Temperature-dependent Emission Research Articles

Highly symmetric lattice environment induced orange-red emitting of Eu3+ in a novel tungstate phosphor with broad-band ultraviolet excitation

In this work, we reported the synthesis and characteristic luminescence of an orange-red emitting phosphor NaBa10Y5W4O30: Eu3+ for ultra-violet white light emitting diodes. The phase compound, crystalline structure and morphology are analyzed. The results indicate that a heavy doping of Eu3+ (x = 50%) is realized in NaBa10Y5-5xW4O30: xEu3+ without any impurity phase. Moreover, the optical band gap is analyzed by diffuse reflectance spectroscopy and further confirmed by density function theory (DFT). Meanwhile, the as-synthesized NaBa10Y5W4O30: Eu3+ phosphor can be efficiently pumped by strong broad-band excitation around 315 nm due to the charge transfer transition from [WO6]6- groups to Eu3+. Owing to the highly symmetric lattice environment of Eu3+ in YO6 sites, a strong orange-red emission at 596 nm with color purity of 95.34% is obtained, corresponding to the 5D0→7F1 magnetic dipole transition of Eu3+ ions. The critical concentration is obtained to be x = 15%, and the quenching mechanism is discussed to be dipole–dipole interaction. Furthermore, the temperature dependent emission behavior are analyzed, and the thermal quenching mechanism are explained by the variable temperature decay curve and configuration coordination diagram. Finally, an orange-red light emitting diode lamp is fabricated based on NaBa10Y5W4O30: 15%Eu3+ phosphor and 315 nm semiconductor chip. In summary, the results indicate that NaBa10Y5W4O30: Eu3+ phosphor has the potential to be an orange-red phosphor for white light emitting diodes.

Luminescence Performance of Mn4+ Activated BaLa2Al2O7 Phosphors

Mn4+ doped BaLa2Al2O7 phosphors were developed after a sintering process at 1400 °C for 3 h. The phase and luminescence performance of them were researched. The XRD patterns confirm single phase of the Mn4+ doped BaLa2Al2O7 phosphors. Upon the UV light excitation, the Mn4+ doped BaLa2Al2O7 phosphors emit strong deep-red emission. The concentration-dependence emission spectra demonstrate that the critical concentration for Mn4+ ion in BaLa2Al2O7 host is 0.006. On the basis of the temperature-dependence emission spectra, the activation energy for Mn4+ has been calculated as 0.292 eV, which suggests excellent thermostability of the Mn4+ activated BaLa2Al2O7 phosphors.

Measurement report: MAX-DOAS measurements characterise Central London ozone pollution episodes during 2022 heatwaves

Abstract. Heatwaves are a substantial health threat in the UK, exacerbated by co-occurrence of ozone pollution episodes. Here we report on the first use of retrieved vertical profiles of nitrogen dioxide (NO2) and formaldehyde (HCHO) over Central London from a newly installed multi-axis differential optical absorption spectroscopy (MAX-DOAS) instrument coincident with two of three heatwaves for the hottest summer on record. We evaluate space-based sensor observations routinely used to quantify temporal changes in air pollution and precursor emissions over London. Collocated daily mean tropospheric column densities from the high-spatial-resolution space-based TROPOspheric Monitoring Instrument (TROPOMI) and MAX-DOAS, after accounting for differences in vertical sensitivities, are temporally consistent for NO2 and HCHO (both R = 0.71). TROPOMI NO2 is 27 %–31 % less than MAX-DOAS NO2, as expected from horizontal dilution of NO2 by TROPOMI pixels in polluted cities. TROPOMI HCHO is 20 % more than MAX-DOAS HCHO, greater than differences in past validation studies but within the range of systematic errors in the MAX-DOAS retrieval. The MAX-DOAS near-surface (0–110 m) retrievals have similar day-to-day and hourly variability to the surface sites for comparison of NO2 (R ≥ 0.7) and for MAX-DOAS HCHO versus surface site isoprene (R ≥ 0.7) that oxidises to HCHO in prompt and high yields. Daytime ozone production, diagnosed with MAX-DOAS HCHO-to-NO2 tropospheric vertical column ratios, is mostly limited by availability of volatile organic compounds (VOCs), except on heatwave days. Temperature-dependent biogenic VOC emissions of isoprene increase exponentially, resulting in ozone concentrations that exceed the regulatory standard for ozone and cause non-compliance at urban background sites in Central London. Locations in Central London heavily influenced by traffic remain in compliance, but this is likely to change with stricter controls on vehicle emissions of NOx and higher likelihood of heatwave frequency, severity, and persistence due to anthropogenic climate change.

Thermometric Judd-Ofelt model for Dy3+ ion tested in CaYAlO4 host and evaluation of its sensing performances for luminescence thermometry

Luminescence thermometry uses temperature-dependent emission of light for remote sensing. Dy3+ is established as a perspective ion for high-temperature probes, but given that there is an infinite number of potential hosts it is impossible to find conventionally the one with the best performance. Judd-Ofelt thermometric model can predict sensitivities but it was not yet experimentally validated on Dy3+ ion. Pure phase CaYAlO4:Dy3+ powder was synthesized via the modified Pechini method. Photoluminescence spectra were taken from 300 to 600 K. Luminescence intensity ratio was estimated using 4I15/2 and 4F9/2 levels. Experimentally obtained thermometric parameters and sensitivities showed an excellent matching with those obtained from the Judd-Ofelt, indicating the potential application of the Judd-Ofelt model for fast assessment of Dy3+-doped luminescent sensor thermometric perspective. The maximum absolute and relative sensitivities are ∼0.001 K−1 at 600 K and ∼1.4% K−1 at 300 K, respectively. The optimum temperature range for the CaYAlO4:Dy3+ probe is from 370 to 616 K.

Policy-Related Gains in Urban Air Quality May Be Offset by Increased Emissions in a Warming Climate.

Air quality policies have made substantial gains by reducing pollutant emissions from the transportation sector. In March 2020, New York City's activities were severely curtailed in response to the COVID-19 pandemic, resulting in 60-90% reductions in human activity. We continuously measured major volatile organic compounds (VOCs) during January-April 2020 and 2021 in Manhattan. Concentrations of many VOCs decreased significantly during the shutdown with variations in daily patterns reflective of human activity perturbations, resulting in a temporary ∼28% reduction in chemical reactivity. However, the limited effect of these dramatic measures was outweighed by larger increases in VOC-related reactivity during the anomalously warm spring 2021. This emphasizes the diminishing returns from transportation-focused policies alone and the risk of increased temperature-dependent emissions undermining policy-related gains in a warming climate.

Temperature-dependent particle number emission rates and emission characteristics during heating processes of edible oils

The goal of this research is to investigate the temperature-dependent emission rates of particle numbers and emission characteristics during oil heating. Seven regularly used edible oils were studied in a variety of tests to attain this objective. First, total particle number emission rates ranging from 10 nm to 1 μm were measured, followed by an examination within six size intervals from 0.3 μm to 10 μm. Following that, the impacts of oil volume and oil surface area on the emission rate were investigated, and multiple regression models were developed based on the results. The results showed that corn, sunflower and soybean oils had higher emission rates than other oils above 200 °C, with peak values of 8.22 × 109#/s, 8.19 × 109#/s and 8.17 × 109#/s, respectively. Additionally, peanut and rice oils were observed to emit the most particles larger than 0.3 μm, followed by medium-emission (rapeseed and olive oils) and low-emission oils (corn, sunflower and soybean oils). In most cases, oil temperature (T) has the most significant influence on the emission rate during the smoking stage, but its influence was not as pronounced in the moderate smoking stage. The models obtained are all statistically significant (P < 0.001), with R2 values greater than 0.9, and the classical assumption test concluded that regressions were in accordance with the classical assumptions regarding normality, multicollinearity, and heteroscedasticity. In general, low oil volume and large oil surface area were more recommended for cooking to mitigate UFPs emission.

Er3+ doping YbTaO4 phosphors: Upconversion luminescence and temperature sensing characteristics

Trivalent erbium (Er3+) doped trivalent ytterbium (Yb3+) stoichiometric upconversion (UC) phosphors YbTaO4 (YbTaO4:Er3+) synthesized using the high temperature solid-state reaction method. The phase structure was analyzed using X-ray diffraction (XRD), scanning electron microscope (SEM) and XRD Rietveld refinement methods. The vibration of the bonds was revealed through Fourier transform infrared (FT-IR) spectroscopy. The multi-photon UC green and red luminescence were investigated upon excitation with a 980 nm semiconductor laser, and the critical quenching concentration of Er3+ in the YbTaO4 stoichiometric host was derived as high as 15 at.%. The power-dependent UC emission spectra confirmed a two-photon population process for the UC green and red emissions. Furthermore, the temperature-dependent UC emission spectra were measured in the range of 300–570 K, and the optical temperature sensing performance of YbTaO4:Er3+ was demonstrated using the fluorescence intensity ratio (FIR) technique. The maximum absolute sensing sensitivity (SA) and relative sensing sensitivity (SR) of YbTaO4:Er3+ were determined as 0.0038 K-1 (@450 K) and 0.0102 K-1 (@300 K), respectively. These results suggest that Er3+ doped YbTaO4 stoichiometric phosphors hold great promise as upconversion materials for optical temperature sensing applications.

Blue light emitting Sr2MgSi2O7:Eu2+ nanophosphor for latent fingerprint, anti-counterfeiting and near UV-LED applications

Eu2+ doped Sr2MgSi2O7 nanophosphors (SMSO:Eu2+ NPs) have been synthesized by using solid-state reaction method. As Eu2+ concentration increases, energy transfer (ET) between Eu2+ ions dominated attributed to dipole-dipole (d-d) interaction. Besides, temperature-dependent photoluminescence (PL) of optimized SMSO:7Eu2+ NPs is investigated. The emission shifts towards blue with increased temperature. From the temperature-dependent emission, the activation energy, is ∼0.40 eV. CIE coordinate is (0.1476, 0.1141) with CCT value of 3633 K. The optimized phosphor is used to detect LFPs on various surfaces. The level I-III features are clearly identified under UV 365 nm excitation. Several pores properties namely pore size, shape, number, position, type and pore inter-distance are analyzed in detail. The anti-counterfeiting results clearly showed the enhanced intensity owing to its nano-size, reduced light dispersion and increased light absorption. The overall results clearly suggest the optimized SMSO:7Eu2+ NPs are promising luminescent platform for nUV light-emitting diode (LED) and latent fingerprint (LFP) applications.

Optical thermometry based on fluorescence intensity ratio of doped ions and matrix in CaWO4: Eu3+ phosphors

In this work, Eu3+ doped CaWO4 phosphors with various concentrations were obtained by hydrothermal method. XRD and the FE-SEM were used to indicate the structure and morphology of the samples. The temperature-dependent excitation and emission spectra of Eu3+ doped CaWO4 phosphors were measured. Analyzing the test results found that the luminescence of WO42− decreased significantly with the increase of temperature, showing a normal thermal quenching trend, but the luminescence of Eu3+ showed a novel trend of first rising and then decreasing. This novel phenomenon is the result of enhancement of energy transfer effect from the matrix to Eu3+ with temperature increase. The thermal quenching trend of Eu3+ and WO42− luminescence is markedly different. So, the high relative sensitivity is obtained by using FIR of Eu3+ and WO42− to represent temperature. The maximum of relative sensitivity was 3.25% K−1 at 303 K. Meanwhile, the luminescence color of phosphor changed significantly from blue to orange-red with increasing temperature. To sum up, Eu3+ doped CaWO4 phosphor was a potential optical temperature sensing material.

Color-tunable persistent luminescence phosphor for multimode dynamic anti-counterfeiting

Using a solid-state approach, the persistent luminescence property in sodium yttrium silicate which was single-doped or co-doped by europium or cerium was studied. The orthorhombic structure with the space group P212121 could be indexed to all samples, according to X-ray powder diffraction. The luminescence characteristics of these phosphors, including photoluminescence, luminescence degradation, and temperature-dependent emission, were systematically investigated. Under UV (∼365 nm) irradiation, blue/green emissions with broad bands peaking at 450/510 nm attributed to the characteristic 5d→4f/4f65d→4f7 transitions of Ce3+/Eu2+ could be observed in Na3LuSi3O9:Ce3+ and Na3LuSi3O9:Eu2+, respectively. Moreover, blue and green persistent luminescence was also observed in Ce3+ or Eu2+ single-doped samples. Thermoluminescence curve of Na3LuSi3O9:Eu2+, Ce3+ reveals that Na3LuSi3O9:Ce3+ and Na3LuSi3O9:Eu2+ have similar trap distribution. Tunable persistent luminescence can be realized via ratio control of Ce3+ and Eu2+. A possible afterglow mechanism was presented and discussed. The prepared materials have the potential of multimode dynamic luminescence, because they are highly sensitive to the composition, the excitation wavelength, and the detecting time. The outstanding abilities of Na3LuSi3O9:Ce3+, Eu2+ demonstrate the practical capability of this material for fingerprint identification and anti-counterfeiting.

A novel multifunctional double perovskite structure phosphor La2MgTiO6:Mn4+, Eu3+

A series of La2MgTiO6: Mn4+ and La2MgTiO6: Mn4+, Eu3+ phosphors were prepared by high-temperature solid-phase method. The emission spectra of La2MgTiO6: Mn4+, Eu3+ phosphor samples under 328 nm excitation overlap with the absorbing regions of plant phytochromes PR and PFR in the far red and near infrared double wavelength range. The temperature-dependent and wavelength-dependent emission spectra show that the two distinguishable emission peaks of Eu3+ and Mn4+ exhibit clearly different temperature and wavelength responses. Thus, dual-emission optical sensing based on changes in the fluorescence intensity ratio(FIR) of Mn4+ and Eu3+ ions, the relative sensitivity of wavelength detection in the range of 288–348 nm maxima is 8.13% nm−1 at 288 nm, and relative sensitivity of optical temperature sensing in the range of 298–498 K maxima is 2.09% K−1 at 498 K, In this study, La2MgTiO6: Mn4+, Eu3+ phosphor samples with very promising optical properties can provide the possibility of application in multiple fields.

Highly efficient far-red emitting Mn4+-activated Li3La3W2O12 phosphors for plant growth LED lighting

High-efficiency far-red emitting phosphors with an emission peak of around 730 nm are urgently needed for indoor plant growth light-emitting diode (LED) lighting. In this article, we report on the synthesis, crystal structure, and luminescence properties of a new highly efficient Mn4+ ion-activated Li3La3W2O12 (LLWO) far-red emitting phosphor. A group of LLWO:Mn4+ phosphors doped with different Mn4+ ion concentrations have been prepared via the conventional high-temperature solid-state reaction route. X-ray diffraction Rietveld refinement reveals that the LLWO:Mn4+ phosphor has the monoclinic structure with space group P21/n, along with lattice parameters of a = 5.5396 Å, b = 5.6026 Å, c = 7.8802 Å, α = γ = 90°, β = 90.0988°, and V = 244.57 Å3. Interestingly, LLWO:Mn4+ phosphors can generate bright narrowband far-red emission in the 650–800 nm wavelength range peaking at 719 nm due to the spin- and parity-forbidden 2Eg→4A2g transition of Mn4+ ions, matching well with the absorption spectrum of phytochrome PFR. The excitation spectrum monitored at 719 nm has a broad excitation band with the range from 250 to 550 nm centered at 339 nm and 472 nm, indicating that LLWO:Mn4+ phosphors could be efficiently pumped by both ultraviolet and blue LED chips. The highest far-red emission is achieved for the sample doped with 1.2 mol% Mn4+ ion, and this optimal LLWO:1.2%Mn4+ sample shows a high internal quantum efficiency of 88.4% and a decay lifetime of 2.289 ms. Commission Internationale de l’Eclairage (CIE) color coordinates of LLWO:1.2%Mn4+ are determined to be (0.7326, 0.2674). Besides, the crystal field analysis and temperature-dependent emission spectra of the as-prepared samples have been investigated in detail. The emission intensity of LLWO:1.2%Mn4+ sample at 423 K remains about 40% of that at 303 K. Finally, a LED device is fabricated by integrating the LLWO:1.2%Mn4+ phosphors and a 460 nm blue LED chip, which shows bright blue and far-red dual emission bands under 20–300 mA driving currents. This work demonstrates that these newly developed far-red emitting LLWO:Mn4+ phosphors have excellent application prospects in plant growth LED lighting.

Optical property and Judd-Ofelt analysis of Dy3+, Na+:PbGa2S4 crystal grown by Bridgman method

In this research, the high quality Dy3+, Na+:PbGa2S4 single crystal was grown by Bridgman method. The crystal devices with high transmittance were successfully processed. The crystal structure and crystallization property were characterized by the XRD and XRC patterns. The transmission spectrum, temperature-dependent emission spectrum from 77 K to 350 K and decay curves at room temperature of crystal were measured. The strong absorption at 1315 nm of 6H15/2 → 6F11/2+6H9/2 transition could match well with high power 1310 nm semiconductor laser. The spectroscopic parameters were calculated by Judd-Ofelt theory based on the absorption spectra. The fluorescence lifetime of 6H11/2 energy level was fitted to be 2.09 ms and the corresponding fluorescence quantum efficiency η was calculated to be 77%. The emission cross-section at 4325 nm of 6H11/2 → 6H13/2 transition was also calculated to be 0.9 × 10−20 cm2. The experiment results show the advantage of Dy3+, Na+:PbGa2S4 crystal in emitting mid-infrared lasers.

Novel AMoO4:Eu3+ (A = Ca and Ba) optical thermometer: Investigation of effect of local ionic coordination environment on optical performance and temperature measurement sensitivity

A range of Eu3+-doped AMoO4 (A = Ca and Ba) phosphors were successfully synthetized, and their crystal structures, optical performance, and temperature measurement sensitivities were investigated in detail. Peak doping concentration of CaMoO4:Eu3+ phosphor was 0.18, while peak doping concentration of BaMoO4:Eu3+ phosphor may be greater than 0.18. Then, temperature-dependent photoluminescence emission spectra of representative CaMoO4:0.09Eu3+ and BaMoO4:0.03Eu3+ phosphors were recorded. CaMoO4:0.09Eu3+ phosphor exhibited abnormal thermal quenching, which was attributed to defects caused by heterovalent substitution of ions and increase in the temperature, and good thermal stability. Finally, the possibility of using both phosphors as optical thermometers was discussed, which exhibited good temperature sensitivity. However, CaMoO4:0.09Eu3+ phosphor exhibited two peak absolute (Sa, 1.28 %K−1 and 1.39 %K−1) and relative sensitivities (Sr, 1.21 %K−1 and 1.20 %K−1). In addition, variation trend of Sr value with temperature was considerably peculiar. Two optimum Sa and Sr values were attributed to abnormal thermal quenching of CaMoO4:0.09Eu3+ phosphor. Peak Sa and Sr values of BaMoO4:0.03Eu3+ phosphor was 12.39 %K−1 and 0.89 %K−1, respectively. In addition, Sa of AMoO4:Eu3+ phosphor was negatively related to Eu3+ central asymmetry, while peak Sr value was more inclined to appropriate ionic central asymmetry.

Quick and accurate optical thermometry based on chemometrics model strategy in Na0.5Gd0.5TiO3: Er3+

Current optical temperature measurements are confined to materials with high sensitivity, while probes with fluorescence intensity ratio (FIR) sensitivity above 12% K−1 still confront severe challenges. Therefore, we propose a novel strategy to obtain temperatures in one step from the temperature-dependent emission spectra by establishing a chemometrics model instead of calculating FIR values to improve temperature measurement accuracy of materials with a low FIR sensitivity. Here, Er3+-doped Na0.5Gd0.5TiO3 with low sensitivity and the monotonic variation of FIR is used as a temperature sensing material. The temperature-dependent spectra are preprocessed by the moving average filter method, and the useful information is extracted from the preprocessed spectra by the synergy interval partial least squares (siPLS) algorithm. The extracted spectra are then combined with the partial least squares regression (PLSR), the principal component regression (PCR), the multiple linear regression (MLR), and the support vector machine regression (SVM) respectively to build chemometrics models. The errors between the predicted and the actual temperatures of different models are evaluated to verify the feasibility of the proposed strategy and to select the optimal temperature measurement model for Na0.5Gd0.5TiO3: Er3+. The results show small errors and high correlation coefficients over 0.98 between the predicted and the actual temperatures of all models, indicating the applicability of the chemometrics model strategy in optical thermometry. Finally, the best model (a combination of siPLS-PCR + SVM) and the periodic testing of FIR with temperature may make Na0.5Gd0.5TiO3: Er3+ a candidate for optical thermometer with rapidity, durability and accuracy.

Optical temperature-sensing properties in La1.55SiO4.33:Yb3+,Ho3+ phosphors affected by Ho3+-doping concentration

In this paper, the Yb3+-Ho3+ co-doped La1.55SiO4.33 (LSO) phosphors were synthesized by the conventional solid-state reaction method. The phase purity and morphology of the samples were studied by XRD and SEM, respectively. Under 980 nm excitation, the upconversion (UC) luminescence of the LSO:Yb3+,Ho3+ phosphors was checked for different Ho3+ doping content and pump power. The corresponding UC mechanism was interpreted from the changing decay lifetimes and the energy transfer processes between Yb3+ and Ho3+ ions. Meanwhile, the temperature-dependent emission spectra were analyzed to learn the optical temperature-sensing behaviors with the fluorescence intensity ratio (FIR) method. The results revealed that the FIR (I658/I544) value increased when the temperature rose, which followed a linear function. The sensor sensitivity was evaluated, and the LSO:10%Yb3+,2%Ho3+ phosphor showed the highest absolute sensitivity. Besides, the main population way on 5F5 level of Ho3+ for red emission was clarified by the comparison of the UC spectra excited by continuous-wave and pulse light. Based on the above results, the LSO:Yb3+,Ho3+ phosphor can be considered as a new UC luminescent material for optical temperature sensors.

Multicolor tunable luminescence and energy transfer mechanism in Gd2O2S: Dy3+, Sm3+ phosphors

High quality single-phase multicolor emission phosphor is a prerequisite for efficient luminescence devices, but the system design and quantity preparation are still facing substantial challenges. Herein, Gd2O2S-based phosphors with high crystallinity, good dispersibility, and relatively good size uniformity were obtained by optimizing the type and components of flux based on the conventional solid-state method. By single-doping system study, the emission properties of matrix and activated ions are expounded, meanwhile the composition and co-excitation wavelength of co-doping system are designed. In the co-doping system, we mainly realized adjustable emission, interionic energy transfer, and application performance analysis. Firstly, multicolor emission in the range of yellow, orange and white was achieved through the modulation of dopant type and concentration as well as excitation wavelength. Secondly, the phenomena of spectral overlap (between Dy3+ and Sm3+), fluorescence intensity change (606 nm of Sm3+) and the monotonically decreasing fluorescence lifetime (Dy3+ at 578 nm) were evidence of energy transfer in the co-doping system. The theoretical fitting demonstrates that the energy transfer process of Dy3+→Sm3+ is primarily based on the quadrupole-quadrupole interaction mechanism. In addition, the cathodoluminescence spectra, temperature-dependent emission spectra, and magnetic properties tests have demonstrated the characteristics of multicolor adjustable emission (electron-beam excitation), excellent thermal stability, and good paramagnetic properties of the co-doping phosphors, further indicating that the Gd2O2S:Dy3+/Sm3+ system phosphors have potential as an excellent optical-magnetic bifunctional material in the fields of luminescence and bioimaging.

Multicolor emitting luminescent MgO nanocubes for implication in ratiometric optical thermometry

Optical thermometry employing dual emission from two distinct wavelengths for sensing performances has advantages over conventional thermometers due to the self-reference and noninvasive mode of operation. Here, we have demonstrated the synthesis of the multiple colors emitting luminescent MgO nanocubes and explored their temperature-dependent tunable emissions for application in intensity ratio-based optical thermometry. MgO nanocubes are prepared by heating Mg metal ribbons at different temperatures in air ambient. The as-prepared nanocubes exhibit two distinguished photoluminescence emission bands under UV (355 nm) and visible (532 nm) excitations. An excitation and synthesis condition-dependent multicolor emissions are observed in the visible to NIR regions due to the presence of various intermediate defect levels within the band gap of the materials. A temperature-dependent tunable dual emission is realized for different nanocubes, where the two peaks respond to the applied temperature differently, forming an isosbestic point. The difference in the temperature dependency of the two peaks is essential for the fluorescence intensity ratio-based optical thermometry application. The reason for the different responses of the two peaks is explained depending on the presence of the defect levels. From the temperature-dependent intensity ratio variation of MgO nanocubes, the highest sensitivity value of 6.79% K − 1 is achieved, which is very high compared to the various reported ratiometric sensors. The MgO nanocubes demonstrate better stability and reproducibility for application in the 83–513 K wide temperature range.

Design of a narrow-band blue-emitting Rb2Ba3(P2O7)2:Eu2+ phosphor with low thermal quenching for plant growth LEDs

Phosphor-converted light-emitting diodes (pc-LEDs) are commonly used to regulate the light environment to control the growth rates and improve the production efficiency of plant. Among them, the exploration of blue-emitting phosphors with high efficiency, low thermal quenching and excellent spectrum resemblance matching with the plant response spectrum is still challenging. Herein, a narrow-band blue-emitting Rb2Ba3(P2O7)2:Eu2+ phosphor with high color purity of 93.4% has been developed. Under 345 nm excitation, it exhibits a blue emission band centered at 413 nm with a full width at half-maximum (FWHM) of 36 nm, and the emission spectrum of Rb2Ba3(P2O7)2:0.060Eu2+ sample shows 85.7% spectrum resemblance with the absorption spectrum of chlorophyll-a in the blue region from 400 to 500 nm. In addition, the temperature-dependent emission spectra demonstrate that the Rb2Ba3(P2O7)2:0.060Eu2+ phosphor has good thermal stability and small chromaticity shift, with the emission intensity dropping to 72.5% at 423 K of the initial intensity at 298 K and a chromaticity shift of 38 × 10-3 at 498 K. All results suggest that the blue-emitting Rb2Ba3(P2O7)2:Eu2+ phosphor has potential application in plant growth LEDs.

Megapixel large-format colloidal quantum-dot infrared imagers with resonant-cavity enhanced photoresponse

Infrared imaging is extensively explored due to its unique properties of high atmospheric transmission and temperature-dependent emission. Unfortunately, the current epitaxial infrared materials suffer from a complicated fabrication process and low production yield, which hinders the further development of infrared imaging for civilian applications. As an alternative to epitaxial semiconductors, the wide spectral tunability and optical versatility of colloidal quantum dots (CQDs) have provided a promising route for infrared detection. Here, we demonstrate an infrared imager that integrates HgTe CQDs with complementary metal-oxide-semiconductor (CMOS) readout integrated circuits. Moreover, the underlying metal contacts and passivation layer of the CMOS chip play a role as an in-pixel resonant-cavity , which enhances the absorption of the CQDs film. The CQDs imager exhibits a detectivity of 2.8 × 1010 Jones, an external quantum efficiency of 14%, and an operable pixel factor of over 99.99% for a cut-off wavelength of around 2 µm at room-temperature. With a large-format (1280 × 1024 pixels2) and a small pixel pitch of 15 µm, the resolution of the imager can reach 40 line pairs per millimeter (lp/mm). The performance of the CQDs imager is demonstrated by infrared imaging.