Red and green are two of the most‐preferred colors from the entire chromatic spectrum, and red and green dyes are widely used in biochemistry, immunohistochemistry, immune‐staining, and nanochemistry applications. Selective dyes with green and red excitable chromophores can be used in biological environments, such as tissues and cells, and can be irradiated with visible light without cell damage. This critical review, covering a period of five years, provides an overview of the most‐relevant results on the use of red and green fluorescent dyes in the fields of bio‐, chemo‐ and nanoscience. The review focuses on fluorescent dyes containing chromophores such as fluorescein, rhodamine, cyanine, boron–dipyrromethene (BODIPY), 7‐nitobenz‐2‐oxa‐1,3‐diazole‐4‐yl, naphthalimide, acridine orange, perylene diimides, coumarins, rosamine, Nile red, naphthalene diimide, distyrylpyridinium, benzophosphole P‐oxide, benzoresorufins, and tetrapyrrolic macrocycles. Metal complexes and nanomaterials with these dyes are also discussed.

A recently developed thermal lens spectrometry configuration has been used to study CdSe/ZnS core-shell quantum dots (QDs) suspended in toluene and tetrahydrofuran (THF) solvents. The special features of this configuration make it very attractive to measure fluorescence quantum yield (η) excitation spectrum since it simplifies the measurement procedure and consequently improve the accuracy. Furthermore, the precision reached is much higher than in conventional photoluminescence (PL) technique. Two methods, called reference sample and multiwavelength have been applied to determine η, varying excitation wavelength in the UV-visible region (between 335–543 nm). The η and PL spectra are practically independent of the excitation wavelength. For CdSe/ZnS QDs suspended in toluene we have obtained η=76±2%. In addition, the aging effect on η and PL has been studied over a 200 h period for QDs suspended in THF.

Mode-mismatched thermal lens (TL) measurements in ${\mathrm{Cr}}^{3+}$-doped fluoride crystals (${\mathrm{LiSrAlF}}_6$ and ${\mathrm{LiSrGaF}}_6$) are reported. A nonlinear increase of the TL signal, and decrease of quantum efficiency, with increasing excitation power was observed and attributed to energy-transfer upconversion (ETU). Assuming an upconversion rate that is proportional to the excited-state population, $W_{\mathrm{up}}=\gamma N_e$, the theoretical model developed fits the experimental data well. The ETU parameters $\left(\gamma \right)$ were determined with unprecedented accuracy for low Cr concentrations. Thermo-optical parameters $\left(K,\mathrm{d}s/\mathrm{d}T\right)$ were also obtained.

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