Two-step Up-conversion Research Articles

Simulation approach to reach the SQ limit in CIGS-based dual-heterojunction solar cell

In this article, we demonstrate the design and simulation of a copper indium gallium diselenide (CIGS)-based highly-efficient n-CdS/p-CIGS/p+-CGS dual-heterojunction (DH) solar cell. The simulation has been performed using SCAPS-1D software with reported experimental physical parameters. The simulated efficiency of our proposed solar cell arises to 47% with open circuit voltage, VOC = 0.98 V, short circuit current density, JSC = 59.94 mA/cm2 and fill factor, FF = 80.07%, respectively. Such a high short circuit current and corresponding elevated efficiency are predominantly originated from the longer wavelength absorption of photons through a tail-states-assisted (TSA) two-step upconversion in the copper gallium diselenide (CGS) Back surface field (BSF) layer of the DH solar cells. The suggested method numerically approaches the Shockley-Queisser (SQ) detailed balance limit, providing a possible opportunity of enhancing existing photovoltaic (PV) parameters to the researchers as well as manufacturers.

Static volumetric three-dimensional display based on an electric-field-controlled two-dimensional optical beam scanner.

Using the quadratic electro-optic effect and the gradient of the composition ratio m [Nb/(Ta+Nb) in mol. %] in a potassium tantalate niobate crystal, we have designed an electric-field-controlled two-dimensional optical beam scanner with a wide wavelength range and fast response. This scanner is used to realize a volumetric display based on a two-frequency, two-step upconversion technique that is used to address the imaging volume. Use of appropriately designed imaging optics and custom-designed software to convert 2D renderings of volumetric images into control signals for the scanner along with appropriate infrared laser source selection allows efficient single-color image generation with a large viewing zone, without flicker and with natural depth cues. The resulting system has the potential to increase image resolution to nearly 61.5×109 with high scanning frequency and to expand to display three-color imagery.

Upconversion luminescence in bismuth-doped germano-silicate glass optical fiber

We report, for the first time, a broadband upconversion emission (800–1000 nm) in Bi-doped germano-silicate glass optical fibers with excitation in the range of 1515–1585 nm, which can explain the low laser efficiency at wavelengths longer than 1500 nm. The mechanism responsible for the emission is two-step upconversion process. The origin of this upconversion luminescence is discussed and new energy transition schemes are proposed. • We fabricated bismuth-doped germane-silicate glass optical fibers. • New upconversion emission band was observed by pumping around 1.5 μm. • Both emissions at 837 and 945 nm depend quadratically on the incident power. • Two-step upconversion process and new energy transition scheme was proposed.

Finding a Single Lanthanide Ion through Upconversion

Beyond detection: Detection of a single lanthanide ion can be optically achieved by implementing a two-step upconversion process in YAG:Pr(3+) nanocrystals (see picture).

Efficient two-step up-conversion by quantum-correlated photon pairs

We theoretically investigate the sequential two-step upconversion of correlated photon pairs with positive and negative energy correlations, in terms of how the up-conversion efficiency depends on the incident pulse delay. A three-level atomic system having a metastable state is used to evaluate the up-conversion efficiency. It is shown that a photon pair with a positive energy correlation can drastically enhance the up-conversion efficiency compared with uncorrelated photons and correlated photons with a negative energy correlation.

Spectroscopic studies of Er3+ doped Ge-Ga-S glass containing silver nanoparticles

Abstract The spectroscopic characteristics of an erbium-doped Ga 10 Ge 25 S 65 (GGS) glass containing silver were studied and compared with that of an erbium-doped GGS glass without silver. The optical absorption spectra revealed the surface plasmon resonance (SPR) related characteristic of silver nanoparticles (NPs) around 490 nm. Enhancement of Er 3+ luminescence was observed for a broad excitation wavelength region, and the largest enhancement was observed for the excitation at 488 nm, which is near the peak of SPR of silver NPs in GGS glass and in resonance with Er 3+ ions. For the excitation at 405 nm, enhancement of luminescence from both GGS host and Er 3+ ions was observed. A smaller enhancement was observed for a two-step upconversion luminescence excited at 801 nm. The observed enhancement of Er 3+ luminescence is mainly attributed to the local field effects: the SPR of Ag NPs causes an intensified electromagnetic field around NPs, resulting in enhanced optical transitions of Er 3+ ions in the vicinity.

Static Volumetric Three-Dimensional Display

We present here the development of a volumetric display based on the two-frequency, two-step upconversion technique using novel techniques for addressing the imaging volume. Two 1024 times 768 digital micromirror displays, driven by 30-W lasers at 1532 and 850 nm are utilized to generate fast scanning of the image volume in a 17 mm times 17 mm times 60 mm 2% erbium-doped lithium yttrium fluoride (YLF) crystal. Experimentally, images at 532 nm were created at 30 (frames) times 1024 times 768 resolution, resulting in almost 23 million voxels, at 500 frames/s, significantly higher than that obtained with three-dimensional (3D) raster scanning (frame is 2D cross-sectional plane of the 3D image). Imaging optics modified from projector systems and fiber-optically coupled to the source, combined with custom designed software for converting two-dimensional (2D) rendering of volumetric images into control signals for the digital micromirror displays allow single-color image generation with no flicker and natural depth cues. Improvements in optical power efficiency and the speed of digital micromirror display controller boards are needed for the system to reach its full potential. The resulting system has the potential to increase resolution to nearly 800 million voxels without viewpoint obstruction and expand to three-color imagery.

Concentration and temperature dependence of visible up-conversion luminescence in sol-gel SnO 2 doped with erbium

A sol-gel method was used to prepare erbium (Er 3+)-doped tin dioxide (SnO 2). Photoluminescence (PL) properties of Er 3+-doped SnO 2 were investigated using a 798-nm excitation wavelength. We show efficient green and red up-conversion emissions by varying the concentration of erbium. The study of the 4S 3/2 → 4I 15/2 (545 nm) and 4F 9/2 → 4I 15/2 (647 nm) transition intensities of Er 3+ versus the laser pump power has evidenced a two-step up-conversion process. It was found that the increase of Er 3+ concentration leads to a considerable enhancement of the red up-conversion emission compared to the green one. This behaviour has been explained in terms of an energy transfer between excited ions. By increasing the temperature in the range 80–300 K, the up-conversion PL intensity of both green and red presents a weak quenching. This weak thermal quenching is related to the excitation mechanism of Er in SnO 2 host where the multiphonon process is not probable.

Reducing Spurious Output of Balanced Modulators by Dynamic Matching of I, Q Quadrature Paths

This paper presents a technique for reducing spurious output of balanced modulators used in transmitters and arbitrary waveform generators. Two-step upconversion is a convenient way to produce a desired single-sideband (SSB) radio-frequency (RF) signal-baseband quadrature I and Q signals (which are analog outputs of direct digital frequency synthesizers) are upconverted by mixers and local oscillators (LOs)-but mismatches between the DACs in I and Q paths cause spurious output. We propose a method of dynamically matching the I and Q paths by multiplexing two DACs between I and Q paths in a pseudo-random manner. MATLAB simulation shows that multiplexing the two DACs spreads the spurious output, caused by mismatches between the two DACs, in the frequency domain, and reduces the peak level of spurious signals.

Study of the spectroscopic properties and infrared-to-visible up-conversion fluorescence of Er3+-doped germanate glasses

Raman scattering, optical absorption and photoluminescence studies have been performed on Er3+-doped Na2O–Nb2O5–GeO2 germanate-based glasses. The main bands in the Raman spectra involve vibrational modes associated with the germanium oxide network. Judd–Ofelt intensity parameters were determined and then used to calculate the radiative transition rates and excited-state radiative lifetimes. Green and red up-conversion luminescence was observed at room temperature under 800 nm laser line excitation. The emission intensities have a quadratic dependence on the excitation pump power, indicating a two-step up-conversion mechanism. The intensity of the 660 nm red band shows an increase relative to the 554 nm green band with increasing Er3+ content. Combined with the time-resolved luminescence data of the emitting states, we suggest from these results that the up-conversion process is attributed to a competitive situation of excited-state absorption and energy transfer between excited ions accompanied by multiphonon relaxation. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

980 nm excited upconversion in an Er-doped ZnO–TeO2 glass

In this letter, we investigate the upconversion properties of 19ZnO–80TeO2–1Er2O3 glass after excitation into the I11/24 level using 980 nm radiation. At an excitation power density of 880 W/cm2, green emission [(2H11/2, 4S3/2)→4I15/2] dominates the upconversion spectrum with an efficiency of 0.16%. Temporal studies reveal that the I11/24 level is the intermediate state by which the two-step upconversion process occurs. Excited-state absorption and phonon-assisted energy transfer are discussed as possible mechanisms for the upconversion.

Effects of Activator Ion Concentration on the Upconversion Processes in Er3+-Doped TeO2-ZnO Glass

Photoluminescence properties of Er3+-doped 70TeO2–30ZnO glasses are investigated. Infrared to visible upconversion has been observed at room temperature in this tellurite glass using a 797 nm excitation laser. A study of the 4S3/2 → 4I15/2 and 4F9/2 → 4I15/2 transitions versus excitation laser power shows evidence for a two-step upconversion process under this excitation. The red emission originating from the 4F9/2 → 4I15/2 transition is enhanced relative to the green emission with increasing Er3+ ion concentration. This behaviour has been explained as being due to an energy transfer between activator ions. The temperature dependence of the upconversion intensity has also been studied in the range 60–310 K. It was found that the red emission of 4F9/2 → 4I15/2 grows considerably relative to the green transition with increasing temperature in heavily doped samples. This indicates that energy transfer mechanisms, responsible for the red emission enhancement, are temperature dependent.

Excited-state-absorption in low concentrated Er : YAG crystals for pulsed and cw pumping

In this paper we discuss the upconversion processes responsible for violet luminescence from the erbium levels 2P 3/2 (transition 2P 3/2→ 4I 13/2) and 2H2 9/2 ( 2H2 9/2→ 4I 15/2), excited at room temperature in low concentrated Er : YAG crystals with pulsed (at 532 nm) as well with cw (at 488 nm) lasers. Besides the general need for new spectroscopic data concerning laser materials, the interest for this study is generated by the fact that energy levels of very different quantum efficiencies (∼0.25 for 2P 3/2 and ∼0.0004 for 2H2 9/2) can produce, in favorable pumping conditions, fluorescence spectra of comparable intensities. Thus, though for 532 nm pulse excitation (pump transition 4I 15/2→ 4S 3/2), the intensity of the lines originating from 2P 3/2 is much stronger than the lines starting from 2H2 9/2, in accord with the corresponding quantum efficiencies, cw pumping at 488 nm (pump transition 4I 15/2→ 4F 7/2) produces luminescence spectra of comparable intensities. In order to explain the relative intensities of the observed luminescence spectra, various two-step upconversion mechanisms (excited state absorption (ESA) at low erbium concentrations) were proposed. We found that for cw excitation, an analysis of the energetic resonance between ESA transitions and pumping quanta was necessary. For this, we used a simple model to simulate the ESA spectra, in which both initial and final states were approximated with sums of Lorentzian functions and the multiplet to multiplet transition probabilities were estimated with the Judd–Ofelt theory. The choice of the linewidths in our model was based on the analysis of the room temperature absorption and fluorescence spectra and on the possible resonances with the phonons. A fairly good agreement between the observed intensity ratio of the 2P 3/2→ 4I 13/2 and 2H2 9/2→ 4I 15/2 luminescence spectra and that predicted by our model was obtained.

Infrared to visible up-conversion study for erbium-dopedzinc tellurite glasses

Optical absorption and photoluminescence properties of Er3+-doped70TeO2-30ZnO glass are investigated. Judd-Ofelt intensityparameters of Er3+ have been determined to calculate the radiativetransition probabilities and the radiative lifetimes of excited states. Aninfrared to visible up-conversion was observed at room temperature in thistellurite glass system using a 797 nm excitation line. A study of the 4S3/2-4I15/2 transition (554 nm) versus power excitationprovided evidence for a two-step up-conversion process under this excitation.A red emission (663 nm) originating from the 4F9/2-4I15/2 transition has been observed as well. It was found that theefficiency of this up-conversion line is enhanced considerably with the Er3+ concentration relative to the green emission (554 nm). Thisbehaviour has been explained in terms of an energy transfer between excitedions. The temperature dependence of up-conversion intensity has been alsostudied in the range 40-310 K. It was found that the thermal quenching of thegreen emission (4S3/2-4I15/2) is large enoughcompared with those of the red transition (4F9/2-4I15/2 ). This thermal quenching has been discussed using the Riseberg andMoos model of multiphonon emission. It has been shown that the latter approachis not consistent with existing results. A complete analysis of thetemperature-dependent up-conversion has been made using an additional decayrate which may be attributed to a non-radiative energy transfer and/or acharge transfer through trapping impurities. A good agreement has beenachieved between measured and computed data.

Spectroscopic studies on multiphoton processes in erbium doped fluoride and oxide glasses

Spectroscopic analyses of the multiphoton process in erbium doped fluoride and telluride glasses (60TeO 2–25BaO–10ZnO–4YO 3/2–1ErO 3/2 and 40AlF 3–22BaF 2–22CaF 2–15YF 3–1ErF 3 in mol%) were carried out by monitoring the upconversion luminescence with excitation spectra and time-resolved luminescence decays. The two-step upconversion mechanisms by excited state absorption and by energy transfer are explained. Under continuous-wave excitation, the excitation profile of the Er 3+ green emission was correlated with the squared absorption spectra in the fluoride glass, indicating energy transfer upconversion. In the telluride glass, the profiles deviated because the excited state absorption from the 4I 13/2 level was larger. Under pulse excitation, the upconversion by energy transfer was larger in both glasses. To clarify the energy transfer scheme contributing to the green upconversion, the luminescence decay curves were analyzed quantitatively with proper rate equations and calculations of the radiative decay rates. The intermediate level was attributed uniquely to be the 4I 11/2 in both telluride and fluoride glasses.

Energy transfer and photon avalanche in Tm3+:LaF3

Single pulse laser excitation at 656 nm and successive pulse excitation at 635.2 and 648.4 nm produced blue emission at 480 nm by two-step upconversion process in Tm/sup 3+/:LaF/sub 3/. The excited-state absorption cross-section of the /sup 3/F/sub 4/ to /sup 1/G/sub 4/ transition was estimated by a looping mechanism with cross-relaxation processes. The dynamics of up-conversion andthe possibility of the photon avalanche by a pulse laser excitation were studied by numerical simulation with the rate equation model.

Two-step upconversion luminescence in Yb:Tb:YSGG crystal

Multiline upconversion luminescence ranging from 375 to 635 nm was studied in Yb:Tb:YSGG crystal, a possible candidate for a tunable upconversion laser material. This luminescence was attributed to the transitions starting from the 5D3 and 5D4 excited levels of Tb. Two sequential steps in the upconversion were determined: at the first step Yb–Tb cooperative upconversion and cooperative absorption populate level 5D4, and at the second step interaction of excited Yb and Tb (in the 5D4 state) ions populates level 5D3. At 500-mW Ti:sapphire pumping, the excited-state concentration of Tb ions exceeded 2% of Yb excited-state concentration.

Spectroscopy and green upconversion laser emission of Er3+-doped crystals at room temperature

The spectroscopic parameters of Er3+-doped crystals were determined with regard to the upconversion laser parameters of the green transition 4S3/2→4I15/2. The influence of excited-state absorption on this laser channel was determined. Furthermore, upconversion pump mechanisms using ground-state and excited-state absorption around 810 and 970 nm were investigated by direct measurements of excited-state absorption. The spectroscopic results confirm the pulsed room-temperature laser experiments on the 4S3/2→4I15/2 transition. The lasers based on Er:LiYF4, Er:Y3Al5O12, and Er:Lu3Al5O12 were directly excited into the upper laser level by an excimer laser pumped dye laser in the blue spectral range. In Er:LiYF4, Er:KYF4, and Er:Y3Al5O12, laser action was achieved with two-step upconversion pumping by a Ti:sapphire laser and a krypton ion laser. In the case of the fluorides, the additional pumping with the krypton ion laser was not necessary. The laser emission wavelengths were 551 nm for Er:LiYF4, 561 nm for Er:Y3Al5O12 and Er:Lu3Al5O12, and 562 nm for Er:KYF4. In addition, green quasi-cw laser emission of Er:LiYF4 pumped with an argon-ion laser was realized at room temperature.

Efficient infrared detection by two-step upconversion

Detection of infrared radiation by nonlinear upconversion into the visible region is considered. The method enables one to operate the system at room temperature. It is shown that by employing a second-step upconversion in commonly available visible nonlinear crystals like KDP, KD,∗ P and ADP it is possible to detect infrared signals with sensitive photocathodes.

Rhenium(IV) as a sensitizer for two-step blue up-converters

The fluorescence of rhenium(IV) and thulium(III) ions doped singly and together in the most host lattice Cs 2NaYCl 6 is studied. Energy transfer between Re 4+ and Tm 3+ ions is demonstrated and is shown to provide two-step up-conversion to the 1D 2 and 1G 4 levels of the Tm 3+ ion, both of which emit in the blue.