Understanding Bridging Sites and Accelerating Quantum Efficiency for Photocatalytic CO_(2) Reduction

We report a novel double-shelled nanoboxes photocatalyst architecture with tailored interfaces that accelerate quantum efficiency for photocatalytic CO_(2) reduction reaction(CO_(2)RR)via Mo–S bridging bonds sites in S_(v)–In_(2)S_(3)@2H–MoTe_(2).The X-ray absorption near-edge structure shows that the formation of S_(v)–In_(2)S_(3)@2H–MoTe_(2) adjusts the coordination environment via interface engineering and forms Mo–S polarized sites at the interface.The interfacial dynamics and catalytic behavior are clearly revealed by ultrafast femtosecond transient absorption,time-resolved,and in situ diffuse reflectance–Infrared Fourier transform spectroscopy.A tunable electronic structure through steric interaction of Mo–S bridging bonds induces a 1.7-fold enhancement in S_(v)–In_(2)S_(3)@2H–MoTe_(2)(5)photogenerated carrier concentration relative to pristine S_(v)–In_(2)S_(3).Benefiting from lower carrier transport activation energy,an internal quantum efficiency of 94.01%at 380 nm was used for photocatalytic CO_(2)RR.This study proposes a new strategy to design photocatalyst through bridging sites to adjust the selectivity of photocatalytic CO_(2)RR.

Calculation method of quantum efficiency to TiO_2 nanocrystal photocatalysis reaction

The quantum yield is an important factor to evaluate the efficiency of photoreactor. This article gives an overall calculation method of the quantum efficiency( Φ ) and the apparent quantum efficiency( Φ a) to the TiO 2/UV photocatalysis system. Furthermore, for the immobility system (IS), the formulation of the faction of light absorbed by the TiO 2 thin film is proposed so as to calculate the quantum efficiency by using the measured value and theoretic calculated value of transmissivity (T). For the suspension system(SS), due to the difficulty to obtain the absorption coefficient ( α ) of TiO 2 particulates, the quantum efficiency is calculated by means of the relative photonic efficiency ( ζ r) and the standard quantum yield ( Φ standard ).

Internal quantum efficiency drop induced by the heat generation inside of light emitting diodes (LEDs)

The reasons for low output power of AlGalnP Light Emitting Diodes （LEDs） have been analysed. LEDs with AlGaInP material have high internal but low external quantum efficiency and much heat generated inside especially at a large injected current which would reduce both the internal and external quantum efficiencies. Two kinds of LEDs with the same active region but different window layers have been fabricated. The new window layer composed of textured 0.5 μm GaP and thin Indium-Tin-Oxide film has shown that low external quantum efficiency （EQE） has serious impaction on the internal quantum efficiency （IQE）, because the carrier distribution will change with the body temperature increasing due to the heat inside, and the test results have shown the evidence of LEDs with lower output power and bigger wavelength red shift.

High Quantum Efficiency and High Concentration Erbium-Doped Silica Glasses Fabricated by Sintering Nanoporous Glasses

A new method was used to prepare erbium-doped high silica （SiO2 % 〉 96 % ） glasses by sintering nanoporous glasses. The concentration of erbium ions in high silica glasses can be considerably more than that in silica glasses prepared by using conventional methods. The fluorescence of 1532 nm has an FWHM （Full Wave at Half Maximum） of 50 nm, wider than 35 nm of EDSFA （erbium-doped silica fiber amplifer）, and hence the glass possesses potential application in broadband fiber amplifiers. The Judd-Ofelt theoretical analysis reflects that the quantum efficiency of this erbium-doped glass is about 0.78, although the erbium concentration in this glass （6 × 10^3） is about twenty times higher than that in silica glass. These excellent characteristics of Er-doped high silica glass will be conducive to its usage in optical amplifiers and microchip lasers.

Optical simulation of external quantum efficiency spectra of CuIn_(1-x)Ga_xSe_2 solar cells from spectroscopic ellipsometry inputs

Applications of in-situ and ex-situ spectroscopic ellipsometry （SE） are presented for the development of parametric expressions that define the real and imaginary parts （ε1, ε2） of the complex dielectric function spectra of thin film solar cell components. These spectra can then be utilized to analyze the structure of complete thin film solar cells. Optical and structural/compositional models of complete solar cells developed through least squares regression analysis of the SE data acquired for the complete cells enable simulations of external quantum efficiency （EQE） without the need for variable parameters. Such simulations can be compared directly with EQE measurements. From these comparisons, it becomes possible to understand in detail the origins of optical and electronic gains and losses in thin film photovoltaics （PC） technologies and, as a result, the underlying performance limitations. In fact, optical losses that occur when above-bandgap photons are not absorbed in the active layers can be distinguished from electronic losses when electron-hole pairs generated in the active layers are not collected. This overall methodology has been applied to copper indium-gallium diselenide （Culn1-xGaxSe2; CIGS） solar cells, a key commercialized thin film PV technology. CIGS solar cells with both standard thickness （〉2 μm） and thin （〈1 μm） absorber layers are studied by applying SE to obtain inputs for EQE simulations and enabling comparisons of simulated and measured EQE spectra. SE data analysis is challenging for CIGS material components and solar cells because of the need to develop an appropriate （ε1, ε2） database for the CIGS alloys and to extract absorber layer Ga profiles for accurate structural/compositional models. For cells with standard thickness absorbers, excellent agreement is found between the simulated and measured EQE, the latter under the assumption of 100% collection from the active layers, which include the CIGS bulk and CIGS/CdS heterojunction interface layers. For cells with thin absorbers, however, an observed difference between the simulated and measured EQE can be attributed to losses via carrier recombination within a- 0.15 μm thickness of CIGS adjacent to the Mo back contact. By introducing a carrier collection probability profile into the simulation, much closer agreement is obtained between the simulated and measured EQE. In addition to the single spot capability demonstrated in this study, ex-situ SE can be applied as well to generate high resolution maps of thin film multilayer structure, component layer properties and their profiles, as well as short-circuit current density predictions. Such mapping is possible due to the high measurement speed of 〈1 s per （ , 4） spectra achievable by the multichannel ellipsometer.

A quantum efficiency analytical model for complementary metal–oxide–semiconductor image pixels with a pinned photodiode structure

A quantum efficiency analytical model for complementary metal–oxide–semiconductor（CMOS） image pixels with a pinned photodiode structure is developed. The proposed model takes account of the non-uniform doping distribution in the N-type region due to the impurity compensation formed by the actual fabricating process. The characteristics of two boundary PN junctions located in the N-type region for the particular spectral response of a pinned photodiode, are quantitatively analyzed. By solving the minority carrier steady-state diffusion equations and the barrier region photocurrent density equations successively, the analytical relationship between the quantum efficiency and the corresponding parameters such as incident wavelength, N-type width, peak doping concentration, and impurity density gradient of the N-type region is established. The validity of the model is verified by the measurement results with a test chip of 160×160 pixels array,which provides the accurate process with a theoretical guidance for quantum efficiency design in pinned photodiode pixels.

Influence of wet chemical cleaning on quantum efficiency of GaN photocathode

GaN samples 1-3 are cleaned by a 2：2：1 solution of sulfuric acid（98%） to hydrogen peroxide（30%） to de-ionized water;hydrochloric acid（37%）;or a 4：1 solution of sulfuric acid（98%） to hydrogen peroxide（30%）.The samples are activated by Cs/O after the same annealing process.X-ray photoelectron spectroscopy after the different ways of wet chemical cleaning shows：sample 1 has the largest proportion of Ga,N,and O among the three samples,while its C content is the lowest.After activation the quantum efficiency curves show sample 1 has the best photocathode performance.We think the wet chemical cleaning method is a process which will mainly remove C contamination.

Influence of Disassociation Probability on External Quantum Efficiency in Organic Electrophosphorescent Devices

An analytical model is presented to calculate the disassociation probability and the external quantum efficiency at high field in doped organic electrophosphorescence(EPH) devices. The charge recombination process and the triplet(T)-triplet(T) annihilation processes are taken into account in this model. The influences of applied voltage and the thickness of the device on the disassociation probability, and of current density and the thickness of the device on the external quantum efficiency are studied thoroughly by including and ignoring the disassociation of excitons. It is found that the dissociation probability of excitons will come close to 1 at high electric field, and the external EPH quantum efficiency is almost the same at low electric field. There is a large discrepancy of the external EPH quantum efficiency at high electric field for including or ignoring the disassociation of excitons.

Calculation and Improvement on External Quantum Efficiency of OLEDs

The calculation of the external quantum efficiency(η_ ext ) of organic light-emitting devices(OLEDs) is presented theoretically. The basic idea is to obtain η_ ext by calculating the fraction of the generated light that can escape through the top surface and the average transmittance over the escape cone. During the calculation, the effects of the interference, absorption and multiple reflections are neglected. Then a result of a typical 8-tris-hydroxyquinoline aluminum(Alq_ 3 )-based OLEDs on a planar glass substrate is obtained. And a twice increase in η_ ext can be achieved by using a high-index-glass substrate with an antireflection coating(SiO_ 2 ) on substrate surface.

2D Modeling of Solar Cell p-n Radial Junction: Study of Photocurrent Density and Quantum Efficiency in Static Mode under Monochromatic Illumination

A theoretical study of a polysilicon solar cell with a radial junction in static regime under monochromatic illumination is presented in this paper. The junction radial solar cell geometry is illustrated and described. The carriers’ diffusion equation is established and solved under quasi-neutral base assumption with boundaries conditions and Bessel equations. New analytical expressions of electrons and holes photocurrent density and quantum efficiency are found. The wavelength and structural parameters (base radius, base thickness and wavelength) influences on photocurrent density and quantum efficiency are carried out and examined.

External Quantum Efficiency of Quantum Well Solar Cells

The external quantum efficiency of quantum well solar cells （QWSCs） is compared with the control cells without multi-quantum wells. The QWSCs extend the absorption spectrum from 870 to 1000nm. When the wavelength is below 680nm,the external quantum efficiency of the QWSCs is lower than that of the control cells, but when the wavelength is above 680nm, the external quantum efficiency of the QWSCs is higher than that of the control cells. The possible reasons for this phenomenon are discussed. Basing on the experimental data,the possibility of substituting the middle cells of conventional triple-junction solar cells with the QWSCs to improve their performance is also discussed.

Influence of local phonon energy on quantum efficiency of Tb^(3+)-Yb^(3+) co-doped glass ceramics containing fluoride nanocrystals

The Tb3＋single-doped and Tb3＋-Yb3＋co-doped glass ceramics with the precipitation of CaF2, CaF2-SrF2 solid state solu-tion and SrF2 nanocrystals were designed and prepared by taking different amounts of CaF2 and SrF2 as the starting fluorides to inves-tigate the influence of the crystalline phase on the total quantum efficiency. The formation of the fluoride nanocrystals and the incor-poration of the doped rare earth ions into the fluoride nanocrystals were proved by the XRD measurement. The energy transfer from Tb3＋to Yb3＋was studied by the steady and time resolved spectra. The total internal quantum efficiencies were calculated based on the measured Tb3＋lifetime, which was about 10.5%improved in the SrF2 nanocrystals precipitated glass ceramics compared with that in the CaF2 nanocrystals precipitated glass ceramics mainly due to the lower phonon energy environment. Meanwhile, the total external quantum efficiencies were evaluated with the integrating sphere measurement system, which were 18.6%, 19.3%and 24.4%, respec-tively, for the CaF2, CaF2-SrF2 and SrF2 nanocrystals precipitated glass ceramics. Additionally, obvious difference between the calcu-lated total internal quantum efficiency and the measured total external quantum efficiency was also discussed.

Full well capacity and quantum efficiency optimization for small size backside illuminated CMOS image pixels with a new photodiode structure

To improve the full well capacity （FWC） of a small size backside illuminated （BSI） CMOS image sensor （CIS）, the effect of photodiode capacitance （Cpo） on FWC is studied, and a reformed pinned photodiode （PPD） structure is proposed. Two procedures are implemented for the optimization. The first is to form a varying doping concentration and depth stretched new N region, which is implemented by an additional higher-energy and lower-dose N type implant beneath the original N region. The FWC of this structure is increased by extending the side wall junctions in the substrate. Secondly, in order to help the enlarged well capacity achieve full depletion, two step P-type implants with different implant energies are introduced to form a P-type insertion region in the interior of the stretched N region. This vertical inserted P region guarantees that the proposed new PD structure achieves full depletion in the reset period. The simulation results show that the FWC can be improved from 1289e- to 6390e-, and this improvement does not sacrifice any image lag performance. Additionally, quantum efficiency （QE） is enhanced in the full wavelength range, especially 6.3% at 520 nm wavelength. This technique can not only be used in such BSI structures, but also adopted in an FSI pixel with any photodiode-type readout scheme.

Ce^(3+) doped BaLu_(2)Al_(2)Ga_(2)SiO_(12)——A novel blue-light excitable cyan-emitting phosphor with ultra-high quantum efficiency and excellent stability for full-spectrum white LEDs

It is well known that cyan-emitting phosphors play a very important role in full-spectrum white LEDs.A large number of cyan-emitting phosphors have been reported in the past few years,however,most of them can only be effectively excited by near-ultraviolet light.There are very few cyan-emitting phosphors that can be intensively excited by blue light(440 and 470 nm).Here,a novel blue-light excitable cyan-emitting phosphor BaLu_(1.95)Ce_(0.05)Al_(2)Ga_(2)SiO_(12)with excellent performance is reported.The cyan phosphor has a cubic structure in space group Ia3^(-)d with a=1.205379(3)nm,which can be easily obtained through a solid-state reaction pathway.The emission peak of the cyan phosphor is located at 500 nm and its internal quantum efficiency is as high as 90.01%when excited at 455 nm at 25℃.The cyan phosphor exhibits superior resistance against thermal quenching of luminescence,and its intensity at 125℃is as strong as 92.14%of the intensity at room temperature.Meanwhile,it also shows an outstanding resistance against water,where its luminescence intensity is hardly changed after being immersed in pure water for 528 h.The white LED lamp prepared by employing the obtained BaLu_(1.95)-Ce_(0.05)Al_(2)Ga_(2)SiO_(12)as cyan phosphor displays remarkable optical properties with CCT=4441 K,Ra=93.7,CRI=90.4 and CIE 1931(x,y)as(x=0.3648,y=0.3752).The experimental results demonstrate that BaLu_(1.95)Ce_(0.05)Al_(2)Ga_(2)SiO_(12)is a promising cyan-emitting phosphor with great application potential in full-spectrum white LEDs.

Evaluation of new large area PMT with high quantum efficiency

The neutrino detector of the Jiangmen Underground Neutrino Observatory（JUNO） is designed to use20 kilotons of liquid scintillator and approximately 16000 20 inch photomultipliers（PMTs）.One of the options is to use the 20 inch R12860 PMT with high quantum efficiency which has recently been developed by Hamamatsu Photonics.The performance of the newly developed PMT preproduction samples is evaluated.The results show that its quantum efficiency is 30%at 400 nm.Its Peak/Valley（P/V） ratio for the single photoelectron is 4.75 and the dark count rate is 27 kHz at the threshold of 3 mV while the gain is at 1 × 10^7.The transit time spread of a single photoelectron is 2.86 ns.Generally the performances of this new 20 inch PMT are improved over the old one of R3600.

Realization of quantum efficiency enhanced PIN photodetector by assembling resonant waveguide grating

We demonstrate an InP/InGaAs PIN photodetector with enhanced quantum efficiency by assembling silicon resonant waveguide gratings for the application of polarization sensitive systems. The measured results show that quantum efficiency of the photodetector with silicon resonant waveguide gratings can be increased by 31.6% compared with that without silicon resonant waveguide gratings at the wavelength range of 1500 to 1600 nm for TE-polarization.

The enhancement of light-emitting efficiency using GaN-based multiple quantum well light-emitting diodes with nanopillar arrays

The quest for higher modulation speed and lower energy consumption has inevitably promoted the rapid development of semiconductor-based solid lighting devices in recent years. GaN-based light-emitting diodes （LEDs） have emerged as promising candidates for achieving high efficiency and high intensity, and have received increasing attention among many researchers in this field. In this paper, we use a self-assembled array-patterned mask to fabricate InGaN/GaN multi- quantum well （MQW） LEDs with the intention of enhancing the light-emitting efficiency. By utilizing inductively coupled plasma etching with a self-assembled Ni cluster as the mask, nanopillar arrays are formed on the surface of the InGaN/GaN MQWs. We then observe the structure of the nanopillars and find that the V-defects on the surface of the conventional structure and the negative effects of threading dislocation are effectively reduced. Simultaneously, we make a comparison of the photoluminescence （PL） spectrum between the conventional structure and the nanopillar arrays, achieved under an experimental set-up with an excitation wavelength of 325 mm. The analysis demonstrates that MQW-LEDs with nanopillar arrays achieve a PL intensity 2.7 times that of conventional LEDs. In response to the PL spectrum, some reasons are proposed for the enhancement in the light-emitting efficiency as follows： 1） the improvement in crystal quality, namely the reduction in V-defects; 2） the roughened surface effect on the expansion of the critical angle and the attenuated total reflection; and 3） the enhancement of the light-extraction efficiency due to forward scattering by surface plasmon polariton modes in Ni particles deposited above the p-type GaN layer at the top of the nanopillars.

Effect of Particle Size and Capping on Photoluminescence Quantum Efficiency of 1,3,5-Triphenyl-2-pyrazoline Nanocrystals

Organic nanocrystals of 1,3,5-triphenyl-2-pyrazoline (TPP) with a series of sizes were synthesized by reprecipitation method. The luminescence quantum efficiency of TPP nanocrystals increases from 24.2% for the nanocrystals with an average size of 300 nm to 34.6% for those with an average size of 20 nm. Surface capping by polyvinyl pyrrolidone (PVP) will improve the quantum efficiency of TPP nanocrystals. The size-dependence and capping-induced variation of the luminescence quantum efficiency was elucidated in viewpoint of aggregation quenching and the equilibrium between the TPP monomers and the aggregates in TPP nanocrystals.

Probing fluorescence quantum efficiency of single molecules in an organic matrix by monitoring lifetime change during sublimation

Quantum efficiency is a critical piece of information of a quantum emitter and regulates the emitter’s fluorescence decay dynamics in an optical environment through the Purcell effect.Here,we present a simple way to experimentally probe fluorescence quantum efficiency of single dibenzoterrylene molecules embedded in a thin anthracene microcrystal obtained through a co-sublimation process.In particular,we correlate the fluorescence lifetime change of single dibenzoterrylene molecules with the variation of the matrix thickness due to natural sublimation.With the identification of the molecule emission dipole orientation,we could deduce the near-unity intrinsic quantum efficiency of dibenzoterrylene molecules in the anthracene matrix.

Multi－diffused Reflection Spectroscopy of Rare Earths Doped LaOCl Powder Samples and the Calculation of Quantum Efficiency

The excitation and emission spectra, the relaxation time of principal spectral lines and multi-diffused reflection spectra in LaOCl: Er, LaOCl: Ho powder samples were measured. The diffused absorption spectrum was derived from the multi-diffused reflection spectrum. According to Judd-Ofelt theory,the intensity parameters, radiative transition probabilities and quantum efficiencies of luminescence emission were calculated. Then comparison with erbium and holmium doped floride glass and other matrices were made.