RESUMO
TbIII and EuIII systems have been investigated as ratiometric luminescent temperature probes in luminescent coordination polymers due to TbIII â EuIII energy transfer (ET). To help understand how ion-ion separation, chain conformation as well as excitation channel impact their thermometric properties, herein, [Eu(tfaa)3(µ-L)Tb(tfaa)3]n one-dimensional (1D) coordination polymers (tfaa- = trifluoroacetylacetonate, and L = [(diphenylphosphoryl)R](diphenyl)phosphine oxide, R = ethyl - dppeo - or butyl - dppbo) were synthesized. The short µ-dppeo bridge ligand leads to a more linear 1D polymeric chain, while the longer µ-dppbo bridge leads to tighter packed chains. As the temperature rises from 80 K, upon direct TbIII excitation at 488 nm, the TbIII emission intensity decreases, while the EuIII emission intensity increases after 160 and 200 K when L = dppeo or dppbo, respectively. The temperature-dependent emission intensities, due to TbIII â EuIII ET, enable the development of ratiometric luminescent temperature probes featuring maximum relative thermal sensitivity up to 3.8% K-1 (250 K, L = dppbo, excitation at 488 nm). On the other hand, the same system displays maximum thermal sensitivity up to 3.5% K-1 (323 K) upon ligand excitation at 300 nm. Thus, by changing the excitation channel and bridge ligand that leads to modification of the polymer conformations, the maximum relative thermal sensitivity can be tuned.
RESUMO
The chemical composition, shape and size of upconverting nanoparticles are known to have a great influence on their spectroscopic properties, such as the emission color and the emission intensity variation as a function of temperature. This work shows the color tuning and the thermal sensitivity of NaYb0.67Gd0.30F4:Tm0.015:Ho0.015 nanoparticles synthesized by two different approaches of the same synthetic method showing the influence of size and morphology, 250 nm hexagonal-plated and 30 nm spheroidal nanoparticles, on the visible upconversion color under NIR irradiation. According to the 1931-CIE diagram, the hexagonal-shaped nanoparticles show white light emission and the spheroidal ones generate red light emission under 980 nm excitation. Besides, the variation of the luminescence intensity ratio of Tm3+ emissions as a function of temperature was monitored in the 77-293 K temperature range, and the maximum relative sensitivity (Sm) of the samples reached 1.33% K-1 for the hexagonal-plated nanoparticles and 1.76% K-1 for the spheroidal nanoparticles. These maximum sensitivity values are higher compared to the ones found in the literature for temperature sensing using upconverting nanoparticles. These data suggest the versatility of these nanoparticles for applications on white light emission and nanothermometry.