Di02 r488

To obtain isolated Bi₄NbO₈Cl particles, a well-dispersed methanol suspension of Bi₄NbO₈Cl in low concentration was spin-coated onto a cleaned cover glass. The particle-coated cover glass was annealed at 363 K for 30 min to immobilize the particles on the glass surface, and then placed in a chamber filled with an Ar-saturated aqueous methanol solution of MS-DN-BODIPY (1 μM). A 488 nm CW laser (OBIS 488LX, Coherent; 10 mW cm⁻²) passing through an objective lens (CFI Plan Apo λ100 × H, Nikon; NA 1.45) after reflection by a dichroic mirror (Di02-R488, Semrock) was reflected completely at the cover glass–solution interface to generate an evanescent field, which made it possible to detect the fluorescent products selectively on the bottom surface of the crystal. The emission from the sample was collected by the same objective lens, after which it was magnified by a 1.5× built-in magnification changer, and passed through a band-pass filter (FF01-535/50, Semrock) to remove undesired scattered light. The emission images were recorded using an electron-multiplying charge-coupled device (EMCCD) camera (Evolve 512, Roper Scientific) using Micro-Manager (https://www.micro-manager.org/). All experimental data were obtained at room temperature.

PL microscopy measurement was also conducted based on a Nikon Ti-E inverted fluorescence microscope. For wide-field microscopy, the 405 nm CW laser (OBIS 405LX, Coherent; 30 mW cm⁻²) was used to excite the Bi₄NbO₈Cl. The emission images were recorded on an EMCCD at a rate of 30 frames s⁻¹. A suitable dichroic mirror (Di02-R488, Semrock) and a long-pass filter (BLP01-488R, Semrock) were used to improve the signal-to-noise ratio. For confocal microscopy, the 405 nm pulsed diode laser (Advanced Laser Diode System, PiL040X; 45 ps FWHM, 1 MHz repetition rate) was used to excite the samples. The emitted photons were passed through a 100 μm pinhole and then directed onto a single-photon avalanche diode (Micro Photon Devices, SPD-050). The signals from the detector were sent to a time-correlated single photon counting module (Becker & Hickl, SPC-130EM) for further analysis. A dichroic mirror (Semrock, Di02-R405) and a longpass filter (Semrock, BLP01-458R) were used to remove the scattering from the excitation light. PL spectra were obtained by directing the emission into an imaging spectrograph (SOL instruments, MS3504i) equipped with a CCD camera (Andor, DU416A-LDC-DD) through a slit. All experimental data were obtained at room temperature in air. The data were analyzed using the open source image software ImageJ (http://rsb.info.nih.gov/ij/) and Origin 2015 (Origin-Lab).