Photoluminescence of Sm3+, Dy3+, and Tm3+-doped transparent glass ceramics containing CaF2 nanocrystals

Photoluminescence properties of Sm³⁺, Dy³⁺, and Tm³⁺-doped transparent oxyfluoride silicate glass ceramics containing CaF₂ nanocrystals were reported. Emission bands of ⁴G_5/2 → ⁶H_5/2 (562 nm), ⁴G_5/2 → ⁶H_7/2 (598 nm), ⁴G_5/2 → ⁶H_9/2 (645 nm) and ⁴G_5/2 → ⁶H_11/2 (706 nm) for the Sm³⁺: glass and glass ceramic, with an excitation at ⁶H_5/2 → ⁴F_7/2 (402 nm) have been recorded. Of them, ⁴G_5/2 → ⁶H_7/2 (598 nm) has shown a bright orange emission. With regard to the Dy³⁺: glass, a bright fluorescent yellow emission at 575 nm (⁴F_9/2 → ⁶H_13/2) and blue emission at 481 nm (⁴F_9/2 → ⁶H_15/2) have been observed, apart from 662 nm (⁴F_9/2 → ⁶H_11/2) emission transition with an excitation at 386 nm (⁶H_15/2 → ⁴I_13/2 + ⁴F_7/2) wavelength. Emission bands of ¹G₄ → ³F₄ (650 nm) and ¹G₄ → ³H₅ (795 nm) transitions for the Tm³⁺: glass and glass ceramic, with an excitation at ³H₆ → ¹G₄ (467 nm) have been observed. Of them, ¹G₄ → ³F₄ (650 nm) has shown bright red emission. Decay lifetime measurements were also carried out for all the observed Sm³⁺, Dy³⁺, and Tm³⁺-doped glass and glass ceramic emission bands.     

Spectroscopic properties and energy transfer in Ga2O3– Bi2O3–PbO–GeO2 glasses codoped with Tm3+ and Ho3+

This paper reports on the spectroscopic properties and energy transfer in Ga₂O₃–Bi₂O₃–PbO–GeO₂ glasses doped with Tm³⁺ and/or Ho³⁺. From the optical absorption spectra of Tm³⁺, Judd–Ofelt intensity parameters, radiative transitions probabilities, fluorescence branching ratios, and radiative lifetimes have been calculated using Judd–Ofelt theory. The measured differential scanning calorimetry result shows that the glass exhibits excellent stability against devitrification with ΔT = 129 °C. The measured luminescence spectra show that the ³H₄ → ³F₄ transition of Tm³⁺ upon 808 nm laser diode excitation possess a broad full width at half-maximum of ∼126 nm. The maximum value calculated stimulated emission cross-section and the measured lifetime of ³H₄ level from the 1.47-μm transition are ∼4.73 × 10⁻²¹ cm² and ∼0.239 ms, respectively. It is noticed that codoping of Ho³⁺ could significantly enhanced the ratio of the intensity of 1.47–1.80 μm by energy transfer via Tm³⁺: ³F₄ → Ho³⁺: ⁵I₇.     

Enhanced mid-IR luminescence of Tm3+ ions in Ga2S3 nanocrystals embedded chalcohalide glass ceramics

Chalcohalide glass with a composition of 65GeS₂–25Ga₂S₃–10CsI (in mol%) doped with 0.6 wt% Tm³⁺ ions was prepared by conventional melt–quench method. By heat treating the precursor glass at 20 °C above its glass transition temperature T_g for different durations, IR transparent glass ceramics were obtained. X-ray diffraction (XRD) and scanning electron microscope (SEM) showed that Ga₂S₃ crystallites were precipitated after heat treatment and their grain sizes were in nano-scale and increased with the elongation of heat treated time. Mid-IR luminescence properties of the glass and transparent glass ceramic samples were investigated. The emissions at 2.3 and 3.8 μm corresponding to optical transitions of ³H₄ → ³H₅ and ³H₅ → ³F₄ of Tm³⁺ ions were significantly enhanced by the presence of Ga₂S₃ nanocrystals and reached a maximum after 8 hours treatment.     

Spectroscopic properties of the 1.8 μm emission of Tm3+/Yb3+ codoped TeO2–ZnO–Bi2O3 glasses with efficient energy transfer

Tm³⁺-doped and Tm³⁺/Yb³⁺-codoped TeO₂–ZnO–Bi₂O₃ (TZB) glasses are prepared by melt-quenching method. The Judd-Ofelt intensity parameters (Ω_t t = 2, 4, 6), radiative transition rate, and radiative lifetime of Tm³⁺ are calculated based on the absorption spectra. The 1.8 μm emission of the samples is investigated under 980 nm laser excitation. The absorption, emission cross-sections, and gain coefficient of Tm³⁺:³F₄ → ³H₆ are calculated. The energy transfer processes of Yb³⁺–Yb³⁺ and Yb³⁺–Tm³⁺ are analyzed, the results show that the Yb³⁺ ions can transfer their energy to Tm³⁺ ions with large energy transfer coefficient, and a maximum efficiency of 79%.     

Broadband near-infrared emission from Bi–Er–Tm Co-doped germanate glasses

Bi–Er–Tm co-doped germanate glasses and Bi, Er, Tm singly doped glasses were prepared and characterized through absorption spectra, NIR emission spectra and decay lifetime. A super broadband near-infrared emission from 1000 nm to 1600 nm, covering the whole O, E, S, C, and L bands, was observed in the Bi–Er–Tm co-doped samples due to the result of the overlapping of the Bi related emission band (centered at 1300 nm), the emission from Er^{3+ 4}I_13/2 → ⁴I_15/2 transition (centered at 1534 nm) as well as the emission from Tm^{3+ 3}H₄ → ³F₄ transition (centered at 1440 nm), which is essential for broadly tunable laser sources and broadband optical amplifiers. The energy transfer process was also discussed at the end of the paper.     

Compositional dependences on the mechanism of upconversion in Nd3+/Tm3+ co-doped chalcohalide glasses

Mechanisms of the compositional dependence of blue emission from Nd³⁺/Tm³⁺ co-doped Ge–Ga–S–CsBr chalcohalide glasses were investigated. The blue upconversion emissions (centered at 475 nm) due to the Tm³⁺: ¹G₄ → ³H₆ transition decreased as the CsBr/Ga ratio in glasses while the other upconversion emissions from the Nd³⁺ ions increased. Changes in the local environment of rare-earth ions incurred by the CsBr addition significantly increased the excited state absorption within Nd³⁺ ions. This resulted in the decrease in the Nd³⁺ → Tm³⁺ energy transfer rates that led to the large decrease in blue upconversion emission.     

Thermal and spectroscopic properties of Tm3 + doped TZPPN transparent glass laser material

In this work a transparent bulk glass with the mol% composition 76TeO₂·10ZnO·9.0PbO·1.0PbF₂·3.0Na₂O doped with Tm^3 + has been synthesized. Results of differential thermal analysis (DTA) indicate a high thermal stability and low tendency to crystallization of this glass. The refractive indices at different wavelengths, the Urbach energy, the optical energy gap, the Sellmeier gap energy and the dispersion energy have been estimated. Spectroscopic quality factor of Tm^3 + was evaluated from optical absorption spectra. Electric and magnetic dipole transition probabilities, branching ratios, and radiative lifetimes of several excited states of Tm^3 + have been predicted using calculated intensity Judd–Ofelt parameters. The classical McCumber theory has been applied to evaluate the emission cross-sections for ³F₄ → ³H₆ transition around 1.8 μm. This study shows that TZPPN glass doped with Tm^3 + ions is a promising candidate for laser applications.     

Fabrication and characterization of Er3+-doped GeO2–PbO and GeO2–PbO–Bi2O3 glass fibers

Glass fibers were drawn from GeO₂–PbO–Bi₂O₃ and GeO₂–PbO melts previously doped with Er³⁺. From the differential thermal analysis curve, the glass transition temperature was determined to be 420 °C, and no crystallization peak was observed in the temperature range of that analysis, indicating stability with regard to devitrification. Raman spectroscopy was performed to characterize the structure of the glasses, which exhibited large transmission windows (0.5–5.0 μm) and large refractive indices (∼2.0). Infrared to visible upconversion of Er³⁺ was observed in the fibers. The visible emissions were related to the upconverted green emissions at about 530 nm (²H_11/2 → ⁴I_15/2) and 550 nm (⁴S_3/2 → ⁴I_15/2), and red emission at 668 nm (⁴F_9/2 → ⁴I_15/2) under 980 nm excitation. The infrared transition (⁴I_13/2 → ⁴I_15/2) was peaked at 1.53 μm. The results obtained suggest that the fibers exhibit the same structures as the parent glasses and can be used in upconversion fiber optical devices.     

Upconversion and concentration quenching in Er3+-doped TeO2–Na2O binary glasses

The spectroscopic properties of Er³⁺-doped alkali tellurite TeO₂–Na₂O glasses are investigated. Infrared-to-visible upconversion emission bands are observed at 410, 525, 550 and 658 nm using 797 nm excitation wavelength. These bands are assigned to the ²H_9/2 → ⁴I_15/2, ²H_11/2 → ⁴I_15/2, ⁴S_3/2 → ⁴I_15/2 and ⁴F_9/2 → ⁴I_15/2 transition, respectively. The power dependence study reveals that the ²H_9/2 → ⁴I_15/2 transition involves a three-step process while the other upconversion transitions involve only two steps. An excitation with 532 nm wavelength, two upconversion bands are observed in the UV region at 380 and 404 nm in addition to bands in the visible region at 410, 475, 525, 550, 658 and 843 nm. These bands are ascribed to ⁴G_11/2 → ⁴I_15/2, ²P_3/2 → ⁴I_13/2, ²H_9/2 → ⁴I_15/2, ²P_3/2 → ⁴I_11/2, ²H_11/2 → ⁴I_15/2, ⁴S_3/2 → ⁴I_15/2, ⁴F_9/2 → ⁴I_15/2 and ⁴S_3/2 → ⁴I_13/2 transition, respectively. Increasing Er³⁺ concentration leads to a rapid growth in the intensity of red emission relative to that for the green emission. An explanation for this observation has been suggested. The temperature dependence profile for the two thermally coupled levels (²H_11/2, ⁴S_3/2) shows that they can be used for measuring the temperature.     

Upconversion luminescence in Ho3+/Yb3+- and Tb3+/Yb3+-codoped fluorogermanate glass and glass ceramic

Energy-transfer excited upconversion luminescence in Ho³⁺/Yb³⁺- and Tb³⁺/Yb³⁺-codoped PbGeO₃–PbF₂–CdF₂ glass and glass–ceramic under infrared excitation is investigated. In Ho³⁺/Yb³⁺-codoped samples, green (545 nm), red (652 nm), and near-infrared (754 nm) upconversion emission corresponding to the ⁵S₂(⁵F₄) → ⁵I₈, ⁵F₅ → ⁵I₈, and ⁵S₂(⁵F₄) → ⁵I₇ transitions, respectively, was observed. Blue (490 nm) emission assigned to the ⁵F_2,3 → ⁵I₈ transition was also detected. In the Tb³⁺/Yb³⁺-codoped system, bright UV–visible emission around 384, 415, 438, 473–490, 545, 587, and 623 nm, identified as due to the ⁵D₃(⁵G₆) → ⁷F_J(J = 6, 5, 4) and ⁵D₄ → ⁷F_J(J = 6, 5, 4, 3) transitions, was measured. The comparison of the upconversion process in glass ceramic and its glassy precursor revealed that the former samples present much higher upconversion efficiencies. The dependence of the upconversion emission upon pump power, and doping contents was also examined. The results indicated that successive energy-transfer between ytterbium and holmium ions and cooperative energy-transfer between ytterbium and terbium ions followed by excited-state absorption are the dominant upconversion excitation mechanisms herein involved. The viability of using the samples for three-dimensional solid-state color displays is also discussed.     

Effect of OH-content on thermal and chemical properties of SnOP2O5 glasses

Glasses with 55–60 mol% SnO and 40–45 mol% P₂O₅ have shown extremely large differences in the chemical and thermal properties depending on the temperature at which they were melted. Glasses prepared at low melting temperature, 450–550 °C, had low T_g, 150–200 °C, and low chemical stability. Glasses prepared at high melting temperature, 800–1200 °C, had much higher T_g, 250–300 °C, and much higher chemical stability. No significant differences were found by ¹¹⁹Sn Mössbauer and ³¹P Nuclear Magnetic Resonance spectroscopy. Large differences in the OH-content could be detected as the reason by infrared absorption spectroscopy, thermal analyses, and ¹H Nuclear Magnetic Resonance spectroscopy. In samples with low T_g, a broad OH – vibration band around 3000 nm with an absorption intensity >20 cm^?1, bands at 2140 nm with intensity ～5 cm^?1, at 2038 nm with intensity ～2.7 cm^?1, and at 1564 nm with intensity ～0.4 cm^?1 were measured. These samples have shown a mass loss of 3–4 wt% by thermal gravimetric analyses under argon in the temperature range 400–1000 °C. No mass loss and only one broad OH-band with a maximum at 3150 nm and low absorption intensity <4 cm^?1 could be detected in samples melted at high temperature, 1000–1200 °C, which have much higher T_g, ～300 °C, and much higher chemical stability.     

Tm-doped aluminate glass fibers for S-band optical amplification

Thulium-doped fiber amplifiers (TDFAs) have been proposed as practical devices for the amplification of light signals in the so-called S-band (1460–1530 nm) of the transparency window of standard telecommunications fiber. As the quantum efficiency of the desired ³H₄ → ³F₄ luminescence of Tm³⁺ is adversely affected by non-radiative decay when high maximum phonon energy (MPE) host glasses are used, a practical TDFA requires an active fiber made from a glass with intermediate to low MPE. We have explored the possibility of using aluminate fibers for this application, as bulk samples of Tm-doped alkaline earth aluminate glass are characterized by a MPE of 780 cm⁻¹ and a quantum efficiency for the 1460 nm fluorescence of ∼35%. Despite the high devitrification tendency of aluminate glass, pure aluminate core fibers with minimum losses of ∼0.5 dB/m have been successfully fabricated by the rod-in-tube technique using viscosity- and expansion-matched alkaline earth aluminosilicate cladding glasses.     

Judd–Ofelt analysis of Nd3+ ions in poly(styrene sulfonate) films

In this work, we present the synthetic route and the optical characterization of poly(styrene sulfonate) (PSS) films doped with Neodymium ions (Nd³⁺). In the synthesis optimization we obtained the maximum incorporation of Nd³⁺ in the matrix about 14.0%. The UV–Vis–NIR curve presents an intense characteristic electronic transition ⁴I_9/2 → ⁴F_5/2 + ²H_9/2 at 800 nm. It was also shown the radiative transition ⁴F_3/2 → ⁴I_11/2 at about 1060 nm. Judd–Ofelt theory was used in order to obtain the near infrared Nd³⁺ radiative transition rate, emission cross-section and radiative lifetime.     

Intense luminescence of amorphous Eu2O3 prepared by aqueous sol–gel method

Amorphous Eu₂O₃ was prepared by an aqueous sol–gel method. Emission due to the ⁵D₀ → ⁷F_J (J = 0, 1, 2) transitions of Eu³⁺ ions were observed. The dominant transition was the ⁵D₀ → ⁷F₂ red emission of Eu³⁺. The properties of the as-prepared samples were different with changes in the annealing temperature. To investigate the luminescence properties of the amorphous Eu₂O₃, the temperature-dependent photoluminescence (PL) spectra of samples annealed at 600 °C were measured in the temperature range 77–300 K. PL peak positions were unchanged with the change of temperature.     

Thulium environment in a silica doped optical fibre

Thulium-doped optical fibre amplifiers (TDFA) are developed to extend the optical telecommunication wavelength division multiplexing (WDM) bandwidth in the so-called S-band (1460–1530 nm). The radiative transition at 1.47 μm (³H₄ → ³F₄) competes with a non-radiative multi-phonon de-excitation (³H₄ → ³H₅). The quantum efficiency of the transition of interest is then highly affected by the phonon energy (E_p) of the material. For reliability reasons, oxide glasses are preferred but suffer from high phonon energy. In the case of silica glass, E_p is around 1100 cm^?1 and quantum efficiency is as low as 2%. To improve it, phonon energy in the thulium environment must be lowered. For that reason, aluminium is added and we explore three different core compositions: pure silica, and silica slightly modified with germanium or phosphorus. The role of aluminium is studied through fluorescence decay curves, fitted according to the continuous function decay analysis. From this analysis, modification of the thulium local environment due to aluminium is evidenced.     

Strong green emission from Er3+ in a fluorine containing (Pb,La)–tellurite glass without using up-conversion route

Absorption, emission, excitation spectra and the lifetime of the ⁴S_3/2 excited luminescent state of Er³⁺ ions in a fluorine containing (lead, lanthanum)–tellurite glass have been studied. The glass exhibits a strong green luminescence upon excitation through 380 nm (⁴I_15/2 → ⁴G_11/2) absorption band of its Er³⁺ ions. The spectrum consists of a strong green component in the wavelength range 534–553 nm due to luminescence transitions ²H_11/2 → ⁴I_15/2 and ⁴S_3/2 → ⁴I_15/2 and a very weak red component in the range 650–710 nm due to ⁴F_9/2 → ⁴I_15/2 transition. The Stark split components of the ⁴S_3/2 state are not very clear in the spectrum, but the biexponential luminescence decay of the ⁴S_3/2 state confirms the presence of the Stark levels. A rapid conversion of the upper Stark level to the lower level is also evident from the decay kinetics which helps greater number of ions to populate in the lower stark level of the ⁴S_3/2 state. Thus, the present study indicates that the glass may be a suitable candidate for use as a laser medium in making a solid state green laser by pumping the later by normal route.     

Enhanced 2.0 μm emission in oxyfluoride glass-ceramics containing nanocrystals MF2 (MF3): Ho3+,Tm3+ (M = Ca,Ba, and La)

Transparent glass-ceramics containing MF₂(MF₃):Ho³⁺,Tm³⁺ (M = Ca, Ba, and La) nanocrystals have been prepared by melt quenching and subsequent thermal treatment. X-ray diffraction and transmission electron microscopy analysis confirmed the precipitation of MF₂ (MF₃) nanocrystals among the glass matrix. Energy-dispersive X-ray spectroscopy results evidenced the incorporation of Tm³⁺ and Ho³⁺ into the MF₂ nanocrystals. Intense 2.0 μm emission originating from the Ho³⁺: ⁵I₇ → ⁵I₈ transition was achieved upon excitation with 808 nm laser diode. A large ratio of the forward Tm³⁺ → Ho³⁺ energy transfer constant to that of the backward process indicated high efficient energy transfer from Tm³⁺ (³F₄) to Ho³⁺ (⁵I₇), and benefited from the reduced ionic distances of Tm³⁺–Tm³⁺ and Tm³⁺–Ho³⁺ pairs and low phonon energy environment with the incorporation of rare earth ions into the precipitated MF₂ nanocrystals. The results indicate that oxyfluoride glass-ceramic is a promising candidate for 2.0 μm laser.     

Optical properties and infrared-to-visible upconversion in Er3+-doped GeO2–Bi2O3 and GeO2–PbO–Bi2O3 glasses

Luminescence properties and upconversion studies of germanate glasses in ternary GeO₂–PbO–Bi₂O₃ and binary GeO₂–Bi₂O₃ systems containing Er₂O₃ (0.1–1.0 wt%) are presented for the first time. The Judd-Ofelt parameters found for these glasses are: Ω₂ = 4.50 × 10⁻²⁰ cm², Ω₄ = 1.55 × 10⁻²⁰ cm² and Ω₆ = 0.69 × 10⁻²⁰ cm² for binary glasses and Ω₂ = 4.44 × 10⁻²⁰ cm², Ω₄ = 1.82 × 10⁻²⁰ cm² and Ω₆ = 0.39 × 10⁻²⁰ cm² for ternary glasses. The refractive index of these glasses is found to be ∼2. The transition ⁴I_13/2 → ⁴I_15/2 is peaked at ∼1.53 μm and shows a radiative lifetime around 5 ms. Both systems exhibit similar emission cross-section at 1.53 μm around 0.8 × 10⁻²⁰ cm². Upconverted green emission at ∼530 nm (²H_11/2 → ⁴I_15/2) and ∼550 nm (⁴S_3/2 → ⁴I_15/2) and red emission at ∼668 nm (⁴F_9/2 → ⁴I_15/2) are observed under 980 nm cw excitation. Our results suggest that these glasses are promising candidates for applications in photonics.     

Preparation and characterization of telluride glasses

Chalcogenide bulk glasses Ge₂₀Se_80?xTe_x for x ∈ (0, 10) have been prepared by systematic replacement of Se by Te. Selected glasses have been doped with Er and Pr, and all systems have been characterized by transmission spectroscopy, measurements of dc electrical conductivity and low-temperature photoluminescence. Absorption coefficient has been derived from measured transmittance and estimated reflectance. Both absorption and low-temperature photoluminescence spectra reveal shifts of absorption edge and/or dominant luminescence band to longer wavelength due to Te → Se substitution. Arrhenius plots of dc electrical conductivity, in the temperature range 300–450 K, are characterized by activation energies roughly equal to the half of the optical gap. Arrhenius plots for temperatures below 300 K yield much lower activation energies. The dominant low-temperature luminescence band centered at about half the band gap energy starts to quench above 200 K and a new band appears at 900 nm. The band at 900 nm, due to band to band transitions, overwhelms the spectra at room temperature. Systems doped with Er exhibit a strong luminescence due to ⁴I_13/2 → I_15/2 transition of Er³⁺ ion at 1539 nm, and Pr doped samples exhibit a relatively weak luminescence peak at 1590 nm, which we tentatively assign to ³F₃ → ³H₄ transition of Pr³⁺ ion.     

Compositional trends in low-temperature photoluminescence of heavily Er-doped GeS2–Ga2S3 glasses

The influence of temperature and glass composition on the photoluminescence (PL) efficiency of Er³⁺ ions embedded in (GeS₂)_100?x(Ga₂S₃)_x (x = 20, 25 and 33 mol%) glasses has been studied. The typical 4f–4f emission bands of Er³⁺ ions at around 830, 1000 and 1550 nm have been observed in the whole investigated temperature range from 300 K down to 10 K for all the compositions. New 4f–4f luminescence bands, in excess of the three basic ones, have been observed at 670, 870, 1120, 1260 and 1350 nm for (GeS₂)₇₅(Ga₂S₃)₂₅ glass composition, and are tentatively assigned to ²H_9/2 → ⁴I_11/2, ⁴G_11/2 → ⁴F_9/2, ²H_11/2 → ⁴I_11/2, ⁴F_7/2 → ⁴I_9/2 and ⁴F_3/2 → ⁴I_9/2 transitions, respectively. Thus a considerable influence of GeGaS host composition on the efficiency of 4f–4f transitions of embedded Er³⁺ ions is documented with the outcome that (GeS₂)₇₅Ga₂S₃)₂₅ composition appears near optimal for the emission efficiency of Er³⁺ ions. With decreasing temperature the PL efficiency is enhanced considerably with pronounced narrowing of all bands. In the case of the strongest PL band at ~ 1550 nm, corresponding to ⁴I_13/2 → ⁴I_15/2 transition, the narrowing at low temperature is further accompanied by the resolution of well pronounced fine structure due to “crystal field” splitting of corresponding electronic terms. The relationship between the photoluminescence and reflectance spectra as a function of Er content has been discussed.