Concentrations Of HO Research Articles

Degradation of aliphatic halogenated contaminants in water by UVA/Cu–TiO2 and UVA/TiO2 photocatalytic processes: Structure-activity relationship and role of reactive species

This study investigated the degradation of eight aliphatic halogenated contaminants (one brominated flame retardant and seven disinfection by-products) in synthetic drinking water by the UVA/TiO2 and UVA/Cu–TiO2 processes. The degradation rate constants of 2,2-bis(bromomethyl)-1,3-propanediol and trichloromethane in the UVA/Cu–TiO2 process were 10.1 and 1.29 times, respectively, higher than those in the UVA/TiO2 process. In contrast, the degradation rate constants of dichloroacetaldehyde, monochloroacetonitrile, monobromoacetonitrile and dibromonitromethane in the UVA/Cu–TiO2 process were 8.15, 2.33, 2.84 and 1.80 times, respectively, lower than those in the UVA/TiO2 process. The degradation rate constants of monobromonitromethane and dichloronitromethane were comparable in the two processes. The relationships between the degradation rate constants and the structural characteristics of the selected contaminants were examined to explain the different degradation efficacies of the contaminants in the two processes. As suggested by a quantitative structure-activity relationship (QSAR) model, the UVA/TiO2 process favored the degradation of contaminants with more polar electron-withdrawing moieties and higher degrees of chlorination. While the UVA/Cu–TiO2 process favored the degradation of hydrophilic unsaturated contaminants with multiple bonds. The concentrations of the reactive species (e.g., HO and e−) generated in the two photocatalytic processes were quantified using competition kinetics. The UVA/Cu–TiO2 process generated >10 times higher concentrations of HO than the UVA/TiO2 process, suggesting that the former process was more suitable for the degradation of contaminants that are reactive towards HO, while e− and e−-derived superoxide radicals were non-negligible contributors to contaminant degradation in the UVA/TiO2 process.

Determination methods for steady-state concentrations of HO• and SO4•− in electrochemical advanced oxidation processes

Competitive kinetics and scavenging assay are commonly used for radical quantification. However, the accuracy of the two methods has been challenged in electrochemical advanced oxidation processes (EAOPs) since the strong reactivity of electrode against organic indicators may disrupt the quantitative relationship between indicator consumption and radical concentration. The present study focused on screening suitable indicators and developing suitable methods for determining the steady-state concentrations of SO4•− and HO• ([SO4•−]ss and [HO•]ss) in several EAOPs for water treatment based on competitive kinetics and scavenging assay. The applicability of the modified methods and available indicators were investigated through experimental and kinetic analysis. In anode alone process, the competitive kinetics was more appropriate than scavenging assay and benzoic acid (BA) met the basic requirement of being a competitor to determine the [HO•]ss. In cathode alone process, BA was more resistant to interfering factors than other competitors (ibuprofen, atrazine and nitrobenzene) and its reaction rate involved only the radical oxidation even when the reaction conditions varied over a wide range. Therefore, the [HO•]ss could be obtained by the competitive kinetic equation of BA when HO• existed alone. When HO• coexisted with SO4•−, a two-step method combining scavenging assay and competitive kinetics was proposed to measure [SO4•−]ss and [HO•]ss, in which tert-butyl alcohol and BA were added as scavenger and competitor, respectively. Furthermore, the reliability of each approach was verified by the experimental results and kinetic analysis.

An iron-dependent burst of hydroxyl radicals stimulates straw decomposition and CO2 emission from soil hotspots: Consequences of Fenton or Fenton-like reactions

Plant residues in soil create temporal and spatial hotspots of extremely high microbial activities leading to very intensive greenhouse gas (GHG) fluxes that challenge our mechanistic understanding and predictive power. Using a series of well-controlled soil microcosm experiments, we examine how abiotic processes (e.g., iron reduction-oxidation cycling) at residue/soil interfaces contribute to hotspot dynamics. We quantify for the first time the contributions of microbially-initiated Fenton reactions, which produce strongly oxidizing hydroxyl radicals (HO), to organic matter solubilization and mineralization in hotspots 0–3 mm from the litter surface. The concentrations of ferrous iron (Fe2+), hydrogen peroxide (H2O2) and HO were 2.1–3.0, 3.0–9.0 and 2.6–2.8 times higher, respectively, at the straw-soil interface than in the bulk soil. Thus, iron minerals, especially in concert with microorganisms, produce a burst of hydroxyl radicals that explain extremely high GHG fluxes from soil hotspots. Our findings highlight how Fe minerals and microorganisms synergistically influence global carbon cycling. These synergistic effects should be accounted for mechanistic understanding of processes in soil hotspots.

UV Photolysis of Mono- and Dichloramine Using UV-LEDs as Radiation Sources: Photodecay Rates and Radical Concentrations

UV-LEDs with four characteristic wavelengths (255, 265, 285, and 300 nm) were used to investigate the wavelength-dependence of the photolysis of two inorganic chloramines (NH2Cl and NHCl2) and their subsequent radical formation. The fluence-based photodecay rates of NH2Cl decreased with increasing wavelength from 255 to 300 nm, while NHCl2 photodecay rates exhibited the opposite wavelength-dependence. The fluence-based photodecay rate of NH2Cl was comparable to that of NHCl2 at 255 nm, but was lower than NHCl2 at other tested wavelengths. The wavelength-dependence was more influenced by the molar absorption coefficient than the apparent/innate quantum yield and the lower photosensitivity was mainly attributed to the higher bond (N-Cl) dissociation energy (BDE) of NH2Cl than NHCl2. The steady-state concentrations of HO• and reactive chlorine species (e.g., Cl2•-, ClO•, and Cl•) that were generated from the photolysis of NH2Cl and NHCl2 at different wavelengths were determined experimentally and compared with the simulated results by a kinetic model. UV photolysis of NHCl2 at 265, 285, and 300 nm generated higher concentrations of radicals (e.g., HO•, ClO•, Cl•, and Cl2-•) than NH2Cl, while UV photolysis of NH2Cl at 255 nm generated higher concentrations of HO•, ClO•, and Cl• but not Cl2-• than NHCl2. The findings of this study provide fundamental information to be used in selecting specific wavelengths of UV radiation for enhancing/optimizing NH2Cl/NHCl2 photodecay in swimming pools and radical generation for micropollutant abatement in drinking water treatment or potable water reuse.

Bone Mineral Density in Population Long-Term Exposed to Rare Earth Elements from a Mining Area of China.

This study aims to investigate the effects of individuals' exposure to rare earth elements (REEs) on bone metabolism. Adopting the inductively coupled plasma mass spectrometry, we measured REEs and eight other elements (Ca, Fe, Cu, Na, K, Zn, Mg, and P) in the hair of 53 miners exposed to REEs from Baiyunebo and 57 healthy farmers as the control group. Furthermore, bone mineral density (BMD) in both groups was assessed by dual-energy X-ray absorptiometry. Analysis of variance showed that the concentrations of La, Ce, Pr, Nd, Tb, Ho, Tm, and Yb in male hair of exposed group were significantly higher compared with the control group, whereas the concentrations of Ca and Fe in exposed group were significantly lower; the results of female hair, except for Ce, Tb, Ho, Tm, and Yb, were consistent with male hair. Student's t test showed that the BMD of exposed males at lumbar vertebrae, femoral neck, greater trochanter, and intertrochanter was significantly lower than that of controls, and exposed females reported lower BMD values at lumbar vertebrae and femoral neck. Multiple linear regression analysis showed that concentrations of differential REEs were inversely related to BMD in males, and concentrations of Ca and Fe were positively related to BMD both in males and females. Our study suggests that long-term environmental and occupational exposure leads to REE accumulation, and a low level of iron and calcium due to the competitive binding of REEs, which together induce bone metabolism disorders, and further reduce BMD.

Removal of artificial sweeteners using UV/persulfate: Radical-based degradation kinetic model in wastewater, pathways and toxicity

Artificial sweeteners (ASs) have been frequently detected in aquatic environment and are of emerging concern due to their environmental persistence, acesulfame (ACE) and sucralose (SUC) are two ASs that are difficult to remove. The ultraviolet/persulfate (UV/PS) advanced oxidation process has been proven to remove ASs in real wastewater effectively. In this study, radical-based degradation kinetic model, pathways and toxicity evaluation of ASs by UV/PS process were explored. ACE and SUC were effectively removed by UV/PS process, and UV photolysis, hydroxyl radicals (HO∙) and sulfate radicals (SO4∙-) contributes the degradation of ASs. A kinetic prediction model for ASs degradation was established based on the second-order rate constants with HO∙ and SO4∙-, and the steady state concentrations of HO∙ and SO4∙- were calculated through the degradations of two reference compounds. The kinetic model could predict the degradation process of ASs in five real wastewaters effluents. Furthermore, two models based on the kinetic and the water matrices parameters for ASs degradation in wastewater were compared. Finally, the tentative pathways of ASs degradations by UV/PS were proposed. Also, toxicity evaluation showed that ASs after UV/PS treatment enhanced the toxicity on C. carpio liver, and prolongation of treatment time and recovery in fresh water can reduce the toxicity on C. carpio.

Reactive Nitrogen Species Are Also Involved in the Transformation of Micropollutants by the UV/Monochloramine Process.

The UV/monochloramine (NH2Cl) process is an emerging advanced oxidation process (AOP) in water treatment via radicals produced from the UV photolysis of NH2Cl. This study investigated the degradation of micropollutants by the UV/NH2Cl AOP, with ibuprofen (IBP) and naproxen (NPX) selected as representative micropollutants. Hydroxyl radical (HO•) and chlorine atom (Cl•) were identified in the process, and unexpectedly, we found that reactive nitrogen species (RNS) also played important roles in the transformation of micropollutants. The electron paramagnetic resonance (EPR) analysis proved the production of •NO as well as HO•. The concentrations of HO•, Cl•, and •NO in UV/NH2Cl remained constant at pH 6.0-8.6, resulting in the slightly changed UV fluence-based pseudo-first-order rate constants (k') of IBP and NPX, which were about 1.65 × 10-3 and 2.54 × 10-3 cm2/mJ, respectively. For IBP, the relative contribution of RNS to k' was 27.8% at pH 7 and 50 μM NH2Cl, which was higher than that of Cl• (6.5%) but lower than that of HO• (58.7%). For NPX, the relative contribution of RNS to k' was 13.6%, which was lower than both Cl• (23.2%) and HO• (46.9%). The concentrations of HO•, Cl•, and •NO increased with the increasing NH2Cl dosage. Water matrix components of natural organic matter (NOM) and bicarbonate can scavenge HO•, Cl•, and RNS. The presence of 5 mg/L NOM decreased the k' of IBP and NPX by 66.9 and 57.6%, respectively, while 2 mM bicarbonate decreased the k' of IBP by 57.4% but increased the k' of NPX by 10.5% due to the contribution of CO3•- to NPX degradation. Products containing nitroso-, hydroxyl-, and chlorine-groups were detected during the degradation of IBP and NPX by UV/NH2Cl, indicating the role of nitrogen oxide radical (•NO) as well as HO• and Cl•. Trichloronitromethane formation was strongly enhanced in the UV/NH2Cl-treated samples, further indicating the important roles of RNS in this process. This study first demonstrates the involvement of RNS in the transformation of micropollutants in UV/NH2Cl.

PPCP degradation and DBP formation in the solar/free chlorine system: Effects of pH and dissolved oxygen

The solar/chlorine process produces multiple reactive species by solar photolysis of chlorine, which can be used as an energy-efficient technology for water treatment. This study investigated the effects of pH and dissolved oxygen (DO) on the degradation of pharmaceuticals and personal care products (PPCPs) and on the formation of disinfection byproducts (DBPs) in the solar/chlorine system. The degradation of 24 structurally diverse PPCPs was enhanced appreciably in the solar/chlorine system compared to solar irradiation and dark chlorination. The reactive species in the solar/chlorine system were identified to be hydroxyl radicals (HO), reactive chlorine species (RCS, i.e., Cl and ClO) and ozone. With increasing pH from 6 to 8, the steady-state concentrations of HO and Cl decreased from 1.23 × 10−14 M to 4.79 × 10−15 M and from 9.80 × 10−16 M to 4.31 × 10−16 M, respectively, whereas that of ClO increased from 5.30 × 10−14 M to 2.68 × 10−13 M and the exposure of ozone increased from 0.44 μM min to 1.01 μM min in 90 min. Accordingly, the removal efficiencies of 6 PPCPs decreased and 11 PPCPs increased. The decreased removal of PPCPs with increasing pH was due to the decrease in HO and Cl, while the increased removal was attributed to the increased ClO and ozone. The presence of DO enhanced the degradation of most PPCPs, indicating the role of ozone on the degradation. The formation of total organic chlorine (TOCl) and known DBPs was enhanced by 60.7% and 159.4%, respectively, in the solar/chlorine system compared to chlorination in a simulated drinking water containing 2.5 mg L−1 natural organic matter (NOM). As the pH rose from 6 to 8, TOCl formation decreased by 16.2%, while that of known DBPs increased by 58.6% in solar/chlorine. The absence of DO slightly suppressed the formation of TOCl and known DBPs. This study illustrated the significant role of RCS in the solar/chlorine system, which enhanced the degradation of micropollutants but increased the formation of chlorinated DBPs.

Rare earth elements in the Pearl River Delta of China: Potential impacts of the REE industry on water, suspended particles and oysters

Rare earth element (REE) concentrations and patterns were measured in surface water, suspended particles (SP) and oysters from the Pearl River Estuary, China. During the rainy season of 2017, higher REE concentrations were found at the stations in the estuary (ΣREE = 0.06–0.42 μg L−1) than those at the river mouths (referred to as ‘outlet’ stations, ΣREE = 0.001–0.14 μg L−1). However, the reverse occurred in the dry season of 2016 (ΣREE = 0.07–0.16 μg L−1 in the mid-estuary vs. 0.001–0.02 μg L−1in the outlet stations). Elevated concentrations of Pr, Nd, Dy and Ho, relative to the other REEs were found in water in both seasons at most sampling locations. However, in some estuary stations, no anomalies were detected in the SP or in the oysters while some anomalies were seen in SP from the outlet stations. Significant correlations between REE concentrations in SP and oysters as well as between both total REE concentrations and the La/Yb ratio (reflecting enhanced accumulation of light REEs (LREEs)) in oysters indicate that, in the Pearl River Estuary, the dominant REE uptake pathway in oysters is from particles.The elevated concentrations of Pr, Nd, Dy and Ho, which are reported here for the first time suggest that elevated levels of these elements may result from REE recycling and other industrialized activities in this area of southern China. Specific REEs could be used to indicate emerging contamination by the modern REE industry; furthermore, REE anomalies and patterns may be suitable tools to track REE sources.

Sensing characteristics of clad-modified (Ho-doped Bi2O3 nanoparticles) fibre optic gas sensor

Abstract Sensing characteristics of Ho (1, 3 and 5% mol) – doped Bi 2 O 3 clad-modified fibre optic gas sensor are studied for ammonia, ethanol, methanol and acetone gases at ambient temperature. Bi 2 O 3 doped with all concentrations of Ho shows good gas response to acetone, whereas, 1% and 3% mol of Ho show to methanol. Ammonia and ethanol show very poor gas response for all the doping concentrations. The highest gas sensitivity and gas selectivity property are shown with 3% mol of Ho with acetone. Time response characteristics of the sensor are also reported.

Immobilization of Eu and Ho from synthetic acid mine drainage by precipitation with Fe and Al (hydr)oxides.

Use of lime to mitigate acid mine drainage is, in general, accompanied by precipitation of iron (Fe) and aluminium (Al) (hydr)oxides which may increase the removal of trace elements from water. This work aimed to evaluate the precipitation of Fe/Al (hydr)oxides to remove rare earth elements (REE) from contaminated water and the stability of precipitates. Two sets of 60-day syntheses were carried out using different Fe/Al/REE molar ratios, for europium (Eu) and holmium (Ho). The pH was periodically adjusted to 9.0, and the stability of the resulting precipitates was evaluated by water-soluble and BCR extractable phases, namely (1) acid soluble, extracted by 0.11molL-1 acetic acid; (2) reducible, extracted with 0.5molL-1 hydroxylamine hydrochloride; and (3) oxidisable, extracted with 8.8molL-1 hydrogen peroxide efficiencies of the water treatments for both Eu and Ho that were higher than 99.9% irrespective to the Fe/Al/REE molar ratios. Water-soluble phases of Eu and Ho were lower than 0.01% of the total contents in the precipitates. Recoveries from precipitates by Bureau Communautaire de Référence (BCR) sequential extractions increased with increasing concentrations of Eu and Ho. Acetic acid extracted higher amounts of REE, but Eu recovery was superior to Ho. Lepidocrocite was formed as Eu concentration increased which decreased its stability in the precipitates.

Kinetic Study of Hydroxyl and Sulfate Radical-Mediated Oxidation of Pharmaceuticals in Wastewater Effluents.

Advanced oxidation processes (AOPs), such as hydroxyl radical (HO•)- and sulfate radical (SO4•-)-mediated oxidation, are alternatives for the attenuation of pharmaceuticals and personal care products (PPCPs) in wastewater effluents. However, the kinetics of these reactions needs to be investigated. In this study, kinetic models for 15 PPCPs were built to predict the degradation of PPCPs in both HO•- and SO4•--mediated oxidation. In the UV/H2O2 process, a simplified kinetic model involving only steady state concentrations of HO• and its biomolecular reaction rate constants is suitable for predicting the removal of PPCPs, indicating the dominant role of HO• in the removal of PPCPs. In the UV/K2S2O8 process, the calculated steady state concentrations of CO3•- and bromine radicals (Br•, Br2•- and BrCl•-) were 600-fold and 1-2 orders of magnitude higher than the concentrations of SO4•-, respectively. The kinetic model, involving both SO4•- and CO3•- as reactive species, was more accurate for predicting the removal of the 9 PPCPs, except for salbutamol and nitroimidazoles. The steric and ionic effects of organic matter toward SO4•- could lead to overestimations of the removal efficiencies of the SO4•--mediated oxidation of nitroimidazoles in wastewater effluents.

Rare Earth Element Concentrations in Brazilian Benchmark Soils

ABSTRACT: Studies regarding background concentrations of rare earth elements (REEs) are scarce and have mainly focused on a limited number of soil types from the northern hemisphere. The aim of this study was to determine REE concentrations in thirty-five benchmark soils of Brazil. Composite soil samples were taken from areas under native vegetation or with minimal anthropogenic influence. Concentrations of La, Ce, Pr, Nd, Sm, Eu, Gd, Yb, Lu, Dy, Er, Ho, Tb, Tm, Y, Sc, and Fe were determined [...]

Microwave-Modified Sol-Gel Process for Microcystalline KY(WO<sub>4</sub>)<sub>2</sub>: Ho<sup>3+</sup>/Yb<sup>3+</sup> Phosphors and their Upconversion Photoluminescence Properties

KY 1-x (WO₄)₂:Ho 3+ /Yb 3+ yellow phosphors with doping concentrations of Ho 3+ and Yb 3+ (x = Ho 3+ + Yb 3+ , Ho 3+ = 0.05, 0.1, 0.2 and Yb 3+ = 0.2, 0.45) were successfully prepared using the microwave-modified sol-gel method; their upconversion (UC) photoluminescence properties were investigated in detail. Well-crystallized particles, formed after heat-treatment at 900°C for 16 h, showed a fine and homogeneous morphology with particle sizes of 2-5 μm. Under excitation at 980 nm, the UC KY0.7(WO₄)₂:Ho 0.1 Yb 0.2 and KY 0.5 (WO₄)₂Ho 0.05 Yb 0.45 particles exhibited excellent yellow emissions based on a strong 545-nm emission band in the green region and a very strong 655-nm emission band in the red region. Pump power dependence and Commission Internationale de LEclairage chromaticity of the UC emission intensity were evaluated. The spectroscopic properties were examined comparatively using Raman spectroscopy.

Enhancement of near-infrared to near-infrared upconversion luminescence in sub-10-nm ultra-small LaF(3):Yb(3+)/Tm(3+) nanoparticles through lanthanide doping.

In this Letter, I present a versatile strategy to enhance the near-infrared to near-infrared (NIR-to-NIR) upconversion luminescence from sub-10-nm ultra-small LaF(3):Yb(3+)/Tm(3+) colloidal nanoparticles through lanthanide doping under 980 nm laser excitation. It is interesting that the NIR-to-NIR upconversion emission at 801 nm of LaF(3):Yb(3+)Tm(3+) nanoparticles can be improved by increasing the Tm(3+) doping concentration or by introducing another lanthanide activator (Er(3+) or Ho(3+)) as a sensitizer. The luminescence enhancement effect showed a strong dependence on the doping concentrations of activator ions (Tm(3+), Er(3+), or Ho(3+)). Particularly, adding 1 mol. % Ho(3+) ions into LaF(3):Yb(3+)Tm(3+) nanoparticles induced a 2.85-fold enhancement in NIR 801 nm emission of Tm(3+) ions. The related upconversion emission mechanisms were investigated and discussed.

Modular advanced oxidation process enabled by cathodic hydrogen peroxide production.

Hydrogen peroxide (H2O2) is frequently used in combination with ultraviolet (UV) light to treat trace organic contaminants in advanced oxidation processes (AOPs). In small-scale applications, such as wellhead and point-of-entry water treatment systems, the need to maintain a stock solution of concentrated H2O2 increases the operational cost and complicates the operation of AOPs. To avoid the need for replenishing a stock solution of H2O2, a gas diffusion electrode was used to generate low concentrations of H2O2 directly in the water prior to its exposure to UV light. Following the AOP, the solution was passed through an anodic chamber to lower the solution pH and remove the residual H2O2. The effectiveness of the technology was evaluated using a suite of trace contaminants that spanned a range of reactivity with UV light and hydroxyl radical (HO•) in three different types of source waters (i.e., simulated groundwater, simulated surface water, and municipal wastewater effluent) as well as a sodium chloride solution. Irrespective of the source water, the system produced enough H2O2 to treat up to 120 L water d–1. The extent of transformation of trace organic contaminants was affected by the current density and the concentrations of HO• scavengers in the source water. The electrical energy per order (EEO) ranged from 1 to 3 kWh m–3, with the UV lamp accounting for most of the energy consumption. The gas diffusion electrode exhibited high efficiency for H2O2 production over extended periods and did not show a diminution in performance in any of the matrices.

Simulation and comparative study on the oxidation kinetics of atrazine by UV/H2O2, [formula omitted] and [formula omitted

This study comparatively investigated atrazine (ATZ) degradation by irradiation at the wavelength of 254 nm in the presence of peroxides including hydrogen peroxide (H2O2), peroxymonosulfate (HSO5−), and persulfate (S2O82−) at various initial ATZ concentrations and oxidant dosages. The effects of water matrix, such as carbonate/bicarbonate (HCO3−/CO32−), chloride ions (Cl−), and natural organic matter (NOM), were evaluated on these three advanced oxidation processes. A simple steady-state kinetic model was developed based on the initial rates of ATZ destruction, which could well describe the apparent pseudo-first-order rate constants (kapp, s−1) of ATZ degradation in these three processes. The specific roles of reactive species (i.e., HO, SO4−, CO3−, and Cl2−) under various experimental conditions were quantitatively evaluated based on their steady-state concentrations obtained from this model. Modeling results showed that the steady-state concentrations of HO and SO4− decreased with the increase of CO32−/HCO3− concentration, and the relative contribution of HO to ATZ degradation significantly decreased in UV/H2O2 and UV/HSO5− systems. On the other hand, the scavenging effect of HCO3−/CO32− on the relative contribution of SO4− to ATZ degradation was lower than that on HO. The presence of Cl− (0.5–10 mM) significantly scavenged SO4− but had slightly scavenging effect on HO at the present experimental pH, resulting in greater decrease of kapp in the UV/S2O82− than UV/H2O2 and UV/HSO5− systems. Higher levels of Cl2− were generated in the UV/S2O82− than those in the UV/H2O2 and UV/HSO5− systems at the same Cl− concentrations. NOM significantly decreased kapp due to its effects of competitive UV absorption and radical scavenging with the latter one being dominant. These results improve the understanding of the effects of water constituents for ATZ degradation in the UV-based oxidation processes.

Synthesis of NaY(WO<sub>4</sub>)<sub>2</sub>:Ho<sup>3+</sup>/Yb<sup>3+</sup> Phosphors via The Microwave-Modified Sol-Gel Route and Their Upconversion Photoluminescence Properties

NaY 1-x (WO₄)₂:Ho 3+ /Yb 3+ phosphors with doping concentrations of Ho 3+ and Yb 3+ (x = Ho 3+ + Yb 3+ , Ho 3+ = 0.05, 0.1, 0.2, and Yb 3+ = 0.2, 0.45) were successfully synthesized via the cyclic microwave-modified sol-gel route; their upconversion properties were investigated. Well-crystallized particles showed a fine and homogeneous morphology with particle sizes of 2-5 ㎛. Under excitation at 980 ㎚, the synthesized particles exhibited yellow emissions based on a strong 550-㎚ emission band in the green region and a very strong 655-㎚ emission band in the red region. The Raman spectra of the doped particles indicated the domination of strong peaks at higher and lower frequencies induced by the incorporation of the Ho 3+ and Yb 3+ elements into the Y 3+ sites in the crystal lattice, which resulted in unit cell shrinkage that accompanied a new phase formation of the WO 4-x group.

Ho3+‐doped strontium–aluminium–bismuth–borate glasses for green light emission

Strontium-aluminium-bismuth-borate glasses (SAlBiB) doped with different concentrations of Ho(3+) were prepared using conventional melt quenching technique and their structural and optical properties investigated. X-ray diffraction and scanning electron microscopy analysis were used to study the structural properties. Optical properties were studied by measuring the optical absorption and visible luminescence spectra. The Judd-Ofelt (J-O) theory was applied to evaluate J-O intensity parameters, Ω(λ) (λ = 2, 4 and 6). Using J-O intensity parameters, radiative properties such as spontaneous transition probabilities (A(R)), branching ratios (β(R)) and radiative lifetimes (τ(R)) were determined. From the emission spectra, a strong green emission nearly at 549 nm corresponding to the transition, (5)S2 ((5)F4)→(5)I(8) was observed. Emission peak positions (λ(P)), effective bandwidths (Δλ(eff)) and stimulated emission cross-sections (σ(p)) were calculated for the observed emission transitions, (5)F3 →(5)I(8), (5)S2((5)F4)→(5)I(8) and (5)F5 →(5)I(8) of Ho(3+) in all the glass matrices. Chromaticity color coordinates were calculated using the emission spectra. The experimental results suggest that SAlBiB glass matrix with 1.5 mol% of Ho(3+) has better emission properties.

A resonantly-pumped tunable Q-switched Ho:YAG ceramic laser with diffraction-limit beam quality

We demonstrated a Q-switched Ho:YAG ceramic laser operating at 2097 nm. The Ho:YAG ceramic laser was resonantly pumped by a Tm:YLF laser at 1908 nm. The laser performance with two Ho-doping concentrations of Ho:YAG ceramics in a U-shaped resonator was studied. Different pump spots were investigated to obtain high extract efficiency. The wavelength of Ho:YAG ceramic laser was tuned from 2090.70 nm to 2098.10 nm. The Q-switched pulse energy were 9.6 mJ at a pulse repetition frequency (PRF) of 200 Hz and 10.2 mJ at a PRF of 100 Hz, respectively. The beam quality M(2) factors were measured to be less than 1.1 in both directions.