Upconversion fluorescence in Sm3+-doped zinc phosphate glassy matrix

The mechanism governing the upconversion fluorescence from the ⁴G_5/2 level of Sm³⁺ ion has been investigated in zinc phosphate glass matrices under infrared (1.06?µm) laser excitation. This visible emission is centred at 590?nm and corresponds to the ⁴G_5/2?→?⁶H_7/2 transition. The dependence of the integrated intensity on the excitation power confirms that this emission is due to the three-photon absorption process and is in agreement with the existing theory. The intensity of the upconversion fluorescence has a cubic dependence on the excitation power. An absolute upconversion efficiency of about 10^?7 was obtained for the sample doped with 0.5?wt% Sm³⁺ ions. A quantitative estimate of the number of photons leaving the sample was also determined.     

Infrared spectroscopic characterization of Na5Lu9F32 single crystals doped with various Er3+ concentrations

This work reports on optical spectra of Na₅Lu₉F₃₂ single crystals doped with various Er³⁺ concentrations from 0.5 to 5 mol%. In our improved Bridgman method, the X-ray powder diffractions were investigated and optical parameters were also calculated by the Judd–Ofelt theory. Results showed that Er³⁺ ions entered the Lu³⁺ sites successfully without causing any obvious peak changes, and the doping concentration of Er³⁺ had important influence on the Er³⁺ local structure in Na₅Lu₉F₃₂ crystals. The maximum emission intensities of ~1.5 and ~2.7 μm were obtained in present research when the doping concentration of Er³⁺ were 4 and 5 mol%, respectively, under the excitation of 980 nm LD. In these doping concentration, the maximum emission cross-sections were calculated to be 1.37 × 10^?20 cm² (~1.5 μm) and 2.1 × 10^?20 cm² (~2.7 μm). The gain cross-section at 2.7 μm was also estimated according to the absorption and emission cross section spectra. All these spectroscopic characterizations suggested that this fluoride crystal would possess promising applications in infrared lasers.     

Hydrothermal synthesis and luminescence of MWO4:Tb3+ (M = Ca,Sr, Ba) microsphere phosphors

Spherical MWO₄:Tb³⁺ (M = Ca, Sr, Ba) particles were synthesized by a hydrothermal route at 180 °C for 10 h. The synthesized MWO₄:Tb³⁺ particles were characterized by X-ray powder diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and luminescence spectroscopy. The XRD and FT-IR results show that MWO₄:Tb³⁺ particles with a scheelite-type crystal structure were synthesized successfully. The SEM and TEM results show that uniform spherical particles in the range of hundreds of nanometers were obtained. The possible growth mechanism may be attributed to a typical Ostwald ripening process. The excitation spectra of MWO₄:Tb³⁺ phosphors show a strong absorption band of the WO₄ ^2? group and some weak absorption bands of Tb³⁺ ions. The emission spectra of MWO₄:Tb³⁺ phosphors show the characteristic emission bands of Tb³⁺ ions. CaWO₄:Tb³⁺ sample has the highest excitation and emission intensity.     

Peculiar feature of KCl + SbCl3 phosphors: PL and XRD studies

Photoluminescence of antimony-activated potassium chloride prepared by a mechanical grinding method has been reported. The non-coincidence of the excitation and diffuse absorption band has been found as a result of the peculiar nature of the mixed phosphor, which suggests the different nature of the luminescent centers present in the phosphor. This difference in the nature of the diffuse absorption spectra and excitation spectra has been attributed to the Sb³⁺ and Sb⁵⁺ ions in the KCl+SbCl₃ host lattice. Photoluminescence intensity has been strongly enhanced by reducing the temperature to the liquid nitrogen temperature. The powder diffraction pattern obtained from the XRD analysis shows the presence of complexes over the surface.     

Characterization of <Superscript>4</Superscript>I<Subscript>9/2</Subscript> ↔ <Superscript>4</Superscript>F<Subscript>3/2</Subscript> optical transitions in trivalent Nd<Superscript>3+</Superscript> ions in GaLaS glass

The positions of Stark levels have been determined, using a step-by-step procedure, in the ⁴I_9/2 and ⁴F_3/2 manifolds of Nd³⁺ ions from absorption and photoluminescence measurements in the 12–293 K temperature range. This data has been used to calculate the emission cross-section for which the maximum value turns out to be ～2.3 × 10^?20 cm². The radiative recombination time, calculated using Judd–Ofelt analysis, of the ⁴F_3/2 manifold is in close vicinity to the experimentally determined times that were measured by the conventional decay of PL after interruption of excitation and by QFRS. Moreover, the peak time defined by QFRS is independent of temperature. Therefore, the dominant relaxation mechanism from the ⁴F_3/2 excited manifold of Nd³⁺ ions in GaLaS glass is believed to be by radiative emission.     

Photoluminescence of terbium nitrate hexahydrate incorporated into pores of opal photonic crystals

We have measured photoluminescence (PL) and broadband reflection spectra of the surface of an opal photonic crystal (OPC) filled with terbium nitrate hexahydrate (TNH). The excitation sources used were a halogen lamp, lasers with emission wavelengths of 266 and 337 nm, and semiconductor light-emitting diodes (369 and 385 nm). It has been shown that resonance excitation of the TNH (Tb(NO₃)₃ · 6H₂O) filled OPC by pulsed laser light at a wavelength of 266 nm gives rise to superluminescence: an increase in the relative intensity of the 545-nm PL band, corresponding to the Tb^{3+ 5} D ₄–⁷ F ₅ transition. The efficiency of pumping the upper laser level of the OPC increases due to the increase in the density of photon states (Purcell effect) near the bandgap edge in the OPC. The lack of clear superluminescence under excitation by the other excitation sources is related to specific features of the absorption of incident light by the rare-earth ion and to the low output power of the cw light sources.     

Yellow to violet upconversion processes of Nd3+ in neat Cs2NaNdCl6 elpasolite

Yellow to violet upconversion of Nd³⁺ in neat Cs₂NaNdCl₆ elpasolite is demonstrated in this paper. Three intense bands have been observed at 367, 390 and 422 nm originating from ⁴D_3/2 multiplet upon the excitation of 595.5 nm, which is in resonance with the energy of ⁴G_5/2 level of Nd³⁺. The mechanism of the upconversion has been investigated through upconversion emission intensity dependence on the power of the pumping light and luminescence decay. It is found out that the upconversion is a two-photon process. The ground state absorption (GSA)/energy transfer upconversion (ETU) is responsible for the upconversion with comparison of the excitation spectrum and the one-photon absorption spectrum.     

Photoluminescence of Ti3+ in P2O5-Na2O-Al2O3 glass

The optical properties (absorption and luminescence) of Ti³⁺ in a P₂O₅ Na₂O-Al₂O₃ glass have been studied in the temperature range 12 to 300 K. A very broad infrared emission band at 860 nm, has been observed for the first time in an inorganic glass, when excitation is performed in the Ti³⁺ absorption band (T_2g → E_g transition in cubic field approximation). The spectroscopic characteristics of this system are compared with those of the Ti³⁺ as a dopant in AL₂O₃ single crystals.     

Spectroscopic properties of the Ce-doped borate glasses

The EPR, optical absorption and photoluminescence (emission and excitation) spectra as well as decay kinetics of a series of the Ce-doped glasses with Li₂B₄O₇, LiKB₄O₇, CaB₄O₇, and LiCaBO₃ compositions have been investigated and analysed. The borate glasses were obtained from the corresponding polycrystalline compounds in the air atmosphere, using standard glass technology. The EPR signals of the isolated Ce³⁺ and pair Ce³⁺–Ce³⁺ centres, coupled by magnetic dipolar and exchange interactions were registered at liquid helium temperatures. The characteristic for glass host broad bands corresponding to the 4f → 5d transitions of the Ce³⁺centres have been observed in the optical absorption and photoluminescence (emission and excitation) spectra. The obtained luminescence decay curves can be satisfactory described by exponential function with lifetimes in the 19.8–26.1 ns range, which depend on the basic glass composition. The local structure of Ce³⁺ centres in the investigated glasses has been considered and discussed.     

Photo-luminescence characteristics of binary P2O5–CaO glass ceramic

ABSTRACT

To explore excellent colour display materials, the binary phosphate glass ceramics doped with R (R?=?Tm³⁺, Tb³⁺, Eu³⁺, Sm³⁺, and Mn²⁺) ions were prepared. The X-ray diffraction, transmission electron microscope, absorption, excitation, and emission spectra of the glass ceramics had been studied in detail. It was found that Ca₂P₂O₇ and CaP₂O₆ had excited in the glass ceramics, which can improve the luminescent characteristics of the materials. The results show that the binary phosphate glass ceramics can display abundant colours, which is very helpful for developing the luminescent materials for colour display.     

Hyperfine Structure of the 6P1/2

Abstract

The hyperfine splitting of the 6P_1/2–6P_3/2 fine structure transition in ²⁰⁷Pb⁺ ions at 710 nm has been measured by c.w. laser excitation and subsequent observation of the weak fluorescence radiation at the same wavelength. The ions were confined in an rf quadrupole trap and buffer gas cooled by collisions with He atoms at 10^?5 mbar pressure. From the observed level splitting and the simultaneously recorded transmision of a Fabry-Perot etalon we determined the hyperfine splitting constants A(6P_1/2) = 13·001(48) GHz and A(6P_3/2) = 0·589(23) GHz. From a small impurity of ²⁰⁸Pb of our isotopically enriched sample we determined the isotope shift of the transitions to Δv(207–208) = 252(40) MHz.     

Synthesis and luminescence properties of Eu3+ and Sm3+ doped and co-doped BiPO4 powders by a hydrothermal route

BiPO₄:Eu³⁺, BiPO₄:Sm³⁺, and BiPO₄:(Eu³⁺, Sm³⁺) powders were synthesized by a hydrothermal route. The X-ray diffraction and Fourier-transform infrared spectroscopy results show that the samples are pure hexagonal phases. The excitation spectrum of BiPO₄:Eu³⁺ sample shows the characteristic absorption peaks of Eu³⁺ corresponding to the direct excitation from the ground state to the higher excited states of the europium f-electrons. The excitation spectrum of BiPO₄:Sm³⁺ sample consists of several narrow excitation lines due to the characteristic f–f transition of Sm³⁺. The emission spectrum of BiPO₄:Eu³⁺ specimen excited by 395 nm consists of lines mainly locating in the red area. The emission spectrum of BiPO₄:Sm³⁺ sample is composed of four emission bands, which are attributed to transitions from ⁴G_5/2 excited state to ⁶H_J/2 (J = 5, 7, 9, and 11) ground states of Sm³⁺. The excitation and emission spectra of BiPO₄:(Eu³⁺, Sm³⁺) samples are different from single doped BiPO₄ samples. The introduction of Sm³⁺ can broaden and enhance the excitation intensity of Eu³⁺ and improve the emission dominance of Eu³⁺ at 617 nm.     

Combustion synthesis and photoluminescence study of UV emitting LaBaB<Subscript>9</Subscript>O<Subscript>16</Subscript> phosphors

The borate phosphor LaBaB₉O₁₆ doped with Ce³⁺ ion intentionally and successfully synthesized using solution combustion rout using metal nitrates as precursors and urea as fuel. The phosphors were characterized by X-ray diffraction (XRD), Scanning electron microscopy and photoluminescence spectroscopies. The XRD patterns of the phosphor confirmed the successful crystallization of LaBaB₉O₁₆. The average crystallite size calculated using the Debye Scherer equation. The PL excitation spectra of LaBaB₉O₁₆ exhibited broad spectra peaking at 275 nm. Upon excitation with ultraviolet (UV) radiation at 274 nm the phosphor exhibited a broad band UV emission peaking at a wavelength of 335 nm corresponding to the 4f⁰5d¹??4f¹ transition of the Ce³⁺ ion. Moreover the influence of concentration of Ce³⁺ ion on luminescence properties has also been studied. Optimum concentration of Ce³⁺ ions in the prepared phosphor was found to be 0.05 mol. For this concentration the critical distance R₀ was calculated to be 22.04 Å. Finally, the Stokes shift for the synthesized phosphor was calculated to be 6512 cm^??1 using corresponding excitation and emission.     

Synthesis and luminescent properties of Tb3+ activated AWO4 based (A = Ca and Sr) efficient green emitting phosphors

Optically efficient terbium activated alkaline earth metal tungstate nano phosphors (AWO₄ [A = Ca, Sr]) with different doping concentrations have been prepared by mechanochemically assisted solid state metathesis reaction at room temperature for the first time. The prepared phosphors were characterized by the X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscope (SEM), Fourier transform Raman (FT-Raman) spectroscopy, photoluminescence and diffuse reflectance spectroscopy measurements. The XRD and Raman spectra results showed that the prepared powders present a scheelite-type tetragonal structure. FTIR spectra exhibited a high absorption band situated at around 850 cm^?1, which was ascribed to the W–O antisymmetric stretching vibrations into the [WO₄]^2? tetrahedron groups and the SEM images reveal that the particle sizes were in the range of 20–60 nm. The excitation and the emission spectra were measured to characterize the luminescent properties of the phosphors. The excitation spectrum exhibits a charge transfer broad band along with some sharp peaks from the typical 4f–4f transitions of Tb³⁺. Under excitation of UV light, these AWO₄:xTb³⁺ (A = Ca, Sr) phosphors showed a strong emission band centered at 545 nm (green) which corresponds to ⁵ D ₄ → ⁷ F ₅ transition of Tb³⁺. Analysis of the emission spectra with different Tb³⁺ concentrations revealed that the optimum dopant concentration for CaWO₄:xTb³⁺ and SrWO₄:xTb³⁺ phosphors are about 8 and 6 mol% of Tb³⁺. The green emission intensity of the solid state meta-thesis prepared CaWO₄:0.08Tb³⁺ and SrWO₄:0.06Tb³⁺ phosphors are 1.5 and 1.2 times greater than that of the commercial LaPO₄:Ce, Tb green phosphor. All properties show that AWO₄:Tb³⁺ (A = Ca, Sr) is a very appropriate green-emitting phosphor for fluorescent lamp applications.     

Synthesis and characterizations of Dy3+ doped Sr3Al2O6:Eu2+ powder phosphors through citric acid precursor

Sr₃Al₂O₆:Eu²⁺, Dy³⁺ phosphors were synthesized by the polymer precursor method. The X-ray powder diffraction patterns show that the samples have a cubic structure with a space group of Pa3. In the excitation spectrum, the phosphors show a wide absorption in the UV region from 250 to 450 nm, which corresponds to the crystal field splitting of the Eu²⁺ d-orbital. All the emission spectrum of Sr₃Al₂O₆:Eu²⁺, Dy³⁺ phosphors show the broad band emission peaked at about 518 nm, which can be ascribed to the typical 4f⁶5d¹ → 4f⁷ transitions of Eu²⁺ ions. And the best dopant concentration of Dy³⁺ ions for Sr₃Al₂O₆:2 mol%Eu²⁺, xDy³⁺ phosphors is 2 mol%. The excitation wavelengths have no influences on emission peaks, but have clear influences on emission intensities.     

Fluorescent carbon dots with two absorption bands: luminescence mechanism and ion detection

Herein, we report the synthesis of carbon dots (CDs) with two characterized absorption bands but without excitation wavelength-dependent fluorescence via a one-step hydrothermal method. The structure of CDs was characterized using X-ray photoelectron spectroscopy, high-resolution transmission electron microscopy, Fourier transform infrared, and UV–Vis spectroscopy. The structure and photoluminescence of CDs vary significantly with different raw materials and preparation methods, and the mechanism of luminescence is not clear yet. Hence, we studied the luminescence mechanism behind two characterized absorption bands of CDs using fluorescence quenching method with ninhydrin and several ions as quenchers. The influence of the surface groups of CDs on its photoluminescence properties was also discussed. Ninhydrin and a variety of other ions exhibited different quenching effects on the fluorescence emissions which obtained at the two absorption bands of CDs. Combining with the structure characterization results, it can be concluded that the emission wavelength is mainly determined by the carbon core, while the excitation wavelength is determined by the surface nitrogen-containing groups. (The excitation at 234 nm might be due to the Schiff base structure, while the excitation at 345 nm was mainly due to the amide structure.) Furthermore, based on the interaction of NO₂^? with the surface nitrogen-containing groups of CDs, a quantitative detection method of NO₂^? using CDs was proposed in our study. CDs exhibited high selectivity for NO₂^? at pH 1.6 with good linearity to NO₂^? concentration in the range of 1–10 μM.     

Optical absorption and electron spin resonance studies of Cu2+ in Li2O-Na2O-B2O3-As2O3 glasses

The local structure around Cu²⁺ ion has been examined by means of electron spin resonance and optical absorption measurements in xLi₂O-(40-x)Na₂O-50B₂O₃-10As₂O₃ glasses. The site symmetry around Cu²⁺ ions is tetragonally distorted octahedral. The ground state of Cu²⁺ isd _x ²−y ².The glass exhibited broad absorption band near infrared region and small absorption band around 548 nm, which was assigned to the ²B_1g →²E_g transition.     

Visible quantum cutting in Tb<Superscript>3+</Superscript> doped BaGdF<Subscript>5</Subscript> phosphor for plasma display panel

Visible quantum cutting (QC) via down-conversion and enhancement in photoluminescence properties has been observed in terbium (Tb³⁺) doped BaGdF₅ phosphor. This phosphor was synthesized by varying molar concentration of Tb³⁺ ions via co-precipitation method. The prepared phosphor was characterized through X-ray diffraction technique. The photoluminescence spectra of BaGdF₅:Tb³⁺ phosphor measured under vacuum ultraviolet or UV excitation. The QC process was observed in prepared phosphor due to cross relaxation and direct energy transfer between Tb³⁺ and Tb³⁺ or Tb³⁺ and Gd³⁺ ions depending on the excitation wavelength. The maximum quantum efficiencies were found to be 162, 174 and 177 %, under the excitation of 172, 187 and 240 nm respectively. The green emission of 544 nm was observed at excitation of 172 and 187 nm. Hence this phosphor may be prime candidate for application in plasma display panels and mercury free fluorescent lamps.     

Facile hydrothermal crystallization of NaLn(WO4)2 (Ln=La-Lu,and Y), phase/morphology evolution,and photoluminescence

Abstract

Hydrothermal reaction of Ln nitrate and Na₂WO₄ at pH=8 and 200 °C for 24 hours, in the absence of any additive, has directly produced the scheelite-type sodium lanthanide tungstate of NaLn(WO₄)₂ for the larger Ln³⁺ of Ln=La-Dy (including Y, Group I) and an unknown compound that can be transformed into NaLn(WO₄)₂ by calcination at the low temperature of 600 °C for the smaller Ln³⁺ of Ln=Ho-Lu (Group II). With the successful synthesis of NaLn(WO₄)₂ for the full spectrum of Ln, the effects of lanthanide contraction on the structural features, crystal morphology, and IR responses of the compounds were clarified. The temperature- and time-course phase/morphology evolutions and the phase conversion upon calcination were thoroughly studied for the Group I and Group II compounds with Ln=La and Lu for example, respectively. Unknown intermediates were characterized by elemental analysis, IR absorption, thermogravimetry, and differential scanning calorimetry to better understand their chemical composition and coordination. The photoluminescence properties of NaEu(WO₄)₂ and NaTb(WO₄)₂, including excitation, emission, fluorescence decay, and quantum efficiency of luminescence, were also comparatively studied for the as-synthesized and calcination products.     

On the compositional,optical and electrical characteristics of vacuum‐deposited GaAs1‐xPx films prepared by a successive evaporatron method

Abstract

GaAs_1‐xP_x thin films have been deposited onto glass substrates at a rate of 50Å/min. in a vacuum of 5 x 10^‐5 Torr using a successive evaporation method. Thin films of various compositions (X = 0.3–0.9) were obtained at gallium source temperature T_Ga = 870°C, arsenic source temperature T_As = 275°C, phosphorus source temperature T_P = 330°‐363°C and substrate temperature T_sub = 265°‐330°C. Compositional, optical (absorption) and electrical properties of the films in a thickness range of 1300–1900 Å were determined by using an X‐ray diffractometer, a grating spectrometer and an electrometer respectively. The experimental results were compared with those for simultaneous evaporation and discussed from the atomistic viewpoints.

The values of △X/△T_sub are ‐ 7 x 10^‐3 and ‐1 x 10^‐3 °C^‐1 for successive and simultaneous evaporation respectively, the difference of which can be explained by the absorption effect of a predeposited Ga layer in successive evaporation. The value of △X/△Tp is about +7 x 10^‐3°C^‐1 for the two evaporation methods, however, it levels off more distinctly at higher substrate temperatures. Absorption edge shift and relatively low resistivity suggest that successively vacuum‐deposited films have much more phosphorus vacancies and/or impurities than simultaneously vacuum‐deposited and chemically vapor‐deposited films.