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The perovskite based phosphor materials are widely used to increase the efficiency of solar cells. In this work, Er3+ doped and Er3+/Yb3+ co-doped CaTiO 3 perovskite phosphor samples have been synthesized by solid state reaction technique at 1473 K. The phosphor samples show orthorhombic phase with Pnma (62) space group. The average crystallites and particles size of CaTiO 3 are increased in presence of Er3+ and Yb3+ ions. Er3+ doped CaTiO 3 phosphor samples give downshifting emission under 379 nm excitation. Though upconversion emission is seen in Er3+ under 980 nm excitation without Yb3+ ions in this host. The emission intensity of Er3+ ion is enhanced by 46 and 16 times for green and red emissions, respectively in presence of Yb3+. An intense quantum cutting (QC) emission is observed at 980 nm in presence of Yb3+ in CaTiO 3 :0.5Er3+ phosphor under 379 nm excitation. The QC efficiency has been found to be 119 % for CaTiO 3 :0.5Er3+/5 Yb3+ phosphor. Further an interesting phenomenon of back energy transfer (BEnT) from Yb3+ to Er3+ giving an intense NIR emission from Er3+ at 1002 and 1550 nm have been observed. The phosphor sample also shows an intrinsic optical bistablity (IOB) by upconversion. Thus, the prepared phosphor samples may be useful to increase the efficiency of c-Si solar cell, NIR emission for communication, bistable material and green light emitting source. [Display omitted] [ABSTRACT FROM AUTHOR]

Quantum-cutting luminescent solar concentrators (QC-LSCs) have great potential to serve as large-area solar windows. These QC nanocrystals can realize a photoluminescence quantum yield (PLQY) of as high as 200% with virtually zero self-absorption loss. Based on our previous work, we have constructed a Monte Carlo simulation model that is suitable to simulate the performance of the QC-LSCs, which can take into account the band-edge emissions and near-infrared emissions of the QC-materials. Under ideal PLQY conditions, CsPbClxBr3−x:Yb3+-based LSCs can reach 12% of the size-independent external quantum efficiency (ηext). Even if LSCs have a certain scattering factor, the CsPbClxBr3−x:Yb3+-based LSCs can still obtain an ηext exceeding 6% in the window size (>1 m2). The flux gain (FG) of the CsPbClxBr3−x:Yb3+-based LSC-PV system can reach 14 in the window size, which is a very encouraging result. [ABSTRACT FROM AUTHOR]

A new phosphor Sr5(BO3)3Cl:Ce3+,Yb3+, which enables near-infrared (NIR) quantum cutting, was prepared using traditional solid-state reaction methods. Its properties were examined using X-ray diffraction, photoluminescence emission, excitation spectra, and measurements of fluorescence decay. Upon excitation of Ce3+ with an ultraviolent (UV) photon at 350 nm, broadband emission at 415 nm and an intense NIR emission at 982 nm were observed. Emission at 415 nm corresponds to 5d→4f transition of Ce3+ ions, whereas the NIR emission at 982 nm is ascribed to the characteristic 2F5/2 → 2F7/2 transition of Yb3+ ions. Thorough investigation delved into how the concentration of Ce3+ affects visible and NIR emissions, decay lifetime, and energy transfer efficiency (ηETE). Detailed analysis of photoluminescence excitation, emission spectra, and fluorescence decay measurements revealed a proficient energy transfer from Ce3+ to Yb3+ ions. This transfer was demonstrated as a cooperative energy transfer (CET) process, showcasing a CET efficiency of 71.2% and a total theoretical quantum efficiency of 171.2%. [ABSTRACT FROM AUTHOR]

Silicon solar cells are currently the most widely used type, accounting for more than 90% of the commercial market. However, the spectral mismatch between the solar spectrum and the absorption spectra of the cells is the main cause restricting their conversion efficiency, which cannot exceed the Shockley–Queisser limit. Quantum cutting can convert one high‐energy photon into two or more low‐energy photons and reduce the energy loss of the high‐energy photons, providing a way to improve the photoelectric conversion efficiency (PCE) of silicon solar cells. The unique electronic configuration of rare‐earth elements gives them excellent optical properties and makes them good candidates for the luminescent centers of quantum cutting materials. This article reviews their luminescence mechanism, energy transfer (ET) mechanism, and application in silicon solar cells and outlines the potential problems of broadband‐sensitized near‐infrared (NIR) quantum cutting materials. Some key issues and future directions are also discussed. [ABSTRACT FROM AUTHOR]

Fluorides have a wide bandgap and therefore, when doped with the appropriate ions, exhibit emissions in the ultraviolet C (UVC) region. Some of them can emit two photons in the visible region for one excitation photon, having a quantum efficiency greater than 100%. In a novel exploration, praseodymium (Pr3+) ions were introduced into KLaF4 crystals for the first time. The samples were obtained according to a high-temperature solid-state reaction. They exhibited an orthorhombic crystal structure, which has not been observed for this lattice yet. The optical properties of the material were investigated in the ultraviolet (UV) and visible ranges. The spectroscopic results were used to analyze the Pr3+ electronic-level structure, including the 4f5d configuration. It has been found that KLaF4:Pr3+ crystals exhibit intense luminescence in the UVC range, corresponding to multiple 4f → 4f transitions. Additionally, under vacuum ultraviolet (VUV) excitation, distinct transitions, specifically 1S0 → 1I6 and 3P0 → 3H4, were observed, which signifies the occurrence of photon cascade emission (PCE). The thermal behavior of the luminescence and the thermometric performance of the material were also analyzed. This study not only sheds light on the optical behavior of Pr3+ ions within a KLaF4 lattice but also highlights its potential for efficient photon management and quantum-based technologies. [ABSTRACT FROM AUTHOR]

Rare earth-doped up-conversion materials have attracted considerable attention because of their various applications in solid-state lasers, color displays, bioimaging, and so forth. The emission of most up-conversion materials does not have enough intensity. However, this intensity can be increased by doping of sensitizers. Ho3+-doped compounds show green emission which have various applications. Here, we have reported how the intensity of green emission can be increased by doping of sensitizers Yb3+ and Li+. In this work, we have chosen Y2O3 as the host, Ho3+ as the activator, and Yb3+ as the sensitizer and have studied their up-conversion properties under 980 nm laser. The metal citrate-gel decomposition method provides a homogeneous solid solution formation. Green light intensity increases significantly by the increase in the Yb3+ concentration as well as codoping of Li+. The green light intensity of Ho3+ for Y2O3:10 at % Yb3+–2 at % Ho3+–5 at % Li+ system is 9 times more than that of the Y2O3:10 at % Yb3+–2 at % Ho3+ system. Also, we have carried out down-conversion phenomena of Ho3+ by excitation at 448 nm. Luminescence intensity of Ho3+ in the visible range decreases with doping of Yb3+ or Li+ due to energy transfer from Ho3+ to Yb3+. Interestingly, luminescence peaks corresponding to Yb3+ (1000 nm) and Ho3+ (1200 nm) in the NIR range are also observed under 448 nm excitation. Peak observed at 1000 nm is related to the quantum cutting phenomenon. The quantum efficiency is found to be 180% from calculations. Its applications are extensively shown in different areas such as security ink, consignment identification, and bioimaging of muscle and bone through the NIR light up-conversion process. [ABSTRACT FROM AUTHOR]

Quantum-cutting luminescent solar concentrators (QC-LSCs) have great potential to serve as large-area solar windows. These QC nanocrystals can realize a photoluminescence quantum yield (PLQY) of as high as 200% with virtually zero self-absorption loss. Based on our previous work, we have constructed a Monte Carlo simulation model that is suitable to simulate the performance of the QC-LSCs, which can take into account the band-edge emissions and near-infrared emissions of the QC-materials. Under ideal PLQY conditions, CsPbClxBr3−x:Yb3+-based LSCs can reach 12% of the size-independent external quantum efficiency (ηext). Even if LSCs have a certain scattering factor, the CsPbClxBr3−x:Yb3+-based LSCs can still obtain an ηext exceeding 6% in the window size (>1 m2). The flux gain (FG) of the CsPbClxBr3−x:Yb3+-based LSC-PV system can reach 14 in the window size, which is a very encouraging result.

In this work, the downconversion (DC) behaviour of Ho3+ ions doped in pure YVO 4 , YNbO 4 , YTaO 4 hosts and their intermixed (i.e. Ta/V, Ta/Nb and Nb/V) compositions have been investigated and compared. The samples were synthesized by solid-state reaction technique at 1473 K. The UV–Vis absorption and photoluminescence behaviour of 1 mol % Ho3+ doped YVO 4 , YNbO 4 and YTaO 4 as well as their intermixed compositions have been studied. The DS green emission of Ho3+ ion in vanadate host (λ exc = 326 nm) is 5 times stronger than in niobate host (λ exc = 262 nm) due to efficient energy transfer between [VO 4 ]3- and Ho3+ ion. The downshifting (DS) emissions are also investigated on direct excitation of Ho3+ ion in YVO 4 , YNbO 4 and YTaO 4 hosts on excitation with 450/456 nm (5I 8 →5G 6 transition of Ho3+ ion) wavelength. It is found that the overall DS emission intensity is dominant in YNbO 4 :Ho3+ phosphor due to low phonon frequency and larger particle size of YNbO 4. The Ho3+ doped in mixed hosts viz. YTa 1-x V x O 4 , YTa 1-y Nb y O 4 , YNb 1-z V z O 4 (where x, y and z = 0, 0.25, 0.50, 0.75 and 1.0) phosphors also emit intense green DS emission along with their violet-blue band emission on ultraviolet (UV) excitation. The mixing of Ta/V and Ta/Nb enhances the blue emission of host matrix on UV excitation. The green emission is found to increase with 'V' and 'Nb' concentrations in YTa 1-x V x O 4 :0.01Ho3+, YTa 1-y Nb y O 4 :0.01Ho3+, respectively. Further, we also investigated quantum cutting (QC) in YNb 1-z V z O 4 :5 mol% Yb3+ (where z = 0, 0.25, 0.50, 0.75, 1.0) phosphors on UV excitation (λ exc = 262 and 326 nm). The intensity of QC NIR emission is found to increase with the incorporation of 'V' in YNb 1-z V z O 4 phosphors. The strongest QC emission is observed in pure YVO 4 host as compared to pure YNbO 4 as well as other mixed matrices. The QC efficiency of NIR emission for YVO 4 :5 Yb has been calculated and found to 129%. Therefore, the prepared phosphor material is highly applicable to increase the efficiency of Si- solar cell by QC NIR emission. [ABSTRACT FROM AUTHOR]

The near-infrared downconversion (DC) mechanism in Te4+/Yb3+ co-doped 75TeO 2 –25Li 2 O tellurite glasses (amounts in mol%) was closely followed using optical and thermal spectroscopy techniques. The glasses were prepared by the conventional melt-quenching method, with a melting temperature of 800 °C, in an ambient atmosphere, which were the best synthesis conditions for observing Te4+ in the glass. The results indicated that excitation in the ultraviolet region led to an intense emission of two NIR photons (at around 978 nm) in the co-doped tellurite glasses. This effect revealed the occurrence of a cooperative energy transfer (CET) mechanism in the system, where a Te4+ ion was responsible for the excitation of two Yb3+ ions. The CET efficiency (η CET) was calculated from the Te4+ lifetime, obtaining a maximum of 74% for the tellurite glass prepared with the highest Yb3+ concentration. The use of thermal lens spectroscopy confirmed the quantum cutting effect, by observing the dependence of the thermal properties of the glass on the Yb3+ concentration. A maximum DC efficiency of 137% was measured for the sample with 4 mol% of Yb3+. [ABSTRACT FROM AUTHOR]

Lead–halide perovskite nanocrystals are an attractive class of materials since they can be easily fabricated, their optical properties can be tuned all over the visible spectral range, and they possess high emission quantum yields and narrow photoluminescence linewidths. Doping perovskites with lanthanides is one of the ways to widen the spectral range of their emission, making them attractive for further applications. Herein, we summarize the recent progress in the synthesis of ytterbium-doped perovskite nanocrystals in terms of the varying synthesis parameters such as temperature, ligand molar ratio, ytterbium precursor type, and dopant content. We further consider the dependence of morphology (size and ytterbium content) and optical parameters (photoluminescence quantum yield in visible and near-infrared spectral ranges) on the synthesis parameters. The developed open-source code approximates those dependencies as multiple-parameter linear regression and allows us to estimate the value of the photoluminescence quantum yield from the parameters of the perovskite synthesis. Further use and promotion of an open-source database will expand the possibilities of the developed code to predict the synthesis protocols for doped perovskite nanocrystals. [ABSTRACT FROM AUTHOR]

Phosphors with a longer excitation wavelength exhibit higher energy conversion efficiency. Herein, quantum cutting KGd(CO3)2:Tb3+ phosphors excited by middle-wave ultraviolet were synthesized via a hydrothermal method. All the KGd(CO3)2:xTb3+ phosphors remain in monoclinic structures in a large Tb3+ doping range. In the KGd(CO3)2 host, 6D3/2 and 6I17/2 of Gd3+ were employed for quantum cutting in sensitizing levels. The excited state electrons could easily transfer from Gd3+ to Tb3+ with high efficiency. There are three efficient excited bands for quantum cutting. The excited wavelengths of 244, 273, and 283 nm correspond to the transition processes of 8S7/2→6D3/2 (Gd3+), 8S7/2→6I17/2 (Gd3+), and 7F6→5F4 (Tb3+), and the maximum quantum yields of KGd(CO3)2:Tb3+ can reach 163.5, 119, and 143%, respectively. The continuous and efficient excitation band of 273–283 nm can well match the commercial 275 nm LED chip to expand the usage of solid-state light sources. Meanwhile, the phosphor also shows good excitation efficiency at 365 nm in a high Tb3+ doping concentration. Therefore, KGd(CO3)2:Tb3+ is an efficient green-emitting phosphor for ultraviolet-excited solid-state light sources. [ABSTRACT FROM AUTHOR]

Transparent luminescent solar concentrator (LSC) windows with edge-attached photovoltaic (PV) cells have the potential for improving building efficiency without compromising aesthetics and comfort. Optimization of such windows requires an inexpensive simulator for experimenting with various designs. We report, for the first time to the best of our knowledge, the simulator of a transparent LSC window in the form of a plastic container filled with a colloid of photoluminescent nanoparticles (NPs) in an organic solvent (1-propanol). The exemplary NPs were produced by ball milling of the powder of rare earth (RE)-doped phosphor NaYF4:Yb3+,Er3+ synthesized by the wet method. The NPs converted the ultraviolet (UV) solar spectrum into visible/near infrared (NIR) via spectral down-shifting and down-conversion (quantum cutting). With a photoluminescence quantum yield (PLQY) of the phosphor

It is of great significance to enhance the quantum-cutting (QC) luminescence for practical applications due to the narrow absorption cross-section and low luminescence efficiency of rare earth ions. In this work, NaBaPO 4 :Er3+ phosphors doped with Li+ were synthesized through a solid-state reaction. The QC luminescence of NaBaPO 4 :Er3+ phosphor was enhanced 5.71 times by doping Li+. XRD patterns and Judd-Ofelt calculations demonstrated the crystal field distortion when introduced Li+, which would increase the transition probability of Er3+. Furthermore, NaBaPO 4 :Er3+, Li+ phosphors were decorated with silver nanoparticles (Ag NPs). The effect of Ag NPs on QC luminescence was studied, and the results showed that QC luminescence was further enhanced up to 1.95 times by Ag NPs. FDTD simulations revealed that Ag NPs generated substantial surface plasmons, which would boost the excitation rate of Er3+. Our studies would provide a useful strategy to enhance QC luminescence, which has potential application in germanium-based solar cells. [ABSTRACT FROM AUTHOR]

Highly efficient quantum cutting KY(CO3)2:Tb3+ phosphors excited by ultraviolet B (UVB) and ultraviolet C (UVC) were investigated. The structural and spectroscopic properties were characterized by XRD analysis and fluorescence spectrophotometry, respectively. The results showed that the monoclinic crystal structure of KY(CO3)2:Tb3+ remained in the Tb3+ doping range of 0~100%. In the excitation spectrum, two intense excitation peaks were observed in the ultraviolet range. Under the excitation of 283 nm, the maximum quantum efficiency of KY(CO3)2:0.7Tb3+ could reach 119%. However, the most efficient quantum cutting occurred at the 5K8 excited state in the cross-relaxation of 5K8 + 7F65D4 + 5D4. The Tb3+ content could be selected arbitrarily in the KY(CO3)2 host without any concentration quenching. Optimal quantum cutting concentrations of Tb3+ in KY(CO3)2 were 0.7 and 0.3 for the excitation of UVB and UVC, respectively. UVB-excited phosphors are more popular with high transparency in products such as glass or resin. A quick response code was fabricated by resin to show the hidden information clearly. Therefore, the highly efficient phosphor could be a candidate material for the application in information identification technology. [ABSTRACT FROM AUTHOR]

Numerous investigations have been done in pursuing phosphors with quantum yield (QY) greater than unity in terms of downconversion (DC) strategies, as well as applications in display, lighting, and particularly in novel solar cells with efficiency exceeding the Shockley–Queisser limit (≈30%). It is of significant interest that: i) DC of one high‐energy photon to two or more low‐energy photons is widely found in lanthanide and/or transition‐metal ions activated materials; ii) broadening of absorption spanning ultraviolet/blue range is achieved by introducing sensitizers with spin‐allowed transitions and especially by combining the advancing perovskite quantum dots, nanostructures, and organic dye molecules; iii) internal QY ≫ 1 and even measured QY > 1 are claimed in many near‐infrared (NIR) DC systems; iv) applications of downconverting layer atop commercial solar cells are performed to increase the photon conversion efficiency. In this review, the development of DC in theories, concepts, and experiments is first summarized, then the breakthrough in visible‐DC is briefly highlighted, NIR‐DC with latest progresses in models, materials, techniques as well as the corresponding optimizations and practices as effective downconverting layers is elaborated, and finally concluding remarks and perspectives in advancing NIR‐DC and applications in novel solar cells are given. [ABSTRACT FROM AUTHOR]

Extending near‐infrared (NIR) spectral response and increasing ultraviolet utilization is still a challenge in the context of improving power conversion efficiency (PCE) for perovskite solar cells (PSCs). In this work, to extend NIR light‐harvesting of PSCs, a novel COTIC‐4F: PC61BM: PTB7‐Th ternary organic bulk‐heterojunction together with Au nanotriangles is integrated on the PSCs. The NIR spectral response is thus extended to 1100 nm. In fact, the COTIC‐4F: PC61BM: PTB7‐Th layer enables multi‐functional effects, which can serve as electron transport, trap passivation, and moisture barrier layer in addition to NIR light harvesting. For increasing UV utilization, CsPbCl3:Yb3+, Ce3+, Cr3+ nanophosphors with photoluminescent quantum yield close to 200% are fabricated, which demonstrate excellent down‐conversion ability. Then, CsPbCl3: Yb3+, Ce3+, Cr3+/polymethylmethacrylate composite films are self‐assembled on a hybrid device, resulting in a 6.2% relative enhancement of short circuit current density. After simultaneously improving the NIR and UV spectral response of device, the PCE is increased significantly from 20.52% to 23.40% and the Jsc is increased from 21.79 to 25.96 mA cm−2, representing one of the highest PCE and maximum Jsc enhancements in the reported inverted hybrid organic/PSCs. This work represents an effective and general strategy for obtaining efficient and stable PSC devices with extremely broad spectral responses. [ABSTRACT FROM AUTHOR]

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We report, for the first time to our knowledge, on the polymer nanocomposite sunlight spectrum down-converters made by the concurrent multi-beam multi-target pulsed laser deposition (CMBMT-PLD) of phosphor and polymer in ambient air. Phosphor PLD targets were made of down-converting rare-earth (RE)-doped fluorides NaYF4:Yb3+,Er3+, and NaYF4:Yb3+,Tm3+ with a Stokes shift of 620 nm (from 360 to 980 nm), minimizing the effect of re-absorption. The phosphors were synthesized by the wet method. Polymer target was made of poly (methyl methacrylate) known as PMMA. Target ablation was conducted with 1,064 nm beams from an Nd:YAG Q-switched laser. Beam intensity was 2.8 × 1016 W/cm2 for both targets. The substrate was a microscope glass slide. Phosphor nanoparticles with a size ranging from 10 to 50 nm were evenly distributed in the polymer matrix during deposition. The nanoparticles retained the crystalline structure and the fluorescent properties of the phosphor target. There was no noticeable chemical decomposition of the deposited polymer. The products of laser-induced reaction of the polymer target with atmospheric gases did not reach the substrate during PLD. Post-heating of the substrate at ∼90°C led to fusion of separate polymer droplets into uniform coating. Quantum yield of the down-conversion polymer nanocomposite film was estimated to be not less than ∼5%. The proposed deposition method can find its application in making commercial-size down-converter coatings for photo-voltaic solar power applications.

Quantum cutting (QC) allows the conversion of high-energy photons into lower-energy photons, exhibiting great potential for infrared communications. Yb-doped perovskite nanocrystals can achieve an efficient QC process with extremely high photoluminescence quantum yield (PLQY) thanks to the favorable Yb 3+ incorporation in the perovskite structure. However, conventionally used oleic acid-oleylamine-based ligand pairs cause instability issues due to highly dynamic binding to surface states that have curbed their potential applications. Herein, zwitterionic type C3-sulfobetaine 3-(N,N-Dimethylpalmitylammonio)propanesulfonate molecule is utilized to build a strong binding state on the nanocrystals' surface through a new phosphine oxide synthesis route. Leveraging machine learning and Bayesian Optimization workflow to determine optimal synthesis conditions, near-infrared PLQY above 190% is achieved. The high PLQY is well maintained after over three months of aging, under high-flux continuous UV irradiation, and long continuous annealing. This is the first report of highly efficient and stable perovskite quantum cutters, which will drive the study of fundamental physics phenomena and near-infrared quantum communications., (© 2024 Wiley‐VCH GmbH.)

The structural and optical properties of thin layers based on 70%SiO2–30%HfO2 doped with different concentration of rare earth ions (terbium and ytterbium) have been studied with a view to integrating them in a photovoltaic cell as a spectral conversion layer in order to improve its efficiency, by using down-conversion process. These thin films were synthesized by using sol gel technique and deposited on the pure silica substrate by dip-coating method. The DC layer can be placed on the front side of a solar cell and can enhance the current by converting ultraviolet (UV) photons into a large number of visible photons.In present study two series of samples are compared, the first series corresponds to samples treated at 900 °C (glass- S) while the second series concerns samples treated at 1000 °C (glass-ceramic- SC). These series are based on 70SiO2–30HfO2 activated by different molar concentrations of rare earths [Tb + Yb]/[Si + Hf] = 7%, 9%, 12%, 15%, 17%, 19% and 21%.Photoluminescence results of reference samples (without Yb3+) showed an emission from 5D4 to 7FJ (J = 3, 4, 5, 6) level characteristic transitions of Tb3+, with a maximum peak in the green centered at 543.5 nm corresponding to the 5D4→7F5 transition. For the co-doped samples a clear NIR PL emission around 980 nm was detected, due to the 2F5/2→2F7/2 transition of Yb3+ ions. From luminescence decay curves of Tb3+ maximum emission peak (7F5→5D4 transition at 543.5 nm) we have identified the energy transfer efficiency. The quantum efficiency increases by increasing the total [Tb + Yb] concentration. The most significant yield was achieved with [Tb + Yb]=19%, the maximum quantum transfer efficiency obtained was 190% for glass-ceramic samples and 161% for glassy one.

Quantum cutting involves the absorption of a single high-energy photon, followed by the release of its energy through the emission of two or more lower-energy photons. This approach holds promise as a method to improve the ultraviolet (UV) performance of silicon photodetectors (Si PDs). In this study, we successfully fabricated La3+, Yb3+ co-doped CsPbClBr 2 perovskite quantum dots (PQDs) using a modified hot-injection method, achieving a remarkable photoluminescent quantum yields (PLQYs) of 181 %. Subsequently, we spin-coated a film of La3+, Yb3+ co-doped CsPbClBr 2 PeQDs, serving as a light conversion material, onto the front surface of Si PDs. The resulting configuration exhibited enhanced responsivity (0.131 A/W) and external quantum efficiency (55.6 %), long-term stability at 360 nm, and expanded responsiveness into the deep UV region (200 nm). Simultaneously, the responsivity and external quantum efficiency in the visible and near-infrared regions exhibited minimal reduction. This significant performance can be attributed to two key factors: (1) The higher efficient quantum cutting PLQYs (181 %) of La3+, Yb3+ co-doped CsPbClBr 2 PeQDs and (2) the presence of fewer traps and a larger tolerance factor resulting from La3+ and Yb3+ co-doping. • The La3+-7.4 % doped CsPbClBr 2 PeQDs are synthesized with near-unity PL quantum yield. • Compared to the bare CsPbClBr 2 PeQDs, the La3+, Yb3+ co-doped CsPbClBr 2 PeQDs exhibited higher PLQYs, enhanced stability, and expanded absorption range into deep UV region. • The UV performance of Si PDs was boosted upon the introduction of La3+, Yb3+ co-doped CsPbClBr 2 PeQDs. [ABSTRACT FROM AUTHOR]

Spectroscopic properties play a significant role during the design and development of novel luminescent materials. In this work, quantum cutting (QC) luminescent materials KYF4:Tb3+,Yb3+ phosphors were successfully synthesized by sol–gel method. The crystal structure, morphology, fluorescence spectra, and decay curves were investigated by X-ray diffractometer (XRD), scanning electron microscope (SEM) and spectrofluorometer. The Judd-Ofelt (J-O) parameters, Ωλ (λ = 2, 4, 6), were directly derived from the emission spectra and decay curves, attributed to the transition intensities of Tb3+ ions were dependent on the J-O parameters. Then, the radiative and nonradiative transition rates, fluorescent branching ratios, cross-relaxation rates and lifetimes of QC luminescence were calculated based on the obtained J-O parameters. Moreover, the rate equation models of QC luminescence were established and the time-dependent population densities in excited levels of Tb3+ ions and Yb3+ ions were simulated. Finally, the dynamic processes of QC luminescence were discussed carefully and the corresponding theoretical quantum efficiency was estimated. Our studies would provide an insight into the QC luminescence and give theoretical guidance for developing novel luminescent materials.

Judd–Ofelt (JO) theory explains the optical properties of trivalent lanthanides using only three intensity parameters. The JO parametrization is a complicated procedure of absorption spectra analysis, especially cumbersome for powders and non‐transparent materials. For the Pr3+ activated materials, the procedure is additionally complicated due to strong interaction of low‐lying Pr3+ 4f5d energy levels with the 4f levels. Here, the straightforward JO parametrization method that uses the emission spectrum and the excited state lifetime of the Pr3+ 3P0 level which does not require any fitting procedure are shown. In addition, the theory and software for calculations of JO parameters from Pr3+ emission are explained. The method requirements are low‐temperature photoluminescence measurements of Pr3+ introduced in low phonon energy hosts with a relatively high lying 4f5d energy level. The method is demonstrated on emissions of YF3:Pr3+ and LaF3:Pr3+ powders. [ABSTRACT FROM AUTHOR]

Judd–Ofelt (JO) theory explains the optical properties of trivalent lanthanides using only three intensity parameters. The JO parametrization is a complicated procedure of absorption spectra analysis, especially cumbersome for powders and non‐transparent materials. For the Pr3+ activated materials, the procedure is additionally complicated due to strong interaction of low‐lying Pr3+ 4f5d energy levels with the 4f levels. Here, the straightforward JO parametrization method that uses the emission spectrum and the excited state lifetime of the Pr3+ 3P0 level which does not require any fitting procedure are shown. In addition, the theory and software for calculations of JO parameters from Pr3+ emission are explained. The method requirements are low‐temperature photoluminescence measurements of Pr3+ introduced in low phonon energy hosts with a relatively high lying 4f5d energy level. The method is demonstrated on emissions of YF3:Pr3+ and LaF3:Pr3+ powders. [ABSTRACT FROM AUTHOR]

A series of phosphate glasses with compositions of 30SrO-60P2O5-10Na2O-0.5Tm2O3-xYb2O3(x = 0, 1, 5, 9, 11 in mol%) were manufactured by melt-casting method, the quantum cutting between the Tm3+ and Yb3+ in the phosphate glasses is investigated, the energy transfer from Tm3+:1G4 to Yb3+:2F5/2 is proved. According to calculate, the highest quantum efficiency is up to 159.9%, the emission wavelength is at 1020 nm, matching the energy band gap of a silicon solar cell well, therefor, these phosphate glasses could potentially be used in silicon solar cells.

Abstract Doping metal ions into lead halide perovskite nanocrystals (NCs) has attracted great attention over the past few years due to the emergence of novel properties relevant to optoelectronic applications. Here, the synthesis of Mn2+/Yb3+ codoped CsPbCl3 NCs through a hot‐injection technique is reported. The resulting NCs show a unique triple‐wavelength emission covering ultraviolet/blue, visible, and near‐infrared regions. By optimizing the dopant concentrations, the total photoluminescence quantum yield (PL QY) of the codoped NCs can reach ≈125.3% due to quantum cutting effects. Mechanism studies reveal the efficient energy transfer processes from host NCs to Mn2+ and Yb3+ dopant ions, as well as a possible inter‐dopant energy transfer from Mn2+ to Yb3+ ion centers. Owing to the high PL QYs and minimal reabsorption loss, the codoped perovskite NCs are demonstrated to be used as efficient emitters in luminescent solar concentrators, with greatly enhanced external optical efficiency compared to that of using solely Mn2+ doped CsPbCl3 NCs. This study presents a new model system for enriching doping chemistry studies and future applications of perovskite NCs.

New apatite-type NaLa 9- x Tm x (GeO 4) 6 O 2 (x = 0.025–0.8) germanates (space group P 6 3 / m , Z = 1) have been prepared using both the citrate technique and the conventional solid state method. The samples were characterized by powder X-ray diffraction, scanning electron microscopy, diffuse reflectance and photoluminescence spectroscopy. Photoluminescence measurements of NaLa 9- x Tm x (GeO 4) 6 O 2 compounds were carried out both in the 425–850 nm range under 356 nm excitation and in the infrared region under 808 nm excitation. The most intensive lines at 453 nm, 478 nm and in 625–850 nm wavelength range are associated with the 1D 2 → 3F 4, 1G 4 → 3H 6 and a series of 1G 4 → 3F 4 , 3F 2 → 3H 6 , 3H 4 → 3H 6 transitions in Tm3+ ions. The spectra measured in the infrared spectral range consist of two broad emission bands centered at 1440 nm and 1810 nm, which correspond to the cascade 3H 4 °→°3F 4 and 3F 4 °→°3H 6 transitions in Tm3+. The influence of dopant content and temperature on possible mechanisms promoting the population of Tm3+ excited states has been studied. [ABSTRACT FROM AUTHOR]

The multimodal [Upconversion (UC), Downshifting (DS) and Quantum cutting (QC)] behaviour of Tm3+/Yb3+ co-doped YTaO 4 ceramic material is investigated extensively. The samples are prepared by solid-state reaction method at two different temperatures (at 1573 and 1723 K) and their structural and optical properties are compared with each other. The effect of synthesis temperature as well as doping, on crystal phase was analysed via X-ray diffraction measurements. Particles shape and size are investigated through scanning electron microscopy images. The structural behaviour is further verified through vibrational structural study of material via FTIR measurements. This shows similar structural changes as observed in XRD patterns of the samples prepared at two different temperatures. The optical band gap of YTaO 4 is nearly 4.8 eV at both the temperatures. Intense blue (476 nm), red (648 nm) and NIR (802 nm) peaks are observed in UC emission spectra of Tm3+/Yb3+ co-doped YTaO 4 ceramic on excitation with 980 nm. The blue UC emission is suitable for display devices. The UC emission intensity increases significantly when sample is prepared at higher temperature (1723 K). Addition of Bi3+ ion further enhances the overall UC emission intensity due to change in environment around the activator ion. On excitation with UV radiation (λ Exc = 284 nm), YTaO 4 : 1 Tm3+ produces intense DS emission at 454 nm (blue region) due to energy transfer from charge transfer band of [TaO 4 3- to Tm3+ ion. The sample synthesized at 1723 K shows better DS emission. One interesting result is that addition of Bi3+ ion enhances the DS emission due to formation of metal-metal charge transfer band. We have also observed the quantum cutting phenomenon in which self-activated blue photon is converted into two or more NIR photons. The efficiency of quantum cutting emission increases significantly in presence of Bi3+ ion and shows strong, intense NIR emission through CET. Thus, the multimodal behaviour of Tm3+/Yb3+/Bi3+ doped YTaO 4 makes them a suitable candidate for a spectral converter that can be used in display and solar cell devices. [ABSTRACT FROM AUTHOR]

Doping metal ions into lead halide perovskite nanocrystals (NCs) has attracted great attention over the past few years due to the emergence of novel properties relevant to optoelectronic applications. Here, the synthesis of Mn2+/Yb3+ codoped CsPbCl3 NCs through a hot‐injection technique is reported. The resulting NCs show a unique triple‐wavelength emission covering ultraviolet/blue, visible, and near‐infrared regions. By optimizing the dopant concentrations, the total photoluminescence quantum yield (PL QY) of the codoped NCs can reach ≈125.3% due to quantum cutting effects. Mechanism studies reveal the efficient energy transfer processes from host NCs to Mn2+ and Yb3+ dopant ions, as well as a possible inter‐dopant energy transfer from Mn2+ to Yb3+ ion centers. Owing to the high PL QYs and minimal reabsorption loss, the codoped perovskite NCs are demonstrated to be used as efficient emitters in luminescent solar concentrators, with greatly enhanced external optical efficiency compared to that of using solely Mn2+ doped CsPbCl3 NCs. This study presents a new model system for enriching doping chemistry studies and future applications of perovskite NCs. [ABSTRACT FROM AUTHOR]

• ZnS shells remarkably increase the stability and efficiency of Yb3+-doped PeQDs. • ZnS enables perovskite host to Yb3+ energy transfer efficiencies as high as 81.3 %. • ZnS-coated PeQDs still light up when immersed in water for 70 h. • PeQDs@ZnS led to a 13.5 % relative increase in the photovoltaic efficiency of SSCs. • The T 80 of capped PeQDs@ZnS-SSCs under 25 °C and 50 % RH was 11,224 h. Yb3+ doped lead halide perovskite quantum dots (PeQDs) with efficient quantum cutting emission are thought to be the most promising photon energy converter for improving the performance of silicon-based electronics. Nevertheless, the low external quantum efficiency (EQE) and instability make it unfeasible for industrial use. Here, we present a unique PeQDs@ ZnS core–shell device that achieves outstanding stability and up to 39 % EQE by effectively controlling energy transfer from the PeQDs to the Yb3+ through ZnS coating. These advances are attributed to the large UV absorption and the strong localized effect of the ZnS shells on the conduction band electrons of the PeQDs. Density functional theory (DFT) first-principles simulations indicate that ZnS coating can facilitate the energy transfer of PeQDs to Yb3+. Power conversion efficiency (PCE) of silicon solar cells was significantly enhanced by ZnS-coated Yb3+ doped PeQDs, yielding a noteworthy 13.5 % relative PCE improvement over 30 measurement sets. Significantly, the stability of SSCs with ZnS-coated PeQDs films is considerably improved, resulting in a capped device T 80 lifespan of up to 11,224 h. Moreover, ZnS-coated PeQDs films can significantly boost the EQE of silicon photodiodes (Si-PDs) and extend their response to deep ultraviolet light. This paper presents an efficient and consistently stable photon energy converter with great commercialization potential. [ABSTRACT FROM AUTHOR]

Yb‐doped Scheelite‐like molybdate and tungstate single crystals are promising quantum‐cutting materials. The cooperative downconversion from donor centers to Yb ions occurs in heavily Yb‐doped crystals of this family. This phenomenon can substantially raise the efficiency of crystalline silicon photovoltaic cells. However, the nature of donor centers is still unknown. Herein, several versions of this nature are tested and discussed: Yb3+ ion (its high‐energy charge transfer states); Yb2+ ion; self‐trapped exciton at molybdate/tungstate complex; color centers based on oxygen vacancies; accidental impurities. To test these assumptions, a series of Scheelite‐like molybdate and tungstate single crystals (CaMoO4, CaWO4, NaLa(MoO4)2, NaGd(MoO4)2, NaGd(WO4)2, and NaY1−xGdx(WO4)2) are grown, both undoped and doped with different Yb‐concentrations. The complex spectroscopic investigations of these crystals are performed. As a result of the studies, three versions, self‐trapped excitons at [MoO4]/[WO4] complexes, color centers at oxygen vacancies, and accidental impurities, coming into the crystals with MoO3, are rejected. The applicability of the other versions should be refined. [ABSTRACT FROM AUTHOR]

Abstract The double plasmon modes of noble metals are utilized to efficiently enhance the near-infrared (NIR) quantum cutting (QC) luminescence at 977 nm in β -NaYF 4 :Er 3 + nanoparticles (NPs) under the excitation of 486 nm. The surface plasmon resonance (SPR) of Ag nanocubes (NCs) and Au nanorods (NRs) are simultaneously utilized to enhance the excitation efficiency and emission rate of NIR QC luminescence in β -NaYF 4 : Er 3 + NPs, respectively, and the maximum enhancement factor is 3.5 when the concentration of Au NRs is 0.225% and Ag NCs is 0.06%. It has significantly improved the enhancement factor compared to β -NaYF 4 :Er 3 + NPs decorated with the Ag NCs or Au NRs, respectively. Our research may improve photovoltaic conversion efficiency by making better use of the QC layer on top of silicon-based solar cells. [ABSTRACT FROM AUTHOR]

Abstract Tb3+/Yb3+ co-doped ZrO 2 -SiO 2 nano-crystallized glasses were prepared by a sol-gel process. The crystal structure and optical properties including down-conversion photoluminescence (or, quantum cutting) of the Tb3+-Yb3+ system with respect to gel heat treatment temperature were investigated by X-ray diffraction (XRD), Raman, photoluminescence (PL), and PL decay curves analysis. The energy transfer efficiency from Tb3+ to Yb3+ ions, which converts one photon to two photons with lower energy, increased with heat-treatment temperature. Furthermore, the oxidation state of Tb4+ ions was suspected to influence the emission intensity of Tb3+ and energy conversion efficiency. Thus, a post-treatment reduction was applied to the sample heated at 1100 °C by annealing it at 1100 °C for 1 h under 5%H 2 /95%N 2 reductive atmosphere. Consequently, the thermodynamically generated Tb4+ ions were reduced to a trivalent state, leading to higher energy transfer efficiency. Graphical abstract Image 1 Highlights • Sol-gel method was applied to fabricate transparent Tb3+/Yb3+ co-doped ZrO 2 -SiO 2 nanocomposites. • Thermal evolution of the precipitation of ZrO 2 nanocrystals in SiO 2 glass was investigated. • Tb3+-Yb3+ quantum cutting properties in ZrO 2 nanocrystals was studied. • The high quantum cutting efficiency of 183% was obtained. • The impact of Tb valence state on the quantum cutting behavior was elucidated. [ABSTRACT FROM AUTHOR]

Understanding the photosensitization mechanisms in Yb 3+ -doped perovskite nanocrystals is crucial for developing their anticipated photonic applications. Here, we address this question by investigating near-infrared photoluminescence of Yb 3+ -doped mixed-halide CsPbCl x Br 3- x nanocrystals as a function of temperature and revealing its strong dependence on the stoichiometry of the host perovskite matrix. To explain the observed experimental trends, we developed a theoretical model in which energy transfer from the perovskite matrix to Yb 3+ ions occurs through intermediate trap states situated beneath the conduction band of the host. The developed model provides an excellent agreement with experimental results and is further validated through the measurements of emission saturation at high excitation powers and near-infrared photoluminescence quantum yield as a function of the anion composition. Our findings establish trap-mediated energy transfer as a dominant photosensitization mechanism in Yb 3+ -doped CsPbCl x Br 3- x nanocrystals and open up new ways of engineering their optical properties for light-emitting and light-harvesting applications.

In order to evaluate the quantum efficiency and to establish the mechanism of down-conversion processes in Bi 3+ −Yb 3+ and Ce 3+ −Yb 3+ co-doped YAG (Y 3 Al 5 O 12 ) and GGG (Gd 3 Al 5 O 12 ) garnets, direct measurements of quantum yield (QY) were performed along with studies of photoluminescence (PL), photoluminescence excitation (PLE), and photoluminescence decay kinetics. The studied materials have been prepared either in the form of powders synthesized by the sol-gel method or single crystalline films grown by the liquid phase epitaxy method. Concentrations of Bi 3+ , Ce 3+ and Yb 3+ ions in the studied epitaxial films were estimated using X-ray diffraction and optical absorption techniques. The obtained results testify a non-cooperative energy transfer mechanism for the Ce 3+ –Yb 3+ co-doped YAG with a conversion ratio (which should be 2.0 for an ideal quantum cutting mechanism) less than 1.0. At the same time, for Bi 3+ –Yb 3+ co-doped YAG and GGG this conversion ratio was found to be close to 2.0, suggesting quantum cutting via cooperative energy transfer from one Bi 3+ ion to two Yb 3+ ions. [ABSTRACT FROM AUTHOR]

Crystalline silicon (c-Si) solar cell is to date the most successfully commercialized solar cell. One of the factors which limit the efficiency of c-Si solar cell is a “spectral mismatch”. The mismatch can be removed by modifying the solar spectrum: converting the near UV and blue region of the spectrum, where solar cell response is poor, to NIR region by using suitable phosphors. In the past, several phosphors based on emission of Yb 3+ /Nd 3+ sensitized by f-d transitions of other divalent, or f-f transitions of trivalent rare earths have been studied. These studies demonstrated the concept. However, an ideal phosphor is still not found. In this work tetravalent rare earth, viz. Ce 4+ is studied as the sensitizer. Efficient two-step Ce 4+ →Nd 3+ → Yb 3+ energy transfer from CT band of Ce 4+ is observed. By virtue of this energy transfer, efficient absorption of near UV light and conversion to NIR is achieved. These results are significant for improving efficiency of c-Si solar cells using spectrum modification. [ABSTRACT FROM AUTHOR]

Near-infrared (NIR) quantum cutting phosphors serve as a potential material for fabricating photovoltaic spectral convertors. In many cases, quantum cutting phosphors are obtained via a wet chemical method coupled with a post-annealing treatment—a very costly process. In this report, we used continuous flame spray pyrolysis (FSP) for fabricating Y2O3:Tb3+-Yb3+ quantum-cutting phosphors without any post-treatment. Based on characterizations by scanning electron microscopy, transmission electron microscopy, and X-ray diffraction, we found that as-synthesized Y2O3:Tb3+-Yb3+ phosphors exhibit hollow and shell-like micro-structures composed of highly crystalline and pure cubic-phase nanoparticles (< 50 nm). Photoluminescence studies of the phosphors revealed that NIR emissions appeared with the introduction of Yb to Y2O3:Tb3+. Phosphor size was successfully controlled by managing the concentration of the metal precursor solution for FSP. The Y2O3:Tb3+-Yb3+ phosphors were then embedded into transparent poly-ethylene-co-vinyl acetate (EVA) film to form a spectral convertor. The composite films of Y2O3:Tb3+-Yb3+ phosphors and poly-EVA were found to be highly transparent in the visible range (> 500 nm), making them suitable as spectral photovoltaic convertors. [ABSTRACT FROM AUTHOR]

Crystalline silicon solar cells are most successfully commercialized devices. However, there is spectral mismatch between the incident solar radiation and the spectral response curve of crystalline silicon. In particular, near ultraviolet and blue radiations are not fully utilized. In the past, several phosphors have been proposed for spectrum modification. However, most of them were based on the f-f transitions of rare earths. These are too weak and too narrow to be of much practical use. A phosphor with strong excitation in near ultraviolet /blue region is desired. Such phosphors may be derived from allowed f-d transitions of rare earths. Synthesis and characterization of one such phosphor viz. KCl.SrCl 2 :Eu 2+ ,Nd 3+ is reported. It shows good absorption in near ultraviolet region arising from f-d transition of Eu 2+ , and emission around 1065 nm due to efficient energy transfer from Eu 2+ to Nd 3+ . [ABSTRACT FROM AUTHOR]

Recent advances in the ytterbium doping of CsPbX3 (X = Cl or Cl/Br) nanocrystals have presented exciting new opportunities for their application as downconverters in solar-energy-conversion technologies. Here, we describe a hot-injection synthesis of Yb3+:CsPbCl3 nanocrystals that reproducibly yields sensitized Yb3+ 2F5/2 → 2F7/2 luminescence with near-infrared photoluminescence quantum yields (PLQYs) well over 100% and almost no excitonic luminescence. Near-infrared PLQYs of 170% have been measured. Through a combination of synthesis, variable-temperature photoluminescence spectroscopy, and transient-absorption and time-resolved photoluminescence spectroscopies, we show that the formation of shallow Yb3+-induced defects play a critical role in facilitating a picosecond nonradiative energy-transfer process that de-excites the photoexcited nanocrystal and simultaneously excites two Yb3+ dopant ions, i.e., quantum cutting. Energy transfer is very efficient at all temperatures between 5 K and room temperature but only grows more efficient as the temperature is elevated in this range. Our results provide insights into the microscopic mechanism behind the extremely efficient sensitization of Yb3+ luminescence in CsPbX3 nanocrystals, with ramifications for future applications of high-efficiency spectral-conversion nanomaterials in solar technologies. [ABSTRACT FROM AUTHOR]

BaZn 2 (BO 3 ) 2 self-activated phosphors were prepared by the conventional high temperature solid-state method. The PL spectra of BaZn 2 (BO 3 ) 2 powders prepared under reductive and air atmosphere consist of a weak ultraviolet emission band (∼410 nm) and a broad emission band which were centered at ∼ 500 and 545 nm, respectively. According to the spectral analysis and EPR results, the green and yellow emissions may arise from the transitions of photo-generated electron close to the conduction band to the deeply trapped hole in single ionized oxygen vacancy (V+ o) centers and single negatively charged interstitial oxygen ion (O- i), respectively. An efficient broadband near-infrared (NIR) quantum cutting was demonstrated in Yb 3+ doped BaZn 2 (BO 3 ) 2 phosphor. Upon excitation with an ultraviolet photon at 375 nm, the emissions of two NIR photons at 983 nm from Yb 3+ ions were achieved. The dependences of the visible and NIR emissions, the decay lifetime, the energy transfer efficiency, and the quantum efficiency on the Yb 3+ doping content were investigated in detail. The results indicated that the maximum energy transfer and the corresponding downconversion quantum efficiency could reach between 68.5% and 168.5%. [ABSTRACT FROM AUTHOR]

New results on NIR emission in Ba 2 SiO 4 :Eu 2+ , Nd 3+ phosphors are reported. Though excitation for Eu 2+ emission is in predominantly near UV (nUV) region, that for the Nd 3+ emission around 1067 nm extends into visible region covering violet and blue part of the spectrum. These results are highly significant for applications where NIR emission with nUV/blue excitation is required, e.g. for improving efficiency of c-Si solar cell, for designing NIR sources using efficient blue LEDs, etc. Energy transfer efficiencies for Eu 2+ → Nd 3+ energy transfer are estimated by measuring reduction of Eu 2+ emission lifetime, and are close to 80%. Possible mechanisms for Eu 2+ → Nd 3+ energy transfer are suggested. These involve down shifting or quantum cutting. [ABSTRACT FROM AUTHOR]