Sensitized emission of lead halide perovskite nanoparticles (LHPNPs) can be achieved by near-infrared (NIR) excitation of nearby lanthanide-doped upconversion nanoparticles (UCNPs) by using a low-cost diode laser. Here, the first preparation of linear assemblies of core and core-shell NPs, as well as linear coassemblies of LHPNPs and UCNPs, within an open peapodlike lead sulfate shell are reported. UCNPs with a NaYF 4 matrix doped with ytterbium and thulium or erbium, and with an inert shell of NaYF 4 in the case of core-shell, and all-inorganic CsPbX 3 NPs (X = halide) are chosen for these studies. Interestingly, the lead sulfate shell enhances the luminescence of the core/core-shell UCNPs in the polymers by ≈20-fold and it also plays a role in the efficiency of the sensitized emission of the LHPNPs under NIR excitation of the UCNP-LHPNP copolymers, as well as in the chemical stability of the LHPNPs in contact with water. The (co)polymers are prepared as colloids and deposited as solid films on a glass substrate. The lifetime of the sensitized LHP emission and the efficiency of the process wholly depends on the irradiance and on the sample state. These copolymers are promising candidates for the manufacture of photonic devices.

Chemical/biological sensing by means of luminescence still requires improvement of signal contrast and depth of sample imaging. Though there is a considerable number of emissive molecular and quantum dot probes, most of them absorb in the UV–vis range and emit in the visible and exhibit emission lifetime in the nanoscale. Optical bioimaging in the near infrared window based on these dyes offers reduced light scattering, lower competitive absorption, and reduced background autofluorescence, but it requires a high‐power pulsed laser. An approach to lengthening the emission lifetime of common fluorophores/probes is presented. It consists of coupling them to lanthanide‐based upconversion nanoparticles (UCNPs) via an easy, jigsaw‐like strategy. As a proof of concept, nanohybrids comprising UCNPs attached to fluorescein (a well‐known pH sensor) are prepared by connecting the key pieces through ionic interactions, i.e., without using any other reagents. Fluorescence imaging of the nanohybrids clearly shows the co‐occurrence of the UCNP and the chemical probe and as a consequence the long‐lived fluorescence of the probe due to resonance energy transfer from the UCNP. This strategy opens up endless possibilities to prepare new nanohybrids by selecting the key jigsaw pieces to exploit the color emission of common probes.

Photophysical characterization of upconversion nanoparticles (UCNPs) and nanohybrids (UCNHs) is more challenging than that of down-conversion nanomaterials. Moreover, it is still difficult to gain knowledge about the homogeneity of the...