Enhanced Frequency Upconversion Research Articles

A speed-amplified tri-stable piezoelectric-electromagnetic-triboelectric hybrid energy harvester for low-frequency applications

This work proposes a new speed-amplified multi-stable tri-hybrid energy harvesting technique via the multi-stable nonlinearity enhanced frequency up-conversion and rack-pinion mechanisms to efficiently harness structural and biomechanical vibration energy. In the present design, two frequency up-conversion piezoelectric generators, an array-type electromagnetic generator and a sliding-mode triboelectric nanogenerator are integrated together to form a compact and interactive system. By utilizing the rack-pinion mechanism, the relative speed between the stators and the translators of the electromagnetic and triboelectric generators are both doubled. Meanwhile, the process of frequency up-conversion in the piezoelectric generators is also doubled per each cycle. This results in better performance under wideband and low-frequency vibration sources. For verification, a prototype of this design is tested by mechanical excitations and body-induced motions. In the shaker test, the prototype can generate a peak output power of 446.16 mW under an optimal resistance load, resulting in a normalized power density of 4.20 mW cm–3 g–2 at 5 Hz under 1 g. The prototype also exhibits exceptional performance under various human motion tests, it can drive 600 commercial light-emitting diodes simultaneously. Using a commercial DC/DC voltage regulator circuit, the proposed harvester can serve as a universal power source to charge commercial electronic devices, including smartphones and GPS sensors. The present design shows great potential as a sustainable power source for wearable/portable electronics as well as wireless monitoring systems.

Albumin-based near-infrared phototheranostics for frequency upconversion luminescence/photoacoustic dual-modal imaging-guided photothermal therapy.

Engineering versatile phototheranostics for multimodal diagnostic imaging and effective therapy has great potential in cancer treatment. However, developing an inherently versatile molecule is a huge challenge. In this work, a near-infrared organic dye (NRh) was synthesized and further bound with bovine serum albumin (BSA) to construct facile "one-for-all" phototheranostics (NRh-BSA NPs), which exhibited enhanced frequency upconversion luminescence (FUCL, λex/em = 850/825 nm) and excellent photoacoustic (PA) and photothermal properties (λ'ex = 808 nm). Additionally, the BSA-modified phototheranostics NRh-BSA NPs showed specific accumulation in the tumor region through passive targeting. Based on the FUCL/PA dual modal imaging-guidance, the NRh-BSA NPs not only can guarantee the accuracy of imaging of the U87MG tumor sites, but also can improve the therapeutic effect on ablating tumors without recurrence by photothermal therapy (PTT). Collectively, our work proposed a novel strategy to construct versatile phototheranostics with the unique FUCL/PA imaging-guided technique for accurate cancer theranostics.

Enhanced frequency up-conversion based on four-wave mixing assisted by a Bessel-Gaussian beam in 85Rb atoms

We present an enhanced frequency up-conversion based on four-wave mixing process assisted by a Bessel-Gaussian beam in a 5S1/2 − 5P3/2 − 5D5/2 − 6P3/2 − 5S1/2 diamond-type atomic system of 85Rb. The 420 nm coherent blue light (CBL) is generated and an enhanced conversion efficiency of approximately two times is realized using the Bessel-Gaussian beam as a pump laser compared with that of the Gaussian beam. The non-diffracting property of the Bessel-Gaussian beam, which overcomes the diffractive spread and retains a high intensity over a long distance, leads to the high conversion efficiency. The influence of different pump powers on the enhancement effect is investigated in detail. Furthermore, the CBL generated by the Bessel-Gaussian beam is immune to obstacles owing to the self-healing ability, which extends its application scenarios. The enhanced frequency up-conversion based on structured light is beneficial to the applications of the blue-violet light source, and holds tremendous promises for extending the existing nonlinear toolkit.

Enhanced frequency upconversion in Er3+–Yb3+ codoped heavy metal oxides based tellurite glasses

The spectroscopic investigations on the Er3+/Yb3+ ions doped/codoped TeO2–ZnO (TZ), TeO2–ZnO–WO3 (TZW) and TeO2–ZnO–WO3–TiO2 (TZWTi) heavy metal oxide (HMO) glasses have been made. The absorption, photoluminescence, decay curve and Judd–Ofelt analysis have been performed to optimise the optical properties of the Er3+/Yb3+ ions. The effect of incorporation of HMOs like WO3 and TiO2 in the Er3+/Yb3+ doped/codoped TZ glass on its optical properties have been investigated. The enhancement in upconversion emission intensity has been explained on the basis of efficient energy transfer and inhomogeneous local field generation around the rare earth ions. The spectroscopic quality factor, absorption and stimulated emission cross-sections, optical gain, quantum efficiency (∼17.53%), energy transfer efficiency (∼61.64%), colour purity (∼94.7%) and ionic nature of the bonding have been determined. The Er3+–Yb3+–TZWTi glass can be used in visible lasers, yellowish green optical devices and home appliances.

Spectroscopy and enhanced frequency upconversion in Nd3+–Yb3+ codoped TPO glasses: energy transfer and NIR to visible upconverter

TeO2–Pb3O4 (TPO) glasses codoped with Nd3+ and Yb3+ ions have been fabricated by conventional melting technique. The absorption, emission and excitation spectra of the samples have been recorded. The optical band gap in both the doped/codoped glasses is found to be ∼3.31 eV. Judd–Ofelt analysis has been carried out by using the absorption spectrum of 0.8 mol% Nd3+ doped glass to determine the radiative properties viz radiative transition probabilities, branching ratios, radiative lifetimes, quality factor and emission cross sections of some emitting levels for Nd3+ ions. The radiative transition probability for the 4G7/2 → 4I9/2 transition (∼1926 Hz) is found to be maximum compared to other 4G5/2 → 4I9/2 (∼1622 Hz) and 4F5/2 → 4I9/2 (∼865 Hz) transitions. Upconversion (UC) luminescence of the samples has been examined by the 980 nm CW diode laser excitation. Effect of addition of Yb3+ ions in the Nd3+ doped glasses on UC emission intensity has been discussed. The UC emission intensity corresponding to the green, red and NIR bands in the codoped glass has been enhanced by ∼17, ∼12 and ∼42 times as compared to that of the Nd3+ singly doped glass. The quantum efficiency for the 4G7/2 level is found to be ∼32%. The nephelauxetic ratio, bonding parameter and covalency of Nd3+ ions have been found positive which represents the covalent bonding between Nd3+ ion and oxygen atom. The colour tunability from yellowish-green to dominant green region has been obtained in the optimized codoped TPO glass.

Yb3+ sensitized Na2Y2B2O7:Er3+ phosphors in enhanced frequency upconversion, temperature sensing and field emission display

Na2Y2B2O7:Er3+/Yb3+ crystalline phosphors with single monoclinic phase have been synthesized by urea assisted solution combustion method and characterized through X-ray diffraction and Field emission scanning electron microscopy analysis. Frequency upconversion (UC) emission study has been carried out upon 980nm laser diode excitation and maximum enhancement of about ∼1433 times for the UC emission intensity of the green band in the codoped phosphor compared to that of the singly Er3+ doped phosphor has been reported. Optical temperature sensing study performed in the developed codoped phosphor reveals that the material can be used temperature sensing application within 300–613K temperature range with maximum sensitivity ∼7.9×10−3K−1 at 300K. The low-voltage cathodoluminescence measurements have been performed for Na2Y2B2O7:Er3+-Yb3+ phosphors as a function of accelerating voltage and filament current. The developed phosphors exhibit highly intense green emission with some weak emission bands in violet, blue and red regions upon electron beam excitation.

Enhanced frequency upconversion in Ho3+/Yb3+/Li+:YMoO4 nanophosphors for photonic and security ink applications

The YMoO4 nanophosphors codoped with Ho3+/Yb3+/Li+ ions synthesized by the chemical coprecipitation method have been structurally characterized by using X-Ray Diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM), and Transmission Electron Microscopy (TEM) techniques. The TEM bright field imaging shows that the developed nanophosphors are crystalline in nature with particle size ∼45 nm. The upconversion (UC) emission spectra upon excitation at 980 nm of the nanophosphors at low pump power (<900 mW) show the emission peaks in the UV, green, and red regions, whereas at high pump power (≥900 mW) an intense broad band ranging from 400–900 nm along with a UV band has been observed. The enhancement of about ∼104 times corresponding to the green band in the Ho3+-Yb3+-Li+ codoped nanophosphors compared to that of the Ho3+ singly doped nanophosphors has been observed. This enhancement is caused by the energy transfer from the Yb3+ to Ho3+ ions and modified the local crystal field developed around the rare earth ions. A higher value of the slope (i.e., n ∼ 6.38) for broad band emission within the 944 mW-1200 mW pump power region in the Ho3+-Yb3+-Li+ codoped nanophosphors is found to be due to the involvement of the photon avalanche population process but it is not related to the black body radiation. The intense peak at ∼564 nm and ∼648 nm for the broad band emission is attributed to the charge transfer luminescence of codoped nanophosphors, which is related to the oxygen ion present in the MoO4 group and Yb3+ ion. The observations described in this paper may be of significant interest for developing the visible upconverters, security ink, and novel devices for displays in the low and high pump power region.

Enhanced frequency upconversion and non-colour tunability in Er3+–Yb3+ codoped TeO2–WO3–Pb3O4 glasses

TeO2–WO3–Pb3O4 glasses codoped with Er3+–Yb3+ ions have been prepared by melting and quenching process. Judd–Ofelt analysis has been performed to calculate the various radiative parameters viz., radiative lifetime, branching ratio and stimulated emission crosssections by using the absorption spectra. The nephelauxetic ratio, bonding and covalency parameters have been determined to get the information about the nature of bonding between the rare earth ions and neighbouring oxygen atoms. The near infrared (NIR) to visible frequency upconversion (UC) study upon excitations with 980 nm and 808 nm diode lasers has been performed. The variations observed in the UC emission intensity arising from the Er3+ ions have been explained on the basis of efficient energy transfer Yb3+ → Er3+ ions and back energy transfer Er3+ → Yb3+ processes. On codoping with Yb3+ ions the intensity of the UC emission bands observed in the codoped glass upon excitation at 980 nm has been enhanced by many folds and explained on the basis of the oscillator strengths, UC emission crosssection and temporal evolution analysis. No tuning in the colour emitted from the codoped glass upon excitation at 980 nm is reported. The results suggested that the codoped glass may be suitable in making the NIR to visible upconverter and colour non-tunable optical devices.

Strong quantum interferences in frequency up-conversion towards short vacuum-ultraviolet radiation pulses

We present experimental data on quantum interferences in resonantly enhanced frequency up-conversion towards the vacuum-ultraviolet spectral regime. The process is driven in xenon atoms by ultrashort (picosecond) laser pulses. We use two simultaneous frequency conversion pathways via an excited intermediate state, i.e., fifth harmonicgenerationofthefundamentalwavelengthandfour-wavemixingofthefundamentalandtwophotonsof itssecondharmonicwavelength.Bothconversionpathwaysyieldradiationat102nm.Thetwopathwaysinterfere, depending on the relative phase of the fundamental and second harmonic. By appropriate choice of the phase we get constructive interference (resulting in increased conversion efficiency) or destructive interference (resulting in reduced conversion efficiency). The total conversion yield shows very pronounced constructive and destructive quantum interference with a visibility of roughly 90%. A stable and highly accurate phase control setup enables suchstrongquantuminterferencesformorethan260oscillationcycles.Inanextensionoftheexperiment,simultaneouslytofrequencyconversionwealsomonitorlaser-inducedfluorescenceasameasurefortheexcitationprobabilitytotheexcitedintermediatestate.Also,intheexcitationprobabilityweobservestrongquantuminterferences. As an interesting feature, a small phase lag occurs between the quantum interference patterns of frequency conversion and population transfer. This is due to an additional atomic phase acquired during frequency conversion.

Enhanced frequency upconversion in Er3+-doped sodium lead tellurite glass containing silver nanoparticles

A series of silver nanoparticle embedded in erbium-doped tellurite glasses were synthesized using a one step melt-quenching method. Density and refractive index of glasses were measured. Thermal and optical characterizations were performed and plasmon bands of elliptical nanoparticles were observed. An enhancement of green (525 and 550 nm) and red (632 nm) lines in luminescence spectra of Er3+-doped silver-embedded tellurite glass was recorded and explained by energy transfer mechanism from silver nanoparticles to erbium ion in addition to enhanced local field in vicinity of metallic nanoparticles in the glass. The presence of nanoparticles was confirmed by transmission electron microscopy imaging and reduction of silver ions to silver neutral particles discussed through the redox potential estimation in probable reactions. Silver-erbium co-doped tellurite glass exhibits strong novel optical properties which nominate it as the promising glass for laser, color displays, and photonic applications.

Infrared-to-visible upconversion in Yb 3+/Er 3+ co-doped PbO–GeO 2 glass with silver nanoparticles

Enhanced frequency upconversion (UC) emission was studied in Yb 3+/Er 3+ co-doped PbO–GeO 2 glass containing silver nanoparticles (NPs). Optical excitation was achieved with a laser operating at 980 nm in resonance with the Yb 3+ transition 4F 5/2 → 4F 7/2. The intensity of the whole UC spectrum from 400 to 700 nm was intensified due to the influence of silver NPs. The green and red emissions were enhanced by more than 300%. Emission bands centered at 408 nm and 480 nm were also detected corresponding to the 2H 9/2 → 4I 15/2 and 4F 7/2 → 4I 15/2 transitions of Er 3+ ion. An intensity enhancement of ≈ 150% due to the NPs was measured. For the first time the influence of silver NPs on the blue emission of Yb 3+/Er 3+ co-doped PbO–GeO 2 glass is reported. The large enhancement in the whole UC spectrum is due to the increased local field in the Er 3+ ions locations and the proximity between the luminescence wavelengths and the NPs surface plasmon resonance.

Enhanced frequency upconversion of Sm3+ ions by elliptical Au nanoparticles in dichroic Sm3+: Au-antimony glass nanocomposites

Dichroic Sm(3+): Au-antimony glass nanocomposites are synthesized in a new reducing glass (dielectric) matrix (mol%) K(2)O-B(2)O(3)-Sb(2)O(3) (KBS) by a single-step melt-quench technique involving selective thermochemical reduction. X-ray diffraction (XRD) and selected area electron diffraction (SAED) results indicate that Au(0) nanoparticles are grown along the (200) plane direction. The transmission electron microscopic (TEM) image reveals the elliptical Au(0) nanoparticles having major axis range 12-17 nm. Dichroic behavior is due to elliptical shape of Au(0) nanoparticles of aspect ratio approximately 1.2. Au(0) NPs of concentration of 0.03 wt% (4.1 x 10(18)atoms/cm(3)) drastically enhances the intensity ( approximately 7-folds) of electric dipole (4)G(5/2)-->(6)H(9/2) red transition (636 nm) of Sm(3+) ions and then attenuates with further increase in Au(0) concentration. The magnetic dipole (4)G(5/2)-->(6)H(5/2) green (566 nm) and (4)G(5/2)-->(6)H(7/2) orange (602 nm) transitions remain almost unaffected by presence of nano Au(0). Local field enhancement (LFE) induced by Au(0) SPR and energy transfer (ET) from fluorescent Au(0)-->Sm(3+) ions are found to be responsible for the enhancement while reverse ET from Sm(3+)-->Au(0) and optical re-absorption due to Au(0) SPR for attenuation.

Observation of ESA, ET and thermally enhanced frequency upconversion in Nd3+: LiTeO2glass

Infrared to visible upconversion emission bands are observed in Nd 3+ : LiTeO 2 glass at 430, 482, 525, 535, 580, 600, 664 and 766 nm wavelengths due to the 2 P 1/2 4 I 9/2 , 2 P 1/2 4 I 11/2 , 2 P 1/2 4 I 13/2 , 4 G 7/2 4 I 9/2 , 2 P 1/2 4 I 15/2 , 4 G 7/2 4 I 11/2 & 4 G 5/2 + 2 G 7/2 4 I 9/2 , 4 G 7/2 4 I 13/2 and 4 G 7/2 4 I 15/2 transitions, respectively. Mechanisms involved in these upconversion emissions are shown to either involve excited state absorption or energy transfer depending upon the concentration of the rare earth ions. The emission bands at 755 and 968 nm are also observed due to the thermally excited phonon absorption, on excitation with 800 nm wavelength. A 90 fold enhancement in the intensity of anti-Stokes emission at 755 nm is observed in this glass when temperature is raised from 298 to 523 K. Fluorescence intensity ratio (FIR) and sensitivity ( S ) of the two thermally coupled levels viz. 4 F 3/2 and 4 F 5/2 are calculated at different temperatures and results show that these levels could act as temperature sensor in tellurite host. Lifetimes of the excited levels 2 P 1/2 , 4 G 7/2 , 4 F 3/2 , 4 F 5/2 and 4 F 7/2 involved in the emission process are also determined and their temperature dependence is described.

Enhanced frequency upconversion in Er 3+ doped fluoroindate glass due to energy transfer from Tm 3+

Energy transfer processes between Er 3+ and Tm 3+ were investigated examining the frequency upconversion emissions in a fluoroindate glass pumped at 790 nm. A 60-fold enhancement in the emission at ≈670 nm originating from Er 3+ was observed when Tm 3+ at concentration of 2% was introduced in a sample containing 2% of Er 3+. The results are explained considering the influence of cross-relaxation processes between the active ions.

Thermally enhanced frequency upconversion in Nd3+-doped fluoroindate glass

Multiphonon assisted frequency upconversion was observed in a Nd3+-doped fluoroindate glass pumped at 866 nm. A near-infrared upconverted emission at 750 nm with a peculiar linear dependence with the laser intensity was observed and explained. The intensity of the upconverted emission experienced a 40-fold enhancement when the sample’s temperature was varied from 298 to 498 K. A rate equation model that includes light pumping and multiphonon absorption via thermally coupled electronic excited states of Nd3+ was used, describing quite well the experimental results.

Efficient and thermally enhanced frequency upconversion in Yb3+-sensitized Tm3+-doped silica-on-silicon buried waveguides excited at 1.064 μm

Efficient and thermally enhanced frequency upconversion of cw infrared radiation at 1.064 μm into blue (480 nm), red (660 nm) and near-infrared (800 nm) light in integrated Tm 3+ /Yb 3+ -codoped phosphosilicate silica-on-silicon buried waveguides is reported. Thermally induced frequency upconversion enhancement is observed for the first time in Tm 3+ /Yb 3+ -codoped systems excited off-resonance at 1.064 μm. A times seven thermally induced upconversion efficiency enhancement was obtained when the waveguide's temperature was varied in the 20–120°C range. The thermal effect is believed to be associated with a temperature dependent effective absorption cross-section for the Yb 3+ -sensitizer, which depends upon the phonon occupation number in the host matrix.