Luminescent ratiometric thermometers combining high spatial and temporal resolution at the micro- and nanoscale, where the conventional methods are ineffective, have emerged over the last decade as an effervescent field of research, essentially motivated by their potential applications in nanotechnology, photonics, and biomedicine. Among the distinct luminescent thermal probes, lanthanide-based materials play a central role in the field due to their unique thermometric response and intriguing emission features (eg, high quantum yield, narrow bandwidth, long-lived emission, large Stokes shifts, and ligand-dependent luminescence sensitization). This chapter offers a general overview of recent examples of single- and dual-center Ln3 +-based thermometers, emphasizing those working at nanometric scale, being focused on how to quantify their performance accordingly to the relevant parameters: relative sensitivity, temperature uncertainty, spatial and temporal resolution, repeatability (or test–retest reliability), and reproducibility. The emission mechanisms supporting single- and dual-center emissions are reviewed, together with the advantages and limitations of each approach. Illustrative examples of the rich variety of systems designed and developed to sense temperature are provided and explored. Finally, we discuss the challenges and opportunities in the development of highly sensitive luminescent ratiometric thermometers that are currently facing the scientists in this exciting research field.

Lanthanides in Luminescent Thermometry

The paper describes a new solid state detector which fulfils all the requirements of the ideal detector for optical radiation measurements. This trap detector is shown to be spatially uniform, linear, stable and to have a predictable relative spectral response so that it can be used to realize a relative spectral response scale with an uncertainty of less than 0,05%. The detector is also shown to be capable of disseminating an absolute spectral responsivity scale with an uncertainty of less than 0,02% at specific laser wavelengths and, independently, of realizing such a scale with an uncertainty of better than 0,05%.

https://iopscience.iop.org/article/10.1088/0026-1394/28/3/018/pdf

Trap Detectors and their Properties

Detectors have historically been calibrated for spectral power responsivity at the National Institute of Standards and Technology by using a lamp-monochromator system to tune the wavelength of the excitation source. Silicon detectors can be calibrated in the visible spectral region with combined standard uncertainties at the 0.1% level. However, uncertainties increase dramatically when measuring an instrument's spectral irradiance or radiance responsivity. We describe what we believe to be a new laser-based facility for spectral irradiance and radiance responsivity calibrations using uniform sources (SIRCUS) that was developed to calibrate instruments directly in irradiance or radiance mode with uncertainties approaching or exceeding those available for spectral power responsivity calibrations. In SIRCUS, the emission from high-power, tunable lasers is introduced into an integrating sphere using optical fibers, producing uniform, quasi-Lambertian, high-radiant-flux sources. Reference standard irradiance detectors, calibrated directly against national primary standards for spectral power responsivity and aperture area measurement, are used to determine the irradiance at a reference plane. Knowing the measurement geometry, the source radiance can be readily determined as well. The radiometric properties of the SIRCUS source coupled with state-of-the-art transfer standard radiometers whose responses are directly traceable to primary national radiometric scales result in typical combined standard uncertainties in irradiance and radiance responsivity calibrations of less than 0.1%. The details of the facility and its effect on primary national radiometric scales are discussed.

/pdf/facility-for-spectral-irradiance-and-radiance-responsivity-sg8oe2flt4.pdf

Facility for spectral irradiance and radiance responsivity calibrations using uniform sources

The stability of the quantum efficiency of inversion layer, phosphorus-diffused (n on p), and boron-diffused (p on n) photodiodes has been investigated. Unsatisfactory silicon-silicon dioxide interfaces, latent recombination centers in the diffused layers, and moisture absorption by the device were identified as possible causes of instability. Diodes were fabricated using processes in which these sources of instability were carefully controlled. The resulting diodes were subjected to various accelerated aging tests, and the external quantum efficiency of the diodes was monitored during the tests. Diodes made by older procedures, in which some important parameters affecting stability were not controlled, were included in the study for comparison. The major result of this work is the demonstration that n on p photodiodes are inherently more stable than p on n types in the ultraviolet and blue spectral regions, but that stable p on n devices can also be produced with sufficient care.

Quantum efficiency stability of silicon photodiodes

A high-accuracy cryogenic radiometer has been developed at the National Institute of Standards and Technology to serve as a primary standard for optical power measurements. This instrument is an electrical-substitution radiometer that can be operated at cryogenic temperatures to achieve a relative standard uncertainty of 0.021% at an optical power level of 0.8 mW. The construction and operation of the high-accuracy cryogenic radiometer and the uncertainties in optical power measurements are detailed.

/pdf/national-institute-of-standards-and-technology-high-accuracy-1kos4me1fq.pdf

National Institute of Standards and Technology high-accuracy cryogenic radiometer

A device utilizing four inversion layer photodiodes in a light-trapping arrangement was constructed and tested. The device was found to have a photon-to-electron conversion efficiency of 0.999 for short wavelength and low power visible radiation. It was found that applying a reverse bias voltage extended the high quantum efficiency response over the entire visible spectrum and up to the highest radiant power level studied (several milliwatts). Several radiometrically important characteristics were studied and the results presented: spectral reflectance; polarization sensitivity; quantum efficiency vs wavelength, photon flux density, and reverse bias voltage; and dark current vs reverse bias.

C. Richard Duda

Papers

Silicon photodiode device with 100% external quantum efficiency