Luminescence thermal sensing and deep-tissue imaging using nanomaterials operating within the first biological window (ca. 700–980 nm) are of great interest, prompted by the ever-growing demands in the fields of nanotechnology and nanomedicine. Here, we show that (Gd_1−xNd_x)₂O₃ (x = 0.009, 0.024 and 0.049) nanorods exhibit one of the highest thermal sensitivity and temperature uncertainty reported so far (1.75 ± 0.04% K⁻¹ and 0.14 ± 0.05 K, respectively) for a nanothermometer operating in the first transparent near infrared window at temperatures in the physiological range. This sensitivity value is achieved using a common R928 photomultiplier tube that allows defining the thermometric parameter as the integrated intensity ratio between the ⁴F_5/2 → ⁴I_9/2 and ⁴F_3/2 → ⁴I_9/2 transitions (with an energy difference between the barycentres of the two transitions >1000 cm⁻¹). Moreover, the measured sensitivity is one order of magnitude higher than the values reported so far for Nd³⁺-based nanothermometers enlarging, therefore, the potential of using Nd³⁺ ions in luminescence thermal sensing and deep-tissue imaging.

It is reported in this work the preparation, characterisation and photoluminescence study of poly(methylmethacrylate) (PMMA) thin films co-doped with [Eu(tta)₃(H₂O)₂] and [Tb(acac)₃(H₂O)₃] complexes. Both the composition and excitation wavelength may be tailored to fine-tune the emission properties of these Ln³⁺–β-diketonate doped polymer films, exhibiting green and red primary colours, as well as intermediate colours. In addition to the ligand–Ln³⁺ intramolecular energy transfer, it is observed an unprecedented intermolecular energy transfer process from the ⁵D₄ emitting level of the Tb³⁺ ion to the excited triplet state T₁ of the tta ligand coordinated to the Eu³⁺ ion. The PMMA polymer matrix acts as a co-sensitizer and enhances the overall luminescence intensity of the polymer films. Furthermore, it provides considerable UV protection for the luminescent species and improves the photostability of the doped system.

Thermally excited state absorption in Eu ³⁺ is used to propose a new ratiometric luminescent thermometer with a predicted calibration factor.

An absolute thermal lens method to determine fluorescence quantum efficiency and concentration quenching of solids is described in this work. The quantum efficiency of low silica calcium aluminate glasses doped with different concentrations of neodymium dioxide and melted under vacuum conditions to remove water has been measured by using mode-mismatched thermal lens spectrometry. It has been shown that the thermal lens signal amplitude is linearly dependent on neodymium concentrations up to 4.0 wt %, changing significantly from 4.5 to 5.0 wt %, indicating that there was quenching of the fluorescence only above 4.0 wt % neodymium dioxide. The quantitative treatment for the thermal lens effect provided the absolute value of the sample’s fluorescence quantum efficiency. The technique is simple to perform and can be applied for a wide range of fluorescent materials.

The Nd–Nd and Nd–Yb energy transfer processes are studied in lead fluoroindogallate glasses with the following molar composition: 30PbF2–20GaF3–15InF3–15ZnF2–(20–X)CaF2–XNdF3 (with X=0.1, 0.5, 1, 2, 4, and 5), 30PbF2–20GaF3–15InF3–15ZnF2–(20–X)CaF2–XYbF3 (with X=0.1, 0.5, 1, 2, 3, and 5), and 30PbF2–20GaF3–15InF3–15ZnF2–(19–X)CaF2–XYbF3–1NdF3 (with X=0.1, 0.5, 1, 2, 3, and 5.5). The Dexter, Yokota–Tanimoto, and Holstein formalisms were used to treat the experimental data. The following microparameters of energy transfer were obtained: CDD(Nd–Nd)≈7×10−40, CDA(Nd–Nd)=2.5×10−40, and CDA(Nd–Yb)≈3×10−40 cm6/s. It was also shown that the energy migration between Nd ions depends on the third power of temperature (T3) up to a saturation value of about 80 K. This behavior was attributed to the site to site energy migration. The Yb doped samples presented no nonradiative losses for the Yb3+ emission at 969 nm.