No abstract

No abstract

We experimentally demonstrate the high sensitivity of a novel liquid state, whispering-gallery-mode optical resonator to humidity changes. The optical resonator used consists of a droplet made of glycerol, a transparent liquid that enables high optical quality factor, doped with fluorescent material. As glycerol is highly hygroscopic, the refractive index and radius of the droplet change with ambient humidity. This produces a shift on the whispering gallery mode's wavelengths, which modulates the emission of the fluorescent material. This device shows an unpreceded sensitivity of 10^-3 per relative humidity percent.

The effect of ligands' energy levels on thermal dependence of lanthanide emission was examined to create new molecular nanothermometers. A series of Ln 2 Ga 8 L 8 ′L 8 ″ metallacrowns (shorthand Ln 2 L 8 ′), where Ln = Gd 3+ , Tb 3+ , or Sm 3+ (H 3 L′ = salicylhydroxamic acid (H 3 shi), 5-methylsalicylhydroxamic acid (H 3 mshi), 5-methoxysalicylhydroxamic acid (H 3 moshi), and 3-hydroxy-2naphthohydroxamic acid (H 3 nha)) and H 2 L″ = isophthalic acid (H 2 iph), was synthesized and characterized. Within the series, ligand-centered singlet state (S 1 ) energy levels ranged from 23,300 to 27,800 cm −1 , while triplet (T 1 ) energy levels ranged from 18,150 to 21,980 cm −1 . We demonstrated that the difference between T 1 levels and relevant energies of the excited 4 G 5/2 level of Sm 3+ (17,800 cm −1 ) and 5 D 4 level of Tb 3+ (20,400 cm −1 ) is the major parameter controlling thermal dependence of the emission intensity via the back energy transfer mechanism. However, when the energy difference between S 1 and T 1 levels is small (below 3760 cm −1 ), the S 1 → T 1 intersystem crossing (and its reverse, S 1 ← T 1 ) mechanism contributes to the thermal behavior of metallacrowns. Both mechanisms affect Ln 3+ -centered room-temperature quantum yields with values ranging from 2.07(6)% to 31.2(2)% for Tb 2 L 8 ′ and from 0.0267(7)% to 2.27(5)% for Sm 2 L 8 ′. The maximal thermal dependence varies over a wide thermal range (ca. 150−350 K) based on energy gaps between relevant ligand-based and lanthanide-based electronic states. By mixing Tb 2 moshi 8 ′ with Sm 2 moshi 8 ′ in a 1:1 ratio, an optical thermometer with a relative thermal sensitivity larger than 3%/K at 225 K was created. Other temperature ranges are also accessible with this approach.

The poor photochemical stability of R-phycoerythrin (R-PE) has been a bottleneck for its broad-spectrum applications. Inspired by nature, we studied a sustainable strategy of protein cohabitation to enhance R-PE stability by embedding it in a solid matrix of gelatin. Both pure R-PE and fresh phycobiliprotein (PBP) extracts recovered from Gracilaria gracilis were studied. The incorporation of R-PE in the gelatin-based films (gelatin-RPE and gelatin-PBPs) has improved its photochemical stability for at least 8 months, the longest time period reported so far. These results were evidenced by not only absorption but also emission quantum yield measurements (Φ). Moreover, the photostability of gelatin-RPE films upon continuous excitation with an AM1.5G solar simulator was tested and found to remain stable for 23 h after initial decreasing up to 250 min. In the end, another approach was established to allow 100% photostability for a 3 h exposure to an AM1.5G solar simulator by doping the gelatin-based film including R-Phycoerythrin with n-propyl gallate stabilized with Tween 80, allowing their use as naturally based optically active centers in photovoltaic applications.

The luminescent solar concentrator (LSC) concept appeared almost forty years ago, as a solution to overcome the limitations related to photovoltaic cell efficiency. Nowadays, they are seen as a promising approach to integrate photovoltaic elements into the built environment, in an invisible way and without detrimental effects to the aesthetics of the building or the quality of life of the inhabitants. LSCs are devices comprising a transparent matrix embedding optically active centers that absorb the incident radiation, which is re-emitted at a specific wavelength and transferred by total internal reflection to photovoltaic cells located at the edges of the matrix. During the last few decades, several optically active materials have been tested for LSCs in an endless quest for the most efficient device. Nowadays, one of the world's major concerns is the environmental impact of our choices. Thus, the present and future path for LSCs must include the search for nature-friendly materials, with little environmental impact, and, in this sense, this Perspective offers a general overview of the potential of environmentally-friendly materials for LSCs.

The remarkable advances in molecular logic reported in the last decade demonstrated the potential of luminescent molecules for logical operations, a paradigm-changing concerning silicon-based electronics. Trivalent lanthanide (Ln 3+ ) ions, with their characteristic narrow line emissions, long-lived excited states, and photostability under illumination, may improve the state-of-the-art of molecular logical devices. Here is reported the use of monolithic siliconbased structures incorporating Ln 3+ complexes for performing logical functions. Elementary logic gates (AND, INH and DEMUX), sequential logic (KEYPAD LOCK), and arithmetic operations (HALF ADDER and HALF SUBTRACTOR) exhibiting a switching ratio >60 % are demonstrated for the first time using non-wet conditions. Additionally, this is the first report showing sequential logic and arithmetic operations combining molecular Ln 3+ complexes and physical inputs. Contrary to chemical inputs, physical inputs may enable the future concatenation of distinct logical functions and reuse of the logical devices, a clear step-forward towards input-output homogeneity that is precluding the integration of nowadays molecular logic devices.

Nd 3+-doped RE 3 Ga 5 O 12 (RE = Gd, Y, and Lu) nano-crystalline garnets of 40-45 nm in size have been synthesized by a sol-gel method. With the decrease of the RE atom size, the chemical pressure related to the decreasing volumes of the GaO 4 tetrahedral, GaO 6 octahedral and REO 8 dodecahedral units drive the nano-garnets toward a more compacted structure, which is evidenced by the change of the vibrational phonon mode frequencies. The chemical pressure also increases the crystal-field strength felt by the RE 3+ ions while decreases the orthorhombic distortion of the REO 8 local environment. These effects alter the absorption and emission properties of the Nd 3+ ion measured in the near-infrared luminescence range from 0.87 to 1.43 μm associated with the 4 F 3/2 → 4 I J (J = 9/2, 11/2, 13/2) transitions. The 4 F 3/2 luminescence decay curves show non-exponential behavior due to dipole-dipole energy transfer interactions among Nd 3+ ions that increases with pressure.