increasing of temperature, while the upconversion luminescence of Y2Ti2O7:Yb3+, Er3+ phosphor decreases upon the 980 nm laser excitation. A novel upconversion luminescence temperature sensor was obtained by the intensity ratio of the upconversion luminescence of negative thermal expansion Y2Mo3O12:Yb3+, Er3+ to the upconversion luminescence of positive thermal expansion Y2Ti2O7:Yb3+, Er3+. The near infrared-red fluorescence intensity ratio (FIR) (I860/I675) was researched in the range from 293 K to 574 K, which suggests that FIR increases with rising temperature. The maximum relative sensitivity (Sr) was 1.61% K−1 in near infrared-red FIR (I860/I675) at 293 K. The result suggests that the mixed phosphor exhibits potential application as a new temperature sensing device.

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.

Broadband-sensitive up-conversion phosphor of Ni2+,Tm3+ co-doped LiGa5O8

Ni2+, Tm3+ co-doped LiGa5O8 phosphors have been synthesized by solid state reaction method. It is found that the Ni2+ ions can absorb excitation light in region of 850–1300 nm and then sensitize the Tm3+ ions by successive radiation–reabsorption energy transfers. Consequently up-conversion emission of Tm3+ at 800 nm can be observed excited by light in the 850–1300 nm wavelength range. The novel broadband-sensitive near infrared up-conversion material developed in this work offers a possible route towards surpassing the limiting conversion efficiency of GaAs or CdTe based single junction solar cells, and possibly enables new applications in sub-bandgap detector sensitization and many more.

Nd3+/Yb3+ codoped SrWO4 for highly sensitive optical thermometry based on the near infrared emission

In this paper, Nd3+/Yb3+ codoped SrWO4 phosphors for temperature sensing are investigated. Firstly, the doping ratio of Nd3+ and Yb3+ was optimized. Then, under a 980 nm excitation, the temperature response of the near infrared (NIR) upconversion emission spectra in the temperature range of 313 K–453 K was characterized. The results show that the NIR emission peaks increase notably with the increase of temperature. With the fluorescence intensity ratio (FIR) technique, thermal sensing property of the optimized phosphor was investigated. A maximum thermal sensitivity of 0.02857 K−1 (I801/I869) at 453 K was achieved, which is higher than that of the other previously reported similar materials. The minimum temperature uncertainty is about 1 K at 453 K. The results reveal that SrWO4: Nd3+/Yb3+ is a promising material for optical thermometry.

Multicolor-tunable upconversion emission of lanthanide doped 12CaO·7Al2O3 polycrystals

A novel multicolor-tunable lanthanide doped 12CaO·7Al2O3 (Ln3+:C12A7; Ln3+ = Yb3+, Tm3+ and Er3+) synthesized by solid-state reaction method would greatly enhance the scope of its applications ranging from infrared solar cells to field emission display. The scanning electron microscopy (SEM) was used to characterize the morphology of Ln3+:C12A7. Under 980 nm excitation, the emission color was tuned from green-yellow to red region through adjusting the concentrations of Ln3+ ions. The obtained near infrared upconversion (UC) emissions in Ln3+:C12A7 was corresponded to “window of optical transparency”. All blue, green and red UC emissions were populated by one-photon process, and the proposed UC mechanisms were studied in Ln3+:C12A7.

La2O2SO4:RE/Yb new phosphors for near infrared to visible and near infrared upconversion luminescence (RE=Ho, Er, Tm)

AbstractThe 3 new upconversion (UC) phosphors of La2O2SO4:RE/Yb (RE=Ho, Er, and Tm, respectively) were derived via facile dehydration of their layered hydroxide precursors that were hydrothermally synthesized at 100°C. Rietveld XRD refinement found contracting cell dimension with decreasing RE3+ size, confirming the direct crystallization of solid solution. The Er3+ and Ho3+ activators both exhibited simultaneous green and red (dominant) emissions under 978‐nm near‐infrared (NIR) laser excitation (NIR‐Vis UC). Particularly, Tm3+ produced a Gaussian‐shaped pure NIR emission band at ~812 nm via its 3H4 → 3H6 transition (NIR‐NIR UC), which is highly desired for NIR biological application. Analysis of the excitation‐power dependent UC properties manifested a 3‐photon mechanism for the 3 phosphors, and the possible photon reactions leading to UC were illustrated.

Thermometry properties of Er, Yb–Gd2O2S microparticles: dependence on the excitation mode (cw versus pulsed excitation) and excitation wavelength (980 nm versus 1500 nm)

Herein, we present a first report on the luminescence thermometry properties of Er, Yb doped Gd2O2S microparticles under near infrared up-conversion excitation at 980 and 1500 nm measured in the 280–800 K interval. The thermometry properties are assessed using both cw and ns pulsed excitation as well as tuning the excitation wavelength across Yb and Er absorption profiles. For low cw (300 mW cm−1) and pulsed ns (400 ÷ 550 mW cm−1) excitation modes, no thermal load is observed. At room-temperature (280 K), the maximum relative sensitivity values are comparable under pulsed excitation at 980 and 1500 nm, around ∼0.01 and ∼0.008% K−1, respectively. In addition, a relative intense up-conversion emission at 980 nm under excitation at 1500 nm is measured. Our findings evidence attractive up-conversion and thermometry properties Er, Yb doped Gd2O2S under near-infrared excitation and highlight the need to explore further these properties in the nanoparticulate regime.

NIR upconversion characteristics of carbon dots for selective detection of glutathione

In the current study, we report the near infrared (NIR) upconversion (in the range of 850–950 nm) properties of carbon nanoparticles and their utility as a fluorescence probe for selective and sensitive detection of glutathione (GSH).

Visible and near infrared upconversion photoluminescence from Y2O3:Er3+, Yb3+, Li+ phosphors under 1532 nm excitation light

Visible and near-infrared upconversion luminescence from Y2O3 co-doped with Er3+, Yb3+ and Li+ phosphors under continuous excitation with 1532 nm light are reported. The upconversion emissions at 530–570 nm (green light emission region), and 640–700 nm (red light emission region) correspond to transitions from the 4S3/2to4I15/2and (4F9/2 + 4I9/2) to 4I15/2 electronic energy levels of the Er3+ ions respectively. The near infrared emissions at 900–1100 nm region correspond to inter-electronic energy levels transitions from 4I11/2 to 4I15/2 of Er3+ ions and 2F5/2 to 2F7/2 of Yb3+ ions. The role of Li+ and Yb3+ ions were to enhance the luminescence emission of these phosphors around 9, 7 and 11 times, respectively in comparison with only-erbium doped samples. The luminescence spectra of these phosphors remain unchanged when dispersed in deionized water, cholesterol and in bovine serum.

Enhanced energy transfer in heterogeneous nanocrystals for near infrared upconversion photocurrent generation.

The key to produce inorganic heterogeneous nanostructures, and to integrate multiple functionalities, is to enhance or at least retain the functionalities of different components of materials. However, this ideal scenario is often deteriorated at the interface of the heterogeneous nanostructures due to lattice mismatches, resulting in downgraded performance in most hybrid nanomaterials. Here, we report that there is a narrow window in controlling temperature in a Lewis acid-base reaction process to facilitate epitaxial alignment during the synthesis of hybrid nanomaterials. We demonstrate a perfectly fused NaYF4:Yb,Tm@ZnO heterogeneous nanostructure, in which the semiconductor ZnO shell can be epitaxially grown onto lanthanide-doped upconversion nanoparticles. By achieving a matched crystal lattice, the interface defects and crystalline grain boundaries are minimized to enable more efficient energy transfer from the upconversion nanoparticles to the semiconductor, resulting in both enhanced upconversion luminescence intensity and superior photoelectrochemical properties. This strategy provides an outstanding approach to endow lanthanide-doped upconversion nanoparticles with versatile properties.

Spectroscopy and near infrared upconversion of Er3+-doped TZNT glasses

In this paper we report on the near infrared (NIR) upconversion (UC) and spectroscopic properties of erbium (Er3+)-doped TeO2–ZnO–Nb2O5–TiO2 (TZNT) oxide glasses. Judd–Ofelt theory has been applied to investigate the intensity parameters (Ωλ, λ=2, 4 and 6) which are used to derive radiative properties of the fluorescent levels. The different glasses present high refractive indices, low dispersion and Abbe numbers, as determined by variable angle spectroscopic ellipsometry. Under 980nm excitation, the NIR emission profile and full width at half maximum have been studied in a broad range of Er3+ concentrations (0.01–3.0mol%). On the other side, NIR UC has been obtained by exciting at 1523nm, showing an increase of the intensity with Er3+ ion density in the studied range. The decay curves of the 4I13/2 level exhibit single exponential nature for all the different concentrations. The lifetime of the 4I13/2 level has been found to decrease (3.73–1.20ms) after an initial increase (3.65–3.73ms) with increasing of Er3+ ion concentration. The TZNT samples show broadband UC emission at 1.0µm, which match with the band gap of silicon. This reveals that the investigated glasses could find application in photonics, for example non-linear optics and photovoltaic’s.

Upconversion Luminescent NaYbF<sub>4</sub>: Er<sup>3+</sup>, Tm<sup>3+</sup> Nanoparticles: Spectrally Pure and Intense near Infrared to near Infrared Emission

NaYbF4: Yb3+, Tm3+ nanoparticles (UCNPs) capped with oleic acid (OA) have been synthesized via high-temperature solvent reaction. The optimization sample of NaYb0.96Er0.02Tm0.02F4 nanoparticles possess spectral purity (the Snw value is bigger than 0.7) and intense near infrared to near infrared (NIR-to-NIR) upconversion luminescence (UCL) (the power of laser is as low as 3.8 W), which makes them ideal and promising platforms for high contrast bioimaging.

Optical investigation in shuttle like BaMoO4:Er3+–Yb3+ phosphor in display and temperature sensing

The crystal structure of the Er3+–Yb3+ codoped BaMoO4 phosphors synthesized through co-precipitation method has been studied by using the X-ray diffraction analysis. The impurity contents and surface morphology have been examined by field emission scanning electron microscopy (FE-SEM) and Fourier transform infrared (FTIR) analysis respectively. The introduction of the Er3+/Yb3+ did not change the crystal structure and morphology of the developed phosphor. The developed phosphor upon excitation at 980nm diode laser radiation shows strong green, relatively weak red and near infrared upconversion emission bands. The codoping with Yb3+ ions in the BaMoO4:Er3+ phosphor enhanced the green emission intensity about ∼236-folds. The decay curve analysis and temperature dependence intensity variations for the most intense green bands arising from the 2H11/2 and 4S3/2 levels to the ground level (4I15/2) in Er3+ ion have been performed. The pump power and temperature dependent study shows the feasibility of using the developed phosphor in display and temperature sensing devices.

Color tunability in green, red and infra-red upconversion emission in Tm3+/Yb3+/Ho3+ co-doped CeO2 with potential application for improvement of efficiency in solar cells

The preparation of Tm3+/Yb3+/Ho3+ co-doped CeO2 prepared by the precipitation method using ammonium hydroxide as a precursor is presented. By X-ray diffraction the materials show the phase-type of fluorite structure and the crystallite sizes were calculated by the Scherrer׳s equation. No other phase was observed evincing that the rare earth ions were inserted into the fluorite phase as substitutional or interstitial dopants. The microstrain calculated by the Williamson–Hall method do not show significant changes in their values, indicating that the inclusion of rare earths does not causes structural changes in the CeO2 used as a host matrix. All material showed intense upconversion emission at red and green region under excitation with diode laser at 980nm. The color of emission changes from green to red with increasing excitation power pump. The materials showed suitable photoluminescent properties for applications as a laser source, solar cells, and great emitter at 800nm.

Tm3+浓度对Y2(MoO4)3∶Tm3+,Yb3+荧光粉上转换发光性质的影响

采用传统的高温固相反应法合成了Tm3+/Yb3+共掺杂Y2(MoO4)3系列荧光粉。XRD结果表明合成的样品为相纯度好的Y2(MoO4)3。在980 nm光激发下,样品具有较强的位于487 nm和800 nm的蓝色和近红外发射,同时伴有较弱的位于649 nm的红光发射。它们分别来自于Tm3+的1G4→3H6、3H4→3H16和G4→3F4跃迁。根据功率相关的上转换发射和能级图分析了Tm3+的上转换发光机制。结果表明,1G4和3H4能级的布居分别来自于三光子和两光子的能量传递上转换。此外,随着Tm3+浓度的增加,蓝色、红色和近红外发射带均呈先增加后降低的趋势,即发生了浓度猝灭。同时,蓝光发射和近红外发射的强度比随Tm3+掺杂浓度的增加而减小。