Investigating nonradiative relaxation in optically pumped Er3+-doped BaTiO3 nanocrystals

Luminescent Er3+-doped BaTiO3 nanocrystals were investigated in different media (air, water and glycerol) and temperatures (27 to 47 °C). The results showed that the nonradiative relaxation rate experienced by Er3+ changes with the particle size

Upconversion in Er<SUP>3+</SUP>-doped ZrO<SUB>2</SUB> nanocrystals pumped at 1.426μm

The effect of frequency upconversion (UC) was investigated in 0.05 and 2.00 mol % Er2O3 doped in ZrO2 nanocrystals prepared by a sol-emulsion-gel process. Laser excitation at 1.426 μm produced UC luminescence at ∼ 0.800, ∼ 0.525, ∼ 0.550, and ∼ 0.660 μm corresponding to Er3+ transitions 4I9/2→ 4I15/2, 4H11/2→ 4I15/2, 4S3/2→ 4I15/2, and 4F9/2→4I15/2 respectively. The role played by excited state absorption and energy transfer mechanisms in the UC process was analyzed using rate equations for Er3+ energy level populations. The energy transfer rate between pairs of Er3+ ions (4I9/2+4I13/2→4I15/2+4S3/2) was determined from comparison between theoretical predictions and experimental data

Er<SUP>3+</SUP>-doped BaTiO<SUB>3</SUB> nanocrystals for thermometry: Influence of nanoenvironment on the sensitivity of a fluorescence based temperature sensor

Frequency upconverted emissions centered at 526 and 547 nm from two thermodynamically coupled excited states of Er3+ doped in BaTiO3 nanocrystals were recorded in the temperature range from 322 to 466 K using a diode laser emitting at 980 nm as the excitation source. The ensemble measurements of the fluorescence intensity ratio (FIR) of the signals at 526 and 547 nm as a function of the temperature showed that the sensitivity (the rate in which the FIR changes with the temperature) of such sensor depends on the size of the nanocrystal. This is explained taking into consideration modifications of nonraditive relaxation mechanisms with the size of the nanocrystals

Blue upconversion emission of Tm<SUP>3+</SUP>–Yb<SUP>3+</SUP> in ZrO<SUB>2</SUB> nanocrystals: Role of Yb<SUP>3+</SUP> ions

The effect of Yb<SUP>3+</SUP> ions on the blue upconversion (UPC) emission of Yb<SUP>3+</SUP>–Tm<SUP>3+</SUP> co-doped ZrO<SUB>2</SUB> nanocrystals is reported. The blue (490 nm) UPC emission is due to <SUP>1</SUP>G<SUB>4</SUB>–<SUP>3</SUP>H<SUB>6</SUB> transition of Tm<SUP>3+</SUP> and the pump power dependence of this UPC emission band are cubic indicating that three excitation photons are involved in the UPC process. An additional UPC emission band at 505 nm is observed when the Yb<SUP>3+</SUP> concentration is above 1.25 mol%. The pump power dependence of the emission at 505 nm is quadratic, indicating that this emission may have its origin from excited Yb<SUP>3+</SUP> pairs producing cooperative UPC

Frequency upconversion in rare-earth doped fluoroindate glasses

We present recent results on frequency upconversion (UPC) obtained in fluoroindate glasses (FIG) doped with Ho3+, Tm3+ and Nd3+ ions and codoped with Pr3+/Nd3+ and Yb3+/Tb3+ ions. The results for the Ho3+-doped samples show strong evidence of energy transfer (ET) between Ho3+ ions resonantly excited at 640 nm. The origin of the blue-green upconverted fluorescence observed was identified and the dynamics of the signals revealed the pathways involved in the UPC process. In the case of Tm3+-doped FIG, the samples were resonantly excited at 650 nm and the main mechanism that contributes for the red-to-blue upconversion is excited-state absorption (ESA). The FIG samples codoped with Pr3+/Nd3+ were excited at 588 nm in resonance with transitions starting from the ground state of the Nd 3+ and the Pr3+ ions. It was observed that the presence of Nd3+ ions enhanced the Pr3+ emission at 480 nm by two orders of magnitude. Multiphonon (MP)-assisted upconversion is also discussed for Nd3+-doped FIG pumped at 866 nm. Emission at 750 nm with a peculiar linear dependence with the laser intensity was observed and explained. A rate-equation model that includes MP absorption via thermally coupled electronic excited states of Nd3+ was developed and describes well the experimental results. The role played by effective phonon modes is clearly demonstrated. MP-assisted UPC process was also studied in Yb3+/ Tb3+-codoped FIG samples excited at 1064 nm, which is off-resonance with electronic transitions starting from the ground state. It was determined that the mechanism leading to Tb3+ emission in the blue is due to ET from a pair of excited Yb3+ ions followed by ESA in the Tb 3+ ions. © 2002 Académie des sciences/Éditions scientifiques et médicales Elsevier SAS

Red to blue tunable upconversion in Tm<SUP>3+</SUP>-doped ZrO<SUB>2</SUB> nanocrystals

The effect of dopant concentration on the blue upconversion (UPC) emission of Tm3+ -doped ZrO2 nanocrystals under different excitation wavelengths in the red region is reported. The UPC emissions are due to the f−f electronic transitions from excited states 1G4 and 1D2 of Tm3+. We observed a chromatic change in the UPC with tuning the excitation wavelength. The UPC emission bands at 475, 488, and 501 nm are observed under excitation at 649 nm, but bands centered at 454 and 460 nm are observed when the excitation wavelength is tuned to 655 nm. The UPC emission could be tuned from 501 to 454 nm (∼47 nm) by changing the excitation wavelength from 649 to 655 nm (∼6 nm). The pump power dependence of the emission bands at 475, 488, and 501 nm were investigated on excitation intensity at 649 nm, and the emission bands at 454 and 460 nm are investigated on excitation intensity at 655 nm, which confirms that all of these UPC emission lines are a two-photon absorption process

Cooling performance of an acrylic serpentine with a rectangular cross section

In recent years, photovoltaic panels have been established as one of the main sources of electricity considered to be clean. Its efficiency and lifetime are greatly influenced by the operating temperature. Active cooling using cylindrical copper serpentines is one of the most common methods for many systems. However, due to the cylindrical geometry of the tubes, the contact with the plate is a point and its area tends to be zero. In this way, serpentines that provide a bigger contact area between the heat removal system and the solar panel board are desired. Serpentines manufactured by machining acrylic plates in CNC milling machines allow the construction of a channel with a rectangular cross-section with a considerable area of contact between the channel and the plate. The obtained results show that there was a significant improvement in the heat exchange between the plate and the thermofluid when the acrylic serpentine with a rectangular section was used.This work has been partially funded through national funds FCT/MCTES (PIDDAC) from the following research units: UIDB/00532/2020, UIDB/04077/2020, UIDP/04436/2020, UIDB/00690/2020 and UIDP/00690/2020. The authors are also grateful for FCT funding through PTDC/EMETED/7801/2020,NORTE-01-0145- FEDER-030171 funded by COMPETE2020, NORTE2020, PORTUGAL2020, and FEDER. National funding by FCT, Foundation for Science and Technology, through the individual research grant PRT/BD/153088/2021 of Glauco Tapijara Vallicelli Nobregainfo:eu-repo/semantics/publishedVersio