Journal article Open Access
Martínez, Eduardo D.; Brites, Carlos D. S.; Carlos, Luís D.; García-Flores, Alí F.; Urbano, Ricardo R.; Rettori, Carlos
The hasty progress in smart, portable, flexible, and transparent integrated electronics and optoelectronics is currently one of the driving forces in nanoscience and nanotechnology. A promising approach is the combination of transparent conducting electrode materials (e.g., silver nanowires, AgNWs) and luminescent nanoparticles. Here, tunable electrochromic transparent devices covering a broad range of the chromatic diagram are fabricated by combining the electrical control of the heat dissipation in AgNWs networks with size-dependent thermal properties of upconverting nanoparticles (UCNPs). The electrochromic devices are based on transparent nanocomposite films of poly(methyl methacrylate) and AgNWs covered by UCNPs of different sizes and compositions. As illustrative examples, devices mixing large-sized (>70 nm) β-NaYF4:Yb,Ln and small-sized (<15 nm) NaGdF4:Yb,Ln@NaYF4 core@shell UCNPs (Ln=Tm, Er, Ce/Ho) are presented. The temperature-dependent emission of the particles is monitored by the intensity ratio of the Er3+ 2H11/2 and 4S3/2 ® 4I15/2 emission lines, while externally controlling the current flow in the AgNWs network. Moreover, by defining a new thermometric parameter involving the intensity ratio of transitions from large- and small-sized UCNPs, a relative thermal sensitivity of 5.88 % K−1 (at 339 K) is obtained; a 6-fold improvement over the values reported so far.