Efficient Down-conversion Research Articles

Impact of solvent on the downconversion efficiency of the N-GQDs/PMMA layer: Application in CIGS solar cells

Due to lowering the material cost, the thin film-based photovoltaic (PV) technologies are progressively drawing substantial concentration in the PV community. Among them, Cu(In, Ga)Se2 (CIGS) is considered a potential absorbing material due to its higher absorption and changeable band-gap. But it produced a low value of current at the short wavelength region. Thus, the short circuit current density (Jsc) is greatly reduced, which results in a lower value of the conversion efficiency. Here, N-doped graphene quantum dots (N-GQDs) are used as luminescent photon downshifters (LDS). Furthermore, the N-GQDs are embedded in the poly(methylmethacrylate) (PMMA) to enhance the chemical and mechanical stability of the LDS. However, the PMMA creates the photoluminescence (PL) quenching, which lessens the efficacy of the LDS layer. The LDS composite layer is formed in the various solvents. Furthermore, these LDS composites were evaluated via deployment onto the CIGS solar cells. The best performance is obtained in the chlorobenzene solvent. By insertion of the LDS composite layer, the Jsc was enhanced from 33.58 to 35.32 mA/cm2, which resulted in an enhancement in the efficiency from 13.08% to 14.62%. The PV cell parameters analysis revealed that recombination is reduced due to growing the number of photons, which results in the performance enhancement of the CIGS solar cells.

DDC Pool: Efficient down-conversion of signals for RFI monitoring

DDC Pool: Efficient down-conversion of signals for RFI monitoring

Potential of Sub-THz-Wave Generation in Li2B4O7 Nonlinear Crystal at Room and Cryogenic Temperatures

Due to their high optical damage threshold, borate crystals can be used for the efficient nonlinear down-conversion of terawatt laser radiation into the terahertz (THz) frequency range of the electromagnetic spectrum. In this work, we carried out a thorough study of the terahertz optical properties of the lithium tetraborate crystal (Li2B4O7; LB4) at 295 and 77 K. Approximating the terahertz refractive index in the form of Sellmeier’s equations, we assessed the possibility of converting the radiation of widespread high-power laser sources with wavelengths of 1064 and 800 nm, as well as their second and third harmonics, into the THz range. It was found that four out of eight types of three-wave mixing processes are possible. The conditions for collinear phase matching were fulfilled only for the o − e → o type of interaction, while cooling the crystal to 77 K did not practically affect the phase-matching curves. However, a noticeable increase of birefringence in the THz range with cooling (from 0.12 to 0.16) led to an increase in the coherence length for o − o → e and e − e → e types of interaction, which are potentially attractive for the down-conversion of ultrashort laser pulses.

Scaling up quantum metrology for higher multiphoton resolution

Efficient parametric down-conversion together with photon-number-resolving detection makes multiphoton quantum metrology robust and scalable.

2.1 μm self frequency conversion optical parameter oscillator based on Nd3+ doped MgO:PPLN

A 2.1 μm integrated self frequency conversion optical parametric oscillator which based on Nd3+ doped MgO:PPLN with intra-cavity acousto-optic Q-switched is reported. Under different thermal focal lengths of Nd3+ doped MgO:PPLN, the focusing parameter ratio of 1084 nm and 2168 nm and the spot radius of 1084 nm are simulated, and the optimal parameters of the composite resonant cavity are determined. According to the quasi-phase matching principle, 1093 nm is effectively suppressed by the design of the composite resonator, and a single-wavelength output of 1084 nm is obtained. The 2.1 μm self frequency conversion optical parametric oscillator with Nd3+ doped MgO:PPLN is realized for the first time, the output power is 1.21 W, the highest down-conversion efficiency from 1084 nm to 2.1 μm is 15.1%. The pulse width of 2168 nm is around 7.8 ns when the repetition rate is 40 kHz.

Field-effect silicon-plasmonic photodetector for coherent T-wave reception

Plasmonic internal photoemission detectors (PIPED) have recently been shown to combine compact footprint and high bandwidth with monolithic co-integration into silicon photonic circuits, thereby opening an attractive route towards optoelectronic generation and detection of waveforms in the sub-THz and THz frequency range, so-called T-waves. In this paper, we further expand the PIPED concept by introducing a metal-oxide-semiconductor (MOS) interface with an additional gate electrode that allows to control the carrier dynamics in the device and the degree of internal photoemission at the metal-semiconductor interfaces. We experimentally study the behavior of dedicated field-effect (FE-)PIPED test structures and develop a physical understanding of the underlying principles. We find that the THz down-conversion efficiency of FE-PIPED can be significantly increased when applying a gate potential. Building upon the improved understanding of the device physics, we further perform simulations and show that the gate field increases the carrier density in the conductive channel below the gate oxide to the extent that the device dynamics are determined by ultra-fast dielectric relaxation rather than by the carrier transit time. In this regime, the bandwidth can be increased to more than 1 THz. We believe that our experiments open a new path towards understanding the principles of internal photoemission in plasmonic structures, leading to PIPED-based optoelectronic signal processing systems with unprecedented bandwidth and efficiency.

Stable and ultraviolet-enhanced broadband photodetectors based on Si nanowire arrays-Cs3Cu2I5 nanocrystals hybrid structures

Silicon has been the most widely used material for broadband photodetectors. However, the weak response in ultraviolet (UV), especially in deep-UV region, and the large dark current are still their critical drawbacks for practical applications. In this study, a strategy of decorating Cs3Cu2I5 nanocrystals (NCs) on Si nanowire arrays (NWAs) to form a hybrid structure was proposed to overcome the above two issues. Because of the wide and direct bandgap of Cs3Cu2I5 with intrinsic UV light absorption, the photodetection ability of the hybrid detector in UV region was substantially enhanced owing to the efficient down-conversion of the UV incident light. Moreover, driven by a designed Schottky junction from asymmetric electrodes, the hybrid detector can be operated without external power supply. Typically, at 265 nm light excitation, the Si NWA-Cs3Cu2I5 NCs hybrid device achieved a high photoresponsivity of 83.6 mA W−1, a specific detectivity of 2.1 × 1012 Jones, and a large on/off ratio of 3.72 × 103 at 0 V, nearly 350 times higher than the bare Si NWA device. More importantly, the unencapsulated photodetector demonstrates an outstanding operational stability over the aging test for 10 h, and can endure a high humidity (75%, 7 days) and a long-term storage for 300 days in air ambient. Since the different deep-UV light sensitivity of the devices modified with/without Cs3Cu2I5 NCs, a monolithically deep-UV light recognition system was therefore fabricated. It is anticipated that the present strategy provides a new avenue for the preparation of UV-enhanced broadband photodetectors, opening up opportunities for development of integrated optoelectronic systems in the future.

Nonlinear acoustic metamaterial for efficient frequency down-conversion.

Frequency conversion is one of the most important nonlinear wave phenomena that has been widely used in the field of electromagnetic waves for changing signal frequencies. Recently, studies on frequency conversion have been actively performed in the field of acoustics owing to its importance in nonlinear ultrasonic nondestructive evaluation and directional speakers. However, acoustic frequency conversion presents relatively poor efficiency owing to the small amplitudes of the converted frequencies and undesired intermodulation. Herein, we propose an acoustic metamaterial to achieve an efficient frequency down-conversion of acoustic waves. Based on background theory, we discovered that the amplitudes of the converted frequencies are inversely proportional to the cube of the speed of sound. Accordingly, we amplify the converted frequency components by reducing the effective speed of sound by coiling up space while suppressing undesired intermodulation by the Bragg gap. Numerical simulation and analytical results show that efficient frequency down-conversion is possible using the corresponding metamaterial. Additionally, dissipation due to viscosity and boundary layer effects is considered. We expect our study results to facilitate research regarding acoustic frequency conversion.

Spatiotemporal effects on squeezing measurements

The role of the spatiotemporal degrees of freedom in the preparation and observation of squeezed photonic states, produced by parametric down-conversion, is investigated. The analysis is done with the aid of a functional approach under the semi-classical approximation and the thin-crystal approximation. It is found that the squeezed state loses its minimum uncertainty property as the efficiency of down-conversion is increased, in a way that depends on the conditions of the homodyne measurements with which the amount of squeezing is determined.

Rare-earth quantum cutting in metal halide perovskites – a review

Ytterbium-doped lead halide perovskite (Yb3+:CsPbX3 with x = Cl or Cl/Br) nanocrystals and thin films have shown surprisingly efficient downconversion by quantum cutting with PLQYs up to 193%. After excitation of the perovskite host with high-energy photons, the excited states of two Yb ions are rapidly populated, subsequently emitting lower-energy photons. Several synthesis routes lead to highly efficient materials, and we review the progress on both the synthesis, material quality and applicability of these downconversion layers. For solar cells they could be used to increase the power converted from high-energy photons, and first applications have already shown an increase in the power conversion efficiency of silicon and CIGS solar cells. Applications such as luminescent solar concentrators an LEDs are also explored. With further research to overcome challenges regarding power saturation and stability, this material has great potential for a simple route to enhance solar cells.

Pump depletion in parametric down-conversion with low pump energies.

We report the efficient generation of high-gain parametric down-conversion, including pump depletion, with pump powers as low as 100 µW (energies 0.1 µJ/pulse) and conversion efficiencies up to 33%. In our simple configuration, the pump beam is tightly focused into a bulk periodically poled lithium niobate crystal placed in free space. We also observe a change in the photon number statistics for both the pump and down-converted beams as the pump power increases to reach the depleted pump regime. The experimental results are a clear signature of the interplay between the pump and the down-converted beams in highly efficient parametric down-conversion sources.

Down-conversion luminescence of Yb3+ in novel Ba4Y3F17:Yb:Ce solid solution by excitation of Ce3+ in UV spectral range

Abstract The down-conversion luminescence under UV excitation was demonstrated in single-phase Ba4Y3F17 solid solution nanoparticles codoped with Ce3+/Yb3+. The complex photodynamic processes occurred in the samples including excited state absorption, excitons and color centers formation. The Yb doping suppressed the solarization effect. The efficiency of down-conversion from UV to near IR luminescence of Yb3+ appeared to be high due to Ce4+-Yb2+ charge transfer mechanism responsible for energy transfer between Ce3+ and Yb3+ ions. The direct measurements of down-conversion luminescence quantum yield by means of integrating sphere and calculations of energy transfer efficiency from luminescence spectra data were carried out. The down-conversion luminescence quantum yield reached the maximum value of about 1% for the sample with 0,1 mol.% of Ce3+ and 5,0 mol.% of Yb3+ ions contents, whereas energy transfer coefficient reached its maximum of about 6,3% for 0,05 mol.% of Ce3+ and 5,0 mol.% of Yb3+ ions.

Effect of surface impurities on downconversion luminescence of Pr3+, Yb3+ activated SrF2 nanoparticles

Pr3+,Yb3+ activated SrF2 nanoparticles synthesized by low-temperature hydrothermal method were studied. The composition and size of nanoparticles were intentionally changed by controlling synthesis conditions. After structural and morphological characterization, the spectroscopic properties of the nanoparticles were analyzed in the visible and near infrared spectra ranges. The results show correlation between the gradual change of the amount of carboxylate and hydroxyl moieties on the nanoparticle surface, varied by the size nanoparticles and the quenching of the luminescence. The size-related amount of surface quenchers is strongly connected to the decrease of the downconversion efficiency.

InGaN Nanohole Arrays Coated by Lead Halide Perovskite Nanocrystals for Solid-State Lighting

In this work, we demonstrate efficient light down-conversion via FRET in InGaN/GaN multiple quantum well (MQW) nanohole arrays, coated with green-emitting CsPbBr3 and FAPbBr3 nanocrystals (NCs) and...

A poly(urethane)-encapsulated benzo[2,3-d:6,7-d′]diimidazole organic down-converter for green hybrid LEDs

A novel green emissive material embedded in a resin provides efficient down-conversion in a hybrid LED.

Frequency downconversion of low-power Raman laser using intracavity difference frequency mixing

We report efficient frequency downconversion of a continuous-wave low-power Raman laser using intracavity difference frequency mixing in a periodically poled lithium niobate (PPLN)-adopted optical parametric oscillator (OPO). The Raman laser was obtained using a 1060-nm fiber laser and 137-m passive fiber. Its central wavelength was fixed at 1111 nm with the power ranging from 320 mW to 5.984 W. The 1060- and 1111-nm pump beams were incident into the OPO at the same time. The high-power 1060-nm pump beam built parametric oscillation first, and the difference frequency generation (DFG) occurred between the low-power Raman laser and intracavity signal laser. The PPLN temperature was properly controlled at 45°C to ensure both the OPO and DFG processes synchronously satisfy phase matching conditions. Benefiting from intracavity high signal power, the Raman laser was successfully converted to the 3560-nm midinfrared radiation under every investigated pump power level. The maximum 3560-nm idler power reached 1.026 W, indicating a 17.4% pump-to-idler slope efficiency and about 15% optical-to-optical conversion efficiency. The comparative experiments also verified that the phase matching conditions were satisfied maximally at 45°C.

Eu3+-doped AlO(OH) as a spectral converter for broadband solar-blind UV photodetection

There has been a growing interest in the application of solar-blind ultraviolet (UV) in fields including astronomy, solar energy, as well as space physics. However, efficient detection of UV in this region remains difficult for most Si-based detectors. The use of a spectral down-converter that converts solar-blind UV into visible emission that is detectable by Si-based devices has been regarded as a simple but cost-efficient strategy. Here, Eu3+-doped AlO(OH) nanoparticles, fabricated by a hydrothermal synthesis method, are demonstrated as spectral converters that converts broadband UV (from 200 to 400 nm) to visible emissions by Eu3+. In this work, the morphology and crystal phase of the Eu3+-doped AlO(OH) nanoparticles were carefully controlled to enable efficient down-conversion luminescence from Eu3+-doped AlO(OH) nanoparticles under the excitation by solar-blind UV light. A photodetector device was constructed by incorporating the Eu3+-doped AlO(OH) nanoparticles into a transparent organic/inorganic composite thin film (AlO(OH): Eu3+-PMMA) that is coated onto a Si-based photosensitive resistance. An efficient photo-voltage response was observed by using an oscilloscope under broadband solar-blind UV irradiation from 200 nm to 400 nm. The results reveal a prospective strategy for the design of detectors operating in the solar-blind UV region.

Electrically Injected Hybrid Organic/Inorganic III-Nitride White Light-Emitting Diodes Based on Rubrene/(InGaN/GaN) Multiple-Quantum-Wells P-N Junction

It is known that the commercialized white light-emitting diodes (WLEDs) depend on phosphor conversion, which is limited by the unbalanced carrier injection in multiple quantum wells (MQWs) and low down-conversion efficiency. To solve these problems, hybrid organic/inorganic III-nitride WLEDs were designed and fabricated based on Rubrene/(InGaN/GaN) MQWs p-n junction. In such new structure, Rubrene can act as yellow–red emitter and play an important role in hole transport layer owing to its high carrier mobility. By optimizing the hybrid LED structure, the charge balance and recombination zone in radiative region were significantly improved. In this work, the optimal hybrid WLED with color coordinates of (0.31, 0.33) shows a maximum current efficiency of 15.22 cd/A with excellent long lifetime stability. The hybrid WLEDs based on organic/inorganic p-n junction were demonstrated with a good performance, which provides an attractive route to achieve high performance phosphor-free WLED sources for microdisplay or large-area WLED applications.

Emission-wavelength-dependent photoluminescence decay lifetime of N-functionalized graphene quantum dot downconverters: Impact on conversion efficiency of Cu(In, Ga)Se2 solar cells

Graphene quantum dots (GQDs) have several advantages over inorganic quantum dots owing to their beneficial properties. Recently, GQDs have been used as downconverters in photovoltaic devices. However, the application of GQDs in most emergent thin-film-based Cu(In, Ga)Se2 (CIGS) photovoltaic cells is limited because of either low photoluminescence (PL) quantum yield (QY) or a small Stokes shift (Δλ). Therefore, GQDs with an ultrahigh QY and large Δλ are essential to realizing the two emergent fields, i.e., the application of GQDs in CIGS photovoltaic solar cells. In this regard, we synthesized nitrogen-functionalized GQDs (NGQDs) with an ultrahigh QY (77–99%) and a large Δλ (95–155 nm) via tailoring of the nitrogen and oxygen moieties. The NGQDs were applied in CIGS solar cells to evaluate their downconversion efficiency. Our study shows that the emission wavelength (λem)-dependent photoluminescence decay lifetime (τem) determines the down-conversion efficiency of the nitrogen-functionalized graphene quantum dots. With the increase in τem at λem > 500 nm, the conversion efficiencies of the NGQDs coated-CIGS solar cells increased by 12.22%. Thus, the increase in τem at λem > 500 nm significantly increased the maximum current output and thus enhanced the solar-cell performance.

Enhancement of efficiency in femtosecond optical parametric oscillators using group-velocity-matching in long nonlinear crystals

The authors describe the exploitation of group-velocity-matching in femtosecond optical parametric oscillators (OPOs) for enhanced down-conversion efficiency into the mid-infrared (mid-IR). We demonstrate the concept in a femtosecond OPO based on a long MgO:PPLN crystal, for the first time, by utilizing group-velocity-matching between pump and idler pulses. Taking advantage of the wide phase-matching bandwidth when pumped near 1 µm enables the use of a 42-mm-long crystal, resulting in an oscillation threshold as low as 5 mW, pump depletion of 78%, and an idler quantum conversion efficiency up to 48% into the mid-IR. Using 80–100 fs pump pulses tunable across 997–1070 nm, we have generated idler radiation across 3132–4273 nm (2340–3193 cm−1) with spectral bandwidth of 140–180 nm, providing up to 65 mW of average power at 80 MHz repetition rate. The near-IR signal is tunable across 1392–1568 nm, with up to 76 mW of average power in transform-limited pulses of ∼400–600 fs duration without dispersion compensation. Preferential operation at group-velocity-matched wavelengths leads to intrinsically high passive power stability with <1% rms fluctuation over 1 h for both signal and idler. With the capability for rapid pump tuning in the mid-IR, this OPO represents a viable source for spectroscopic applications, which we demonstrate using CH4 gas. Extension to other quasi-phase-matched nonlinear crystals is also discussed.