Yb3+-optimized core–shell structured luminescent material for dual-mode encryption and deep learning fluorescence imaging

NaYF 4 :Yb 3+ , Nd 3+ Ln 3+ (Er 3+ , Tm 3+ )@NaYF 4 :Yb 3+ core–shell upconversion luminescent (UCL) materials were prepared by combining the hydrothermal and epitaxial growth methods. Under the excitation of 980 nm laser, the prepared NaYF 4 :Yb 3+ , Nd 3+ , Er 3+ @NaYF 4 :Yb 3+ UCL materials can emit green light, and NaYF 4 :Yb 3+ , Nd 3+ , Tm 3+ @NaYF 4 :Yb 3+ UCL materials can emit blue light, respectively. Under the optimized Yb 3+ doping concentration, the luminescence intensity was enhanced by 16.54 and 17.56 times compared to the nucleus, respectively. Anti-counterfeiting ink was made using the resulting UCL materials as its source ingredient. First, through precise screen-printing techniques, we fabricated QR code patterns that demonstrated the unique luminescent characteristics of the core–shell UCL materials. Also, we implemented a Morse code-based dot-line combination pattern to demonstrate the practical application. Multi-level security features integrating structural (Morse code patterns) and information (QR codes) encryption were developed, significantly enhancing information protection reliability. Furthermore, a snowflake-patterned categorization recognition model was constructed through a residual neural network developed on PyCharm platform. This recognition system achieved 96.55% classification accuracy, demonstrating substantial technical advantages for advanced anti-counterfeiting authentication applications.