Flexible double narrowband near-infrared photodetector based on PMMA/core-shell upconversion nanoparticle composites

Flexible narrowband near infrared(NIR)photodetectors(PDs)are urgently in demand in the fastdeveloping era of flexible electronics,due to their crucial roles in various innovative applications.Hence,we designed and synthesized the core-shell structured NaYF4:Yb³⁺,Er³⁺@NaYF4:Nd³⁺upconversion nanoparticles(UCNPs),which can be pumped by the 808 and 980 nm lights.The upconversion luminescence(UCL)are significantly enhanced after being assembled with the opal photonic crystals(OPCs)due to the photonic crystal effect,with 55 and 48 folds of enhancement factors under illuminations of 808 and 980 nm lights,respectively.Based on this hybrid,the flexible narrowband PDs were successfully fabricated on the PET substrate with the structure of OPCs/NaYF4:Yb³⁺,Er³⁺@Nd³⁺/MAPbl3,which displays excellent detection performance to double narrowband NIR light(808 and 980 nm)benefiting from the amplified UCL,with responsivity of 8.79 and 7.39 A/W,detectivity of 3.01×10¹¹and2.68×10¹¹cm·Hz^1/2/W for 808 and 980 nm lights detection respectively,along with short response time in the range of 120-160 ms.Furthermore,the OPCs/NaYF4:Yb³⁺,Er³⁺@NaYF4:Nd³⁺/MAPbI3 double narrowband PDs display low photodetection power threshold(0.05 W/cm2),outstanding flexibility,prominent moisture resistance,and good long-time stability.This work displays a new concept of narrowband NIR PDs,which open a new field for specific NIR light detections.     

Growth and property enhancement of Er3+-doped 0.68Pb(Mg1/3Nb2/3)O3-0.32PbTiO3 single crystal

Er~(3+)-modified 0.68 Pb(Mg_(1/3)Nb_(2/3))O_3-0.32 PbTiO_3(PMN-32 PT) single crystals were grown by using the flux method. The growth mechanism of the crystal and influences of Er~(3+) ions on phase structure,electrical and optical properties were investigated. Results reveal that the crystals are still pure perovskite structure with Er3+ ions doping, but lattice enlarges slightly. The coercive electric field is increased from 4.83 to 6.37 kV/cm for [100]-oriented crystals comparing to undoped PMN-32 PT single crystals.Moreover, the crystal exhibits upconversion emission properties. Green(531 and 552 nm) and red(670 nm) emission bands are recorded under the excitation of 980 nm diode laser, which correspond to the ~2 H_(11/2)→~4 I_(15/2), ~4 S_(3/2)→~4 I_(15/2) and ~4 F_(9/2)→~4 I_(15/2) transitions of Er~(3+) ions. Our results show the feasibility of using this crystal in photoelectric multifunctional devices.     

Boosting single-band red upconversion luminescence in colloidal NaErF_4 nanocrystals:Effects of doping and inert shell

Single-band red upconversion luminescence(UCL) is vital to in vivo bioimaging as well as "see and treat" biomedicines. Herein, starting with the previously reported β-NaErF4:Tm UCNPs, we examined the effects of both Yb~(3+) doping and inert shell coating on the red-to-green(R/G) ratio for Er3+ based UCL. The doping of Yb~(3+) into the β-NaErF4:Tm3+ core not only enhances the whole UCL intensity, but also raises the R/G ratio by 1.25 times. In addition, the coating of an inert NaYF4 shell, which is usually adopted for the enhancement of UCL intensity, further boosts the R/G value up to as high as 77.92. This work may benefit the potential bioimaging application of single-band red UCL.     

Enhancement of red upconversion emission intensity of Ho3+ ions in NaLuF4:Yb3+/Ho3+/Ce3+@NaLuF4 core–shell nanoparticles

The red upconversion emission of Ho³⁺ ions, in the optical window of biological tissue, exhibits excellent prospects in biological applications. This study aims to enhance the red upconversion emission intensity of Ho³⁺ ions in NaLuF₄:20%Yb³⁺/2%Ho³⁺/12%Ce³⁺ nanoparticles through building different core–shell structures with different excitation wavelengths. A significantly enhanced red upconversion emission with a higher red-to-green ratio was successfully obtained in NaLuF₄:20%Yb³⁺/2%Ho³⁺/12%Ce³⁺@NaLuF₄ core–shell nanoparticles by introducing the Yb³⁺ and Yb³⁺/Nd³⁺ ions into the NaLuF₄ shell, with enhancement of the red emission occurring when Yb³⁺ and Nd³⁺ ions in the shell transfer more excitation energy to the Ho³⁺ ions. Investigation of the red emission enhancement mechanism is based on spectral characteristics and lifetimes. We examined the synergistic effect of dual-wavelength co-excitation NaLuF₄:20%Yb³⁺/2%Ho³⁺/12%Ce³⁺ @NaLuF₄:10%Yb³⁺/15%Nd³⁺ core–shell nanoparticles to establish optimal excitation conditions. It is hoped that this method, using red upconversion emission core–shell nanoparticles with multi-mode excitation, can provide new ways to expand the applications of rare-earth luminescent materials in biomedicine and anti-counterfeiting.     

Upconversion luminescence of Gd2O3:Er3+ and Gd2O3:Er3+/silica nanophosphors fabricated by EDTA combustion method

Gd_2O_3:Er~(3+) nanophosphors were fabricated by the combustion method in presence of Na_2 ethylene diamine tetra acetic acid(EDTA-Na_2) as fuel at not high temperature(≤350℃) within a very short time of 5 min.The added concentration of Er~(3+)ions in Gd_2O_3 matrix was changed from 0.5 mol% to 5.0 mol%.The X-ray diffraction pattern of samples indicates the monoclinic structure of Gd_2O_3:Er3+.The morphology and chemical composition analysis of the Gd_2O_3:Er~(3+) samples are characterized by a field emission scanning electron microscope(FESEM) and a Fourier-transform infrared spectrometer(FTIR).The photoluminescence(PL),photo luminescence excitation(PLE) and upconversion(UC) at room temperature of the prepared materials with different concentrations of Er~(3+) were investigated.The PL of Gd_2O_3:Er~(3+)nanomaterials are shown in visible at 545,594,623,648,688 nm under excitation at 275 nm.The emission bands from transitions of Er~(3+) from ~2P_(3/2) to ~4F_(9/2) are observed,UC luminescent spectra of the Gd_2O_3:Er~(3+)/silica nanocomposites under 976 nm excitation show the bands at 548 and 670 nm.The influence of excitation power at 980 nm for transitions were measured and calculated.The results indicate that the upconversion process of Gd_2O_3:Er~(3+)/silica is two photons absorption mechanism.The low temperature dependence of UC luminescent intensities of the main bands of Gd_2O_3:Er~(3+)was investigated towards development of a nanotemperature sensor in the range of 10-300 K.     

Magnetic and thermosensitive luminescent nanocomposites based on Fe3O4/SiO2/poly (N-isopropylacrylamide)/lanthanide-polyoxometalates and their controllable luminescence properties

Magnetic and temperature-responsive luminescent composites based on poly(N-isopropylacrylamide),magnetic nanoparticles and Na_9[EuW_(10)O_(36)] were fabricated. The composites were investigated by IR, UV,XRD, TGA, SEM and TEM. The prepared nanocomposites exhibit good superparamagnetic property and thermo-responsive switchable luminescence properties. The multifunctional nanocomposites can be separated by external magnetic field. Moreover, the nanocomposites exhibit an appreciable temperature response, and the red luminescence of the nanocomposites in solution can be controlled by the temperature stimuli. The hydrogel emits strong redluminescence in solution at 25 ℃,which can be seen by naked eyes. When the external temperature is 40 ℃, the red luminescence almost disappears in solution.It is expected that the multifunctional nanoparticles have potential applications in the field of biomedicine.     

Synthesis,upconversion luminescence and optical heating of hexagonal NaGdF4:Yb3+,Er3+

An optical heater based on hexagonal NaGdF_4:Yb~(3+)/Er~(3+) is reported. XRD, SEM and EDS characterization results show that F~-/Ln~(3+) can not only control the phase composition, particle size and morphology, but also affect the effective doping concentration of Yb~(3+) and Er~(3+).When F~-/Ln~(3+) is 12/1, the strongest upconversion luminescence is obtained. Based on the luminescent temperature sensing behavior of Er~(3+),the photo-thermal conversion performance was investigated. The results indicate that the temperature of irradiation spot is linearly dependent on the power density, and the photo-thermal responsivity is determined to be 3.3K·cm~2/W. Also, it is found that the photo-thermal conversion efficiency can be regulated by changing the Yb~(3+) doping concentration. Compared with the nano-gold, copper sulfide and carbon nanotubes, the NaGdF_4:Yb~(3+)/Er~(3+) has the triple functions of upconversion luminescence, temperature sensing, and photo-thermal conversion, and may therefore be a promising optical heater for photo-thermal therapy of tumors.     

Er~(3+)-Yb~(3+)-Na~+:ZnWO_4 phosphors for enhanced visible upconversion and temperature sensing applications

The crystal structure and surface morphology of the Er³⁺/Yb³⁺/Na+:ZnWO₄ phosphors synthesized by solid state reaction method were analyzed by X-ray diffraction(XRD) and field emission scanning electron microscopy(FESEM) analysis.The frequency upconversion(UC) emission study in the developed phosphors was investigated by using 980 nm laser diode excitation.The effect of codoping in the Er³⁺:ZnWO₄ phosphors on the UC emission intensity was studied.The UC emission bands that are exhibited in the blue(490 nm),green(530,552 nm),red(668 nm) and NIR(800 nm) region correspond to the ⁴F_7/2→⁴I_15/2.²H_11/2,⁴S_3/2→⁴I_15/2,⁴F_9/2→⁴I_15/2 and ⁴I9/2→⁴I_15/2 transitions,respectively.The temperature sensing performance of the Er³⁺-Yb³⁺-Na+:ZnWO₄ phosphors was investigated based on the 2 H_11/2→⁴I_15/2 and ⁴S_3/2→⁴I_15/2 thermally coupled transitions of the Er³⁺ions.The photometric study was also carried out for the developed phosphors.     

Hierarchical porous cellulose/lanthanide hybrid materials as luminescent sensor

Photoluminescent hybrid materials containing carboxymethyl cellulose and lanthanide ions (Eu³⁺, Tb³⁺) were prepared by a facile method under ambient conditions. Lanthanide ions were covalently grafted to the cellulose framework through coordination with the carboxylic groups of the cellulose. Hybrid materials were fabricated as hydrogel and aerogel. As shown by SEM and pore parameters, aerogel materials which were obtained by supercritical CO₂ drying show hierarchical porous structure. The photoluminescence spectrum of the hybrid materials shows the characteristic red emission of Eu³⁺ ion and green emission of Tb³⁺. Further luminescent investigations reveal that these hybrid materials can detect Fe³⁺ with relative selectivity and high sensitivity, which suggests that the hybrid materials could be a promising luminescent probe for selectively sensing Fe³⁺ ion.