Luminescence Thermometry Based on the Upconversion Luminescence from the Stark Sublevels of BaY2F8:Yb3+, Tm3+ Phosphor.

Visible and near-infrared (NIR) upconversion luminescence (UCL) emissions originating from the BaY2F8: Yb3+, Tm3+ systems were investigated under a laser excitation at 980 nm. The BaY2F8:20 mol% Yb3+, x mol% Tm3+ and BaY2F8: y mol% Yb3+, 0.5 mol% Tm3+ phosphors showed prominent UCL at 800 and 810 nm. The optimized doping concentrations of Yb3+ and Tm3+ in the BaY2F8 host matrix were evaluated, their spectroscopic properties were determined, and studies on their temperature-dependent behaviour were carried out. The temperature-sensing properties were studied by generating the fluorescence intensity ratio (FIR) of the UCL peaks originating from the thermally-coupled energy levels of the Tm3+ ions. The Stark sublevels of 1G4 level of Tm3+ ions were utilized to estimate the temperature-sensing abilities of the phosphor.

Optical limiting applications of resonating plasmonic Au nanoparticles in a dielectric glass medium.

Plasmonic nanostructures exhibiting high optical nonlinearities are widely used in the rapidly growing modern nanotechnology of nonlinear optics including biomedical applications due to their tunable plasmonic behavior. In this work, we investigate the nonlinear optical properties of uniformly distributed Au nanoparticles (NPs) embedded in pre-synthesized sodium-zinc borate glass by the well-known ion-exchange technique for optical limiting (OL) applications. Various techniques such as optical absorption spectroscopy, x-ray photoelectron spectroscopy, Transmission Electron Microscope (TEM), Photoluminescence, Time of Flight secondary mass spectroscopy and the Z scan technique were used for the characterization of these NPs. TEM confirmed spherically shaped Au NPs with varying sizes of up to 16 nm, in agreement with optical absorption spectroscopy. Nonlinear optical (NLO) properties of these Au NPs were investigated by using an open as well as close aperture Z scan technique which exhibited enhanced optical nonlinearities. The two-photon absorption (2PA) coefficients demonstrated an increasing trend while the OL threshold values demonstrated a decreasing trend as a function of heat treatment. The improved 2PA coefficients and decreased OL threshold values endorsed the Au NPs containing glasses as contending materials for the fabrication of promising optical limiters for the protection of eyes and other sensitive instruments from laser induced damages.

Upconversion process in BaY2 F8 :Yb3+ ,Ho3+ phosphor for optical thermometry.

A BaY2 F8 :Yb3+ ,Ho3+ phosphor was synthesized using a simple precipitation method. The temperature-sensing properties of BaY2 F8 :Yb3+ ,Ho3+ phosphor were investigated using the fluorescence intensity ratio (FIR) of the thermally coupled energy levels (5 F4 and 5 S2 ) of Ho3+ . Energy transitions 5 F4 →5 I8 and 5 S2 →5 I8 gave rise to emission peaks at 538 nm and 549 nm, respectively. The areas under these two emission peaks were used to calculate the FIR. Temperature-dependent upconversion luminescence was recorded in the temperature range 303-623 K using a 980 nm laser excitation source. The results suggested that the BaY2 F8 :Yb3+ , Ho3+ phosphor has the potential to be used as a non-contact optical temperature sensor.

Role of Li+ ions on the surface morphology and thermoluminescence properties of Y2 O3 :Tm3+ nanophosphor.

Y2 O3 :Tm3+ and Li+ co-doped Y2 O3 :Tm3+ nanopowders were synthesized using the solution combustion method for possible application in ultraviolet (UV) light dosimetry. X-ray diffraction revealed the crystallite sizes to be in the range 21-44 nm and 30-121 nm using the Scherrer equation and the W-H plot relationship, respectively. Field emission scanning electron microscopy confirmed that, after co-doping with 4 mol% concentration of Li+ , the particles were spherical in nature with an average size of ~30 nm. Fourier transformed infrared spectroscopy results showed bands at wavenumbers of 556, 1499, 1704, 2342, 2358, 2973, 3433, and 3610 cm-1 that corresponded to the stretching and bending vibrations of Y-O, C=O and O-H. Thermoluminescence (TL) glow peaks for Y2 O3 :Tm3+ nanophosphors observed at 399 and 590 K were attributed to oxygen defects caused using UV irradiation. These oxygen defects firstly resulted in an increased prominent peak TL intensity for up to 270 min of irradiation and then a decrease. This was attributed to the presence of oxygen defect clusters that caused a reduction in recombination centres. The Li+ co-doped sample showed peaks at 356, 430, and 583 K and its intensity sublinearly increased up to 90 min and then thereafter decreased. The TL trapping parameters were calculated using computerized glow curve deconvolution methods. The Li+ co-doped sample exhibited less fading and high trap density under the UV radiation.

Luminescence characterization of Dy and Eu doped Na6 Mg(SO4 )4 phosphors.

A series of single-phase phosphors based on Na6 Mg(SO4 )4 (Zeff  = 11.70) doped with Dy and Eu was prepared by the wet chemical method. The photoluminescence (PL) and thermoluminescence (TL) properties of Dy3+ - and Eu3+ -activated Na6 Mg(SO4 )4 phosphors were investigated. The characteristic emissions of Dy3+ and Eu3+ were observed in the Na6 Mg(SO4 )4 host. The TL glow curve of the Na6 Mg(SO4 )4 :Dy phosphor consisted of a prominent peak at 234°C and a very small hump at 158°C. The TL sensitivity of the Na6 Mg(SO4 )4 :Dy phosphor was found to be four times less than the commercialized CaSO4 :Dy phosphor. The TL dose-response of the Na6 Mg(SO4 )4 :Dy phosphor was studied from a dose range of 5-10 kGy and the linear dose-response was observed up to 1 kGy which is good for a microcrystalline phosphor. Trapping parameters for both the samples were calculated using the Initial Rise and Chen's peak shape methods.

Synthesis, characterization and multifunctional properties of plasmonic Ag-TiO2 nanocomposites.

We report on the synthesis of multifunctional Ag-TiO2 nanocomposites and their optical, physio-chemical, surface enhanced Raman scattering (SERS) and antibacterial properties. A series of Ag-TiO2 nanocomposites were synthesized by sol-gel technique and characterized by x-ray diffraction, scanning and transmission electron microscopy, energy-dispersed x-ray analysis, photoluminescence, UV-vis, x-ray photoelectron and Raman spectroscopy and Brunauer-Emmett-Teller method. The Ag nanoparticles (NPs) (7-20 nm) were found to be uniformly distributed around and strongly attached to TiO2 NPs. The novel optical responses of the nanocomposites are due to the strong electric field from the localized surface plasmon (LSP) excitation of the Ag NPs and decreased recombination of photo-induced electrons and holes at Ag-TiO2 interface providing potential materials for photocatalysis. The nanocomposites show enhancement in the SERS signals of methyl orange (MO) molecules with increasing Ag content attributed to the long-range electromagnetic enhancement from the excited LSP of the Ag NPs. To further understand the SERS activity, molecular mechanics and molecular dynamics simulations were used to study the geometries and SERS enhancement of MO adsorbed onto Ag-TiO2 respectively. Simulation results indicate that number of ligands (MO) that adsorb onto the Ag NPs as well as binding energy per ligand increases with increasing NP density and molecule-to-surface orientation is mainly flat resulting in strong bond strength between MO and Ag NP surface and enhanced SERS signals. The antimicrobial activity of the Ag-TiO2 nanocomposites was tested against the bacterium Staphylococcus aureus and enhanced antibacterial effect was observed with increasing Ag content explained by contact killing action mechanism. These results foresee promising applications of the plasmonic metal-semiconductor based nano-biocomposites for both chemical and biological samples.

Optical and surface enhanced Raman scattering properties of Au nanoparticles embedded in and located on a carbonaceous matrix.

Au nanoparticles (NPs) on the surface and embedded in a matrix have been the subject of studies dealing with a variety of spectroscopic and sensing applications. Here, we report on low energy Ar ion induced evolution of the morphology of a thin Au film on a polyethylene terephthalate (PET) substrate along with thermodynamic interpretations, and corresponding unique surface plasmon resonance (SPR) and photoluminescence (PL) properties. These properties are linked to the variation of surface nanostructures and the surface enhanced Raman scattering (SERS) effect of methyl orange (MO) dye molecules adsorbed on the surface. Ion induced thermal spike and sputtering resulted in dewetting of the film with subsequent formation of spherical NPs. This was followed by embedding of the NPs in the modified PET due to the thermodynamic driving forces involved. The surface and interface morphologies were studied using atomic force microscopy and cross-sectional transmission electron microscopy. X-ray photoelectron spectroscopy was used to study the chemical changes in the system upon irradiation. The optical properties were studied by diffuse reflectance UV-Vis spectroscopy and PL using a 325 nm He-Cd laser. The red shift of the SPR absorption and the blue shift of the PL emission have been correlated with the surface morphology. The blue PL emission bands at around 3.0 eV are in good agreement with the literature with respect to the morphological changes and the blue shift is attributed to compressive strain on the embedded Au NPs. Enhancement of the SERS signals is observed and found to be correlated with the SPR response of the Au nanostructures. The SERS analyses indicate that MO molecules may be adsorbed with different orientations on these surfaces i.e. Au NPs located on the surface or embedded in the modified PET. These polymeric substrates modified by NPs can have a potential application in solid-state light emitting devices and can be applied in SERS based sensors for the detection of organic compounds.

Effect of Ga3+ and Gd3+ ions substitution on the structural and optical properties of Ce3+ -doped yttrium aluminium garnet phosphor nanopowders.

The structural and optical properties of commercially obtained Y3 Al5 O12 :Ce3+ phosphor were investigated by replacing Al3+ with Ga3+ and Y3+ with Gd3+ in the Y3 Al5 O12 :Ce3+ structure to form Y3 (Al,Ga)5 O12 :Ce3+ and (Y,Gd)3 Al5 O12 :Ce3+ . X-Ray diffraction (XRD) results showed slight 2-theta peak shifts to lower angles when Ga3+ was used and to higher angles when Gd3+ was used, with respect to peaks from Y3 Al5 O12 :Ce3+ and JCPDS card no. 73-1370. This could be attributed to induced crystal-field effects due to the different ionic sizes of Ga3+ and Gd3+ compared with Al3+ and Y3+ . The photoluminescence (PL) spectra showed broad excitation from 350 to 550 nm with a maximum at 472 nm, and broad emission bands from 500 to 650 nm, centred at 578 nm for Y3 Al5 O12 :Ce3+ arising from the 5d â†’ 4f transition of Ce3+ . PL revealed a blue shift for Ga3+ substitution and a red shift for Gd3+ substitution. UV-Vis showed two absorption peaks at 357 and 457 nm for Y3 Al5 O12 :Ce3+ , with peaks shifting to 432 nm for Ga3+ and 460 nm for Gd3+ substitutions. Changes in the trap levels or in the depth and number of traps due to Ce3+ were analysed using thermoluminescence (TL) spectroscopy. This revealed the existence of shallow and deep traps. It was observed that Ga3+ substitution contributes to the shallowest traps at 74 °C and fewer deep traps at 163 °C, followed by Gd3+ with shallow traps at 87 °C and deep traps at 146 °C. Copyright © 2016 John Wiley & Sons, Ltd.

Use of ZnO:Tb down-conversion phosphor for Ag nanoparticle plasmon absorption using a He-Cd ultraviolet laser.

Although noble metal nanoparticles (NPs) have attracted some attention for potentially enhancing the luminescence of rare earth ions for phosphor lighting applications, the absorption of energy by NPs can also be beneficial in biological and polymer applications where local heating is desired, e.g. photothermal applications. Strong interaction between incident laser light and NPs occurs only when the laser wavelength matches the NP plasmon resonance. Although lasers with different wavelengths are available and the NP plasmon resonance can be tuned by changing its size and shape or the dielectric medium (host material), in this work, we consider exciting the plasmon resonance of Ag NPs indirectly with a He-Cd UV laser using the down-conversion properties of Tb(3+) ions in ZnO. The formation of Ag NPs was confirmed by X-ray diffraction, transmission electron microscopy and UV-vis diffuse reflectance measurements. Radiative energy transfer from the Tb(3+) ions to the Ag NPs resulted in quenching of the green luminescence of ZnO:Tb and was studied by means of spectral overlap and lifetime measurements. The use of a down-converting phosphor, possibly with other rare earth ions, to indirectly couple a laser to the plasmon resonance wavelength of metal NPs is therefore successfully demonstrated and adds to the flexibility of such systems. Copyright © 2016 John Wiley & Sons, Ltd.

The role of neutral and ionized oxygen defects in the emission of tin oxide nanocrystals for near white light application.

Tin oxide (SnO2) nanocrystals (NCs) based phosphor was synthesized by a green chemistry microwave-assisted hydrothermal method at different reactor pressures. The x-ray diffraction analysis showed that a single rutile SnO2 phase with a tetragonal lattice structure was formed. The photoluminescence emission was measured for He-Cd laser excitation at 325 nm and it showed a broad band emission from 400 to 800 nm for all the synthesized reactor pressures. The broad emission spectra were due to the creation of various oxygen and tin defects as confirmed by x-ray photoelectron spectroscopy data. The origin of the emission in the SnO2 NCs is discussed with the help of an energy band diagram. Analysis suggests that the visible emission of SnO2 NCs is due to a transition of an electron from a level close to the conduction band edge to a deeply trapped hole in the SnO2 NCs. The NCs were found to be suitable for warm near white light emission device applications.

Plasmonic resonance of Ag nanoclusters diffused in soda-lime glasses.

Silver nanoclusters were prepared in a soda-lime glass matrix through the ion-exchange (Ag(+)↔ Na(+)) method followed by thermal annealing in an air atmosphere. The nanoscale patterning of Ag nanoclusters embedded in a soda lime glass matrix in an air atmosphere at different annealing temperatures has been investigated. During annealing, Ag(+) is reduced to Ag(0) and subsequently forms silver nanoparticles inside the glass matrix. A blue shift of 20 nm has been observed as a function of the post annealing temperature. The photoluminescence intensity is highest for an annealing temperature of 500 °C for 1 h and continuously decreases as annealing temperature increases up to 600 °C. The presence of spherical nanoparticles with a maximum particle size of 7.2 nm has been observed after annealing at 600 °C for 1 hour, which is consistent with Mie theory based results.

The role of surface and deep-level defects on the emission of tin oxide quantum dots.

This paper reports on the role of surface and deep-level defects on the blue emission of tin oxide quantum dots (SnO2 QDs) synthesized by the solution-combustion method at different combustion temperatures. X-ray diffraction studies showed the formation of a single rutile SnO2 phase with a tetragonal lattice structure. High resolution transmission electron microscopy studies revealed an increase in the average dot size from 2.2 to 3.6 nm with an increase of the combustion temperature from 350 to 550 °C. A decrease in the band gap value from 3.37 to 2.76 eV was observed with the increase in dot size due to the quantum confinement effect. The photoluminescence emission was measured for excitation at 325 nm and it showed a broad blue emission band for all the combustion temperatures studied. This was due to the creation of various oxygen and tin vacancies/defects as confirmed by x-ray photoelectron spectroscopy data. The origin of the blue emission in the SnO2 QDs is discussed with the help of an energy band diagram.

Structural and optical characteristics of α-Bi2O3/ Bi2O(3-x):Ho3+ thin films deposited by pulsed laser deposition for improved green and near-infrared emissions and photocatalytic activity.

Pulsed laser deposited films on glass substrate deposited at different substrate temperatures (Ts) and partial pressures of oxygen, Ho3+-doped Bi2O3 films were produced. The degradation capability of the Rhodamine B dye using the Bi2O3:Ho3+ films was explored. The impact of the Bi2O3:Ho3+ content on the dye degradation performance was analyzed. The X-ray powder diffraction patterns showed that the films deposited at 400 °C had an α-Bi2O3 phase. The impacts of various Ts and O2 partial pressures were correlated with the surface morphology and the thickness of the films using results of field emission scanning electron microscope. The thin films deposited at a low O2 partial pressure of 5-20 mTorr at Ts = 400 °C exhibited nano-needles with an average size of 80 nm and a length of ∼750 nm. The estimated band gap of the prepared films was found to vary between 2.6 and 3.0 eV. The photoluminescence (PL) of the Bi2O3:Ho3+ thin films excited at 450 nm showed an intense green band emission observed at 548 nm, and the feeble emissions at 654 and 753 nm were ascribed to the transitions of Ho3+. The nano-needle particles of the α-Bi2O3:Ho3+ exhibited a maximum PL intensity for the 20 mTorr O2 partial pressure thin film. The films prepared in vacuum and with an O2 partial pressure of 5 mTorr exhibited a 41 % dye degradation efficiency during a duration of 270 min of the photocatalysis experiment.

Bi doped LaOCl and LaOF thin films grown by pulsed laser deposition.

Thin films of Bi3+ doped LaOCl and LaOF phosphors prepared via the pulsed laser deposition (PLD) technique in vacuum and different argon (Ar) pressures were compared in order to assess their luminescence properties. All peaks of the X-ray diffraction patterns of the films were consistent with the tetragonal structure of the LaOCl and LaOF, but in the case of LaOF the signal was weaker and not all peaks were present, suggesting some preferred orientation. Photoluminescence measurements revealed that the films exhibited emission around 344 nm for LaOCl:Bi and 518 nm for LaOF:Bi under excitations of 266 nm and 263 nm, respectively. The luminescence from the LaOF:Bi sample was less intense compared to the LaOCl:Bi sample prepared under the same conditions, which was also the case for the powder samples. The amount of ablated material present on the substrate was much less for LaOF:Bi compared to LaOCl:Bi, which is attributed to the greater bandgap and hence weaker absorption of the laser pulses for LaOF:Bi. Therefore phosphors based on LaOCl as the host material were found to be preferable over LaOF under the PLD conditions used in this study.

Towards Room Temperature Thermochromic Coatings with controllable NIR-IR modulation for solar heat management & smart windows applications.

Solar heat management & green air-conditioning are among the major technologies that could mitigate heat islands phenomenon while minimizing significantly the CO2 global foot-print within the building & automotive sectors. Chromogenic materials in general, and thermochromic smart coatings especially are promising candidates that consent a noteworthy dynamic solar radiation Infrared (NIR-IR) regulation and hence an efficient solar heat management especially with the expected increase of the global seasonal temperature. Within this contribution, two major challenging bottlenecks in vanadium oxide based smart coatings were addressed. It is validated for the first time that the NIR-IR modulation of the optical transmission (∆TTRANS = T(T〈TMIT) - T(T〉TMIT) of Vanadium oxide based smart coatings can be controlled & tuned. This upmost challenging bottle-neck controllability/tunability is confirmed via a genuine approach alongside to a simultaneous drastic reduction of the phase transition temperature TMIT from 68.8 °C to nearly room temperature. More precisely, a substantial thermochromism in multilayered V2O5/V/V2O5 stacks equivalent to that of standard pure VO2 thin films but with a far lower transition temperature, is reported. Such a multilayered V2O5/V/V2O5 thermochromic system exhibited a net control & tunability of the optical transmission modulation in the NIR-IR (∆TTRANS) via the nano-scaled thickness' control of the intermediate Vanadium layer. In addition, the control of ∆TTRANS is accompanied by a tremendous diminution of the thermochromic transition temperature from the elevated bulk value of 68.8 °C to the range of 27.5-37.5 ºC. The observed remarkable and reversible thermochromism in such multilayered nano-scaled system of V2O5/V/V2O5 is likely to be ascribed to a noteworthy interfacial diffusion, and an indirect doping by alkaline ions diffusing from the borosilicate substrate. It is hoped that the current findings would contribute in advancing thermochromic smart window technology and their applications for solar heat management in glass windows in general, skyscraper especially & in the automotive industry. If so, this would open a path to a sustainable green air-conditioning with zero-energy input.

Luminescence and stability of Tb doped CaF2 nanoparticles.

Luminescence properties of CaF2:Tb3+ nanoparticles were studied in order to investigate the effect of CaF2 native defects on the photoluminescence dynamics of Tb3+ ions. Incorporation of Tb ions into the CaF2 host was confirmed by X-ray diffraction and X-ray photoelectron spectroscopy. Cross-relaxation energy transfer was observed from the photoluminescence spectra and decay curves upon excitation at 257 nm. However, the unusual long lifetime of the Tb3+ ion as well as the decreasing trend of emission lifetime of the 5D3 level suggested the involvement of traps, which were further investigated by using temperature-dependent photoluminescence measurements, thermoluminescence and lifetime measurements at different wavelengths. This work highlights the critical role that the CaF2 native defects play in the photoluminescence dynamics of Tb3+ ions incorporated in a CaF2 matrix. The sample doped with 10 mol% of Tb3+ ions was found to be stable under prolonged 254 nm ultraviolet irradiation.

A holistic review on the recent trends, advances, and challenges for high-precision room temperature liquefied petroleum gas sensors.

Liquefied petroleum gas (LPG), which is mainly composed of hydrocarbons, such as propane and butane, is a flammable gas that is considered a clean source of energy. Currently, the overwhelming use of LPG as fuel in vehicles, domestic settings, and industry has led to several incidents and deaths globally due to leakage. As a result, the appropriate detection of LPG is vital; thus, gas-sensing devices that can monitor this gas rapidly and accurately at room temperature, are required. This work reviews the current advances in LPG gas sensors, which operate at room temperature. The influences of the synthesis methods and parameters, doping, and use of catalysts on the sensing performance are discussed. The formation of heterostructures made from semiconducting metal oxides, polymers, and graphene-based materials, which enhance the sensor selectivity and sensitivity, is also discussed. The future trends and challenges confronted in the advancement of LPG room temperature operational gas sensors, and critical ideas concerning the future evolution of LPG gas sensors, are deliberated. Additionally, the advancements in the next-generation gas sensors, such as the wireless detection of LPG leakage, self-powered sensors driven by triboelectric/piezoelectric mechanisms, and artificial intelligent systems are also reviewed. This review further focuses on the use of smartphones to circumvent the use of costly instruments and paves the way for cost-efficient and portable monitoring of LPG. Finally, the approach of utilizing the Internet of Things (IoT) to detect/monitor the leakage of LPG has also been discussed, which will provide better alerts to the users and thus minimize the effects of leakages.

Substrate temperature dependence of structure and optical properties of ZnTiO3:Er3+/Yb3+ thin films synthesized by pulsed laser deposition.

ZnTiO3:Er3+,Yb3+ thin film phosphors were successfully deposited by pulsed laser deposition (PLD) at different substrate temperatures. The distribution of the ions in the films was investigated and the chemical analysis showed that the doping ions were homogeneously distributed in the thin films. The optical response of the phosphors revealed that the reflectance percentages of the ZnTiO3:Er3+,Yb3+ vary with the silicon substrate temperature due to the differences in the thickness and morphological roughness of the thin films. Under 980 nm diode laser excitation, the ZnTiO3:Er3+,Yb3+ film phosphors displayed up-conversion emission from the Er3+ electronic transitions, with violet, blue, green, and red emission lines at 410, 480, 525, 545 and 660 nm from 2H9/2 â†’ 4I15/2, 4F7/2 â†’ 4I15/2, 2H11/2 â†’ 4I15/2, 4S3/2 â†’ 4I15/2 and 4F9/2 â†’ 4I15/2 transitions, respectively. The up-conversion emission was enhanced by increasing the silico (Si) substrate temperature during the deposition. Based on the photoluminescence properties and decay lifetime analysis, the energy level diagram was established and the up-conversion energy-transfer mechanism was discussed in detail.

Synthesis, thermal and spectroscopic characterization of Caq2 (calcium 8-hydroxyquinoline) organic phosphor.

Bluish-green photoluminescence from calcium 8-hydroxyquinolate (Caq(2)) powder, synthesized by a co-precipitation route, and a blended Caq(2):PMMA thin film is reported. The film was obtained by mixing the Caq(2) powder with PMMA (Polymethylmethacrylate) in a chloroform solution. X-ray diffraction analyses confirm the formation of the Caq(2) powder and thin film. Further structural elucidation was carried out using Fourier transform infrared spectroscopy (FTIR) in which the stretching frequencies of the Caq(2) bonds were determined. Bluish-green photoluminescence with a maximum at 480 nm was observed from the powder and the emission was red-shift by 10 nm in the case of the thin film. The UV-vis absorption bands were split and shifted due to different orientations of the Caq(2) molecules in both the powder and thin film. It was confirmed by thermogravimetric (TGA) and differential thermal analysis (DTA) that the Caq(2) powder was stable up to ≈ 380 °C. Atomic force microscopy images showed the continuous distribution of the Caq(2) atoms in the PMMA thin film. X-ray photoelectron spectroscopy data was used to estimate the binding energies of the chemical bonding in the Caq(2) powder complex. The optical properties of the Caq(2) powder and thin film were evaluated for possible applicable in organic light emitting devices.

Synthesis of cesium lead bromide nanoparticles by the ultrasonic bath method: A polar-solvent-free approach at room temperature.

Colloidal synthesis of CsPbBr3 nanoparticles (NPs) is often carried out by involving polar solvents that threaten the chemical stability of the NPs. Here, we report a polar-solvent-free synthesis of all-inorganic CsPbBr3 NPs by employing an ultrasonic bath approach. The phase evolution of the CsPbBr3 NPs strongly depended on the duration of ultrasonication. A secondary phase of Cs4PbBr6 was also found to evolve, which emitted narrow blue-emission bands. For the longest period of ultrasonication (12 h), the CsPbBr3 and Cs4PbBr6 phases co-existed to produce blue and green emission bands with a photoluminescence quantum yield (PLQY) of 53%. The purest form of CsPbBr3 phases was observed for the NPs produced by sonicating the precursors for 8 h. They exhibited narrow green emission bands with a PLQY of 50%. The power-conversion efficiency of a silicon solar cell was remarkably increased when coated with the CsPbBr3 NPs, thus, proving its potential to be used as a spectral downshifter for Si solar cells.