The temperature-sensitive luminescence of nanoparticles enables their application as remote thermometers. The size of these nanothermometers makes them ideal to map temperatures with a high spatial resolution. However, high spatial resolution mapping of temperatures >373 K has remained challenging. Here, we realize nanothermometry with high spatial resolutions at elevated temperatures using chemically stable upconversion nanoparticles and confocal microscopy. We test this method on a microelectromechanical heater and study the temperature homogeneity. Our experiments reveal distortions in the luminescence spectra that are intrinsic to high-resolution measurements of samples with nanoscale photonic inhomogeneities. In particular, the spectra are affected by the high-power excitation as well as by scattering and reflection of the emitted light. The latter effect has an increasing impact at elevated temperatures. We present a procedure to correct these distortions. As a result, we extend the range of high-resolution nanothermometry beyond 500 K with a precision of 1–4 K. This work will improve the accuracy of nanothermometry not only in micro- and nanoelectronics but also in other fields with photonically inhomogeneous substrates.

Gratings 1 and holograms 2 are patterned surfaces that tailor optical signals by diffraction. Despite their long history, variants with remarkable functionalities continue to be discovered 3 , 4 . Further advances could exploit Fourier optics 5 , which specifies the surface pattern that generates a desired diffracted output through its Fourier transform. To shape the optical wavefront, the ideal surface profile should contain a precise sum of sinusoidal waves, each with a well-defined amplitude, spatial frequency, and phase. However, because fabrication techniques typically yield profiles with at most a few depth levels, complex ‘wavy’ surfaces cannot be obtained, limiting the straightforward mathematical design and implementation of sophisticated diffractive optics. Here we present a simple yet powerful approach to eliminate this design–fabrication mismatch by demonstrating optical surfaces that contain an arbitrary number of specified sinusoids. We combine thermal scanning-probe lithography 6 – 8 and templating 9 to create periodic and aperiodic surface patterns with continuous depth control and subwavelength spatial resolution. Multicomponent linear gratings allow precise manipulation of electromagnetic signals through Fourier-spectrum engineering 10 . Consequently, we overcome a previous limitation in photonics by creating an ultrathin grating that simultaneously couples red, green, and blue light at the same angle of incidence. More broadly, we analytically design and accurately replicate intricate twodimensional moiré patterns 11 , 12 , quasicrystals 13 , 14 , and holograms 15 , 16 , demonstrating a variety of previously impossible diffractive surfaces. Therefore, this approach can provide benefit for optical devices (biosensors 17 , lasers 18 , 19 , metasurfaces 4 , and modulators 20 ) and emerging topics in photonics (topological structures 21 , transformation optics 22 , and valleytronics 23 ).

on luminescence thermometry offers an alternative that is capable of measuring heat generation and diffusion on the microscopic scale. [3] Among the various choices of luminescent systems, [4-9] crystals doped with lanthanide (Ln 3+) ions represent a particularly promising class of luminescent thermometers, because their dimensions can be tuned from a few nanometers to several micrometers and their photoluminescence spectrum is sensitive to temperature. A characteristic feature of Ln 3+ ions is their rich energy level structure, which results in emission spectra with well-separated lines. Typically, the luminescence intensity ratio (LIR) between two of these emission lines is used as a sensitive measure for the temperature of the Ln 3+-doped crystal. After insertion of these ratiometric thermometers into a system of interest, remote operation simply involves excitation by light and detection of the luminescence with standard spectroscopic equipment. The performance of a ratiometric thermometer is determined by how sensitively the LIR reacts to temperature. In general, the performance at a given temperature (T) is quantified in terms of the relative sensitivity [10]

Trap states can strongly affect semiconductor nanocrystals, by quenching, delaying, and spectrally shifting the photoluminescence (PL). Trap states have proven elusive and difficult to study in detail at the ensemble level, let alone in the single-trap regime. CdSe nanoplatelets (NPLs) exhibit significant fractions of long-lived “delayed emission” and near-infrared “trap emission”. We use these two spectroscopic handles to study trap states at the ensemble and the single-particle level. We find that reversible hole trapping leads to both delayed and trap PL, involving the same trap states. At the single-particle level, reversible trapping induces exponential delayed PL and trap PL, with lifetimes ranging from 40 to 1300 ns. In contrast with exciton PL, single-trap PL is broad and shows spectral diffusion and strictly single-photon emission. Our results highlight the large inhomogeneity of trap states, even at the single-particle level.