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 design of new molecules for photochemical studies typically requires knowledge of spectral features of pertinent chromophores beginning with the absorption spectrum (λabs ) and accompanying molar absorption coefficient (e, m-1 cm-1 ) and often extending to the fluorescence spectrum (λem ) and fluorescence quantum yield (Φf ), where the fluorescence properties may be of direct relevance or useful as proxies to gain insight into the nature of the first excited singlet state. PhotochemCAD databases, developed over a period of 30 years, are described here. The previous databases for 150 compounds have been expanded to encompass 339 compounds for which absorption spectra (including e values), fluorescence spectra (including Φf values) and references to the primary literature have been included where available (552 spectra altogether). The compounds exhibit spectra in the ultraviolet, visible and/or near-infrared spectral regions. The compound classes and number of members include acridines (21), aromatic hydrocarbons (41), arylmethane dyes (11), azo dyes (18), biomolecules (18), chlorins/bacteriochlorins (16), coumarins (14), cyanine dyes (19), dipyrrins (7), heterocycles (26), miscellaneous dyes (13), oligophenylenes (13), oligopyrroles (6), perylenes (5), phthalocyanines (11), polycyclic aromatic hydrocarbons (16), polyenes/polyynes (10), porphyrins (34), quinones (24) and xanthenes (15). A database of 31 solar spectra also is included.

Database of Absorption and Fluorescence Spectra of >300 Common Compounds for use in PhotochemCAD.

Recent advances in bulk heterojunction (BHJ) polymer solar cell (PSC) performance have resulted from compressing the band gap to enhance the short-circuit current density (JSC) while lowering the highest occupied molecular orbital to increase the open-circuit voltage (VOC) and consequently enhance the power conversion efficiencies (PCEs). However, PCEs of PSCs are still constrained by a low JSC, small VOC, and low fill factor (FF). In this study, we report 10.12% PCE from single-junction PSCs based on a novel two-dimensional (2D) conjugated copolymer. By introduction of conjugated 5-alkylthiophene-2-yl side chains to substitute nonconjugated alkoxy side chains in one-dimensional (1D) poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl]] (PTB7), a novel 2D donor–acceptor low-band-gap conjugated copolymer, poly[[4,8-bis[(5-ethylhexyl)thienyl]benzo[1,2-b;3,3-b]dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4...

Single-Junction Polymer Solar Cells with Over 10% Efficiency by a Novel Two-Dimensional Donor–Acceptor Conjugated Copolymer

The adoption in 1979 of a new definition of the candela, which permitted a detector-based approach to the realization of the unit, has emphasized the importance of high-accuracy absolute radiation detectors. This paper describes a new electrical-substitution absolute radiometer operating at 5 K, based on a standard commercial helium cryostat, which has been developed at NPL for optical radiant-power measurements. The principal advantages of operating the radiometer at liquid helium temperatures are that the detector can be a large, highly absorbing cavity (absorptivity 99.998%) and that exact equivalence of electrical and radiant heating can be clearly demonstrated. It will be the primary absolute detector for a new realization of the candela at NPL and will provide the basis for the development of a wider range of radiometric and spectroradiometric standards. The use of the radiometer to measure the radiant power of an intensity-stabilized laser source at the milliwatt level with an uncertainty of 4 parts in 105 is also described, together with its application in the determination of the responsivity of transfer-standard detectors, such as silicon photodiodes.

http://iopscience.iop.org/article/10.1088/0026-1394/21/3/007/pdf

A Cryogenic Radiometer for Absolute Radiometric Measurements

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.

Silicon photodiode device with 100% external quantum efficiency

Silicon photodiode absolute spectral response self-calibration

The possibility of interpolating the internal quantum efficiency of silicon photodiodes using a model with three adjustable parameters is investigated. The three parameters are determined from self-calibration measurements at 351, 476, and 800 nm. The internal quantum efficiency is then interpolated to 407 and 677 nm using the model. The calculated results are compared with direct measurements referenced to an electrical substitution radiometer. A difference of 0.6% was observed at 407 nm. This is probably significant, arising from inadequacies in the internal quantum efficiency model and possibly from volume recombination that is not accounted for by the self-calibration procedure. An insignificant (<0.1%) difference was observed at 677 nm.

Spectral response self-calibration and interpolation of silicon photodiodes.

Absorption spectra enhancement by organic dye laser quenching, considering applications for absorbing species spectroscopic detection

Enhancement of absorption spectra by dye-laser quenching

An explanation is put forth for the observed nonlinearity in the red spectral region of the response of silicon photodiodes. Experiments are described to support the explanation; and the results, implications, and precautions indicated for the use of these diodes are given. Correlation of nonlinearity with spatial nonuniformity of response is demonstrated.

Edward F. Zalewski

Papers

Silicon photodiode device with 100% external quantum efficiency

Silicon photodiode absolute spectral response self-calibration

Spectral response self-calibration and interpolation of silicon photodiodes.

Enhancement of absorption spectra by dye-laser quenching

Silicon detector nonlinearity and related effects.