Fig. 1. Characterization of upconversion particle properties obtained with varying NaF molalities. (a) SEM photo of NaYbF₄ microcrystals synthesized by hydrothermal method; (b) XRD patterns of NaYbF₄∶Tm³⁺; (c) upconversion emission spectra of NaYbF₄∶Tm³⁺ under 980 nm laser excitation

Fig. 2. Characterization of upconversion particle properties obtained with varying EDTA molalities. (a) SEM photo of NaYbF₄ microcrystals synthesized by hydrothermal method and corresponding particle size distribution diagram; (b) XRD patterns of NaYbF₄∶Tm³⁺; (c) upconversion emission spectra of NaYbF₄∶Tm³⁺ under 980 nm laser excitation

Fig. 3. Characterization of the properties of upconversion particles obtained with varying Tm³⁺ doping concentrations. (a) SEM photo of NaYbF₄ microcrystals synthesized by hydrothermal method; (b) XRD patterns of NaYbF₄∶Tm³⁺; (c) upconversion emission spectra of NaYbF₄∶Tm³⁺ under 980 nm laser excitation

Fig. 4. Characterization of the properties of upconversion particles obtained at different reaction temperatures. (a) SEM photo of NaYbF₄ microcrystals synthesized by hydrothermal method; (b) XRD patterns of NaYbF₄∶Tm³⁺; (c) upconversion emission spectra of NaYbF₄∶Tm³⁺ under 980 nm laser excitation

Fig. 5. CIE of UCPs under different synthesis conditions

Fig. 6. Characterization of properties of upconversion particles. (a) Energy dispersive X-Ray spectroscopy of NaYbF₄∶Tm³⁺; (b) UV-Vis absorption spectra of BAPO and upconversion emission spectra of UCPs

Fig. 7. Influence of initiator and UCPs content on the polymerisation process. (a) Effect of BAPO content on the C=C conversion curve of the system; (b) effect of UCPs content on the C=C conversion curve of the system (25 W/cm²)

Fig. 8. Effect of laser power on the luminescence properties of UCPs and polymerisation behaviour. (a) Double bond conversion curves under NIR light irradiation of various laser powers; (b) upconversion emission spectra of UCPs at different powers; (c) dependence curve of the integrated intensity of the emission peak of UCPs in the band near 365 nm on the excitation power; (d) comparison of integrated intensity at 300‒400 nm band and 400‒500 nm band under different laser powers; (e) dependence curve of the ratio of the integrated intensity in the 300‒400 nm band and the 400‒500 nm band on the power

Fig. 9. Double bond conversion curves of UCPs prepared under different conditions. (a) NaF concentration; (b) EDTA concentration; (c) doping ratio of Tm³⁺; (d) reaction temperature

Fig. 10. 3D printed products display images. (a) Chess pieces obtained by 3D printing; (b) partial detail picture; (c) chess pieces under 980 nm NIR laser radiation