Upconverting Plasmonic Polarizer for Selective Enhancement and Polarization of Upconversion Photoluminescence

We demonstrate an upconverting plasmonic polarizer (UPP) as an innovative platform that boosts the upconversion photoluminescence (UCPL) intensity and simultaneously modulates its polarization. The UPP features a metal-insulator-metal structure comprising upconversion nanoparticle-embedded SiO₂ and silver nanogratings. This UPP is deliberately designed to utilize "asymmetric" plasmon resonance excitation, which confines only polarized light perpendicular to the nanogratings. This resonance excitation manifests at specific wavelengths, enabling selective UCPL manipulation of the UPP. Consequently, under transversely polarized light, the UPP substantially amplifies the UCPL intensity over 40-fold through resonance excitation. Moreover, among blue, green, and red UCPL, the UPP selectively polarizes only the blue and green emissions through specific resonant coupling, achieving polarization degrees of 0.47 and 0.40 for blue and green emissions respectively, under transversely polarized light, whereas the degree of polarization for red emission remains low at 0.07. Meticulous single-particle level analysis and simulations reveal that the resonant mode determining the UCPL characteristics exhibits a high position dependence within the UPP; thus, UCPL polarization appears exclusively wherever the resonant mode is active. This study provides a significant advancement in UCPL modulation through the proposed UPP for a wide range of potential applications, such as high-resolution imaging and polarized lasers.