E De la Rosa-Cruz

Luminescence and visible upconversion in nanocrystalline ZrO2:Er3+

The structural and luminescence properties of erbium doped zirconium oxide prepared by the sol-gel processes were analyzed. The annealed powders presented a concentration dependent crystallite sizes and crystalline phase, ranging from 28 to 46 nm and from 40 to 96% for the monoclinic phase, respectively. Green (545 nm) and red (680 nm) emissions bands were observed with 489 and 962 nm excitation. Experimental results showed that the emission bands can be tuned by controlling the Er3+ concentration and that the red band is almost quenched with 489 nm whereas it is enhanced with 962 nm excitation. The nature of this behavior is discussed taking into account the nonradiative energy transfer and cross-relaxation process.

Luminescent properties and energy transfer in ZrO2:Sm3+ nanocrystals

The photoluminescence and crystalline structure characterization of undoped and several samarium doped ZrO2 samples are reported. Strong 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. The energy transfer process from the host to the samarium ion was confirmed by the analysis of the ZrO2 fluorescence decay curve. It is shown that the content of the active ions stabilizes the tetragonal structure of ZrO2 at 1000 °C, being 73% for 2 mol % Sm2O3 doped and 3% for undoped samples. The dependence between the fluorescence emission and the crystalline structure is discussed.

Nanocrystalline tetragonal zirconium oxide stabilization at low temperatures by using rare earth ions: Sm3+ and Tb3+

Zirconium oxide was synthesized by the sol–gel method and the tetragonal structure was stabilized up to 1000 °C by doping with different rare earth ions. The evolution of the crystalline structure as a function of the annealing temperature and rare earth concentration of doped and undoped samples were investigated by X-ray diffraction. Our experimental results show that it is possible to obtain up to 73 wt.% of tetragonal content by doping the ZrO2 with 2 mol% of Sm2O3 or Tb2O3 and annealing at 1000 °C. Variations in the lattice parameters and nanocrystallite size were also obtained. Our results suggest that the stabilization of tetragonal structure can be obtained with other rare earth ions.

High temperature thermoluminescence induced on UV-irradiated tetragonal ZrO2 prepared by sol–gel

Abstract An unpublished high temperature thermoluminiscent signal centered at 400°C induced by UV radiation of pure tetragonal zirconium oxide, is reported. Zirconia samples were prepared by the sol–gel method and annealed at 500°C to produce the tetragonal phase and at 1000°C to obtain the monoclinic phase. Experimental results show that the thermoluminiscent (TL) glow peak depends on both the crystalline structure and crystallite size. The high temperature peak is 270°C shifted up with respect to the main peak of the monoclinic phase. To our knowledge, this is the highest temperature TL signal reported for zirconia samples, opening new possibilities for the design of high temperature dosimeters.

Concentration enhanced red upconversion in nanocrystalline ZrO2:Er under IR excitation

The effects of Er3+ concentration in ZrO2 on the red (680 nm) and green (545 nm) upconversion emission from Er3+ under near infrared radiation (NIR) excitation (at both 1438 and 962 nm) are presented. For the highest Er3+ concentration used, the red band is almost quenched under VIS (489 nm) excitation, whereas it is enhanced under NIR excitation. Such a difference between photoluminescence and upconversion is explained taking into account the concentration dependent cross-relaxation process (2H11/2 + 4I15/2) → (4I9/2 + 4I13/2). Experimental results suggest that two- and three-photon upconversion processes are taking place under 962 nm and 1438 nm excitation, respectively.

Monoclinic ZrO2 as a broad spectral response thermoluminescence UV dosemeter

Abstract The thermoluminescence characterization of polycrystalline monoclinic ZrO 2 samples prepared by the sol–gel process subjected to ultraviolet irradiation was performed. The results show that sol–gel synthesized ZrO 2 possesses good thermoluminescence efficiency as well as linear dose response. The thermoluminescence excitation spectrum covers the complete UVA, UVB and UVC range indicating a major advantage over other ultraviolet detector and dosemeters currently used.

Refractive index measurement of pure and Er3+-doped ZrO2–SiO2 sol–gel film by using the Brewster angle technique

Abstract The application of the Brewster angle technique and a genetic algorithm for the measurements of refractive index and thickness in tetragonal ZrO 2 :Er 3+ and ZrO 2 –SiO 2 films prepared by the sol–gel process and dip–coating technique annealed at 550°C are reported. A precision higher than 99.5% and 98% in the refractive index and thickness measurements were obtained, respectively. Analysis of the capability to tune the refractive index of high-density blend films by changing the molar concentration of zirconium dioxide, with an increment rate of (0.0052±0.0004)/mol, are also presented.

Luminescence and thermoluminescence induced by Gamma and UV-irradiation in pure and rare earth doped zirconium oxide

Abstract Pure and rare earth doped zirconium oxide was prepared by the sol–gel process and annealed at 1000 °C to stabilize the monoclinic phase. Thermoluminescence (TL) and photoluminescence (PL) under Gamma and UV irradiation were performed. A single TL peak was present at 135 °C under gamma irradiation, whereas under UV irradiation the TL presented two peaks at 62 and 130 °C. The PL of pure and rare earth doped samples was also characterized. The experimental spectra suggest the presence of energy transfer processes between the dopant (Sm 3+ ) and the host (ZrO 2 ).

Enhancement of optical properties of Nd3+ doped fluorophosphate glasses by alkali and alkaline earth metal co-doping

Fluorophosphate glasses doped with trivalent Nd and using Li and Ba as network modifier cations are spectroscopically analyzed to understand the effects of these cations on the radiative and non-radiative process. The radiative properties of Nd3+ such as radiative transition probabilities, radiative decay times and stimulated emission cross-sections of the transitions from the 4F3/2 level, and their dependence on network modifiers and active ion concentration are analyzed using the Judd–Ofelt theory. Results show that, eventhough stimulated emission cross-section is maximum in Li based glass, fluorescence quenching is higher, however it is considerably reduced by the presence of Ba. It is found that, Ba and LiBa based glasses yield higher quantum efficiency showing that Ba reduces the fluorescence quenching properties of the matrix. The stimulated emission cross-section of the emission band at 1.055 μm is higher than that of commercial laser glasses. On the other hand, quantitative estimation of the non-radiative processes such as multiphonon relaxation and quenching by water content shows that water content is far below the critical level of optimum laser performance. All these factors pertain to the fact that these Nd3+ doped fluorophosphate glasses can be effectively used for high power lasers in the 0.8 and 1.055 μm regions.

Spectroscopic characterization of Nd3+ ions in barium fluoroborophosphate glasses

Abstract Spectroscopic properties of Nd3+ in barium fluoroborophosphate glassy matrix have been analyzed by fitting the experimental data with the standard Judd–Ofelt theory. Various spectroscopic parameters, viz. radiative transition probabilities, radiative decay time, fluorescence branching ratios, electric dipole line strengths, stimulated emission cross-sections and optical gain of the principal fluorescence transition from the 4 F 3/2 metastable level were obtained to evaluate the potential of the samples as laser material. Results show that addition of borate content to the fluorophosphate matrix will reduce the fluorescence spectral properties of Nd3+. However, the radiative properties of the fluoroborophosphate glassy matrix are found to be well improved over those of pure borate and pure phosphate matrix and are attributed to the influence of fluorine content in the glassy matrix. Quantitative estimation of the non-radiative processes such as multiphonon relaxation and quenching by water content shows that the first process is absent in our sample while the water content is found to be below the critical level for optimum laser performance.