ZBLAN Glass Research Articles

Orange and IR to violet up-conversion processes in Nd:ZBLAN glasses

In this work we investigate, compare and discuss UV and violet emission behaviour under pulsed, multi-photon orange and infra-red excitation in Nd 3+ doped ZBLAN samples of different concentrations ranging from 0.3 to 5 mol.%. Supported by the obtained spectroscopic results, orange and IR excitation schemes were proposed and verified by time dependent rate equation model, which has been employed to confirm the nature of observed processes. Proposed model returns fitting results which qualitatively reflect the experimentally obtained fluorescence decays.

Competition between two types of anti-Stokes emission inHo3+-activated ZBLAN glass

A competition between two anti-Stokes emissions has been observed and interpreted in ZBLAN glassactivated by Ho3+ ions. The first anti-Stokes emission intensity was seen to increase with temperature,whereas another, upconverted emission, was seen to decrease under the same conditions.Both observed tendencies are believed to be caused by the same effect: the multiphononanti-Stokes excitation of the state responsible for the first emission. Analysis of thekinetics and fits of the theoretical model to experimental data are presented.

Excited state absorption spectroscopy ofZBLAN:Ho3+ glass—experiment and simulation

The excited state absorption (ESA) spectra of ZBLAN glass activated by trivalent holmiumions have been measured in a wide spectral range (550–1750 nm) and simulated using suchtheoretical tools as the Judd–Ofelt formalism and McCumber theory of stimulated emission.We also propose a systematic approach for prediction of various types of up-conversionmechanisms in a given type of material. Experimental results on ESA up-conversion processes inZBLAN:Ho3+ under red and infrared laser excitation, which confirm theoretical analysis, arepresented. The optical linewidths were studied using high resolution laser spectroscopyat low temperatures and the existence of different crystallographic sites forHo3+ ions was revealed.

Ultraviolet emission excitation in RE 3+ activated fluoride fibers

Short-wavelength (∼280–410 nm) fluorescence in Er 3+, Tm 3+, Nd 3+ and Ho 3+ doped ZBLAN glasses was studied experimentally and attributed to transitions from the 2P 3/2, 1I 6 and 1D 2, 4D 3/2, 3D 3 states, respectively. Properties of these high-lying metastable levels, such as state energies, transition wavelengths, lifetimes, emission branching ratios and cross-sections, which are important for laser action analysis, were determined. In particular, up-conversion UV emission excitation schemes for Nd 3+ and Ho 3+ doped ZBLAN were studied experimentally and modeled by time dependent rate equations. Violet and ultraviolet laser operation in Nd 3+ and Ho 3+ doped ZBLAN fibers under up-conversion pumping was studied theoretically basing on measured spectroscopic parameters.

Dynamics of excited state relaxation and frequency upconversion in Tm3+ and Tm3+/Tb3+ doped ZBLAN glass

The effects of activator concentration on the relaxation of the 1I6, 1D2, 1G4 and 3H4 levels of Tm3+ were investigated by the analysis of the fluorescence decay curves in Tm3+ and Tm3+/Tb3+ doped ZBLAN glasses. UV and blue upconversion luminescence bands around 362 and 450nm were observed by 655nm laser excitation in all the samples. The upconversion mechanism was attributed to excited state absorption (ESA) by analyzing the decay profiles and the intensity dependence.

Production of defects in ZBLAN, ZBLAN:Tm 3+ and ZBLAN:Cr 3+ glasses by ultra-short pulses laser interaction

In this work we have studied pure and thulium- and chromium-doped ZBLAN glasses irradiated by ultra-short laser pulses. A Ti:sapphire CPA system was used, producing a 500 Hz train of pulses, centered at 830 nm, with 375 μJ of energy and 50 fs of duration (FWHM). The beam was focused by a 20 mm lens, producing a converging beam with a waist of 12 μm. The absorption spectra before and after laser irradiation were obtained showing production of color centers in pure, thulium-doped and chromium-doped ZBLAN glasses. A damage threshold of 9.56 T W/cm 2 was determined for ZBLAN.

Near-infrared emissions and quantum efficiencies in Tm 3+-doped heavy metal gallate glasses for S- and U-band amplifiers and 1.8 μm infrared laser

Intense 1.8 μm and efficient 1.48 μm infrared emissions have been recorded in Tm 3+-doped alkali-barium-bismuth-gallate (LKBBG) glasses with low phonon energies under the excitation of 792 nm diode laser. The maximum emission cross-sections for 1.8 and 1.48 μm emission bands are derived to be 6.26×10 −21 and 3.34×10 −21 cm 2, respectively, and the peak values are much higher than those in Tm 3+-doped ZBLAN glass. In low-concentration doping, the full-widths at half-maximum (FWHMs) of the two emission bands are 223 and 122 nm, and the quantum efficiencies of the 3F 4 and 3H 4 levels are proved to be ∼100% and 86%, respectively. When the doping concentration increases to 1 wt%, the quantum efficiency of the 3H 4 level is reduced to 60% due to the cross-relaxation processes in high-concentration doping. Efficient 1.8 μm infrared emission in Er 3+/Tm 3+-codoped LKBBG glass has also been achieved under the excitation of 970 nm diode laser, and the probability and the efficiency of non-radiative energy transfer from Er 3+ to Tm 3+ are as high as 354 s −1 and 58.4%, respectively. Efficient and broad 1.8 and 1.48 μm infrared emission bands indicate that Tm 3+-doped LKBBG glasses are suitable materials in developing S- and U-band amplifiers and 1.8 μm infrared laser.

Excited state dynamics of the Ho3+ ions in holmium singly doped and holmium, praseodymium-codoped fluoride glasses

The deactivation of the two lowest excited states of Ho3+ was investigated in Ho3+ singly doped and Ho3+, Pr3+-codoped fluoride (ZBLAN) glasses. We establish that 0.1–0.3mol% Pr3+ can efficiently deactivate the first excited (I75) state of Ho3+ while causing a small reduction of ∼40% of the initial population of the second excited (I65) state. The net effect introduced by the Pr3+ ion deactivation of the Ho3+ ion is the fast recovery of the ground state of Ho3+. The Burshstein model parameters relevant to the Ho3+→Pr3+ energy transfer processes were determined using a least squares fit to the measured luminescence decay. The energy transfer upconversion and cross relaxation parameters for 1948, 1151, and 532nm excitations of singly Ho3+-doped ZBLAN were determined. Using the energy transfer rate parameters we determine from the measured luminescence, a rate equation model for 650nm excitation of Ho3+-doped and Ho3+, Pr3+-doped ZBLAN glasses was developed. The rate equations were solved numerically and the population inversion between the I65 and the I75 excited states of Ho3+ was calculated to examine the beneficial effects on the gain associated with Pr3+ codoping.

Model of laser cooling in theYb3+-doped fluorozirconate glass ZBLAN

A quantitative description of optical refrigeration in ${\mathrm{Yb}}^{3+}$-doped ZBLAN glass in the presence of transition-metal and $\mathrm{OH}$ impurities is presented. The model includes the competition of radiative processes with energy migration, energy transfer to transition-metal ions, and multiphonon relaxation. Molecular dynamics calculations of pure ZBLAN and ZBLAN doped with transition-metal ions provide the structural information that, when combined with spectroscopic data, allows for the calculation of electric-dipole energy-transfer rates in the framework of the Dexter theory. The structural data is further used to extend the traditional energy-gap law to multiphonon relaxation via vibrational impurities. The cooling efficiency is sensitive to the presence of both $3d$ metal ions with absorption in the near infrared and high-frequency vibrational impurities such as $\mathrm{OH}$. The calculation establishes maximum impurity concentrations for different operating temperatures and finds ${\mathrm{Cu}}^{2+}$, ${\mathrm{Fe}}^{2+}$, ${\mathrm{Co}}^{2+}$, ${\mathrm{Ni}}^{2+}$, and $\mathrm{OH}$ to be the most problematic species. ${\mathrm{Cu}}^{2+}$ in particular has to be reduced to $l2\phantom{\rule{0.3em}{0ex}}\mathrm{ppb}$, and ${\mathrm{Fe}}^{2+}$, ${\mathrm{Co}}^{2+}$, ${\mathrm{Ni}}^{2+}$, and $\mathrm{OH}$ have to be reduced to $10--100\phantom{\rule{0.3em}{0ex}}\mathrm{ppb}$ for a practical $\mathrm{ZBLAN}:{\mathrm{Yb}}^{3+}$ optical cryocooler to operate at $100--150\phantom{\rule{0.3em}{0ex}}\mathrm{K}$.

Short-wavelength emission analysis in Dy:ZBLAN glasses

In this work we examine short-wavelength (blue, yellow and red) emission properties of dysprosium activated fluorozirconate ZBLAN glass. On the basis of the measured broad band absorption spectrum the intensity parameters Ωi were calculated using Judd–Ofelt formalism, yielding values of transition probabilities and radiative lifetimes. The basic spectroscopic characterization of Dy:ZBLAN was also performed, including visible emission and fluorescence decay measurements under pulsed, direct and two-photon up-conversion excitation. The theoretically predicted properties, specifically concerning the fluorescence lifetimes, were found to be in a rough agreement with experimentally determined values which was improved by isolation of magnetic dipole and impurity contributions to absorption spectrum.

Ultraviolet upconversion emission from ZBLAN glass doped with Tm 3+ ions

The ultraviolet upconversion emission properties from Tm 3+ ions doped ZBLAN glass upon 463 nm laser excitation have been studied. Two ultraviolet emission bands, centered at 347 nm for 1I 6→ 3F 4 Tm 3+ transition and 362 nm for 1D 2→ 3H 6 Tm 3+ transition, have been observed. The responsible upconversion mechanisms were investigated by measuring time evolution spectra.

Energy transfer and frequency upconversion in Pr3+-doped ZBLAN glass

The lifetimes of 3P0 and 1D2 levels of Pr3+ were measured in ZBLAN glasses of composition in mol% 53ZrF4–20BaF2–(4−x)LaF3–3AlF3–20NaF–xPrF3 (x=0.1, 0.5, 1, and 3) by resonant excitation. Energy transfer observed between Pr3+ ions was analyzed by means of the Inokuti–Hirayama theory. The non-exponential dependence of the 1D2 decay on Pr3+ concentration indicates that dipole–dipole interaction between Pr3+ is the main process. Orange-to-blue upconversion luminescence was observed and described by two-ion energy transfer mechanism. The temporal evolution of upconversion luminescence was characterized by rise and decay times related to the dopant concentration.

Gain cross-sections of transparent oxyfluoride glass–ceramics single-doped with Ho 3+ (at 2.0 μm) and with Tm 3+ (at 1.8 μm)

We have developed transparent 3.5 mol% Ho 3+ and Tm 3+ single-doped oxyfluoride glass–ceramics, where a large fraction of dopant ions is segregated into PbF 2-based nano-crystals. The absorption and emission cross-sections corresponding to the 5I 7 ↔ 5I 8 transitions of the Ho 3+ (at 2.0 μm), and to the 3H 6 ↔ 3F 4 transitions of the Tm 3+ (at 1.8 μm), have been obtained and respective gain cross-section spectra have been computed as a function of population inversion. For Ho 3+-doped samples, the maximum gain cross-section increased by 20% on ceramming of the precursor glass and reached, for the ensuing glass–ceramics, a value 1.5 times higher than that reported for fluoride glasses. The maximum gain cross-section for Tm 3+-doped samples increased 2.5 times on ceramming of the precursor glasses and reached for the ensuing glass–ceramics a value 2–3 times higher than for other fluoride hosts, such as ZBLAN glass, and 1.5 times higher than for silicate and germanate glass hosts. Hence, these Ho 3+- and Tm 3+-doped glass–ceramics have an advantage for application in planar and fibre lasers/amplifiers at about 2.0, and 1.8 μm, respectively.

The study of two-color excitation upconversion of Pr(0.5)Yb(3):ZBLAN

The excited state absorption upconversion of Pr(0.5)Yb(3):ZBLAN glass material, under two-color excitation of the 960 nm semiconductor laser and the Xe lamp light simultaneously, is reported in this article. It was found that the upconversion emission spectra of 480.1, 519.0, 601.9 and 631.8 nm coincide with the common emission spectra. Meanwhile, the upconversion-excitation spectrum has three obvious peaks under two-color excitation, and they respectively correspond to the 856.0 nm upconversion excitation transition [1G4(Pr3+)→1I6(Pr3+) and 1G4(Pr3+)→3P1(Pr3+)], the 789.0 nm upconversion excitation transition 1G4(Pr3+)→3P2(Pr3+), and the 803.7 nm upconversion excitation transition 3H6(Pr3+)→1D2(Pr3+). The upconversion excitation transition 1G4(Pr3+)→1I6(Pr3+) is strong because its oscillator strength f = 23.040×10−6 is large, which results in a large peak appearing in the upconversion excitation spectrum. That is just the new interesting two-color excitation upconversion luminescence phenomenon of Pr(0.5)Yb(3):ZBLAN induced by one laser and one continuous normal light simultaneously.

Performance modeling of optical refrigerators

Optical refrigeration using anti-Stokes fluorescence in solids has several advantages over more conventional techniques including low mass, low volume, low cost and no vibration. It also has the potential of allowing miniature cryocoolers on the scale of a few cubic centimeters. It has been the topic of analysis and experimental work by several organizations. In 2003, we demonstrated the first optical refrigerator. We have developed a comprehensive system-level performance model of optical refrigerators. Our current version models the refrigeration cycle based on the fluorescent material emission and absorption data at ambient and reduced temperature for the Ytterbium–ZBLAN glass (Yb:ZBLAN) cooling material. It also includes the heat transfer into the refrigerator cooling assembly due to radiation and conduction. In this paper, we report on modeling results which reveal the interplay between size, power input, and cooling load. This interplay results in practical size limitations using Yb:ZBLAN.

Confirmation of temperature independence in the fluorescence lifetime of the 3P0 → 3F2 transition in praseodymium-doped fluoride glass

The dependence of the fluorescence lifetime from the 3P0→3F2 transition in praseodymium-doped fluoride glass as a function of dopant concentration and temperature was investigated. It was found that the fluorescence lifetime at the concentration of 7000ppm was constant with temperature, confirming the prediction of temperature independence in the lifetime for this transition in Pr3+-doped ZBLAN glass.

Structure inhomogeneities of medium-range order in fluorozirconate glasses

Images of cleaved surfaces were obtained for 53ZrF4-20BaF2-4LaF3-3AlF3-20NaF (ZBLAN) glasses and fused quartz using an NTMDT atomic force microscope. It is shown that the scatter of particle size depends on the cooling rate and is 21–48.5 A for the cleaved surface of ZBLAN glass obtained by very fast cooling and 68–172 A for the cleaved surface of ZBLAN after slow cooling. For cleaved fused quartz, the range is 25-18 A.

Multiple-wavelength up-conversion laser in Tm/sup 3+/-doped ZBLAN glass fiber

In this letter, we report on a multiple-wavelength up-conversion laser in Tm/sup 3+/-doped ZrF/sub 4/--BaF/sub 2/--LaF/sub 3/--AlF/sub 3/--NaF glass fiber pumped by an 1120-nm fiber laser. Single-wavelength, two-wavelength, and three-wavelength up-conversion lasers can be obtained by adjusting the distance between the coupler mirror and the fiber end, which is attributed to the frequency-filter effect in the etalon composed of the coupler mirror and the fiber end. The effects of the pump power on the performance of dual-wavelength laser were also discussed.

Preparation and analysis of Eu 3+- and Eu 2+-doped ZBLAN and ZBLALi fluorozirconate glasses

Fluorozirconate glasses in the ZBLAN and ZBLALi families with varying [Eu 2+] and [Eu 3+] concentrations were prepared and characterized. The reversible electroactivity of Eu 2+/3+ was verified by cyclic voltammetry in the molten salt precursor phase, showing that Eu 2+ would not reduce the other glass components. Eu 2+-containing glasses were prepared by various strategies including inclusion of EuF 2 as a starting material and chemical reduction during melt processing. Glass samples were characterized by differential scanning calorimetry, UV–Visible and IR spectroscopy and temperature-dependent conductivity. Glasses in the range of 0–6% [Eu 3+] and ‘mixed valent’ ones with 0–3% [Eu 2+] and 4–2% [Eu 3+] were successfully prepared, but greater Eu concentrations spoiled the glass optical properties. The temperature-dependent bulk conductivities of numerous glasses were carefully measured using a Fourier analysis that resolves bulk and substantial interfacial contributions to glass conductivity. No systematic changes in glass conductivity were observed for glasses as a function of the [Eu 2+][Eu 3+] concentration product as would be expected were there a substantial rate of electron transfer between Eu sites, implying substantial and static structural differences between these sites.

Spectroscopic properties of thulium-doped zirconium fluoride and indium fluoride glasses

The spectroscopic properties of thulium-doped indium fluoride based bulk glasses with a novel glass composition (IBZP) have been analyzed and compared to the standard ZBLAN glass according to measured absorption and emission spectra in the ultraviolet, visible and infrared wavelength regions. Moreover, lifetime measurements have been done and compared with values published elsewhere. All measurements were carried out with self-made thulium-doped IBZP and ZBLAN bulk glasses at room temperature. For both glass systems, energy level calculations have been performed and evaluated with respect to a usage as host glasses for optical fiber amplifiers or fiber lasers. Tables containing many important calculated properties like radial integrals, state vectors, reduced matrix elements, radiative transitions rates, branching ratios and oscillator strengths are given.