The Aging Effects of Ultraviolet Irradiation on the Optical Properties of Glass

Glass is known for its high mechanical strength, resistance to high temperatures, corrosion resistance, excellent transparency, thermal stability, and good electrical insulation properties, making it widely used in various fields such as construction, household, and automotive applications. In this study, three types of glass samples were exposed to three different environments: outdoor, ultraviolet (UV) irradiation, and UV irradiation in water vapor. The influence of these different environments on light transmittance and surface morphology was investigated using UV-visible-near infrared spectroscopy and scanning electron microscopy. The experimental results indicate that lead-containing glass exhibits excellent resistance to UV irradiation, sodium-calcium glass samples exhibit significant variations in transmittance in the UV and infrared regions, possibly related to iron content, and high borosilicate glass samples show a noticeable decrease in transmittance in the infrared region.


Introduction
With the continuous development of society, there is an increasing demand for materials.In various industries such as construction, daily use, and healthcare, glass, as a direct interface between people and the environment, people and machinery, the development of glass materials and their performance has garnered more and more attention from both consumers and professionals [1][2][3].In glass applications, glass is inevitably affected by factors such as temperature, humidity, and ultraviolet radiation, which can lead to a reduction in the mechanical properties and service life of the glass [4][5].Therefore, studying the ultraviolet radiation performance of glass in comparison to normal environmental conditions is of paramount importance.
Currently, there is a significant amount of research on composite materials in UV environments.However, there is relatively less research focused solely on glass blocks.Ehrt [6] have elucidated that the UV transmittance of glass is often limited by trace impurities introduced during raw material sourcing, as well as potential contamination from the melting techniques and processing methods employed.Luo [7] prepared UV transmittance borosilicate glass containing SrO. Research has confirmed that replacing ZnO with SrO increases density and thermal expansion coefficient, but reduces molar volume.The glass transition temperature and softening point vary within a small range.As the SrO content increases, the UV transmittance of the glass slightly decreases.Kajihara [8] investigated the ultraviolet-vacuum ultraviolet laser-induced phenomena in SiO 2 glass.It is essential to appropriately control the content of SiOH groups and interstitial H 2 for optimizing the optical performance of SiO 2 glass.Rajaram [9] studied the irradiation effects of ultraviolet lasers on sodiumcalcium-silicate glass.The absorption peaks at 627 nm and 431 nm in sodium-calcium-silicate glass are caused by defects in non-bridging oxygen hole centers, and they increase with the duration of laser irradiation or energy density.Syamsir [10] investigated the research progress of glass fiber-reinforced plastics under ultraviolet radiation.The results showed that the tensile strength exhibited a significant decrease after six months.Comparatively, the tensile modulus was less affected.This indicates that the fiber has good resistance to ultraviolet radiation, making it a material with excellent performance.Bazli [11] studied the microstructure damage mechanism of glass fiber-reinforced composite materials under ultraviolet radiation and wet cycling, which mainly includes micro-cracks and fiber/resin debonding.Peng [12] studied the effect of increasing B 2 O 3 on the content of silicon tetrahedra in borosilicate glass.It was found that when the B 2 O 3 content exceeded a certain level, the degree of corrosion of boron-rich phases would increase.Therefore, the ultraviolet transmittance of the glass samples showed a trend of increasing first, then decreasing.
Glass products need to be exposed to outdoor environments for an extended period of time, and it is important to clarify the impact of environmental factors such as ultraviolet radiation on their optical transmittance.This experiment aims to investigate changes in the transmittance and surface morphology of different glass samples under various environmental conditions.The performance of glass blocks will be studied using a UV-visible-near-infrared spectrophotometer and a field emission scanning electron microscope.

Preparation of Glass Samples
In this experiment, three commercial glass pane samples were used as the subjects of the study.Their compositions are shown in table 1 and were labeled as 1#, 2#, and 3#.The samples were cut into glass pieces measuring 25 mm × 25 mm × 5 mm using a glass cutter and were subsequently placed in beakers.These beakers were then positioned in an ultrasonic cleaner for cleaning and drying, preparing them for later use.

Experimental Settings for Irradiation in Different Environments
The cleaned and dried samples were placed in three different environments for irradiation, as shown in figure 1.These environments included outdoor exposure, a UV weathering tester, and a UV weathering tester with an internal 100 ml distilled water supply.The irradiation chamber had a UV wavelength of 260 nm and a power rating of 36 W.

Sample Characterization
The volume density of the three samples was measured using a Mettler Toledo AL204 analytical balance (Archimedes' principle), and the results are shown in table 1.The transmittance of the samples was tested using a Japanese UV3600 UV-visible-near-infrared spectrophotometer.The surface morphology of the samples was observed using a field emission scanning electron microscope (JSM-7500F).

Initial transmittance
Figure 2 investigated the changes in transmittance of different glass samples in the UV-visible-nearinfrared spectral range.It was found that the transmittance of the three samples exhibited more significant variations around 300-350 nm and 1800-2500 nm.The transmittance of lead glass at 300 nm is 0.011%, and at 350 nm, it is 80.313%.Sodium-calcium glass has a transmittance of 4.668% at 300 nm and 84.889% at 350 nm.Borosilicate glass exhibits a transmittance of 3.431% at 300 nm and 84.670% at 350 nm.The initial transmittance of the three glass samples in the ultraviolet region follows the order: 2# > 3# > 1#.The research indicates that under gamma radiation, the transmittance of lead glass is lower than that of regular optical glass, resulting in relatively poorer visual performance.In the visible light region, the transmittance of all three glass types can reach around 90%.The cutoff wavelength for ultraviolet transmittance of pure B 2 O 3 is 170 nm, indicating high transmittance in the far-ultraviolet region.This suggests that all three samples have a high initial transmittance, making them excellent transparent glasses.In the wavelength range of 1800-2500 nm, the infrared transmittance of lead glass remains stable without significant reduction, while sodiumcalcium glass and borosilicate glass both exhibit a noticeable decrease, consistent with related literature.

Outdoor sunlight aging
Figure 3 shows the transmittance curves of the three glass samples before and after 26 days of outdoor irradiation.It can be observed that the transmittance of the glass samples in the ultraviolet region has decreased to varying degrees, with the most significant decrease in the case of sample 3#.In the infrared region, the transmittance changes for samples 1# and 2# are not very noticeable, while there is a moderate decrease in transmittance for sample 3#.Since the samples were placed outdoors, there are many factors affecting transmittance, such as temperature, humidity, impurities in the air, and the elements present in the glass composition, such as Fe, Cr, Ti, and others.In the visible light region, both samples 1# and 2# exhibit a slight decrease in transmittance, while sample 3# shows a slight increase in transmittance around 750 nm, but these changes are not very significant.

UV irradiation aging
Figure 4 shows the transmittance curves before and after 26 days of UV irradiation in a 260 nm shortwave UV irradiation chamber with a power of 36 W for the three glass samples.It can be observed that after UV irradiation, the transmittance in the ultraviolet region has decreased for all samples, with the most significant reduction in sample 2#, followed by 3#, and a slight decrease in 1#.In the infrared region, the transmittance of 1# remains largely unchanged, while the transmittance of sample 2# significantly increases at wavelengths above 2000 nm.Sample 3# shows a significant reduction in transmittance at wavelengths above 1750 nm.In the visible light region, the transmittance of 1# remains unchanged, while there is a slight decrease in the transmittance of 2# samples.Sample 3# exhibits a slight increase in transmittance around 750 nm.

UV irradiation aging in water vapor
The three glass samples were placed in 100 ml distilled water, sealed with plastic wrap, and exposed to 26 days of UV irradiation with a 36 W, 260 nm short-wave UV light source.Figure 5 displays the transmittance curves of the glass samples before and after the experiment.In the far-ultraviolet region, sample 3# exhibited the most significant decrease in transmittance, followed by sample 2#, while the transmittance of sample 1# remained largely unchanged.In the infrared region, the transmittance of 1# slightly increased at wavelengths above 1500 nm, while sample 2# showed a slight decrease in transmittance at wavelengths above 1500 nm, and sample 3# exhibited a noticeable reduction.In the visible light region, the transmittance of 1# slightly decreased around 750 nm, while the transmittance of sample 2# also showed a slight decrease.Sample 3# had a slight increase in transmittance around 750 nm.

(a)Transmittance curves of different samples; (b) Transmittance curves of sample 1# before and after UV irradiation in water vapor; (c) Transmittance curves of sample 2# before and after UV irradiation in water vapor; (d) Transmittance curves of sample 3# before and after UV irradiation in water vapor
In summary, after 26 days of irradiation aging, the overall transmittance of the three samples remained relatively stable.Sample 1# showed almost no change in transmittance in outdoor, UV irradiation, and UV irradiation in water vapor.There was no significant alteration in the UV, visible light, and infrared regions, indicating that lead glass has excellent resistance to irradiation aging.Sample 2# exhibited minimal changes in outdoor and water UV radiation environments, but under UV irradiation, there was a noticeable decrease in UV transmittance, with a reduction of more than 10% at a wavelength of 320 nm.However, transmittance increased significantly in the region above 2000 nm.This may be attributed to the transformation of divalent iron ions to trivalent iron ions in the glass under UV irradiation conditions, as evidenced by the UV absorption peak of trivalent iron ions and the infrared absorption peak of divalent iron ions in the curves.This change in iron ions is less likely to occur in a deoxygenated environment in water, making UV irradiation in the presence of oxygen particularly effective.Sample 3# showed a reduction of approximately 5% in transmittance in the violet region in outdoor and under UV radiation, with a slight decrease in the infrared region.The change was minimal in a deoxygenated water environment.After 26 days of outdoor irradiation testing, the surface morphology of the samples is depicted in figure 6.It can be observed that the surfaces of lead glass, soda-lime glass, and borosilicate glass are smooth and even, with no significant changes, except for deposits of around 10 micrometers, likely due to impurities, dust, and other outdoor contaminants.This indicates that all three types of glass exhibit good resistance to outdoor irradiation, which is consistent with the transmittance results.The samples immersed in water may exhibit slight local irregularities due to ion precipitation.The surface morphology of sample 1# glass is depicted after 26 days of exposure to diverse environments: outdoor conditions, UV irradiation, and UV irradiation in the presence of water vapor in figure 7. It can be observed that when subjected to UV irradiation in an environment containing distilled water, the surface of the lead glass exhibits local irregularities.This may be attributed to ion precipitation in the water.

Conclusion
This article analyzes the transmittance and morphology of three different glass compositions under various ultraviolet irradiation conditions.It is found that ultraviolet irradiation has a certain impact on the optical performance of the glass samples.The results indicate that lead glass exhibits good radiation resistance, with little change in transmittance within the wavelength range of 300-2500 nm under all three irradiation environments, and no significant changes in surface morphology.Sodiumcalcium glass, after aging due to ultraviolet irradiation, shows significant changes in both ultraviolet and infrared transmittance, possibly due to its higher iron impurity content.Borosilicate glass, under all three irradiation environments, experiences a significant decrease in transmittance in the infrared region.

Acknowledgments
This work was supported by the National Key R&D Program of China (2021YFB3701600).

Figure 2 .
Figure 2. Initial transmittance of the samples.

Figure 3 .
Figure 3. Transmittance curves after 26 days of outdoor irradiation.(a)Transmittance curves of different samples; (b) Transmittance curves of sample 1# before and after outdoor irradiation; (c) Transmittance curves of sample 2# before and after outdoor irradiation; (d) Transmittance curves of sample 3# before and after outdoor irradiation 3.1.3.UV irradiation agingFigure4shows the transmittance curves before and after 26 days of UV irradiation in a 260 nm shortwave UV irradiation chamber with a power of 36 W for the three glass samples.It can be observed that after UV irradiation, the transmittance in the ultraviolet region has decreased for all samples, with the most significant reduction in sample 2#, followed by 3#, and a slight decrease in 1#.In the infrared region, the transmittance of 1# remains largely unchanged, while the transmittance of sample 2# significantly increases at wavelengths above 2000 nm.Sample 3# shows a significant reduction in transmittance at wavelengths above 1750 nm.In the visible light region, the transmittance of 1# remains unchanged, while there is a slight decrease in the transmittance of 2# samples.Sample 3# exhibits a slight increase in transmittance around 750 nm.

Figure 4 .
Figure 4. Transmittance curves after 26 days of UV irradiation.(a)Transmittance curves of different samples; (b) Transmittance curves of sample 1# before and after UV irradiation; (c) Transmittance curves of sample 2# before and after UV irradiation; (d) Transmittance curves of sample 3# before and after UV irradiation

Figure 5 .
Figure 5. Transmittance curves after 26 days of UV irradiation in water vapor.(a)Transmittance curves of different samples; (b) Transmittance curves of sample 1# before and after UV irradiation in water vapor; (c) Transmittance curves of sample 2# before and after UV irradiation in water vapor; (d) Transmittance curves of sample 3# before and after UV irradiation in water vapor

Figure 7 .
Figure 7. Surface Morphology of Sample 1 After 26 Days of Irradiation in Different Environments.(a) Outdoor; (b) UV Irradiation; (c) UV Irradiation in Water Vapor