Electrospinning Equipment: Electrospun White Y2 Zr2 O7:Tm3+/Dy3+ Nanotubes with Excellent Thermal Quenching Resistance and Ultralow Color Shift

In recent years, white LEDs have attracted significant attention due to their advantages such as energy efficiency, long lifespan, environmental friendliness, and compact size. They are widely used in various lighting applications. The preparation of white LEDs often relies on rare - earth luminescent materials, especially single - phase full - spectrum white phosphors. These phosphors can simplify the device preparation process and avoid issues like self - absorption and color instability. Currently, co - doping multiple luminescent ions is an important technique for preparing such phosphors. Among numerous rare - earth ions, Dy3+ is a crucial luminescent ion in WLED phosphors because of its distinct blue ((4F9/2→6H15/2)) and yellow ((4F9/2→6H13/2)) emissions. To achieve white - light emission, Dy3+ is often co - doped with Tm3+, and many related phosphors have been reported. However, under high - temperature and high - current driving conditions, the thermal stability of different activator ions in existing phosphors varies greatly, leading to changes in the emission color of LED devices. Developing single - phase full - spectrum white phosphors with good color stability and excellent thermal quenching resistance remains a significant challenge.  

Recently, the research team led by Professor Hongquan Yu and Professor Baojiu Chen from Dalian Maritime University published their latest research findings titled "Bright electrospun white Y2​Zr2​O7​:Tm3+/Dy3+ nanotubes with excellent thermal quenching resistance and ultralow color shift" in the journal CrystEngcomm in the field of materials science. The team successfully prepared high - brightness white - fluorescent nanotube materials through an electrospinning device technology. This achievement breakthroughly realizes high thermal stability and chromaticity retention of rare - earth - doped oxides at the nanoscale. It provides an innovative solution for the development of novel luminescent materials, especially in the field of optical devices operating in high - temperature environments. It offers an important technical approach to solve the problems of thermal inactivation and color shift of traditional fluorescent materials and is expected to optimize the performance of solid - state lighting and display technologies. The preparation process of this material is shown in Fig. 1.

The morphology and size of the nanotubes can be clearly observed from the SEM and TEM images. As shown in Fig. 4 (a) and (b), the outer diameter of the nanotubes ranges from 200 to 215 nm, the wall thickness is between 48 and 53 nm, and the inner diameter is approximately 116 nm. The HR - TEM image in Fig. 4 (d) shows the lattice spacing of the nanotubes, corresponding to the (111) crystal plane of Y2​Zr2​O7​.

The color coordinates of YZO nanotubes with different doping concentrations were tested and analyzed. It was found that the color coordinates of YZO:2% Tm3+/2% Dy3+ nanotubes are (0.3308, 0.332), which are extremely close to those of standard white light (0.33, 0.33). In the CIE coordinate distribution diagrams in Fig. 8 (c) and Fig. 9 (d), the color coordinate distributions of YZO nanotubes with different doping concentrations can be intuitively seen. When the concentrations of Tm3+ and Dy3+ are adjusted to 2%, the corresponding point in the CIE diagram almost coincides with the standard white - light point, indicating that this nanotube can well simulate standard white light in color presentation and meet the color requirements for high - quality lighting.

The luminescent properties of YZO:2%Tm/1%Dy nanotubes were deeply studied and compared with those of YZO:2%Tm/1%Dy powders prepared by the solid - state reaction process at the same calcination temperature. The differences can be clearly seen from the emission spectra and integral intensity comparison diagrams in Fig. 12 (a) - (c). At room temperature, the emission intensity of YZO:2%Tm/1%Dy nanotubes is 1.2 times that of YZO:2%Tm/1%Dy powders. This indicates that under the same excitation conditions, the nanotube structure can more effectively convert the absorbed energy into light emission. In a high - temperature environment, the differences between the two are more significant. Fig. 12 (a) shows the emission spectra of YZO:2%Tm/1%Dy nanotubes at different temperatures from 303 K to 453 K, and Fig. 12 (b) shows the emission spectra of the corresponding powders. From the total integrated emission intensity comparison diagram in Fig. 12 (c), it can be seen that the emission intensity of YZO:2%Tm/1%Dy nanotubes at 453 K still remains 91.23% of that at 303 K, while the emission intensity of YZO:2%Tm/1%Dy powders at 453 K only remains 90.42% of that at room temperature. It can be seen that nanotubes can better maintain their emission intensity at high temperatures, reflecting their advantage in thermal stability.

Color stability is an important performance index for phosphor materials in practical applications. It was found that the maximum color shift of YZO:2%Tm/1%Dy nanotubes at 450 K is only 0.16%, while that of YZO:2%Tm/1%Dy powders at the same temperature reaches 0.9%. From the chromaticity shift comparison diagram in Fig. 5 (d), it can be clearly seen that as the temperature increases from 303 K to 453 K, the color shift of the powders increases rapidly, while that of the nanotubes increases slowly. Due to their unique tubular structure, YZO:Tm3+/Dy3+ nanotubes have better thermal quenching resistance than YZO:Tm3+/Dy3+ powders. The hollow nano - tubular structure of the nanotubes enables a more uniform component distribution at the nanoscale, with fewer crystal defects and crystalline interfaces and weaker thermal conductivity, thus effectively reducing the impact of temperature on color stability.

In the process of researching and preparing high - performance phosphor materials for white LEDs, this study has achieved a series of key results. Single - phase full - spectrum white YZO:Tm/Dy nanotubes with excellent thermal stability and ultralow color drift were successfully prepared by the single - nozzle electrospinning device method at 1300 °C. This innovative preparation method, which uses the electrospinning machine in the process, has opened up a new direction for the application of nanotube materials in the lighting field.

Article source: https://doi.org/10.1039/D5CE00133A