Comparative Assessment of Ambient Air Quality of Major Cities of Pakistan

The deterioration of ambient air quality is one of the emerging environmental problems in developing countries of South Asia. Unplanned urbanization, population growth, degradation of vegetation cover and industrial and vehicular emissions, particularly in urban areas, have resulted in substantial rise in the level of air pollutants and emission sources. This study focused on monitoring of different cities as per traffic volume and flow. Air quality monitoring was conducted on hourly basis to determine the major parameters; i.e. PM₁₀, NO_x, SO₂, CO by using fixed station for 8 h from 1:30 pm to 9:30 pm. All the measuring values were then compared with the National Environment Quality Standards (NEQS) and Air Quality Index (AQI). Results revealed that the concentration of PM₁₀ at the selected areas of these cities ranged from 156 to 390 μg/m³, CO ranged from 1.18 to 6.01 mg/m³, and NO_x ranged from 32.65 to 129.47 μg/m³. It was evident that all these concentration had been higher than the permissible limits of NEQS, whereas only SO₂ was found within the permissible limits (15.60–110.52 μg/m³⁾. Air Quality Index (AQI) of all the designated points of cities was also assessed, and most of the vehicular and commercial areas had shown unhealthy and severe conditions ranging from 191 to 320, respectively.

     

燃煤电厂烟气中Hg的生成、治理、测试及排放特征研究

燃煤电厂是大气Hg排放的主要来源之一，基于文献调研，分析了燃煤电厂烟气中Hg的来源及生成、燃烧后现有设备协同脱Hg技术和吸附剂喷射脱Hg技术、主要离线测试方法、超低排放实施前后燃煤电厂烟气Hg排放特征等，指出燃煤电厂实施更严格的烟气Hg排放控制是非常有必要的，且改性活性炭、改性飞灰喷射脱Hg技术将是未来应对更严格Hg排放限值的主流技术。研究结果可为燃煤电厂烟气Hg排放控制提供参考。     

Blue and white light emission in Tm3+ and Tm3+/Dy3+ doped zinc phosphate glasses upon UV light excitation

A spectroscopic study based on photoluminescence spectra and decay time profiles in Tm³⁺ and Tm³⁺/Dy³⁺ doped Zn(PO₃)₂ glasses is reported. The Tm³⁺ doped Zn(PO₃)₂ glass, upon 357 nm excitation, exhibits blue emission with CIE1931 chromaticity coordinates, x = 0.157 and y = 0.030, and color purity of about 96%. Under excitations at 348, 352 and 363 nm, which match with the emissions of AlGaN and GaN based LEDs, the Tm³⁺/Dy³⁺ co-doped Zn(PO₃)₂ glass displays natural white, bluish white and cool white overall emissions, with correlated color temperature values of 4523, 10700 and 7788 K, respectively, depending strongly on the excitation wavelength. The shortening of the Dy³⁺ emission decay time in presence of Tm³⁺ suggests that Dy³⁺→Tm³⁺ non-radiative energy transfer occurs. By using the Inokuti-Hirayama model, it is inferred that an electric quadrupole-quadrupole interaction might be the dominant mechanism involved in the energy transfer. The efficiency and probability of this energy transfer are 0.12 and 126.70 s⁻¹, respectively.     

2 μm emission properties and hydroxy groups quenching of Tm3+ in germanate-tellurite glass

Tm³⁺ activated germanate-tellurite glasses with good thermal stability and anti-crystallization ability were prepared. Efficient 2 μm fluorescence was observed in the optimal concentration Tm³⁺ doped glass and the corresponding radiative properties were investigated. For Tm³⁺: ³F₄ → ³H₆ transition, high spontaneous radiative transition probability (260.75 s⁻¹) and large emission cross section (7.66 × 10⁻²¹ cm²) were obtained from the prepared glass. According to Dexter's and Forster's theory, energy transfer microscopic parameters were computed to elucidate the observed 2 μm emissions in detail. Besides, the effect of hydroxy groups quenching was also quantificationally investigated based on simplified rate equations. Results demonstrate that the optimal concentration Tm³⁺ doped germanate-tellurite glass possessing excellent spectroscopic properties might be an attractive candidate for 2 μm laser or amplifier.     

Characterization and enhanced field emission properties of carbon nanotube bundle arrays coated with N-doped nanocrystalline anatase TiO2

Anatase TiO₂ nanocrystals (NCs) were deposited onto patterned carbon nanotube (CNT) bundle arrays to form a TiO₂/CNT composite using metal organic chemical vapor deposition (MOCVD) using titanium-tetraisopropoxide (Ti(OC₃H₇)₄) as a source reagent. The N-doped TiO₂/CNT composite was then fabricated using nitrogen plasma treatment. The structural and spectroscopic properties of TiO₂/CNT composites were characterized by field-emission scanning electron microscopy, micro-Raman spectroscopy and X-ray photoelectron spectroscopy. The combined geometrical structure and low electron affinity effects of N-doped TiO₂ led to a low turn-on field of 1.0 V μm⁻¹ at a current density of 10 μA cm⁻², a low threshold field of 1.9 V μm⁻¹ at a current density of 1 mA cm⁻², a high field enhancement factor of 3.0 × 10³, and long-term stability for the N-doped TiO₂/CNT composite. The results revealed that the N-doped TiO₂/CNT composite can be a potential candidate for field emission devices.     

Effects of aging time on phase,morphology, and luminescence by two-photon processes of BiPO4:Er3+, Yb3+ in the solvothermal synthesis

BiPO₄:Er³⁺, Yb³⁺ phosphors were synthesized by the solvothermal process. The phase transformation, morphology, and UC luminescent property were characterized by different analytical techniques. The aging time has obvious influence on the phase, morphology, and luminescence of the samples. With the extension of aging time, the phase of BiPO₄:Er³⁺, Yb³⁺ phosphors changes from hexagon to monocline. The morphology changes from nanorods through nanorugbies to microoctahedra. Under the excitation at 980 nm, BiPO₄:Er³⁺, Yb³⁺ phosphors show green and red UC emissions, which originate from the (²H_11/2, ⁴S_3/2) → ⁴I_15/2 and ⁴F_9/2 → ⁴I_15/2 transitions of Er³⁺ ions. The green and red UC emission intensities increase gradually with the increase of pumping power. On the basis of the luminescent properties, one can conclude that the two-photon process is involved in green and red UC emissions.     

Preparation of grass-like GaN nanostructures: Its PL and excellent field emission properties

We here report highly pure and single crystalline grass-like gallium nitride (GaN) nanostructures obtained on silicon substrate via catalyst-assisted CVD route under NH₃ atmosphere inside horizontal tube furnace (HTF) by pre-treating the precursors with aqueous NH₃. The as-obtained GaN nanostructures were characterized by XRD, SEM, EDS, HRTEM and SAED. The field emission (FE) characteristics of grass-like GaN nanostructures exhibited a turn-on field of 7.82 V μm^− 1 and a threshold field of 8.96 V μm^− 1 which are quite reasonable for applications in electron emission devices, field emission displays and vacuum microelectronic devices. Room temperature photoluminescence (PL) measurements of grass-like GaN nanostructures exhibited a strong near-band-edge emission at 368.8 nm (3.36 eV) without any defects related emissions which shows its potential applications in optoelectronics.     

Up-conversion luminescence and optical temperature sensing behaviour of Yb3+/Er3+ codoped CaWO4 material

Present article report on structural and optical properties of Er³⁺/Yb³⁺ codoped CaWO₄ phosphors. Structural properties are explored using XRD and Raman technologies. The upconversion emission has been investigated with 980 nm excitation. The upconversion emission intensity is dependent on the concentrations of Yb³⁺ ions and reaches a maximum at 7%. Logarithmic plots of power dependencies reveal that the green and red emissions originate from a two-photon upconversion process. Based on the photon energy and the emission spectra, the possible upconversion processes and emission mechanisms are discussed. Finally, the optical temperature sensing properties has been performed using the fluorescence intensity ratio technique based on green upconversion emissions. Its temperature sensitivity is found to be above 0.0025 K^-1 in the whole temperature range of 300–540 K, revealing this phosphor to be a promising optical temperature sensing material.     

Methane Emissions from Grazing Holstein-Friesian Heifers at Different Ages Estimated Using the Sulfur Hexafluoride Tracer Technique

Although the effect of animal and diet factors on enteric methane (CH₄) emissions from confined cattle has been extensively examined, less data is available regarding CH₄ emissions from grazing young cattle. A study was undertaken to evaluate the effect of the physiological state of Holstein-Friesian heifers on their enteric CH₄ emissions while grazing a perennial ryegrass sward. Two experiments were conducted: Experiment 1 ran from May 2011 for 11 weeks and Experiment 2 ran from August 2011 for 10 weeks. In each experiment, Holstein-Friesian heifers were divided into three treatment groups (12 animals/group) consisting of calves, yearling heifers, and in-calf heifers (average ages: 8.5, 14.5, and 20.5 months, respectively). Methane emissions were estimated for each animal in the final week of each experiment using the sulfur hexafluoride tracer technique. Dry matter (DM) intake was estimated using the calculated metabolizable energy (ME) requirement divided by the ME concentration in the grazed grass. As expected, live weight increased with increasing animal age (P < 0.001); however, there was no difference in live weight gain among the three groups in Experiment 1, although in Experiment 2, this variable decreased with increasing animal age (P < 0.001). In Experiment 1, yearling heifers had the highest CH₄ emissions (g·d⁻¹) and in-calf heifers produced more than calves (P < 0.001). When expressed as CH₄ emissions per unit of live weight, DM intake, and gross energy (GE) intake, yearling heifers had higher emission rates than calves and in-calf heifers (P < 0.001). However, the effects on CH₄ emissions were different in Experiment 2, in which CH₄ emissions (g·d⁻¹) increased linearly with increasing animal age (P < 0.001), although the difference between yearling and in-calf heifers was not significant. The CH₄/live weight ratio was lower in in-calf heifers than in the other two groups (P < 0.001), while CH₄ energy output as a proportion of GE intake was lower in calves than in yearling and in-calf heifers (P < 0.05). All data were then pooled and used to develop prediction equations for CH₄ emissions. All relationships are significant (P < 0.001), with R² values ranging from 0.630 to 0.682. These models indicate that CH₄ emissions could be increased by 0.252 g·d⁻¹ with an increase of 1 kg live weight or by 14.9 g·d⁻¹ with an increase of 1 kg·d⁻¹ of DM intake; or, the CH₄ energy output could be increased by 0.046 MJ·d⁻¹ with an increase of 1 MJ·d⁻¹ of GE intake. These results provide an alternative approach for estimating CH₄ emissions from grazing dairy heifers when actual CH₄ emission data are not available.     

2–3 μm emission and fluorescent decaying behavior in Ho3+-doped tellurium germanate glass

In this work, we report the 2.05 μm emission and ∼3 μm broadband spectra of Ho₂O₃-doped 33GeO₂–30TeO₂–27PbO–10CaO (in mol%) glass under 640 nm laser excitation. Clear emission spectra due to the ⁵I₇–⁵I₈ transition and the ⁵I₆–⁵I₇ transition in Ho³⁺ are observed. The 2.05 μm emission intensity and the full width at half maximum (FWHM) of the ∼3 μm broadband depend on the Ho concentration. The peak stimulated emission cross-section of Ho³⁺ is 6.57 × 10⁻²¹ cm² at 2.05 μm, as calculated by the McCumber theory. The emission spectra are recorded and the maximum emission intensity at 2.05 μm is obtained at a doping level of 0.5 mol% Ho₂O₃ in the glass. A broad and flat emission band from 2700 nm to 3050 nm is observed in 2 mol% Ho₂O₃-doped tellurium germanate glass. The lifetime of the ⁵I₇ state decreases with the increase in Ho³⁺ concentration due to non-radiative relaxation processes. An energy transfer coefficient of 271.88 mol⁻¹ s⁻¹ is obtained.     

Study on 2.0 μm fluorescence of Ho-doped water-free fluorotellurite glasses

Ho³⁺-doped water-free fluorotellurite glasses with composition of 60TeO₂–30ZnF₂–10NaF (mol%, TZNF60) were made by using specially-designed physical and chemical dehydration technique. 2.04 μm fluorescence (Ho³⁺: ⁵I₇ → ⁵I₈) was observed experimentally and presented in this paper: A broad bandwidth of ∼149 nm, large simulated emission cross-section of 7.2 × 10⁻²¹ cm², and the longest reported fluorescence lifetime of ∼10 ms among all the reported Ho³⁺-doped oxide glasses. Thanks to the absence of OH groups and low phonon energy with the addition fluorides into tellurite oxide glasses, 1.00Ho-TZNF60 glass demonstrates the maximum figure of merit (σ_em × τ_f) of 7.13 × 10⁻²⁷ m² s, thus regarded as a promising optical material for the development of 2.0 μm fiber lasers.     

Judd–Ofelt analysis and energy transfer processes of Er3+ and Nd3+ doped fluoroaluminate glasses with low phosphate content

Spectroscopic property and energy transfer processes of singly doped and codoped Er³⁺ and Nd³⁺ fluoroaluminate glasses with low phosphate content are systematically analyzed. The absorption spectra of these glasses are tested, and the Judd–Ofelt (J–O) and radiative parameters are discussed based on J–O theory and the parameters changes substantially because of the other codoping ions. As for Nd³⁺: the main emission bands at 0.9 and 1.05 μm decrease in the codoped sample under the excitation of an 800 nm laser diode from the emission spectra because the Er³⁺: ⁴I_11/2 level reduces the Nd³⁺: ⁴F_3/2 level effectively through the energy transfer process Nd³⁺: ⁴F_3/2 → Er³⁺: ⁴I_11/2. For Er³⁺, the emission at 1.5 μm is restrained by codoping with Nd³⁺ ions from the energy transfer process Er³⁺: ⁴I_13/2 → Nd³⁺: ⁴I_15/2. The emission at 2.7 μm is enhanced because the Nd³⁺ ions deplete the lower level and exert a positive effect on the upper laser level. The microparameters of the energy transfer between the Er³⁺ and Nd³⁺ ions are calculated and discussed using Forster–Dexter theory. The energy transfer efficiencies of the Nd³⁺: ⁴F_3/2 to the Er³⁺: ⁴I_11/2 and the Er³⁺: ⁴I_13/2 to the Nd³⁺: ⁴I_15/2 are 28.8% and 74.5%, respectively. These results indicate that Nd³⁺ can be an efficient sensitizer for Er³⁺ to obtain Mid-infrared (Mid-IR) emission and the codoped Er³⁺/Nd³⁺ fluoroaluminate glass with low phosphate content is suitable to be used as the fiber optical gain media for 2.7 μm laser generation.     

Low temperature phase barium borate: A new optical limiter in continuous wave and nano pulsed regime

Low temperature phase barium borate was synthesized by hydrothermal method. XRD analysis confirms the formation of γ-BBO or hydrated barium polyborate (Ba₃B₆O₉(OH)₆) which crystallizes in monoclinic system in the P2/c space group. The molecular structure analysis shows the presence of dominant BO₄ unit and the hydrated nature of material. γ-BBO exhibits sharp absorption edge at 202 nm and highly transparency in the UV–Visible–NIR region. The peak at 347 nm in the emission spectrum is due to the presence of self-trapped exciton. The third order nonlinear optical properties and limiting behavior of low temperature barium borate in both pulsed and continuous wave regime were studied. The effective 2PA absorption coefficient of γ-BBO under ns pulse excitation is estimated to be 0.38 × 10⁻¹⁰ m/W. The nonlinear absorption coefficient, refractive index and optical susceptibility of the material in cw regime were found to be in the order of 10⁻⁵ m W⁻¹, 10⁻¹² m² W⁻¹, 10⁻⁶ esu respectively. In both regimes, low temperature phase barium borate exhibits better optical limiting properties than high temperature phase β-BBO.     

Highly Luminescent Earth-Benign Organometallic Manganese Halide Crystals with Ultrahigh Thermal Stability of Emission from 4 to 623 K

The phosphor-converted light-emitting diode (PC-LED) has become an indispensable solid-state lighting and display technologies in the modern society. Nevertheless, the use of scarce rare-earth elements and the thermal quenching (TQ) behavior are still two most crucial issues yet to be solved. Here, this work successfully demonstrates a highly efficient and thermally stable green emissive MnI₂(XanPO) crystals showing a notable photoluminescence quantum yield (PLQY) of 94% and a super TQ resistance from 4 to 623 K. This unprecedented superior thermal stability is attributed to the low electron–phonon coupling and the unique rigid crystal structure of MnI₂(XanPO) over the whole temperature range based on the temperature-dependent photoluminescence (PL) and single crystal X-ray diffraction (SCXRD) analyses. Considering these appealing properties, green PC-LEDs with a power efficacy of 102.5 lm W⁻¹, an external quantum efficiency (EQE) of 22.7% and a peak luminance up to 7750 000 cd m⁻² are fabricated by integrating MnI₂(XanPO) with commercial blue LEDs. Moreover, the applicability of MnI₂(XanPO) in both micro-LEDs and organic light-emitting diodes (OLEDs) is also demonstrated. In a nutshell, this study uncovers a candidate of highly luminescent and TQ resistant manganese halide suitable for a variety of emission applications.     

Time-dependent PSL studies on CsBrCl:Eu2+: a promising image screen phosphor

The time-resolved PSL studies of CsBr_1−xCl_x:Eu²⁺ system has been studied for different europium concentrations. An efficient PSL material for use in image plate should have very short PSL emission lifetime. PSL emission lifetime for stimulation at 650 and 630 nm (F(Br⁻)- and F(Cl⁻)-centers) for CsBrCl:Eu²⁺ is determined to be 0.69 μs. The lifetime of BaFBr:Eu²⁺, the commercially available image screen phosphor is 0.8 μs. The present observation support the use of CsBrCl:Eu²⁺ as an efficient X-ray image screen phosphor.     

Multicolor up conversion emission and color tunability in Yb/Tm/Ho triply doped heavy metal oxide glasses

Multicolor and white light emissions have been achieved in Yb³⁺, Tm³⁺ and Ho³⁺ triply doped heavy metal oxide glasses upon laser excitation at 980 nm. The red (660 nm), green (547 nm) and blue (478 nm) up conversion emissions of the rare earth (RE) ions triply doped TeO₂–GeO₂–Bi₂O₃–K₂O glass (TGBK) have been investigated as a function of the RE concentration and excitation power of the 980 nm laser diode. The most appropriate combination of RE in the TGBK glass host (1.6 wt% Yb₂O₃, 0.6 wt% Tm₂O₃ and 0.1 wt% Ho₂O₃) has been determined with the purpose to tune the primary colors (RGB) respective emissions and generate white light emission by varying the pump power. The involved infrared to visible up conversion mechanisms mainly consist in a three-photon blue up conversion of Tm³⁺ ions and a two-photon green and red up conversions of Ho³⁺ ions. The resulting multicolor emissions have been described according to the CIE-1931 standards.     

Boosting the Thermoelectric Performance of the Doped DPP-EDOT Conjugated Polymer by Incorporating an Ionic Additive

The thermoelectric (TE) performance of organic materials is limited by the coupling of Seebeck coefficient and electrical conductivity. Herein a new strategy is reported to boost the Seebeck coefficient of conjugated polymer without significantly reducing the electrical conductivity by incorporation of an ionic additive DPPNMe₃Br . The doped polymer PDPP - EDOT thin film exhibits high electrical conductivity up to 1377 ± 109 S cm⁻¹ but low Seebeck coefficient below 30 µV K⁻¹ and a maximum power factor of 59 ± 10 µW m⁻¹ K⁻². Interestingly, incorporation of small amount (at a molar ratio of 1:30) of DPPNMe₃Br into PDPP - EDOT results in the significant enhancement of Seebeck coefficient along with the slight decrease of electrical conductivity after doping. Consequently, the power factor (PF) is boosted to 571 ± 38 µW m⁻¹ K⁻² and ZT reaches 0.28 ± 0.02 at 130 °C, which is among the highest for the reported organic TE materials. Based on the theoretical calculation, it is assumed that the enhancement of TE performance for the doped PDPP - EDOT by DPPNMe₃Br is mainly attributed to the increase of energetic disorder for PDPP - EDOT .     

Alkaline aluminum phosphate glasses for thermal ion-exchanged optical waveguide

Alkaline aluminum phosphate glasses (NMAP) with excellent chemical durability for thermal ion-exchanged optical waveguide have been designed and investigated. The transition temperature Tg (470 °C) is higher than the ion-exchange temperature (390 °C), which is favorable to sustain the stability of the glass structure for planar waveguide fabrication. The effective diffusion coefficient D_e of K⁺–Na⁺ ion exchange in NMAP glasses is 0.110 μm²/min, indicating that ion exchange can be achieved efficiently in the optical glasses. Single-mode channel waveguide has been fabricated on Er³⁺/Yb³⁺ doped NMAP glass substrate by standard micro-fabrication and K⁺–Na⁺ ion exchange. The mode field diameter is 9.6 μm in the horizontal direction and 6.0 μm in the vertical direction, respectively, indicating an excellent overlap with a standard single-mode fiber. Judd–Ofelt intensity parameter Ω₂ is 5.47 × 10⁻²⁰ cm², implying a strong asymmetrical and covalent environment around Er³⁺ in the optical glasses. The full width at half maximum and maximum stimulated emission cross section of the ⁴I_13/2 → ⁴I_15/2 are 30 nm and 6.80 × 10⁻²¹ cm², respectively, demonstrating that the phosphate glasses are potential glass candidates in developing compact optoelectronic devices. Pr³⁺, Tm³⁺ and Ho³⁺ doped NMAP glasses are promising candidates to fabricate waveguide amplifiers and lasers operating at special telecommunication windows.     

Formation of Mn-oxide clusters in Mn-implanted SiO2 probed by soft X-ray emission and absorption spectroscopy

Mn⁺-implanted a-SiO₂-samples were studied with the help of soft X-ray emission and absorption spectroscopy (Si L_2,3 3d3s → 2p_3/2,1/2 and Mn L_2,3 3d4s → 2p_3/2,1/2 emission transitions) using synchrotron excitation. The samples were obtained using a pulsed ion source (ion beam current density ∼2-7 mA/cm², E_impl. = 30 keV, ion fluence ∼2 × 10¹⁷ cm⁻², pulse duration 400 μs) without thermal annealing. It was established that Mn-ion provides a formal valence state 2+, so arranging in implanted a-SiO₂ the low-sized MnO antiferromagnetic clusters probably of crystalline type. The data obtained well coincides with the electronic spin resonance results reported earlier.     

Toward Ultrahigh Thermoelectric Performance of Cu2SnS3-Based Materials by Analog Alloying

Cu₂SnS₃ is a promising thermoelectric candidate for power generation at medium temperature due to its low-cost and environmental-benign features. However, the high electrical resistivity due to low hole concentration severely restricts its final thermoelectric performance. Here, analog alloying with CuInSe₂ is first adopted to optimize the electrical resistivity by promoting the formation of Sn vacancies and the precipitation of In, and optimize lattice thermal conductivity through the formation of stacking faults and nanotwins. Such analog alloying enables a greatly enhanced power factor of 8.03 µW cm⁻¹ K⁻² and a largely reduced lattice thermal conductivity of 0.38 W m⁻¹ K⁻¹ for Cu₂SnS₃ – 9 mol.% CuInSe₂. Eventually, a peak ZT as high as 1.14 at 773 K is achieved for Cu₂SnS₃ – 9 mol.% CuInSe₂, which is one of the highest ZT among the researches on Cu₂SnS₃-based thermoelectric materials. The work implies analog alloying with CuInSe₂ is a very effective route to unleash superior thermoelectric performance of Cu₂SnS₃.