Development of ytterbium-doped oxyfluoride glasses for laser cooling applications (original) (raw)
Related papers
Development of ytterbium-doped oxyfluoride glasses for laser cooling applications OPEN
Oxyfluoride glasses doped with 2, 5, 8, 12, 16 and 20 mol% of ytterbium (Yb 3+) ions have been prepared by the conventional melt-quenching technique. Their optical, thermal and thermo-mechanical properties were characterized. Luminescence intensity at 1020 nm under laser excitation at 920 nm decreases with increasing Yb 3+ concentration, suggesting a decrease in the photoluminescence quantum yield (PLQY). The PLQY of the samples was measured with an integrating sphere using an absolute method. The highest PLQY was found to be 0.99(11) for the 2 mol% Yb 3+ : glass and decreases with increasing Yb 3+ concentration. The mean fluorescence wavelength and background absorption of the samples were also evaluated. Upconversion luminescence under 975 nm laser excitation was observed and attributed to the presence of Tm 3+ and Er 3+ ions which exist as impurity traces with YbF 3 starting powder. Decay curves for the Yb 3+ : 2 F 5/2 → 2 F 7/2 transition exhibit single exponential behavior for all the samples, although lifetime decrease was observed for the excited level of Yb 3+ with increasing Yb 3+ concentration. Also observed are an increase in the PLQY and a slight decrease in lifetime with increasing the pump power. Finally, the potential of these oxyfluoride glasses with high PLQY and low background absorption for laser cooling applications is discussed. Ytterbium (Yb 3+)-doped glasses have been widely investigated for their potential in solid-state lasers 1,2 , down-conversion 3 , upconversion 4 , light emitting diodes 5 , athermal lasers and more recently in solid-state laser induced cooling 6. Basic requirements for laser cooling applications include materials of low phonon energy, low background absorption, high purity and photoluminescence quantum yield (PLQY) 7. Laser induced cooling based on anti-Stokes fluorescence was first proposed by Pringsheim 8 and experimentally demonstrated for solids by Epstein et al. in Yb 3+-doped ZBLANP glass 6. Since 1995 laser cooling based on anti-Stokes fluorescence have been reported in a wide variety of low phonon energy host materials 9–12 doped with Yb 3+ , Er 3+ and Tm 3+ ions 12–15. Studies have been focused on the Yb 3+ (4f 13) ion as it has a very simple energy level structure consisting of only two manifolds, the ground (2 F 7/2) and excited (2 F 5/2) states which are well separated by about 10,000 cm −1. Yb 3+-doped laser materials can be efficiently pumped by high-power commercially available diode lasers with wavelength in the range of 0.9–1.1 μ m. Laser operation takes thus place in the 1.0 μ m wavelength region close to the 1.06 μ m wavelength laser line of Nd 3+ ion. Efficient lasing is possible in Yb 3+-doped materials because of small quantum defect (the energy difference between pump and lasing photons) which is not only the primary source of heating but also the source of anti-Stokes fluorescence for cooling 1,9. The PLQY of rare earth (RE)-doped solids is strongly influenced by the maximum phonon energy of the host, which determines the non-radiative relaxation rate. Fluoride glasses are thus favorable hosts for achieving higher PLQY owing to their low phonon energy (~580 cm −1 , for the ZBLAN fluorozirconate glass) when compared with traditional oxide glasses (~1100 cm −1 , for silicate glass). However, it is difficult to use them for practical applications due to their limited mechanical and chemical resistance. On the other hand, oxide glasses are usually preferred despite their higher phonon energy as they possess excellent chemical and mechanical properties. Oxyfluoride glasses based on heavy metal fluorides and silicates may surpass oxide and fluoride glasses by combining their advantageous properties such as low phonon energy, low melting point, high chemical durability and
Nanocrystallization in Yb3+-doped oxyfluoride glasses for laser cooling
Glass-ceramics are composite materials consisting of crystals which are controllably grown within a glass matrix usually by applying an appropriate heat treatment. They possess outstanding optical properties with applications in solid state lasers, optical amplifiers, and now, laser induced cooling. For laser cooling, the material should exhibit specific properties like low phonon energy environment around the lanthanide ions, low background losses, high transparency and high photoluminescence quantum yield. In the present study, oxyfluoride glasses and ultra-transparent nano glassceramics doped with different concentrations (2, 5, 8, 12, 16 and 20 mol %) of Yb3+ ions have been prepared by conventional melt-quenching and subsequent thermal treatments at different temperatures, respectively. Differential scanning calorimetry (DSC) and X-ray diffraction (XRD) measurements have been performed to characterize the thermal properties of the glass and the structural changes in the glass-ceramics, respectively. The XRD patterns confirm the growth of β-PbF2 nanocrystals as well as progressive incorporation of Yb3+ ions. This enhances the Yb3+ ion emission intensity which depends on the doping concentration and ceramization temperatures. The size (20 nm) of the nanocrystallites was estimated from the Sherrer’s formula and found to increase with increasing ceramization temperature, small enough to avoid scattering losses and ensure an excellent transparency of the glass-ceramics comparable with that of the parent glass. An enhancement of the luminescence properties of Yb3+ ions surrounded by a crystalline low phonon environment is observed. Finally, the utilization of these heavily Yb3+-doped ultra-transparent materials for laser cooling and solid state laser applications is discussed.
Oxyfluoride glasses and glass-ceramics (GCs) have some niche advantages over other oxide and fluoride glasses, as they possess combined properties. This paper reports the structural, thermal, and photo-luminescence (PL) properties of Yb 3þ-doped SiO 2 − Al 2 O 3 − CaO − CaF 2 oxyfluoride glasses and transparent GCs containing CaF 2 nanocrystals. Special efforts were undertaken to minimize the hydroxyl (OH −) content in the prepared samples to improve their optical features. Differential scanning calorimetry analyses were performed to determine the characteristic temperatures of the base glasses. X-ray diffractometry studies have confirmed the fluorite CaF 2 nanocrystals to be 10 nm in size. Reduced transparency in the ultraviolet (UV)–visible to the near-infrared (NIR) regions was observed for the GCs compared to the base glass with increasing thermal treatment temperature. A higher PL intensity upon 920-nm excitation was obtained in the GCs compared to that of the base glass. The absolute photoluminescence quantum yield upon 920-nm laser excitation was evaluated using an integrating sphere and an optical spectrum analyzer. It was observed that the lifetime of the 2 F 5∕2 level of the Yb 3þ ions decreases with increasing ceramization temperature. The potential advantages of using such oxyfluoride GCs over commonly studied single crystals for laser cooling applications are discussed.
Ytterbium-doped oxyfluoride nano-glass-ceramic fibers for laser cooling
Ytterbium (Yb 3+)-doped oxyfluoride SiO 2-Al 2 O 3-CdF 2-PbF 2-YF 3 glass and nano-glass-ceramic (i.e. glass-ceramics containing nanocrystals) single-index optical fibers were fabricated using two methods: by traditional glass preform drawing and by the crucible technique ('direct-melt process'). The latter technique permitted the fabrication of perfectly vitreous optical fibers (of about 200 µm diameter), leading subsequently to the fabrication of nano glass-ceramic fibers by a well-controlled heat-treatment process above the glass transition temperature. Structural characterizations have (i) confirmed the vitreous state (absence of crystals) of the glass preforms and the glass fiber obtained from the 'direct-melt process' and, (ii) evidenced the formation of Pb 1-x-y-z Cd x Y y Yb z F 2 (x + y + z ≈0.3-0.4) fluorite nanocrystals in the final glass-ceramic fibers. In particular, the nanocrystal size was found to be rather homogenous and smaller than 10 nm from TEM measurements for the nano-glass-ceramic fibers produced by controlled crystallization. The absolute photoluminescence quantum efficiency, mean fluorescence wavelength and anti-Stokes fluorescence of the Yb 3+-doped fibers were measured upon laser excitation at wavelengths of 940 nm, 975 nm and 1030 nm, respectively. As expected, higher photoluminescence quantum yield in the near infrared (0.95, close to unity) was obtained for the nano-glass-ceramic fiber when compared with the glass-fiber. Theoretical calculations were also carried out, showing that optical refrigeration would be achievable from these chemically stable and durable nano-glass-ceramic fibers provided that 95% (segregation ratio) of Yb 3+ ions are incorporated into the fluorite nanocrystals.
Ytterbium-doped glass-ceramics for optical refrigeration
We report for the first time the characterization of glass-ceramics for optical refrigeration. Ytterbium-doped nanocrystallites were grown in an oxyfluoride glass matrix of composition 2YbF3:30SiO2-15Al2O3-25CdF2- 22PbF2-4YF3, forming bulk glass-ceramics at three different crystalisation levels. The samples are compared with a corresponding uncrystalised (glass) sample, as well as a Yb:YAG sample which has presented optical cooling. The measured X-ray diffraction spectra, and thermal capacities of the samples are reported. We also report for the first time the use of Yb:YAG as a reference for absolute photometric quantum efficiency measurement, and use the same setup to characterize the glass and glassceramic samples. The cooling figure-of-merit was measured by optical calorimetry using a fiber Bragg grating and found to depend on the level of crystallization of the sample, and that samples with nanocrystallites result in higher quantum efficiency and lower background absorption than the pureglass sample. In addition to laser-induced cooling, the glass-ceramics have the potential to serve as a reference for quantum efficiency measurements.
Latvian Journal of Physics and Technical Sciences, 2008
Temperature Effects in Up-Conversion Processes of Erbium - Ytterbium Doped Oxyfluoride Silicate GlassEr3+- Yb3+doped oxyfluoride glass has been synthesized and investigated. It was found that the up-conversion spectrum of the sample excited by a 980 nm laser diode is highly dependent on the temperature of the sample. Using fluorescence intensity ratio technique the green up-conversion emissions at 525 nm and 550 nm were studied in detail in the temperature range 120-600 K. The potential applicability of the obtained results in the field of the temperature sensing is discussed.
Frontiers of Optoelectronics, 2018
In recent years, our research group has developed and studied new rare-earth doped materials for the promising technology of solid-state laser cooling, which is based on anti-stokes fl uorescence. To the best of our knowledge, our group is the only one in Canada leading the research into the properties of nanoparticles, glasses and glass-ceramics for optical refrigeration applications. In the present work, optical properties of 50GeO 2-30PbF 2-18PbO-2YbF 3 glass-ceramics for laser cooling are presented and discussed as a function of crystallization temperature. Spectroscopic results show that samples have near infrared photoluminescence emission due to the 2 F 5/2-2 F 7/2 Yb 3+ transition, centered at ~1016 nm with an excitation wavelength of 920 nm or 1011 nm, and the highest photoluminescence emission effi ciency occurs for heat-treatment for 5 h at 350°C. The internal photoluminescence quantum yield varies between 99% and 80%, depending on the temperature of heat-treatment, being the most effi cient under 1011 nm excitation. The 2 F 5/2 lifetime increases from 1.472 to 1.970 ms for heat treatments at 330°C to 350°C, respectively, due to energy trapping and the low phonon energy of the nanocrystals. The sample temperature dependence was measured with a fi ber Bragg grating sensor, as a function of input pump laser wavelength and processing temperature. These measurements show that the heating process approaches near zero for an excitation wavelength between 1020 and 1030 nm, which is an indication that phonons are removed effectivelly from the glass-ceramic materials, and they can be used for optical laser cooling applications. On the other hand, the temperature increase as a function of input laser power into samples remains constant between 920 and 980 nm wavelength excitation, a temperature variation of 36 K/W (temperature of 58°C/W) was attained under excitation at 950 nm, showing a possible use for biomedical applications to be explored.
Up-conversion and IR Luminescence of Ytterbium–Erbium Oxyfluoride Silicate Glassceramics
2013
The paper studied the luminescent properties of lead fluoride silicate nanostructured glassceramics doped with ytterbium and erbium ions. We have measured luminescence spectra of glassceramics in the visible and near-IR ranges at temperatures of 300 and 77 K and under their pumping at a wavelength of 975 nm. We have examined changes in the luminescence spectra of glassceramics depending on the time of their secondary thermal treatment, concentration of dopant ions, specimen temperature, and power of excitation radiation.
Optical properties of Yb3+ ions in fluorophosphate glasses for 1.0 lm solid-state infrared lasers
Yb 3?-doped fluorophosphate glasses were prepared by melt-quenching technique and characterized their spectroscopic properties to assess the laser performance parameters. The magnitude of absorption (emission) crosssections at 975 nm for all the studied Yb 3?-doped glasses is found to be in the range of 0.29-1.50 9 10-20 (0.59-1.99 9 10-20 cm 2) which is much higher than those of commercial Kigre QX/Yb: 1.06 9 10-20 (0.5 9 10-20 cm 2) laser glass. The luminescence lifetimes of 2 F 5/2 level decrease (1.15-0.45 ms) with increase in Yb 2 O 3 concentration (0.1-4.0 mol%). Effect of OHcontent on luminescence properties of Yb 3? ions has also been investigated. The effect of radiative trapping has been discussed by using McCumber (McC) and Fuchtbauer-Ladenburge (F-L) methods. The product of experimental lifetimes and emission cross-sections for 0.1 mol% Yb 2 O 3doped glass is found to be 2.28 9 10-20 cm 2 ms which indicates that the higher energy storage and extraction capability could be possible. The detailed spectroscopic results suggest that the studied glasses can be considered for high-power and ultrashort pulse laser applications.