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Lanthanide-activated SrF2 nanoparticles with a multishell architecture were investigated as optical thermometers in the biological windows. A ratiometric approach based on the relative changes in the intensities of different lanthanide (Nd3+ and Yb3+) NIR emissions was applied to investigate the thermometric properties of the nanoparticles. It was found that an appropriate doping with Er3+ ions can increase the thermometric properties of the Nd3+-Yb3+ coupled systems. In addition, a core containing Yb3+ and Tm3+ can generate light in the visible and UV regions upon near-infrared (NIR) laser excitation at 980 nm. The multishell structure combined with the rational choice of dopants proves to be particularly important to control and enhance the performance of nanoparticles as NIR nanothermometers.

The use of infrared-emitting rare-earth-doped luminescent nanoparticles as nanothermometers has attracted great attention during the last few years. The scientific community has identified rare-earth-doped luminescent nanoparticles as one of the most sensitive and versatile systems for contactless local temperature sensing in a great variety of fields, but especially in nanomedicine. Researchers are nowadays focused on the design and development of multifunctional nanothermometers with new spectral operation ranges, outstanding brightness, and enhanced sensitivities. However, no attention has been paid to the assessment of the actual reliability of the measurements provided by rare-earth-doped luminescent nanothermometers. In fact, it is assumed that they are ideal temperature sensors. Nevertheless, this is far from being true. In this work we demonstrate that the emission spectra of rare-earth-doped nanothermometers can be affected by numerous environmental and experimental factors. These include the numerical aperture of the optical elements used for their optical excitation and luminescence collection, the local concentration of nanothermometers, optical length variations, self-absorption of the luminescence by the nanothermometers themselves, and solvent optical absorption. This work concludes that rare-earth-doped luminescent nanothermometers are not as reliable as thought and, consequently, special care has to be taken when extracting temperature estimations from the variation of their emission spectra.

A spectroscopic analysis of Dy3+, Eu3+ and Dy3+/Eu3+ doped lithium-aluminum-zinc phosphate glasses is carried out based on absorption and photoluminescence spectra and decay time measurements. According to the CIE1931 chromaticity coordinates and correlated color temperature (CCT), neutral white and reddish-orange global emissions were observed in the Dy3+ and Eu3+ singly-doped glasses, respectively, after excitations of Dy3+ at 348 nm and Eu3+ at 393 nm. A high red color purity of 97.2% is achieved in the Eu3+ singly-doped glass excited at 393 nm. Upon Dy3+ excitation at 348 nm, the Dy3+/Eu3+ doped glass showed warm white overall emission, with CCT value of 3629 K. Upon Dy3+ and Eu3+ co-excitations at 362, 381 and 387 nm, the Dy3+/Eu3+ doped glass showed reddish-orange overall emissions, with CCT values in the 1620–2385 K range, depending on the excitation wavelength. In the Dy3+/Eu3+ doped glass excited at 348 nm, the warm white emission was achieved by a non-radiative energy transfer from Dy3+ to Eu3+ with an efficiency and probability of 0.08 and 89.51 s−1, respectively. The dominant mechanism could be through an electric quadrupole–quadrupole interaction, as it is suggested from the Inokuti-Hirayama model. A back non-radiative energy transfer from Eu3+ to Dy3+ is also observed, which could also be mediated by an electric quadrupole–quadrupole interaction. The Eu3+ to Dy3+ energy transfer efficiency and probability being of 0.08 and 30.00 s−1, respectively.

A careful engineering of the central metal coordination spheres provides adducts with excellent properties for application as precursors in vapor phase and solution processes. The family of precursors under study concerns the fluorinated metal-organic β-diketonates of alkaline, alkaline-earth and rare-earth metals adducted with a polyether, with general formula M(hfa)n·L (M = Ca, Na, Y, Yb, Er, Tm; Hhfa = 1,1,1,5,5,5 hexafluoroacetylacetone, L = diglyme or tetraglyme). Mass transport properties, such as volatility and thermal stability, of these adducts have been deeply analyzed through thermogravimetric analysis and differential scanning calorimetric measurements. These properties are rationalized in relation to the metal coordination sphere in the precursors and their applications. In particular, the precursors under focus have been applied to metal organic chemical vapor deposition and a combined sol–gel/spin-coating approach. Both methods allow us to obtain selectively and reproducibly CaF2 and NaYF4 phases with several combinations of lanthanide doping ions, using a proper mixture of fluorinated precursors. A careful optimization of both synthetic strategies is the key point for the production of different lanthanide-doped binary and multicomponent fluoride films, i.e., CaF2:Yb3+,Er3+; CaF2:Yb3+,Tm3+; CaF2:Yb3+,Er3+,Tm3+ and NaYF4:Yb3+,Er3+; NaYF4:Yb3+,Tm3+, with suitable morphologies, compositions and crystalline structures. The films show very promising upconversion properties, thus pointing to their appealing applications in photovoltaic systems and white light emission devices.

Starting from fluorinated metal–organic β-diketonates, we report the synthesis of undoped and lanthanide-doped alkaline-earth fluoride (Er3+,Tm3+,Yb3+ tri-doped CaF2) thin films through two different chemical approaches: a metal–organic chemical vapor deposition (MOCVD) method and a combined sol–gel/spin-coating procedure. Both chemical approaches have the advantage of being very reliable and reproducible for the fast production of thin films with a high degree of uniformity over large areas. The fluorinated metal precursors act as a single-source in both processes, and an accurate control of the process parameters allows the optimization of the doped CaF2 films. X-ray diffraction, field emission scanning electron microscopy and energy dispersive X-ray analysis have been used to characterize the deposited films. Upconversion emission, typical of the lanthanide ions, in the visible and near infrared regions upon laser excitation at 980 nm is clearly observable. The emissions are in the central region of the CIE1931 color coordinate space.