Sr430

The geometric features of the MIM nanostructures were characterized with a field-emission scanning electron microscope (JEOL 7401F). The PL spectroscopy was conducted using a confocal laser scanning microscope coupled with a spectrometer (Renishaw InVia). The samples were excited with a 980 nm wavelength laser (CrystaLaser DL980-500) and the emission from the UCNPs green channel (500–600 nm) was collected for analysis.
In the transient PL measurements, an excitation laser source (Thorlabs L980P200) was modulated by a square pulse generated by a function generator (Wavetek model 166). The duty ratio, pulse duration, and voltage amplitude were set appropriately, so that the transient PL had enough time to reach the steady state. Transient PL measurements were performed for both the NIR and green luminescence. The emitted PL from samples was collected by two convex lenses before being focused into a monochromator (Sciencetech 9057F) equipped with two photomultiplier tubes (PMTs), one for the visible (Hamamatsu H11461P-11) and the other for the NIR detection (Hamamatsu H10330B-75). Finally, a photon counter (Stanford Research Systems SR430) was used to convert the PMT output to digital transient waveforms.

For examination of the singlet oxygen production, a near-infrared light emitted from singlet oxygen was directly measured using a photomultiplier-based apparatus (NIR-PII System, Hamamatsu Photonics K.K., Hamamatsu, Japan) [21 (link),22 ]. The emission from singlet oxygen (λ = 1,270 nm) was detected using an infra-red-gated image intensifier after a passage through a polychrometer (250is, Chromex, NM, USA). Signals were accumulated by a repeated gate operation (>300 times), and then averaged. The calibration of wavelength was performed using a spectral calibration lamp (Krypton type, Oriel Instruments, CT, USA).
Singlet oxygen decay curves were monitored using a photo detector (Spectra-Physics, CA, USA). The excitation wavelength was 585 nm. Emission was detected using a photomultiplier (R5509-42, Hamamatsu Photonics K.K., Hamamatsu, Japan) combined with a monochrometer (HR-320, Jobin Yvon, France). Data were stored in a multichannel scaler (SR430, Stanford Research Systems, CA, USA). All measurements were performed at 22°C. The absorption spectra were measured before and after decay measurements to monitor the photobleaching of the dye.