Ricardo Costa de Santana

This work reports, for the first time, the synthesis of single-phase trivalent samarium-doped yttrium pyrogermanate (Y2Ge2O7:xSm3+) phosphors via the sol–gel method. The crystalline structure, photoluminescence mechanisms, energy transfer dynamics, and optical thermometry properties were systematically investigated. The experimental optical bandgap (∼5.99–6.10 eV) shows good agreement with those obtained from the density functional theory (DFT) calculations. Upon Sm3+ incorporation, a concentration quenching effect reduces the quantum yield from 8.1% to 0.3%, correlated with a reduction in the average lifetime from 2.08 to 0.61 ms. Analysis of the decay kinetics via the Van Uitert model indicates a dipole–dipole interaction governing the energy transfer, achieving a cross-relaxation efficiency of ∼73% at 4.0 mol %. Remarkably, the CIE coordinates, correlated color temperature (CCT), and color purity (CP) remain independent of the dopant content, exhibiting an exceptional red color purity above 95% for all samples. These results demonstrate that Y2Ge2O7xSm3+ phosphors are promising candidates for solid-state lighting and multifunctional optical applications. Additionally, the ratio between emission sub-bands from 4G5/2 → 6H9/2 to 4G5/2 → 6H5/2 provides a relative sensitivity value (SR) for the sample with 4.0 mol % up to 0.23%/K, indicating a potential use as an optical sensing thermometer.

The upconversion (UC) luminescent properties of a discrete heterodinuclear complex [{Yb(tta)3}(µ2-bpm){Er(tta)3}] (tta= thenoyltrifluoroacetonate, bpm= 2,2'-bipyrimidine) (YbEr) and its homodinuclear analogue, [{Er(tta)3}2(µ2-bpm)] (Er2) were investigated. Under 980 nm excitation, both systems exhibit the characteristic UC emission bands of the Er3+ ion corresponding to the green emission arising from the 2H11/2 →4I15/2 and 4S3/2 → 4I15/2 transitions, and the red emission associated with the 4F9/2 → 4I15/2 transition. In contrast to Er2, YbEr shows significantly higher intensities of these bands, together with long lifetime (LT) values for the green (511 µs) and red (790 µs) bands. The power dependence of the UC intensity, the emission lifetimes, and the predominance of the red emission over the green one, suggest a three-photon energy transfer upconversion (ETU) mechanism with additional contributions from cross-relaxation (CR) processes accounting for the enhanced red emission. The lower UC intensities of Er2 compared to YbEr reflect the significant contribution of Yb3+ ion in the sensitization of Er3+ UC luminescence in the heterodinuclear complex. Notably, YbEr not only represents one of the few UC reports of Yb3+/Er3+-based coordination compounds but also sets a new benchmark by exhibiting the longest LT values reported for this class of compounds.

A performance competition: the Yb–Er complex enables three thermometric pathways, whereas the Yb ₂ analogue delivers a single, highly sensitive readout.

Tuning the excitation source (UV or NIR) in the Nd ³⁺ dimer allows modulation of its thermal response, providing high relative sensitivities at low and physiological temperature ranges, and setting a new benchmark for Nd-based molecular thermometry.

Lanthanides' luminescent thermometry operating in biological windows highlights its promising applications, constantly improving performances, and interesting new findings. This work presents two MOFs, a homometallic sample based on neodymium (1) and a heterometallic one including ytterbium cations (2) as thermometers in the physiological temperature range, operating in biological windows (BWs). These materials were developed with the aim of understanding their thermometric performance and to gain deep knowledge into the energy transfer between the mentioned cations. The homometallic sample achieved a maximum relative sensitivity (Sr) of 0.59%K ⁻¹ at 20°C by using the luminescence intensity ratio (LIR) of the two components that contribute to the main emission band ca. 1060 nm, which is associated with the ⁴ F _3/2 → ⁴ F _11/2 transition. In the case of the heterometallic sample, interestingly, there is an increase in the intensity of the ytterbium cation emission as the temperature increases. This behavior was rationalized by means of theoretical calculations and matches other examples from the literature. The Yb ^III /Nd ^III intensity ratio achieves a maximum Sr 0.53%K ⁻¹ at 20°C.