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Optical thermometry via luminescence intensity ratio (LIR) is often explored in the visible spectrum range of trivalent rare earth doped materials but much less so in the near infrared region. This work range, which can be explored in Nd3+ and Yb3+ doped materials, overlaps with the first and second biological window thus making these thermometers interesting for bio applications. In this work, proof of concept is given by developing highly sensitive optical thermometers based on Nd3+-singly doped and Nd3+/Yb3+-co-doped fluorophosphate glasses with superior optical properties than phosphate and fluoride glasses. The developed systems offer the possibility of simultaneously using two LIR as thermometric parameters with high measurement accuracy, in wide temperature ranges. The Nd3+-based thermometer operating via three energy level sets emitting in the 730–950 nm range has relative sensitivities spanning from 1.7% K−1 (at room temperature) to 0.6% K−1 (at 520 K). The Nd3+/Yb3+ system presents, in addition to the use of Nd3+ transitions LIR, a new possibility of temperature detection up to 520 K. A decreased intensity of the zero-phonon line of Yb3+ at 975 nm was detected and used by comparison to the Nd3+ emission around 800 nm, resulting in relative sensitivities of ~2% K−1 at room temperature.

Borosilicate glass samples singly- and co-doped with Er3+ and ZnSe, were obtained via the melt quenching technique. Structural and morphological characterization confirmed the formation of ZnSe nanoparticles (NPs) during glass preparation. The glassy samples present the characteristic absorption bands of the respective species. Optical band gap values indicate quantum confinement effect in ZnSe-doped glasses. Excitation spectra of the co-doped glasses also display the characteristic bands of both ZnSe and Er3+. Intensity depleted regions at 377 and 521 nm observed in the excitation band of ZnSe indicate absorption by Er3+, that is, energy transfer from the ZnSe NPs to Er3+ ion. Upon excitation at 367, 447 and 498 nm, ZnSe doped glasses give broad emission bands centered around 696 nm. This reveals a broad multiple-band structure due to the overlap of emissions from NPs (electron-hole recombination) and from defect to traps, formed owing to Se and Zn vacancies. The Er3+-doped glasses display green (526 and 550 nm) and NIR (1530 nm) emissions when excited at 377 nm. The co-doped glasses show emission bands of both Er3+ and ZnSe. When compared to ZnSe and Er3+ singly doped glasses, a decrease is observed in the overall red emission while the green and NIR emissions from Er3+ increase. The intensity enhancement of Er3+ emissions increase with increasing ZnSe content which is attributed to the energy transfer from ZnSe NPs to Er3+. It was also observed that the color of the emitted light from the co-doped glasses, changes with change in excitation slit width.

Made available in DSpace on 2021-06-25T10:21:30Z (GMT). No. of bitstreams: 0 Previous issue date: 2021-05-25 Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Glass-ceramics containing rare earth gallium garnets were obtained using glass compositions as reactional medium. This work reports on the synthesis, and structural, morphological, and optical characterizations of Er3+ and Tm3+-doped Yb3Ga5O12 crystals prepared from controlled cooling of heavy metal oxide glass melts. Micrometric cubic crystals were obtained by controlling the cooling of a rare earth-supersaturated glassy composition melted at high temperature. Crystals with sizes ranging between 5 and 150 µm were formed into the glass matrix. A gallium garnet phase corresponding to space group Ia-3d was identified by X-ray diffraction and confirmed by Rietveld simulations. The morphology of crystals was studied by optical and scanning electron microscopies, while chemical elements were mapped by electron dispersive X-Ray spectroscopy. The glass phase was studied by XRD, thermal analysis and Raman spectroscopy. The optical properties of both glass and glass-ceramic materials were evaluated by UV–Vis and luminescence spectroscopies. Micro-luminescence measurements confirmed that rare earths were incorporated into the crystalline phase. Intense upconversion emissions of Er3+ (550 and 660 nm) and Tm3+ (800 nm) were observed when the glass-ceramics were pumped at 980 nm. These new glass-ceramics are excellent candidates for the development of photonic devices. Institute of Chemistry – São Paulo State University – UNESP São Carlos Institute of Physics University of São Paulo University of Bordeaux CNRS ICMCB UPR 9048 University of Bordeaux CNRS ISM UPR 5803 Institute of Chemistry – São Paulo State University – UNESP FAPESP: 2013/07793-6 FAPESP: 2019/01223-0 CNPq: 502391/2014-6

International audience; In this report, Ti3+, 4+/Eu2+, 3+ co-doped OH− free low silica calcium aluminosilicate glasses (LSCAS) were synthesized and their optical properties investigated aiming applications as phosphors for white light generation. This research explores the possibility of combining the broad emission bands in the visible of these glasses co-doped with Ti3+,4+/Eu2+ ions with those in the red emitted by Eu3+, in addition to the high luminescence quantum yield they present. The excitation and emission results show that exciting the samples at 300 nm, a broad emission band is generated, embracing very well the visible region. The emission spectra were analyzed by (x-y) CIE-1931 chromaticity diagram and the color rendering index (CRI) presented Ra values up to 80, with the correlate color temperature (CCT) varying from 4995 to 6609 K. The luminescence quantum yield determined by Thermal Lens Spectroscopy showed values of 38 and 42% for the samples with (in wt%) 0.1Eu2O3-2.0TiO2 and 0.5Eu2O3-2.0TiO2, respectively. Finally, the energy transfer processes between these luminescent ions were discussed, highlighting the potential of the Eu–Ti LSCAS glasses as candidates for the development of devices for white light generation.

At the present time there is no doubt that almost every country is experiencing a revolutionary change in the used devices for artificial lighting whether for public, for domestic or for work place illumination. This movement is taking place towards the substitution of fluorescent lamps to LED-phosphor based devices under the justification of reduction in energy consumption and mitigation of the contamination of environment produced by the mercury of fluorescent lamps. In this aspect, despite of the great effort of worldwide scientists to obtain a white lighting source with the emitting spectrum similar to that of the sunlight, it is recognized that there is still a challenge to be faced of getting luminescent materials with broad band excitation in the UV–Vis regions and large emission in the visible in order to allow tunable white lighting generation. Motivated by this interest, in this paper, Eu2+,3+/Pr3+ co-doped calcium aluminosilicate glasses were synthesized and spectroscopically investigated aiming at the development of smart white lighting devices. A prototype was developed to study the sample with excitation at 445 nm light emission diode (LED). The results indicate high color rendering index (CRI Ra ∼92–95) and tunable correlated color temperature (CCT from 5700 to 6600 K), covering the whole spectral daylight range. By using a second 405 nm LED together with the 445 nm one, the calculated Du’v’ values are suitable for indoor illumination. In this configuration, by adjusting the LEDs intensities it is possible to tune the CCT close to the white lighting region with CRI Ra nearly 95. These characteristics demonstrate that the Eu2+,3+/Pr3+ co-doped OH− calcium aluminosilicate glass is a strong candidate for smart white lighting with LEDs.