Fábia Castro Cassanjes

Red–green–blue upconversion emission and energy-transfer between Tm3+ and Er3+ ions in tellurite glasses excited at 1.064 μm

Red, green, and blue emission through frequency upconversion and energy-transfer processes in tellurite glasses doped with Tm 3+ and Er 3+ excited at 1.064 μm is investigated. The Tm 3+ /Er 3+ -codoped samples produced intense upconversion emission signals at around 480, 530, 550 and 660 nm. The 480 nm blue emission was originated from the 1 G 4 → 3 H 6 transition of the Tm 3+ ions excited by a multiphoton stepwise phonon-assisted excited-state absorption process. The 530, 550 nm green and 660 nm red upconversion luminescences were identified as originating from the 2 H 11/2 , 4 S 3/2 → 4 I 15/2 and 4 F 9/2 → 4 I 15/2 transitions of the Er 3+ ions, respectively, populated via efficient cross-relaxation processes and excited-state absorption. White light generation employing a single infrared excitation source is also examined.

Infrared-to-visible frequency upconversion in Pr3+/Yb3+- and Er3+/Yb3+-codoped tellurite glasses

Abstract Upconversion luminescence and thermal effects in Pr 3+ /Yb 3+ - and Er 3+ /Yb 3+ -codoped 60TeO 2 –10GeO 2 –10K 2 O–10Li 2 O–10Nb 2 O 5 tellurite glasses excited by CW infrared radiation at 1.064 μm is reported. Generation of intense green and red fluorescence emission in Er 3+ /Yb 3+ -codoped samples and appreciable upconversion luminescence in the wavelength region of 450–680 nm in Pr 3+ /Yb 3+ -codoped samples is observed. Temperature-induced enhancement of ×12 in the upconversion efficiency in Er 3+ /Yb 3+ - and ×10 in the Pr 3+ /Yb 3+ -doped samples is demonstrated.

Optical properties and frequency upconversion fluorescence in a Tm3+-doped alkali niobium tellurite glass

Optical spectroscopic properties of Tm3+-doped 60TeO2−10GeO2−10K2O−10Li2O−10Nb2O5 glass are reported. The absorption spectra were obtained and radiative parameters were determined using the Judd–Ofelt theory. Characteristics of excited states were studied in two sets of experiments. Excitation at 360 nm originates a relatively narrow band emission at 450 nm attributed to transition 1D2→3F4 of the Tm3+ ion with photon energy larger than the band-gap energy of the glass matrix. Excitation at 655 nm originates a frequency upconverted emission at 450 nm (1D2→3F4) and emission at 790 nm (3H4→3H6). The radiative lifetimes of levels 1D2 and 3H4 were measured and the differences between their experimental values and the theoretical predictions are understood as due to the contribution of energy transfer among Tm3+ ions.

Blue cooperative luminescence in Yb3+-doped tellurite glasses excited at 1.064 μm

Blue luminescence emission around 480 nm through cooperative upconversion from pairs of Yb3+ ions implanted into 60TeO2–10GeO2–10K2O–10Li2O–10Nb2O5 tellurite glasses and excited by a cw laser at 1.064 μm is demonstrated. Cooperative luminescence emission enhancement owing to the temperature dependent multiphonon-assisted anti-Stokes excitation process of the ytterbium ions is also observed. The experimental results revealed a fourfold enhancement in the cooperative luminescence emission when the sample was heated in the temperature range of 20 °C–260 °C. The thermally induced enhancement is assigned to the effective absorption cross-section for the ytterbium ions which is an increasing function of the medium temperature.

Energy upconversion luminescence in neodymium-doped tellurite glass

Abstract Infrared-to-visible upconversion luminescence emission in Nd 3+ -doped 60TeO 2 –10GeO 2 –10K 2 O–10Li 2 O–10Nb 2 O 5 tellurite glasses under cw excitation around 800 nm is investigated. Blue (430, and 475 nm), green (530 nm) and yellow-orange (590 nm) energy upconversion emission owing to the 2 P 1/2 → 4 I j ( j =9/2, 11/2, 13/2 and 15/2) transitions of the Nd 3+ ions, respectively, was recorded. The dependence of the upconversion intensity upon the excitation wavelength and pump power is also studied. The upconversion excitation mechanism responsible for the observed emission signals is attributed to stepwise multiphoton absorption.

Study of the most suitable new glass laser to incorporate ytterbium: alkali niobium tellurite, lead fluorborate or heavy metal oxide

Abstract Diode-pumped Yb-doped glass lasers have received considerable attention for applications such as high-power beam production or femtosecond pulses generation. In this paper, we evaluate the laser potential of three different glass families doped with Yb3+: alkali lead fluorborate (PbO–PbF2–B2O3), heavy metal oxide (Bi2O3–PbO–Ga2O3) and niobium tellurite (TeO2–Nb2O5–K2O–Li2O). Spectroscopic properties were studied for the samples and calculations of the minimum laser pump intensity (Imin), saturation fluence (Usat) and the theoretical limit of peak power (Pmax) are also presented. A comparison of laser properties of these three different glasses and their importance is shown and analyzed.

Efficient energy upconversion emission in Tm3+/Yb3+-codoped TeO2-based optical glasses excited at 1.064 μm

Efficient energy upconversion of cw radiation at 1.064 μm into blue, red, and near infrared emission in Tm3+-doped Yb3+-sensitized 60TeO2-10GeO2-10K2O-10Li2O-10Nb2O5 glasses is reported. Intense blue upconversion luminescence at 485 nm corresponding to the Tm3+ 1G4→3H6 transition with a measured absolute power of 0.1 μW for 800 mW excitation power at room temperature is observed. The experimental results also revealed a sevenfold enhancement in the upconversion efficiency when the sample was heated from room temperature to 235 °C yielding 0.7 μW of blue absolute fluorescence power for 800 mW pump power. High brightness emission around 800 nm (3F4→3H6) in addition to a less intense 655 nm (1G4→3H4 and 3F2,3→3H6) fluorescence is also recorded. The energy upconversion excitation mechanism for thulium emitting levels is assigned to multiphonon-assisted anti-Stokes excitation of the ytterbium-sensitizer followed by multiphonon-assisted sequential energy-transfer processes.

Raman scattering, differential scanning calorimetry and Nd3+ spectroscopy in alkali niobium tellurite glasses

Abstract Alkali niobium tellurite glasses have been prepared and some of their properties measured by differential scanning calorimetry and Raman scattering. The vitreous domain was established in the pseudo ternary phases diagram for the system TeO2–Nb2O5–(0.5K2O–0.5Li2O). Raman scattering shows that for samples in the TeO2 rich part of the phase diagram the vitreous structure is composed essentially of (TeO4) units connected by the vertices, as in the α-TeO2 crystal. The addition of alkali and niobium oxides causes depolymerization to occur with structures composed essentially of (TeO3) and (NbO6) units. Samples with the composition (mol%) 80TeO2–10Nb2O5–5K2O–5Li2O, stable against crystallization, were prepared containing up to 10% mol Nd3+. The addition of this oxide increases the rigidity of the vitreous network shifting characteristic temperatures to higher temperatures. For the 10% Nd3+ sample amorphous phase separation is assumed to exist from the observation of two glass transition temperatures. Spectroscopic properties such as Judd–Ofelt Ωλ intensity parameters, radiative emission probabilities, and induced emission cross sections were calculated. From these results and also from the emission quenching observed as a function of Nd3+ concentration, we suggest that these glasses could be utilized in optical amplifying devices.

Time dependence and energy-transfer mechanisms in Tm3+, Ho3+ and Tm3+–Ho3+ co-doped alkali niobium tellurite glasses sensitized by Yb3+

Abstract Glass samples with the composition (mol%) 80TeO2–10Nb2O5–5K2O–5Li2O, stable against crystallization, were prepared containing Yb3+, Tm3+ and Ho3+. The energy transfer and energy back transfer mechanisms in samples containing 5% Yb 3+ –5% Tm 3+ and 5% Yb 3+ –5% Tm 3+ –0.5% Ho 3+ were estimated by measuring the absorption and fluorescence spectra together with the time dependence of the Yb 3+ 2 F 5/2 excited state. A good fit for the luminescence time evolution was obtained with the Yokota–Tanimotos diffusion-limited model. The up-conversion fluorescence was also studied in 5% Yb–5% Tm, 5% Yb–0.5% Ho and 5% Yb–5% Tm–0.5% Ho tellurite glasses under laser excitation at 975 nm. Strong emission was observed from 1 G 4 and 3 F 2 Tm 3+ energy levels in all samples. The 5 S 2 Ho 3+ emission was observed only in Yb3+Ho3+ samples being completely quenched in Yb3+/Tm3+/Tm3+ samples.

Crystallization in Lead Tungsten Fluorophosphate Glasses

The glass forming ability was investigated in the codoped Er3+/Yb3+ ternary system NaPO3-WO3-PbF2 with increasing amounts of PbF2. It has been found that glass samples can be obtained for PbF2 contents ranging from 0 mole% to 50 mole% for the codoped samples and an undoped sample containing 60% of lead fluoride could also be vitrified. Thermal properties of the most PbF2 concentrated glasses exhibit strong dependence of the composition with a decrease of the glass transition temperatures and thermal stabilities against devitrification with increasing the lead fluoride content. These glass samples were heat-treated near the crystallization peaks and the X-ray diffraction measurements pointed out that the dominant phase which precipitates from the glass samples containing 40% and 50% of PbF2 is the lead fluorophosphate phase Pb5F(PO4)3 whereas the sample containing 60% of PbF2 exhibits a preferential bulk crystallization of cubic lead fluoride β-PbF2.