Enhancement Of Green Emission Research Articles

Anomalous thermal activation of green upconversion luminescence in Yb/Er/ZnGdO self-assembled microflowers for high-sensitivity temperature detection.

Non-contact optical temperature detection has shown a great promise in biological systems and microfluidics because of its outstanding spatial resolution, superior accuracy, and non-invasive nature. However, the thermal quenching of photoluminescence significantly hinders the practical applications of optical temperature probes. Herein, we report thermally enhanced green upconversion luminescence in Yb/Er/ZnGdO microflowers by a defect-assisted thermal distribution mechanism. A 1.6-fold enhancement in green emission was demonstrated as the temperature increased from 298 K to 558 K. Experimental results and dynamic analysis demonstrated that this behavior of thermally activating green upconversion luminescence originates from the emission loss compensation, which is attributed to thermally-induced energy transfer from defect levels to the green emitting level. In addition, the Yb/Er/ZnGdO microflowers can act as self-referenced radiometric optical thermometers. The ultrahigh absolute sensitivity of 1.61% K-1 and an excellent relative sensitivity of 15.5% K-1 based on the 4F9/2/2H11/2(2) level pair were synchronously achieved at room temperature. These findings provide a novel strategy for surmounting the thermal quenching luminescence, thereby greatly promoting the application of non-contact sensitive radiometric thermometers.

Tremendous enhancement of green emission from Er3+/In3+ co-doped β-Ga2O3 ultrawide bandgap semiconductors

Er3+ singly doped and Er3+/In3+ co-doped gallium oxide ceramics with intense green emission were prepared using the conventional solid-state reaction method. The Ga2-x-yErxInyO3 ceramics exhibit green and red emission at 555 and 673 nm, and follow the two-photon absorption process under the excitation of 980 nm. Systematic measurements of the upconversion luminescence spectra of Ga2-x-yErxInyO3 show that the optimal doping concentrations, sintering temperature and time are x = 0.015, y = 0.035, 1250 °C, and 8 h, respectively. For a fixed Er3+ doping concentration of x = 0.015, the green emission intensity at 555 nm can be enhanced by 60 folds through 3.5 mol% In3+ doping, which is attributed to reduced non-radiative decay, enhanced energy transfer from In3+ ions to Er3+ ions via defect states, and increased photon absorption. The introduction of 3.5 mol% In3+ also increases the fluorescence lifetime by 235–272%. These observations provide compelling evidence for the presence of effective energy transfer between In3+ and Er3+ ions.

Optical and photoelectrical properties of low-concentration-Mn-doped CsPbBr3 nanocrystals

Doping of cesium lead bromide (CsPbBr3) perovskite nanocrystals offers effective control of their optical and optoelectrical properties, leading to possibilities of several new applications. Herein, cesium lead bromide perovskite nanocrystals are synthesized with doping of a low concentration of manganese (Mn) into the perovskite lattice using manganese (II) chloride (MnCl2) as a precursor. The shift in X-ray diffraction peaks toward higher angles indicates that manganese as a dopant is present inside the cesium lead bromide lattice. A change in the manganese (II) chloride precursor concentration from 5 to 10 mmol results in an increment in the atomic percentage of manganese from 0.3 to 0.5% in the cesium lead bromide crystal. Doping of a low concentration of manganese (0.3 at.%) into cesium lead bromide results in enhancement of green emission, while doping with a higher concentration of manganese (0.5 at.%) results in blue emission. The band gap of cesium lead bromide nanocrystals increases from 2.31 to 2.53 eV with an increase in the concentration of manganese. The dark and photoelectrical conductivity of cesium lead bromide nanocrystals is improved in the case of doping with a low concentration (0.3 at.%) of manganese. The ratio of photocurrent against dark current is found to be ∼182 in manganese-doped cesium lead bromide crystal film as compared with ∼101 for undoped cesium lead bromide crystal film. Doping with a low concentration of manganese improves the overall electrical and photoelectrical conductivity of cesium lead bromide perovskite nanocrystals.

Ambient- and calcination- temperature induced color-tunable upconversion luminescence in Yb3+/Er3+ co-doped Y2(MoO4)3 phosphors for optical thermometer

Trivalent lanthanides (Ln 3+ )-doped upconversion luminescent (UCL) materials with negative thermal expansion (NTE) property are endowed an exciting thermal enhancement performance. Hitherto, selectively thermal enhancement for the multi-narrow-band emissions of phosphor with NTE property is not implemented. Herein, Y 2 Mo 3 O 12 :Yb 3+ /Er 3+ phosphor synthesized by the modified sol-gel method is explored in selectively enhanced green emission (Er 3+ : 2 H 11/2 / 4 S 3/2 → 4 I 15/2 ) due to the formation of Yb-MoO 4 dimer at high ambient-temperature. The 54-fold selectively enhancement of green emission is obtained from 298 K to 523 K. In addition, the influences of dopant-concentration and calcination-temperature on UCL properties are analyzed. Accordingly, based on the fluorescence intensity ratio (FIR) of non-thermally coupled levels (NTCLs) for 2 H 11/2 / 2 F 9/2 and 4 S 3/2 / 2 F 9/2 as well as ( 2 H 11/2 + 4 S 3/2 )/ 2 F 9/2 , the optimal relative sensitivity of temperature sensing in the Y 2 Mo 3 O 12 :Yb 3+ /Er 3+ sample could reach 0.14 K −1 at 298 K. All these indicate that this Y 2 Mo 3 O 12 :Yb 3+ /Er 3+ material is a promising candidate for high-sensitivity optical temperature sensing.

Sulphur doping induced band gap narrowing and enhancement of green emission in ZnO nanorods

Sulphur doping induced band gap narrowing and enhancement of green emission in ZnO nanorods

HBr-mediated preparation of Cs4PbBr6/CsPbBr3 perovskites and green emission enhancement by Eu3+ doping

Rare earth doping is an effective way to improve optical properties and reduce toxicity of lead-related perovskite. Herein, by using HBr to provide a Br-rich reaction environment, Cs4PbBr6/CsPbBr3 perovskites with intense 520 nm green emission originated from Cs4PbBr6 are prepared by supersaturated recrystallization method without ligand involvement. The emission intensity increases with the increasing of HBr volume. Then, Eu3+ ions are introduced to the Cs4PbBr6/CsPbBr3 perovskites system by adding HBr to increase their solubility, and the emission intensity is enhanced 1.5 times with the photoluminescence quantum yield of 90.94% in 5% Eu3+ doped sample. The low-toxicity Eu3+ doped Cs4PbBr6/CsPbBr3 with excellent green emission is beneficial for applications in lighting and displaying devices.

Near-UV excited green-emission enhancement by efficient energy transfer in Na1.8Mg0.9Si1.1O4:Ce3+,Tb3+ phosphor for solid-state lighting applications

Luminescence properties of phosphor play a key role in the performance of white light-emitting-diodes (LEDs). The Tb3+ emission under near-UV excitation is usually very weak due to f-f spin-forbidden transitions. In this paper, we report that Tb3+ emission under near-UV excitation enhances up successfully in Ce3+,Tb3+ co-doped Na1.8Mg0.9Si1.1O4 (NMSO) phosphor, as a result of efficient energy transfer from Ce3+ to Tb3+. The newly-prepared NMSO:Ce3+,Tb3+ exhibits a strong green-emission line at λmax = 545 nm under 340 nm excitation, and the quantum efficiency is 0.82. The maximum energy transfer efficiency is up to 92.3%. The good thermal quenching resistance, high color-rendering index Ra (91.5) and low CCT (4752 K) of the packaged white LED demonstrate that energy transfer of rare earth phosphors is an effective strategy to target tailored optical performance. NMSO:Ce3+,Tb3+ phosphor has potential applications in near-UV chip excited white LEDs as a green-emitting component.

Pressure‐Treated Engineering to Harvest Enhanced Green Emission in Mn‐Based Organic–Inorganic Metal Halides at Ambient Conditions

AbstractIn the pressure‐induced emission enhancement paradigms, harvesting enhanced emission on the basis of original color is still largely hampered due to the recovery or decrement of emission intensity upon decompression. Here, a pressure‐treated strategy is reported to achieve the remarkable green emission enhancement of organic–inorganic metal halide (OIMH) [PP14]2[MnBr4] (N‐butyl‐N‐methylpiperidinium [PP14]+) at ambient conditions. After a cycle of 1 atm to 15.2 GPa, the [PP14]2[MnBr4] shows a 1.67‐fold enhancement in the photoluminescence quantum yield from 54.5% to 90.8%, and green emission monochromaticity is unexpectedly retained. The restriction of motion freedom of [MnBr4]2− by increased Br···H interactions is highly responsible for the intense emission. Furthermore, [PP14]2[MnBr4] exhibits significant piezochromism that shifts from green to red, and an ultrabroad tunability of 185 nm is observed below 12.5 GPa. The enhancement of the crystal field splitting energy and the reduction of the relaxation from the low‐energy excited state 4T1 to the ground state 6A1 that is caused by the shrinkage of MnBr bond result in the red shift of emission. This work sheds light on the effects of pressure treatment in boosting emission enhancement and facilitates the design of new OIMHs with the desired emission properties.

The enhanced up-conversion green by Yb-Mn dimer in NaBiF4:Yb3+/Er3+/Mn2+ for optical fiber temperature sensor

Through doping Mn2+ into the NaBiF4:Yb3+/Er3+, it can be achieved that NaBiF4 :Yb3+/Er3+/Mn2+ possess superior temperature sensing performance and application in temperature optical fiber sensing on the premise of enhancing the green emission upon the 980 nm excitation. The effect of Mn2+ content on the phase and luminescence of NaBiF4:Yb3+/Er3+/Mn2+ is investigated by X-ray diffraction (XRD) and fluorescence spectrophotometer characterization. The up-conversion (UC) green emission intensity is enhanced by 3 times by Mn2+ doping. The Yb3+-Mn2+ dimer is introduced to clarify the mechanism of UC red and green emission enhancement, where involved in is three-photon process. Moreover, the optical thermometric behaviors of the synthetic compounds are analyzed according to the fact that Er3+ processes a couple of green emission levels 2H11/2 and 4S3/2, and the maximum Sa (absolute sensor sensitivity) reaches 0.00559 K−1. The preliminary design and application of NaBiF4:Yb3+/Er3+/Mn2+ as a probe in the temperature optical fiber sensor has been carried out, suggesting that NaBiF4: Yb3+/Er3+/Mn2+ is expected to be a kind of promising material for non-contact optical thermometer.

Improvement of sensing sensitivity based on green emissions from Er-doped (AlGa)2O3 films

The temperature-dependent photoluminescence behaviors in green region of Er-doped (AlGa)2O3 films with different Al contents have been studied in the temperature range of 77–400 K. A reduced thermal quenching in green region was observed with the increase of host bandgap, resulting in an enhancement of green emissions. Subsequently, the temperature sensing properties of films were studied by using the fluorescent intensity ratio (FIR) technique based on the thermally coupled levels of 2H11/2 and 4S3/2 in Er3+. The enhanced thermal sensing properties were found with the increase of Al content in films. The absolute sensitivity of 0.0056 K−1 at 400 K was obtained at the Al content of 0.77, which is twice that of Ga2O3:Er film. Finally, the effect of adding Al content on the thermal effect induced by the laser pump power was investigated, and the results suggest that the thermal effect in all samples induced by the pump power can be negligible in this work. This work provides a useful insight for developing optical temperature sensors with high luminescence efficiency and sensitivity.

Enhancement of green emission from Ca14Al10Zn6O35: Tb3+ phosphors via cross-relaxation energy transfer by Li+ ions

Tb3+ doped Ca14Al10Zn6O35 phosphors were prepared by a traditional solid-state reaction approach. The Tb3+ doped phosphors exhibit blue and green emission under the 285 nm excitation. The green to blue emission ratio is gradually enhanced as the Tb3+ concentration increases, which is ascribed to the enhanced cross-relaxation energy transfer (CRET) processes between Tb3+ ions. Li+ ions were introduced to the composition as an attempt to address the charge mismatch induced by Tb3+ for Ca2+ ion substitution. An enhancement of green emission from Tb3+ ions is observed after co-doping with Li+ ions. The lifetime measurement confirms that the CRET efficiency and energy transfer rate are simultaneously increased by Li+ ions. The results suggest that the incorporation of Li+ ions is a feasible approach to overcome charge vacancy defects and enhance CRET processes.

Role of defects in optical, photoluminescence and magnetic properties of Zn0.96−xNi0.04CrxO nanoparticles

Cr, Ni doubly doped ZnO nanoparticles for Cr = 0%–5% have been synthesized successfully by sol-gel route. X-ray diffraction spectra revealed the hexagonal wurtzite structure of the samples without any detectable secondary phases up to Cr = 3% and a secondary spine ZnCr2O4 phase was noticed at higher Cr doping (Cr = 5%). The rapid decrease in crystallite size derived from Debye formula by incorporation of Cr was understood in terms of the dissimilarity in ionic radii among Cr3+ (0.063 nm) and Zn2+ (0.074 nm). The shape of the synthesized nanoparticles and the generation of defect concentrations by Cr-doping in ithe host Zn-Ni-O lattice plays major role in the reduction of optical energy gap from Cr = 1% (Eg ≈ 4 eV) to Cr = 5% (Eg ≈ 3.87 eV). The broad and dominant infrared absorption peaks between 483 cm−1 and 490 cm−1 revealed the occurrence of Zn-O stretching mode with octahedral co-ordinates. The steady enhancement of green emission by Cr addition from photoluminescence spectra supports total increase of defect states like oxygen vacancies. Room temperature ferromagnetism was noted in whole Cr range where Cr = 3% scored maximum magnetization and dropped off for Cr = 5% due to the secondary ZnCr2O4 phase.

Photon upconversion characteristics of intense green emitting BaYF5:Yb3+,Er3+ nanoclusters prepared by reverse microemulsion

This work presents the first time synthesis of photon upconverting cubic BaYF5:Yb3+,Er3+ nanoclusters by a novel reverse microemulsion method. Rietveld refinement analysis confirmed the cubic BaYF5 and BaYF5:Yb,Er. The spherical nanoclusters (∼35 nm) are formed by an ensemble of ∼10 nm individual nanocrystals. A plausible formation mechanism is explained based on HRSEM and HRTEM investigations. FTIR revealed the effect of CTAB and oleic acid surfactants on amine and carboxyl functionalization. The cubic BaYF5:Yb,Er nanoclusters exhibited an intense green upconversion emission under 980 nm excitation. A three-fold upconversion green emission enhancement was achieved by increasing the calcination temperature from 200 °C to 400 °C. The energy transfer mechanism is described based on pump power dependent upconversion luminescence intensity. Furthermore, cytotoxicity effect of the different concentrations (2.5–300 μg/mL) of the BaYF5:Yb,Er were investigated against human colon adenocarcinoma cell line (HT29 cells) for 24 h and 48 h treatment.

Morphological evolution in nanocrystalline CdS thin films from flowers to salt rock like structures

Surface morphological evolution is observed in thermally activated nanocrystalline CdS (nc-CdS) thin films. The chemical bath deposited nc-CdS thin films show flower like structures on micro-crack background. Thermal annealing of nc-CdS thin films at different temperatures viz. 300, 350, 400 and 450 °C for 3 h in Ar ambient developed surface morphology towards salt rock like structures with clear particle boundaries at higher temperatures. Besides, structural phase transition from zincblende to wurtzite is observed, at 350 °C in nc-CdS thin films. It is observed that on increasing the annealing temperature longitudinal optical phonon Raman mode shifts toward higher frequency side in either of the crystal structure and bandgap reduces. Photoluminescence study illustrates thermally activated enhancement in green emission and disappearance of yellow and red emission in both the structures. The variation in emission intensity is described on the bases of morphology and structural changes occur due to thermal activation.

Integrating AlInN interlayers into InGaN/GaN multiple quantum wells for enhanced green emission

Significant enhancement in green emission by integrating a thin AlInN barrier layer, or interlayer (IL), in an InGaN/GaN multiple quantum well (MQW) is demonstrated. The MQWs investigated here contains 5 periods of an InGaN QW, a 1 nm thick AlInN IL, and a 10 nm thick GaN barrier grown by metalorganic chemical vapor deposition. To accommodate the optimum low-pressure (20 Torr) growth of the AlInN layer a growth flow sequence with changing pressure is devised. The AlInN IL MQWs are compared to InGaN/AlGaN/GaN MQWs (AlGaN IL MQWs) and conventional InGaN/GaN MQWs. The AlInN IL MQWs provide benefits that are similar to AlGaN ILs, by aiding in the formation of abrupt heterointerfaces as indicated by X-ray diffraction omega-2theta (ω-2θ) scans, and also efficiency improvements due to high temperature annealing schedules during barrier growth. Room temperature photoluminescence of the MQW with AlInN ILs shows similar performance to MQWs with AlGaN ILs, and ∼4–7 times larger radiative efficiency (pump intensity dependent) at green wavelengths than conventional InGaN/GaN MQWs. This study shows the InGaN-based MQWs with AlInN ILs are capable of achieving superior performance to conventional InGaN MQWs emitting at green wavelengths.

Enhanced green upconversion luminescence in ZnO:Er3+, Yb3+ on Mo6+ co-doping for temperature sensor application

Erbium (Er) doped zinc oxide (ZnO) powder was prepared using co-precipitation method. Effect of ytterbium (Yb) and molybdenum (Mo) co-doping on upconversion emission was studied. The emission intensity has been enhanced on Yb co-doping due to energy transfer from Yb to Er. Co-doping Mo in ZnO:Er, Yb has brought a significant enhancement in green upconversion emission, when excited with 980 nm laser. The enhancement in green emission on Mo doping is because of the formation of dimer. Since ZnO is a material having high thermal stability, the enhanced green emission in Mo, Er, Yb doped ZnO can be used for temperature sensor applications. The variation in relative intensity ratio of 2H11/2 → 4I15/2, 4S3/2 → 4I15/2 transition can be used to sense the sample temperature.

Plasmon-Induced Selective Enhancement of Green Emission in Lanthanide-Doped Nanoparticles.

By introducing an 18 nm thick Au nanofilm, selective enhancement of green emission from lanthanide-doped (β-NaYF4:Yb3+/Er3+) upconversion nanoparticles (UCNPs) is demonstrated. The Au nanofilm is deposited on a microfiber surface by the sputtering method and then covered with the UCNPs. The plasma on the surface of the Au nanofilm can be excited by launching a 980 nm wavelength laser beam into the microfiber, resulting in an enhancement of the local electric field and a strong thermal effect. A 36-fold luminescence intensity enhancement of the UCNPs at 523 nm is observed, with no obvious reduction in the photostability of the UCNPs. Further, the intensity ratios of the emissions at 523-545 nm and at 523-655 nm are enhanced with increasing pump power, which is attributed to the increasing plasmon-induced thermal effect. Therefore, the fabricated device is further demonstrated to exhibit an excellent ability in temperature sensing. By controlling the pump power and the UCNP concentration, a wide temperature range (325-811 K) and a high temperature resolution (0.035-0.046 K) are achieved in the fabricated device.

Defect-induced excitonic recombination in TixZn1−xO thin films grown by DC-unbalanced magnetron sputtering

We study the effects of Ti doping on the near-band-edge emission (NBE) and defect-related deep-level emission (DLE) of ZnO thin films grown by DC unbalanced magnetron sputtering. DLE in pure ZnO is contributed by zinc and oxygen vacancies (VZn+VO), as revealed by photoluminescence (PL) spectroscopy, current–voltage (I–V) characteristic measurement, and spectroscopic ellipsometry. The reduction in the number of VZn states is clearly observed upon Ti doping, resulting in the enhancement of green emission from VO. Interestingly, the thin film with a Ti concentration of 1 at. % shows a higher excitonic emission. Furthermore, the temperature dependence of PL spectra shows that the enhanced excitonic emission originates from the donor-bound exciton promoted by the Ti dopant and native VO. This study shows an important role of the defects in controlling the optical and electronic properties of ZnO films for future optoelectronic applications.

Managing Green Emission in Coupled InGaN QW–QDs Nanostructures via Nanoengineering

By utilizing and designing coupled InGaN QW-QDs nanostructures as active layer, we show a demonstration of significant enhancement of green emission in the hybrid nanostructure with a 4.5 nm GaN barrier layer at high temperatures. Such enhancement is ascribed to temperature dependent phonon-assisted tunneling of excitons from QW to QDs and suppression of non-radiative recombination of excitons localized in the QDs layer in the sample with a 4.5 nm barrier layer. This study shall be useful for optimization design of high-efficiency InGaN-based green LEDs, and also could shed some light on the complicated internal luminescence mechanisms in InGaN QW-QDs hybrid nanostructures.

Opto-electronic properties of Zn(1-x)VxO: Green emission enhancement due to V4+ state

Vanadium incorporation in ZnO modifies the lattice structure. The valence state of V plays an important role, controlling the oxygen content and thereby dimensions of the lattice. Both V4+ and V5+ are more electropositive than Zn2+ and reduce oxygen vacancies, resulting in lattice expansion. However, the sizes of both V4+ and V5+ are smaller than Zn2+, thereby resulting in the lattice contraction. The internal competition of increasing oxygen content and reducing effective crystal radius decides the lattice expansion and contraction. This affects the lattice strain and changes electronic levels, which modify absorption and emission processes in between the valence and conduction bands. A strong green emission band not due to oxygen vacancy but due to defects contributed by vanadium is also dependent on the oxidation state of vanadium. Bandgap also increases with the increase in the V4+ content.