Lead−barium fluoroborate glass ceramics doped with Nd<Superscript>3+</Superscript> or Er<Superscript>3+</Superscript>

Lead?barium fluoroborate glasses in the PbF₂–BaF₂–B₂O₃, PbF₂–BaO–B₂O₃, and PbO_– BaF₂–B₂O₃ systems doped with rare-earth ions (Nd³⁺ or Er³⁺) are synthesized and studied. It is shown that, based on these glasses, it is possible to produce transparent glass ceramics with fluoride crystalline phases, including ceramics with one crystalline phase of the fluorite structure. The spectral and luminescent properties of the doped glasses, glass ceramics, and polycrystalline complex fluorides containing Pb, Ba, and rare ions are studied.     

Gain characteristics of 980 nm-pumped Er<Superscript>3+</Superscript>–Tm<Superscript>3+</Superscript>–Pr<Superscript>3+</Superscript>-co-doped fiber

We present a numerical model of Er³⁺–Tm³⁺–Pr³⁺-co-doped fiber amplifier pumped with 980 nm laser for the first time, to the best of our knowledge. The rate and power propagation equations are solved numerically to analyze the effects of the pump power and active ion concentrations on the gains at 1310, 1470, 1530, 1600, 1650 nm windows. The results show that with pump power of 200 mW and when Pr³⁺, Tm³⁺, Er³⁺ concentrations are around 2.0×10²⁴, 3.0×10²⁴, 1.5×10²⁴ (ions/m³), respectively, the signals at 1470, 1530, 1600 nm may be nearly equally amplified with gain of 11–12.0 dB in the active fiber with length of 11.0 m, and the signals at 1310, 1470 and 1600 nm windows may be nearly equally amplified with gain of 12.0 dB in the active gain medium with length of 15.0 m. With pump power of 300 mW, the signals at 1470, 1530, 1600 nm may be nearly equally amplified with a gain of 16.0 dB in the active medium with a length of 15.0 m.     

Cooperative downconversion and near-infrared luminescence of Tb<Superscript>3+</Superscript>–Yb<Superscript>3+</Superscript> codoped lanthanum borogermanate glasses

In the present paper, we investigate the near-infrared (NIR) luminescence of Tb³⁺–Yb³⁺ codoped lanthanum borogermanate (LBG) glasses under visible and ultraviolet light excitation. The results indicate that NIR quantum cutting occurs through cooperative energy transfer from Tb³⁺ to Yb³⁺ ions when only 4f ⁸ levels of Tb³⁺ ions are excited in the wavelength region of 300–490 nm. The highest quantum efficiency under the excitation ⁵ D ₄ level of Tb³⁺ at 484 nm is 146%. Ultraviolet excitation that populates the charge transfer band (CTB) of Yb³⁺ near 270 nm does not result in quantum cutting as the fast nonradiative decay from CTB to ² F _5/2 level dominates. These materials are expected to be used as a converting layer for silicon solar cells to enhance their efficiency by splitting each high-energy photon into two NIR photons.     

Pulse generation at 1.5-μm wavelength in new EAT14 glasses doped with Er<Superscript>3+</Superscript> and Yb<Superscript>3+</Superscript> ions

The paper describes investigation of pulse laser generation in newly developed EAT14 glasses with the use of MALO saturable absorber. Different initial transmission of the saturable absorbers and different transmission of the output coupler were investigated. The laser generation was carried out using 976-nm pump wavelength. Comparison of peak powers, slop efficiencies and thresholds was made with a view to choose the best set of glass and saturable absorber for “eye-safe” microchip laser range-finder. The generated wavelengths by each sample were measured.     

Visualization of 2-μm radiation by BiF<Subscript>3</Subscript>:Ho<Superscript>3+</Superscript> and BiF<Subscript>3</Subscript>:Ho<Superscript>3+</Superscript>/Yb<Superscript>3+</Superscript> ceramics

A series of ceramic samples of the compositions BiF₃:1%Ho³⁺, BiF₃:4%Ho³⁺, BiF₃:1%Ho³⁺ + 1%Yb³⁺, and BiF₃:1%Ho³⁺ + 3%Yb³⁺ is synthesized and the conversion of Tm:YLF laser radiation (λ = 1908 nm) is studied. The luminescence spectra exhibit bands in the regions of 490, 545, and 650 nm. The kinetic measurements of the afterglow of the green and red bands show that the population of the ⁵S₂ and ⁵F₄ states in the BiF₃:1%Ho³⁺ samples occurs due to successive absorption of excitation photons, while the ⁵F₅ level of Ho³⁺ is populated due to the ion–ion interaction. Codoping with Yb³⁺ leads to a decrease in the visualization threshold power density to 2 W/cm².     

Visible upconversion and infrared luminescence investigations of Al<Subscript>2</Subscript>O<Subscript>3</Subscript> powders doped with Er<Superscript>3+</Superscript>, Yb<Superscript>3+</Superscript> and Zn<Superscript>2+</Superscript> ions

Alumina (Al₂O₃) powders doped with Er³⁺, Yb³⁺ and Zn²⁺ ions have been prepared by a low-temperature combustion synthesis technique. The phase purity and crystalline structure of the combustion products are confirmed by powder X-ray diffraction. An efficient frequency upconversion in the visible region and the emission in the infrared (IR) region respectively corresponding to the ²H_11/2, ⁴S_3/2→⁴I_15/2, ⁴F_9/2→⁴I_15/2 and ⁴I_13/2→⁴I_15/2 transitions upon direct excitation with a CW laser lasing at ∼980 nm are discussed. The enhancement observed in the intensity of the upconversion emission bands in the visible region and the emission band in the IR region due to the presence of Yb³⁺ and Zn²⁺ in Er³⁺:Al₂O₃ powders is reported and explained in detail.     

Blue upconversion emission from Tm<Superscript>3+</Superscript> sensitized by Nd<Superscript>3+</Superscript> in aluminum oxide crystalline ceramic powders

Upconversion (UC) emission in thulium (Tm³⁺) and neodymium (Nd³⁺) co-doped aluminum oxide ceramic powders prepared by combustion synthesis was investigated at room temperature using a continuous wave laser operating at 800 nm. Our sample containing Tm³⁺ (1 wt.%) did not show any UC emission but our sample co-doped with Tm³⁺ and Nd³⁺ in 1:2 wt.% proportion presented blue (∼480 nm) UC intensity more than one order of magnitude larger than our sample co-doped with Tm³⁺ and Nd³⁺ in 1:1 wt.% proportion. X-ray diffraction data showed the presence of α-Al₂O₃ and REAlO₃ (RE=Tm or Nd) crystalline phases in co-doped powders, while the singly doped powder has only α-Al₂O₃ phase. Our results show that the UC emission efficiency of Tm³⁺ and the host crystalline structure can be tailored by manipulating the Nd³⁺ doping concentration.     

LiNbO<Subscript>3</Subscript>–Yb<Superscript>3+</Superscript> crystal as a material for optical temperature sensor

The method of optical determination of temperature based on cooperative luminescence in the LiNbO₃ crystals doped with rare earth ions is proposed. As a temperature-dependent measurable characteristic, the quantum yield of luminescence is considered taking into account the processes of nonradiative redistribution of the electron excitation energy in the impurity subsystem. It is shown that the LiNbO₃–Yb³⁺ crystals can be used as a material for optical temperature sensors in the temperature range of 200–500 K with the average sensitivity of 0.12%K^–1.     

Er<Superscript>3+</Superscript> as glass structure modifier of Ga–Ge–S chalcogenide system

Er³⁺ clustering phenomenon in Ga–Ge–S chalcogenide system is studied using Raman spectroscopy. The Raman spectra from 10 to 500 cm⁻¹ for glasses (100−y)[15Ga₂S₃–85GeS₂]–yEr₂S₃ (y=0.08−5.00 mol. %) have been analyzed. To reveal the influence of the chemical composition on the glass structure the intensity of the peak corresponding to Ge–Ge (Ga–Ga) homopolar bonds has been examined. The peak intensity increase with Er₂S₃ concentration change in the region 0<C(Er₂S₃)<2 mol. % has been interpreted in terms of the sulphur deficiency in the glass resulting in the formation of S₃Ge–GeS₃ (S₃Ga-GaS₃) structural units. The further increase in concentration beyond 2 mol. % reduces the sulphur deficiency, which can be attributed to the formation of the ternary compound Er₃GaS₆. The structural units Er₃GaS₆ contain a large mol. fraction of Er³⁺ or, in other words, Er³⁺ clusters. The data obtained from the low-frequency Raman spectra (boson band) indicate strong variations of the medium-range order (MRO) in the glasses induced by Er³⁺. The observed behavior of the MRO size (the correlation length) with increasing of Er₂S₃ concentration provides for additional evidence of the Er³⁺ clustering.     

Frequency upconversion properties of Ag: TeO<Subscript>2</Subscript>–ZnO nanocomposites codoped with Yb<Superscript>3+</Superscript> and Tm<Superscript>3+</Superscript> ions

Yb³⁺–Tm³⁺ codoped tellurite glasses containing silver nanoparticles (NPs) were synthesized and characterized using transmission electron microscopy and optical techniques. The samples’ composition and the nucleation of NPs were investigated using electron diffraction and energy dispersive spectroscopy. For the optical experiments, the samples were excited using a diode laser operating at 980 nm, in resonance with the Yb³⁺ transition ²F_7/2→²F_5/2. Photoluminescence (PL) bands corresponding to Tm³⁺ transitions were observed at 480, 650, and 800 nm due to the Yb³⁺→ Tm³⁺ energy transfer. PL enhancement was achieved by heat-treatment of the samples at 325°C during different time intervals. The growth of the PL bands correlates with the increase of the silver NPs concentration. The relevant mechanisms contributing for the PL characteristics are discussed.     

Anti-Stokes Luminescence in LiYF<Subscript>4</Subscript>:Ho<Superscript>3+</Superscript>, Yb<Superscript>3+</Superscript> Ceramics Excited at 1.93 μm

Conversion of IR radiation of a Tm:YAP laser with a wavelength of 1930 nm into visible light by ceramics of composition LiY_(1–x–y) Ho _x Yb _y , where х = 1–5 mol % and y = 0–15 mol %, is demonstrated. It is shown that the threshold power density of IR light visualization decreases with increasing concentration of Ho³⁺ ions, while additional doping of ceramic samples with Yb³⁺ ions changes the anti-Stokes luminescence spectrum. The threshold power density of visualization of the Tm:YAP laser radiation decreases with increasing concentration of holmium ions and is I_thr ≈ 0.8 W cm^–2 in the samples of composition LiYF₄:5%Ho³⁺–15%Yb³⁺.     

Luminescence properties of Nd<Superscript>3+</Superscript>-doped Y<Subscript>2</Subscript>O<Subscript>3</Subscript> nanoparticles in organic media

Nd³⁺-doped yttrium oxide nanoparticles (Y₂O₃:Nd) with cubic phase were obtained successfully by a glycine-nitrate solution combustion method. The results of Fourier transform infrared spectra (FTIR) showed that the –OH groups residing on the nanoparticles surfaces were reduced effectively by modifying with capping agent. The modified Y₂O₃:Nd nanoparticles displayed good monodispersity and excellent luminescence in N,N-dimethylformamide (DMF) solvent. Some optical parameters were calculated by Judd–Ofelt analysis based on absorption and fluorescence spectra. A relative large stimulated emission cross section, 1.7×10⁻²⁰ cm², of the ⁴F_3/2→⁴I_11/2 transition was calculated. Theses results show that the modified Y₂O₃:Nd nanoparticles display good luminescence behavior in organic media.     

Enhancing up conversion luminescence effect of β-NaYF<Subscript>4</Subscript>: Yb<Superscript>3+</Superscript> and Tm<Superscript>3+</Superscript> by Li<Superscript>+</Superscript> ion doped approach

Up-conversion (UC) is a photoluminescence process which converts few low energy photons to a higher energy photon. This process has more potential usages in many different fields like bioimaging, solar spectrum tuning, and security encoding. Nowadays, researches about UC mostly focusing on biomedical signory and synthesis of nanoparticles. The synthesis of NaYF₄ nanoparticles executed under series of pH value condition results in different morphology and photoluminescence effect. Samples in low pH value created better consequent and quality than the specimen which had higher pH value. In addition, we observed NaYF₄ samples of doping Li⁺, realizing that the action of distorting in the local symmetry around rare-earth ions is caused by Li⁺ doping. The NaYF₄ microparticles which doped higher concentration of Li⁺ has strong fluorescence properties and intensities compared with their corresponding group of Li⁺-free, the blue emission 479 nm luminescence intensities and 454 nm luminescence intensities in NaYF₄:Yb³⁺, Tm³⁺ microparticles doped 20 mol% Li⁺ are enhanced 3 and 8 times, separately. And violet emission luminescence intensities around 345 and 360 nm are about 10 and 7 times, respectively. The result indicated that the improved UC luminescence of NaYF₄:Yb³⁺. Tm³⁺ microparticles with Li⁺ doping have potentially applications.     

110 W ceramic Nd<Superscript>3+</Superscript> : Y<Subscript>3</Subscript>Al<Subscript>5</Subscript>O<Subscript>12</Subscript> laser

A high-power, continuous-wave 0.6% Nd³⁺-doped ceramic Y₃Al₅O₁₂ (Nd:YAG) laser has been developed. 110 W laser output at 1064 nm was obtained, with a slope efficiency of about 41%. The M² factor was found to be around 6. The laser performance of the ceramic laser material was found to compare favorably with that obtained with single crystal Nd:YAG. PACS 42.55.-f; 42.55.Xi; 42.70.Hj     

Sensitivity of laser-induced upconversion fluorescence dynamics to exciting wavelength in Er<Superscript>3+</Superscript>-doped YAG

A novel sensitivity of laser-induced upconversion (UC) fluorescence dynamics to the exciting wavelength in Er³⁺:YAG crystal has been observed. The sensitivities to exciting wavelength variations are only 0.02 and 0.06 nm for ² G _9/2 and ² P _3/2 UC luminescence, respectively. The observation of this sensitivity reveals that when a certain level is populated by more than one UC mechanisms, a precise determination of suitable exciting wavelength is crucial because the competition between different UC mechanisms has a sensitive variation with exciting wavelength in near-resonant range.     

Photoluminescence of sol–gel-derived Y<Subscript>2</Subscript>O<Subscript>3</Subscript>:Eu<Superscript>3+</Superscript> thin-film phosphors with Mg<Superscript>2+</Superscript> and Al<Superscript>3+</Superscript> co-doping

Red-light-emitting Y₂O₃:Eu³⁺ thin-film phosphors were synthesized using a sol–gel process. The effect of Mg²⁺ and Al³⁺ co-dopants on the Y₂O₃:Eu³⁺ thin-film phosphor photoluminescence (PL) property was investigated. At a certain concentration, both Mg²⁺ and Al³⁺ co-dopants were found to further enhance the PL emission intensity of Y₂O₃:Eu³⁺ thin-film phosphors. The optimum PL emission intensity was observed in Y₂O₃:12%Eu³⁺, 7%Mg²⁺ and Y₂O₃:12%Eu³⁺, 2%Al³⁺ phosphor films. From our results, the enhancement of the emission intensity by the Mg²⁺ and Al³⁺ co-dopants is explained in terms of the creation of defect states near the Y(4d+5s) conduction band, which overlap with the Eu³⁺ charge-transfer state (CTS). The overlapping leads to CTS broadening and consequently induces higher absorption and hence an increase of the emission intensity. From X-ray diffraction results, we have found that there is no additional phase formed in the co-doped phosphor films. PACS 68.55.Ln; 78.55.-m; 81.20.Fw     

Mechanism of the Yb<Superscript>2+</Superscript> → Yb<Superscript>3+</Superscript> valence transition in ytterbium nanofilms upon chemisorption of CO and O<Subscript>2</Subscript> molecules on their surface

The dependences of the work function of ytterbium nanofilms with a thickness ranging from 1 to 32 monolayers on the amount of CO or O₂ molecules chemisorbed on their surface have been investigated experimentally. It has been found that these dependences have a pronounced nonmonotonic character. The mechanism of the Yb²⁺ → Yb³⁺ valence transition, which occurs upon the chemisorption of CO or O₂ molecules on the surface of ytterbium nanofilms, has been developed using the results of this study together with the previously obtained data.     

Visible up-conversion and NIR luminescence studies of LiAl<Subscript>5</Subscript>O<Subscript>8</Subscript>:Er phosphor co-doped with Yb<Superscript>3+</Superscript> and Zn<Superscript>2+</Superscript>

The frequency up-conversion, an efficient laser emission and amplification in Er³⁺:LiAl₅O₈ phosphors co-doped with Yb³⁺ and Zn²⁺ phosphor powders in the 520–560, 640–680 nm regions and at ∼1.5 μm, respectively, have been reported. The emission corresponds to the ²H_11/2, ⁴S_3/2→⁴I_15/2, ⁴F_9/2→⁴I_15/2 and ⁴I_13/2→⁴I_15/2 transitions upon direct excitation into the intermediated ⁴I_11/2 level using ∼980 nm radiation from a CW laser. Possible mechanisms involved for the up-conversion processes based on the energy level matching scheme, the pump-power dependence and the dynamical behaviour have been discussed. The effect of the addition of Yb³⁺ and Zn²⁺ for the amplification in the 1.5 μm eye-safe telecommunication window has been elaborated and characterized in detail.     

Ionoluminescence of Eu<Superscript>2+</Superscript>–Eu<Superscript>3+</Superscript> clusters in NaF: Eu single crystals

The radiation-impurity modification of NaF: Eu crystals results in the formation of optically active planar heterostructures with a complex set of luminescence centers, including, in particular, clusters of the Eu²⁺–Eu³⁺ type. The luminescence spectra of Eu²⁺–Eu³⁺ centers exhibit bands at wavelengths of 409 and 442 nm, which are associated with Eu²⁺ ions in nonequivalent crystallographic positions, and a band at a wavelength of 610 nm, which is attributed to Eu³⁺ ions. The luminescence spectra of irradiated NaF: Eu samples contain a broad band with a maximum at 506 nm due to the presence of F₂ + F ₊ ³ color centers in the crystal.