Co-doped NaYF4:Yb/Er/Tm upconversion luminescent coating to enhance the efficiency of photovoltaic cells.

The use of upconversion luminescent materials to broaden the utilization range of the solar spectrum to enhance the efficiency of photovoltaic cells offers a promising and sustainable approach. However, the low luminescence intensity and easy quenching of upconversion luminescent materials bring serious challenges to the practical application. Herein, a novel method using Co2+ ion doping to regulate the luminescence properties of NaYF4:Yb/Er/Tm is proposed. NaYF4:Yb/Er/Tm microcrystals doped with different proportions of Co2+ ions are prepared and used as coatings on the surface of photovoltaic cells. Co2+ ions regulate the crystallinity and size of the NaYF4:Yb/Er/Tm microcrystals and reduce the crystal field symmetry of the activator (Er3+ and Tm3+) ions. The results show that the emission intensity of green and red light is 18.19% and 83.24% times higher than that of undoped Co2+ ion materials, respectively. Besides, the efficiency of photovoltaic cells after coating Co2+ ion doped NaYF4:Yb/Er/Tm is 2.08% higher than that of the uncoated one. This work underscores the importance of Co2+ ion doping to improve and enhance the luminescence properties of NaYF4:Yb/Er/Tm, to further enhance the efficiency of photovoltaic cells.

Study on the Freeze-Thaw Resistance of Concrete Pavements in Seasonally Frozen Regions.

In seasonally frozen regions, concrete pavement is exposed to cycles of freeze-thaw and erosion from de-icing salt, which can lead to unfavorable service conditions and vulnerability to damage. This paper examines the compressive strength, flexural-tensile strength, abrasion resistance, permeability, and spacing factor of concrete, taking into account the impact of various curing conditions, de-icing salt solutions, and mass fractions on the concrete's freeze-thaw resistance. Two test methods, the single-face method and the fast-freezing method, were used to comparatively analyze the freeze-thaw resistance of concrete. The analysis was based on the surface scaling, water absorption rate, mass loss rate, relative dynamic elastic modulus, and relative durability index. The results indicate that the presence of salt solution significantly worsened the degree of concrete damage caused by freeze-thaw cycles. The use of freeze-thaw media, specifically sodium chloride (NaCl), calcium chloride (CaCl2), and potassium acetate (KAc) at mass fractions of 5%, 4.74%, and 5%, respectively, had the greatest impact on the surface scaling of concrete. However, their effect on the water absorption rate was inconsistent. When the freeze-thaw medium was water, the concrete's relative dynamic elastic modulus and relative durability index were 9.6% and 75.3% higher, respectively, for concrete cured in 20 °C-95% RH conditions compared to those cured in 0 °C-50% RH conditions. We propose a comprehensive relative durability index (DFw) by combining the results of two methods of freeze-thaw tests. The DFw of concrete cured in 0 °C-50% RH conditions was 83.8% lower than that of concrete cured in 20 °C-95% RH conditions when exposed to a freeze-thaw medium of 5% mass fraction NaCl solution. To evaluate the salt freeze-thaw resistance of concrete pavement, it is recommended to use surface scaling and DFw together.

Effect of Mud Powder on the Performance of Bridge Deck Leveling Concrete in a Seasonally Frozen Region.

Mud powders in aggregates are often found to cause deterioration of concrete properties. Based on a study of the mechanical properties of bridge deck leveling concrete (BDLC) containing different mud powders at various ages, the effects of mud powders on concrete durability were evaluated through rapid chloride permeability testing, freeze-thaw testing, and the coupling of salt solution and a freeze-thaw test. The properties of the interfacial transition zone (ITZ) were also investigated via microhardness testing. The test results showed that mud powder reduced the compressive strength, static compressive elastic modulus, and bond strength at early stages of curing. Moreover, mud powder was found to reduce the tensile properties and durability of concrete, with clay powder causing a greater reduction than mud powder in river sands and coarse aggregate. In addition, the width of the ITZ of concrete containing mud powder was found to increase by 23.1-48.3%. A significant correlation between the ITZ and the tensile properties, as well as the durability of concrete, was also observed. Therefore, in order to improve the tensile properties and durability of BDLC in seasonally frozen regions, the content of mud powder in the aggregates should be minimized according to the different compositions of mud powders. The coupling effect of salt solution and a freeze-thaw cycle should also be taken into consideration.

Research on Pavement Performance of Cement-Stabilized Municipal Solid Waste Incineration Bottom Ash Base.

In order to clarify the influence of the municipal solid waste incineration bottom ash (MSWI BA) content on the pavement performance of the cement-stabilized macadam, the MSWI BA with 0%, 25%, 38% and 50% content was used instead of fine aggregates. To explore the feasibility of building pavement base with cement stabilized MSWI BA, the cement-stabilized MSWI BA mixture was prepared by mixing the MSWI BA at the mass fraction of 50%, 75% and 100% with fine crushed stuff. Subsequently, the compaction test and 7 days unconfined compression test were conducted with 4%, 5% and 6% cement dosage. The compaction test, unconfined compressive strength test, splitting strength test, compressive resilient modulus test and frost resistance tests were carried out based on the long-age samples with an optimal cement dosage of 5%. Furthermore, the unconfined compressive constitutive model was established based on the test data. Afterwards, the test road was built to measure the practical effect of MSWI BA on road construction. Meanwhile, energy-saving and emission-reduction analyses were conducted on the MSWI BA road. The results showed that under 5% cement dosage, the mechanical properties and frost resistance of the mixture with different MSWI BA content both satisfied the specification requirements; during the construction, the appropriate MSWI BA content could be selected according to the requirements of different highway grades in the specification. The established segmented constitutive model could well simulate the stress-strain relationship of the mixture in the compressive process. Using cement-stabilized MSWI BA to build the pavement base was feasible, which provided not only an important reference for the engineering design but also had positive significance for promoting carbon peaking, carbon neutrality and sustainable development of highway engineering construction.