R.A. Rodríguez

Strong green upconversion emission in ZrO2:Yb3+–Ho3+ nanocrystals

Structural and upconversion emission properties of ZrO2:Yb3+–Ho3+ nanocrystals were analyzed as function of Yb3+ concentration. Structural characterization shows a crystallite size up to 80 nm and tetragonal and cubic phase as the main crystalline structures. Strong green (540 nm) and weak red (670 nm) and near infrared (760 nm) emission bands were observed with 968 nm excitation. The upconversion is based on two photons absorption either by the energy transfers from Yb3+ ion or by the excited state absorption. The energy transfer efficiency was calculated to be 50% for 2 molu2009% of Yb3+ diminishing to less than 20% for higher concentration. The Yb3+ concentration also affects the decay time of the green emission of Ho3+ ion diminishing from 140μs for 2 molu2009% of Yb to 76μs for higher concentration.

Thermoluminescence and optically stimulated luminescence properties of nanocrystalline Er3+ and Yb3+ doped Y3Al5O12 exposed to β-rays

The thermoluminescence (TL) and optically stimulated luminescence (OSL) characterization of Er3+ and Yb3+ doped Y3Al5O12 nanocrystalline samples prepared by the precipitation process and exposed to β-rays are discussed. The TL as well as the OSL were two orders of magnitude higher in Er3+ doped than in Yb3+ specimens. The charge trapping and the radiative thermally stimulated recombination processes in Y3Al5O12u2009:u2009Er3+ involve four trapping states at 166, 243, 342 and 424u2009°C, but just two trapping levels at 219 and 413u2009°C for Y3Al5O12u2009:u2009Yb3+ at a heating rate of 10u2009°Cu2009s−1. The photostimulation with 470u2009nm light causes in both phosphors a radiative recombination of the optically free charge carriers belonging to the same trapping states. The TL and the OSL as a function of radiation dose behaviour were linear in the 10–100u2009Gy dose range. The results provide evidence of the potential uses of these materials in radiation storage and dosimeter devices.

Concentration and crystallite size dependence of the photoluminescence in YAG:Ce3+ nanophosphor

Nanocrystalline yttrium aluminum garnet doped with Cerium (YAG:Ce3+), was synthesized by means of a modified sol-gel method that consists of a mixture of salts in an aqueous media. Structure and morphology were characterized by X-ray diffraction and Transmission Electron Microscopy. Single crystalline phase were obtained and the crystallite size range from 26 nm to 96 nm depending on the annealing temperature (from 800 to 1150 °C, respectively). The photoluminescence dependence on the crystallite size and ion concentration was performed. The experimental results show that the best ion concentration where the highest luminescence was obtained correspond to 0.1 mol% and that increases as the crystallite size increases. The feasibility of the modified sol-gel method for the preparation of nanocrystalline YAG is discussed.

Temperature effect in the crystallite size and the photoluminescence of nanocrystalline ZrO2:Sm3+ phosphor

Nanocrystalline ZrO2:Sm3+ doped at 2 mol% was prepared by sol-gel process and the structure and photoluminescence characterization as function of the annealing temperature were performed. Strong visible fluorescence emission produced by transitions 4G5/2→4H5/2,7/2,9/2 of Sm3+ was obtained by energy transfer process exciting the host at 320 nm and by direct excitation at 408 nm. The experimental results show a quenching of the emission bands by reducing the annealing temperature that is associated with a high content of tetragonal structure. Furthermore, an important change in the structure of the signal emitted was observed when ion was excited directly and the annealing temperature was reduced. These results suggest the possibility to tune the emission of ZrO2:Sm3+ nanophosphor.

Visible emission of rare-earth-doped ZrO2 nanocrystalline phosphor under UV and IR excitation

The photoluminescence and crystalline structure characterization of undoped and several samarium and erbium doped ZrO2 samples are reported. Strong visible fluorescence emission produced by the transitions 4G5/2→6H5/2,7/2,9/2 of Sm3+ was obtained by the excitation of the host at 320 nm (downconversion). Green (545 nm) and red (680 nm) emissions bands were observed under 962 nm excitation (upconversion). Experimental results showed that the emission bands could be tuned by controlling the Er3+ concentration. In particular, for the highest Er3+ concentration, the red band is enhanced under 962 nm excitation. The nature of this behavior is discussed taking into account the concentration dependent non-radiative energy transfer (4I13/2 + 4I11/2) → (4F9/2 + 4I15/2) and cross-relaxation (2H11/2 + 4I15/2) → (4I9/2 + 4I13/2) process.

Facile synthesis and optical applications of ceramic nanophosphors

Facile wet synthesis methods for nanocrystalline rare earth doped oxide ceramics ZrO₂, YAG, Y₂O₃, and BaZrO₃ is presented. Visible emission under UV and NIR excitation is observed in all nanophosphors. Scintillating as well as dosimeter properties of ZrO2 and YAG are reported.

Dopant concentration effect on the TL response of ZrO2:Lu3+ nanocrystals under β-ray irradiation

The thermoluminescence (TL) characterization of undoped and Lu3+ doped nanocrystalline ZrO2 under β-ray irradiation is presented. The average crystallite size was 40 nm and the crystalline structure was monoclinic although for doped samples 5 wt% of tetragonal was observed. The TL results show a typical second order kinetic with four TL peaks centered around 120, 170, 240 and 280 °C when the sample is exposed to β-ray irradiation. The presence of dopant ion induces changes in the trapping process and recombination efficiency in the TL response. The result is that dominant peak typically centered at 120 °C was quenched while the peak centered at 240 °C was enhanced. This shifting to higher temperature of the dominant peak induces important changes in the dosimetric properties of nanocrystals. The dosimetric behavior for TL method and the TL fading of the samples under β-irradiation was systematically characterized as function of the dopant concentration. The high efficiency of the TL suggest a good potential of this nanophosphor as β- irradiation dosimeter.

Structural and photoluminescence characterization of nanocrystalline YAG: Er3+ prepared with the addition of PVA and UREA

The Photoluminescence (PL), FFTIR, Raman characterization, XRD and TEM of Er doped nanocrystals (Y3Al5O12:Er) prepared by glycolate method modified with PVA and UREA is reported. Irregular morphology was observed but for some concentration of PVA and UREA nanorods was observed, being PVA dominant in final morphology. XRD patterns show the presence of hexagonal phase of YAG (YAH) when the UREA was used but pure YAG crystalline structure was obtained with only PVA. Raman spectroscopy confirms the crystalline phase and in combination with infrared spectroscopy the presence of oxygen deficiency was observed. Strong green emission was observed as a result of the upconversion mechanism due to the two photon process. Luminescence results show that both PVA and UREA do not modify the emission properties but control the morphology.