Detailed spectroscopic analysis of the electronic configuration of Cr3+ in Bi2Ga4O9 is reported. The material exhibits unique luminescent properties arising from the crystal field experienced by Cr3+, with simultaneous strong sharp and broadband near-infrared emissions from the 2E and 4T2 excited states, in a wide range of temperature. The system displays dual near-infrared emission characterized by a remarkable thermal sensitivity over the whole explored range of temperatures, reaching a value of 0.7 %•K-1 in the physiological range. Moreover, the possibility to absorb and emit in the first biological window, allows to consider the system as a new promising candidate for ratiometric fluorescent thermal sensing in biotechnological applications

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The development of nanomaterials with high sensitivity to external stimuli such as temperature is critical to investigate the driving force of not only biological processes but also catalytic mechanisms in extreme environments. However, the instability of nano-objects at high temperatures and different environments is a serious drawback limiting often their real use. This is particularly severe in the case of bismuth-based compounds, making the development of highly stable bismuth-based nanosystems a challenge. Here, we report the synthesis of uniform crystalline lanthanide-doped Bi 2 SiO 5 nanoparticles into a silica shell of a controlled thickness (Bi 2 SiO 5 :Ln@SiO 2 ) for the design of a reliable ratiometric optical thermometer stable at high temperatures and extreme acid environments. The fine control of the SiO 2 shell thickness is modeled based on a theoretical and experimental approach. The formation of the Bi 2 SiO 5 single phase is triggered by the local reactivity between Bi 2 O 3 and SiO 2 in the Bi 2 O 3 @SiO 2 system, leading to a double-layered Bi 2 SiO 5 @SiO 2 hollow nanosystem. The potential of the Bi 2 SiO 5 :Ln@SiO 2 nanosystem as a ratiometric nanothermometer is demonstrated for the upconverting Yb−Er couple. The performances were evaluated in the wide range of linearity of the Boltzmann law (280−800 K) showing suitable values of relative sensitivity, temperature uncertainty, and repeatability (R > 99%) not only for biological applications but also to probe the temperature in extreme environments. In fact, the strategy results in an acid-inert thermal probe up to pH < 1 overcoming the weakness of bismuthbased materials to acid environments with promising properties for in situ thermometry of catalytic reactions.

Highly sensitive Boltzmann thermometry by double-layered Bi2SiO5:Yb3+,Tm3+@SiO2 hollow nanoparticles with exceptional thermometric performances and biocompatibility are demonstrated.

Silica films co-implanted with Er and Au ions show an enhancement of rare earth photoluminescence after gold introduction in the matrix. Er excitation originates in a broad spectral region, from the red to the near ultraviolet. We have investigated the influence of gold aggregation on the optical properties of co-doped samples by varying the temperature of post-Au implantation annealing in the 400-900 degrees C range. Optical measurements and extended x-ray absorption analysis support the hypothesis of an energy transfer process mediated by sub-nanometric Au aggregates with metallic character that are optically activated mostly through electron interband transitions between d and sp-conduction levels

After more than a century of studies on the optical properties of Bi 3+ ions, the assignment of the nature of the emissions and the bands of the absorption spectra remain ambiguous. Here, we report an insight into the spectroscopy of Bi 3+ -activated CaMO 3 perovskites (M = Zr, Sn, and Ti), discussing the factors driving the metal-to-metal charge transfer and sp → s 2 transitions. With the aim to figure out the whole scenario, a combined experimental and theoretical approach is employed. The comparison between the temperature dependence of the photoluminescence emissions with the temperature dependence of the exciton energy of the systems has led to an unprecedented evidence of the chargetransfer character of the emitting states in Bi 3+ -activated phosphors. Low-temperature vacuum ultraviolet spectroscopy together with the design of the vacuum-referred binding energy diagram of the luminescent center is exploited to shed light on the origin of the absorption bands. In addition, the X-ray absorption near the edge structure unambiguously confirmed the stabilization of Bi 3+ in the Ca 2+ site in both CaSnO 3 and CaZrO 3 perovskites. This breakthrough into the understanding of the excited-state origin of Bi 3+ could pave the way toward the design of a new generation of effective Bi 3+ -activated phosphors.

The silver ion environment and the microstructural rearrangement of Ag+-Na+ ion-exchanged glasses were investigated by means of micro-Raman and photoluminescence spectroscopies. The samples were produced by immersing borosilicate glasses in NaNO3:AgNO3 molten salts baths with different molar ratios of silver nitrate. The modifications of the silica network microstructure were inspected by analysis of the Raman peak at about 1100 cm-1, and the evolution with the silver concentration at the glass surface of the spectral components related to the different silica tetrahedral groups was studied. The formation of silver metal nanoparticles was inferred from the occurrence of the low-frequency Raman peak due to confinement of acoustic vibrations in metal clusters, and their dimensions were evaluated from the position of its maximum. In the light of the structural analyses performed by means of Raman spectroscopy, a final assignment of the different luminescence bands of silver embedded in silicate glasses was attained

In the field of novel applications involving upconverting processes, the determination of new strategies for realizing emission-tunable nanomaterials is a challenge. In this work the design of Y and Er codoped bismuth oxide-based upconverting nanoparticles is presented, evidencing that the active role of the matrix allows for the emission selectivity with chromaticity control. The bandgap of the bismuth oxide-based host can be manipulated in the range of 0.65 eV, consequently leading to upconversion emission color tunability from red to yellow-greenish. The resulting fine control of the nanoparticle chromaticity through accurate host bandgap engineering reveals a novel concept for the development of a new generation of upconverting nanophosphors.