Tm3+/Tb3+/Mn2+ tri-doped phosphate glass ceramic for enhanced white-light-emitting material

For developing the white-light-emitting (WLE) material, we prepared Tm³⁺/Tb³⁺/Mn²⁺ tri-doped phosphate glass and glass ceramic samples. At 360 nm ultraviolet light excitation, the colors of the luminescence of the glass and glass ceramic samples are white. The CIE chromaticity coordinates (X = 0.324, Y = 0.335) of the emission from the glass ceramic are close to the standard white-light illumination (0.333, 0.333). The intensity of the fluorescence in the glass ceramic is approximately 20 times stronger than that in the glass.     

Preparation and photoluminescence properties of fluorosilicate glass ceramics containing CeOF: Dy nanocrystals

The Ce³⁺ and Dy³⁺ co-doped oxyfluoride glasses and glass ceramics containing CeOF or CeF₃ nanocrystals have been prepared in the reducing atmosphere. The crystallinity increased significantly with the Ce³⁺ concentration, while the crystal size of nanocrystals is mainly influenced by the annealing temperatures. The glasses and glass ceramics emitted white light, deriving from a combination of the Ce³⁺ blue and the Dy³⁺ yellow light. The emission intensity and CIE chromaticity coordinates of the Ce³⁺ and Dy³⁺ co-doped glasses can be tuned by adjusting the ratio of Ce³⁺/Dy³⁺ concentration or the annealing temperature.     

Cold white light generation through the simultaneous emission from Ce3+ and Tb3+ in sodium germanate glass

A spectroscopic investigation of sodium germanate glasses activated with Ce³⁺, Tb³⁺ and Ce³⁺/Tb³⁺ is carried out by analyzing their photoluminescence spectra and decay times. Non-radiative energy transfer from Ce³⁺ to Tb³⁺ is observed upon near-UV excitation at 310 nm (peak emission wavelength of AlGaN-based LEDs). The non-radiative nature of this energy transfer is inferred from the increase in the decay rate of the Ce³⁺ emission when the glass is co-doped with Tb³⁺. From an analysis of the Ce³⁺ emission decay time curve it is inferred that an electric dipole–quadrupole interaction might to be the dominant mechanism for the Tb³⁺ emission sensitized by Ce³⁺. Energy transfer from Ce³⁺ to Tb³⁺ leads to a simultaneous emission of these ions in the blue, green, yellow and red, resulting in white light with CIE1931 chromaticity coordinates, x = 0.30 and y = 0.32, which correspond to cold white light with a colour temperature of 7320 K and very small deviation from the Planckian black-body radiator locus (0.005).     

Spectroscopic properties of Eu3+/Nd3+ co-doped phosphate glasses and opaque glass–ceramics

This paper reports the fabrication and characterization of Eu³⁺/Nd³⁺ co-doped phosphate (PNE) glasses and glass–ceramics as a function of Eu³⁺ concentration. The precursor glasses were prepared by the conventional melt quenching technique and the opaque glass–ceramics were obtained by heating the precursor glasses at 450 °C for 30 h. The structural and optical properties of the glass and glass–ceramics were analyzed by means of X-ray diffraction, Raman spectroscopy, UV–VIS–IR absorption spectroscopy, photoluminescence spectra and lifetimes. The amorphous and crystalline structures of the precursor glass and opaque glass–ceramic were confirmed by X-ray diffraction respectively. The Raman spectra showed that the maximum phonon energy decreased from 1317 cm⁻¹ to 1277 cm⁻¹ with the thermal treatment. The luminescence spectra of the glass and glass–ceramic samples were studied under 396 nm and 806 nm excitation. The emission intensity of the bands observed in opaque glass–ceramic is stronger than that of the precursor glass. The luminescence spectra show strong dependence on the Eu³⁺ ion concentration in the Nd³⁺ ion photoluminescence (PL) intensity, which suggest the presence of energy transfer (ET) and cross-relaxation (CR) processes. The lifetimes of the ⁴F_3/2 state of Nd³⁺ ion in Eu³⁺/Nd³⁺ co-doped phosphate glasses and glass–ceramics under 806 nm excitation were measured. It was observed that the lifetimes of the ⁴F_3/2 level of Nd³⁺ of both glasses and glass–ceramics decrease with the increasing Eu³⁺ concentration. However in the case of opaque glass–ceramics the lifetimes decrease only 16%.     

Luminescence properties of Na3SrB5O10:Dy3+ plate-like microstructures for solid state lighting applications

A series of novel plate-like microstructure Na₃SrB₅O₁₀ doped with various Dy³⁺ ions concentration have been synthesized for the first time by solid-state reaction (SSR) method. X-ray diffraction (XRD) results demonstrated that the prepared Na₃SrB₅O₁₀:Dy³⁺ phosphors are single-phase pentaborates with triclinic structure. The plate-like morphology of the phosphor is examined by Field emission scanning electron microscopy (FE-SEM). The existence of both BO₃ and BO₄ groups in Na₃SrB₅O₁₀:Dy³⁺ phosphors are identified by Fourier transform infrared (FT-IR) spectroscopy. Upon excitation at 385 nm, the PL spectra mainly comprising of two broad bands: one is a blue light emission (∼486 nm) and another is a yellow light emission (∼581 nm), originating from the transitions of ⁴F_9/2 → ⁶H_15/2 and ⁴F_9/2 → ⁶H_13/2 in 4f⁹ configuration of Dy³⁺ ions, respectively and the optimized dopant concentration is determined to be 3 at.%. Interestingly, the yellow-to-blue (Y/B) emission integrated intensity ratio is close to unity (0.99) for 3 at.% Dy³⁺ ions, suggesting that the phosphors are favor for white illumination. Moreover, the calculated Commission International de l’Eclairage (CIE) chromaticity coordinates of Na₃SrB₅O₁₀:Dy³⁺ phosphors shows the values lie in white light region and the estimated CCT values are located in cool/day white light region.     

Photoluminescence and color tunability of γ-irradiated Tb3+–Sm3+-codoped oxyfluoride aluminoborate glasses

The main goal of this paper is to generate a warm white light through γ-irradiated Tb³⁺/Sm³⁺-codoped oxyfluoride aluminoborate glasses under 387 nm excitation xenon lamp. The transparent Tb³⁺/Sm³⁺-codoped oxyfluoride aluminoborate glass samples were prepared by melt-quenching technique. The energy transfer mechanism between Tb³⁺ and Sm³⁺ ions with an emphasis on the role of Al₂O₃/Al³⁺ is systematically studied before and after γ-irradiation. The characteristics of white light emission defined by chromaticity color coordinates and correlated color temperature are evaluated. In the present glass systems, the tuning of cold-to-warm white light as a function of Al₂O₃ and γ-irradiation is demonstrated.     

Enhanced luminescence in Er3+-doped chalcogenide glass–ceramics based on selenium

Rare earth doped glass–ceramics transparent in the infrared region up to 16 μm have been prepared and studied. The enhancement of the emission of Er³⁺ ions at 1.54 μm with increasing crystallinity was demonstrated in a selenium-based glass–ceramic having a composition of 80GeSe₂–20Ga₂Se₃ + 1000 ppm Er. The optical transmission, microstructure and luminescence properties of a base glass and glass–ceramics were investigated. Luminescence intensities up to 7 times greater were obtained in glass–ceramics in comparison to the base glass. These materials are promising candidates for the production of new laser sources in the mid-infrared region.     

Investigation on preparation and spectroscopic properties of Yb2+-doped silica-based glass prepared by the oxyhydrogen flame fusing process

In this paper, we report the preparation and spectroscopic properties of Yb²⁺-doped silica-based glass prepared by the solid state reaction using the oxyhydrogen flame fusing process. The glass exhibits broadband emission in the visible region due to a 5d–4f transition of the rare earth ions. The emission peak wavelength and bandwidth are especially 505 nm and 147 nm for Yb²⁺-doped silica-based glass at the room temperature. The color coordinate calculation shows that the Yb²⁺-doped silica-based glass has a better color coordinate (0.28, 0.37) in the white light region.     

Bifunction in Er3+/Yb3+ co-doped BaTi2O5–Gd2O3 glasses prepared by aerodynamic levitation method

Novel Er³⁺/Yb³⁺ co-doped BaTi₂O₅–Gd₂O₃ spherical glasses have been fabricated by aerodynamic levitation method. The thermal stability, upconversion luminescence, and magnetic properties of the present glass have been studied. The glasses show high thermal stability with 763.3 °C of the onset temperature of the glass transition. Red and green emissions centered at 671 nm, 548 nm and 535 nm are obtained at 980 nm excitation. The upconversion is based on a two-photon process by energy transfer, excited-state absorption, and energy back transfer. Yb³⁺ ions are more than Er³⁺ ions in the glass, resulting in efficient energy back transfer from Er³⁺ to Yb³⁺. So the red emission is stronger than the green emissions. Magnetization curves indicate that magnetic rare earth ions are paramagnetic and the distribution is homogeneous and random in the glass matrix. Aerodynamic levitation method is an efficient way to prepare glasses with homogeneous rare earth ions.     

Luminescence properties of Eu2+-activated Sr5(PO4)2(SiO4) for green-emitting phosphor

A green-emitting phosphor of Eu²⁺-activated Sr₅(PO₄)₂(SiO₄) was synthesized by the conventional solid-state reaction. It was characterized by photoluminescence excitation and emission spectra, and lifetimes. In Sr₅(PO₄)₂(SiO₄):Eu²⁺, there are at least two distinguishable Eu²⁺ sites, which result in one broad emission situating at about 495 nm and 560 nm. The phosphor can be efficiently excited in the wavelength range of 250–440 nm where the near UV (～ 395 nm) Ga(In)N LED is well matched. The dependence of luminescence intensities on temperature was investigated. With the increasing of temperature, the luminescence of the phosphor shows good thermal stability and stable color chromaticity. The luminescence characteristics indicate that this phosphor has a potential application as a white light emitting diode phosphor.     

Tunable luminescence of Dy3+ single-doped and Dy3+/Tm3+ co-doped tungsten borate glasses

RE³⁺ (RE³⁺ = Tm³⁺, Dy³⁺) ion single and co-doped tungsten borate glasses for white light emitting diodes (LEDs) were prepared by melt quenching method. Emission and excitation spectra of the glasses were measured. The color of luminescence can be tuned by changing the composition of glass matrix or the concentrations of Tm³⁺ and Dy³⁺ ions. White light emission can be achieved from 0.5Dy³⁺ single-doped 15WO₃–25La₂O₃–60B₂O₃ and 0.4Tm³⁺/1.5Dy³⁺ co-doped 50WO₃–25La₂O₃–25B₂O₃ glasses. In addition, energy transfers between Tm³⁺ and Dy³⁺ were also analyzed. The Dy³⁺/Tm³⁺ co-doped tungsten borate glasses may be potential candidates for white LED application.     

The structural influence of aluminium ions on emission characteristics of Sm3+ ions in lead aluminium silicate glass system

Optical absorption and photoluminescence characteristics of Sm³⁺ ions in lead silicate glasses mixed with different concentrations of Al₂O₃ (5–10 mol%) have been investigated. From these studies, the radiative properties viz., spontaneous emission probability A, the total emission probability, the radiative lifetime τ_R, the fluorescent branching ratio β of emission transition of ⁴G_5/2 → ⁶H_7/2 along with other transitions for Sm³⁺ have been evaluated and found to be the highest for the glass mixed with 8.0 mol% of Al₂O₃.The IR spectral studies have indicated that Al³⁺ ions do participate in the glass network with AlO₄ and AlO₆ structural units and further revealed that the concentration of octahedral aluminium ions induce bonding defects in the glass network. Such bonding defects are assumed to be responsible for low phonon losses in these glasses and lead to higher values of radiative parameters for the glass mixed with 8.0 mol% of Al₂O₃.     

Tunable white light emitting from mono Ce3+ doped Sr5(PO4)2SiO4 phosphors for light emitting diodes

The photoluminescence properties of mono Ce³⁺ doped Sr₅(PO₄)₂SiO₄ (SPS) apatite phosphors, prepared via a solid-state reaction at high temperature, were investigated in the ultraviolet region. The white light can be realized by adjusting the contents of activator Ce³⁺ or the excitation wavelength. Upon 365 nm excitation, SPS: 0.05Ce³⁺ shows bright white light (34.74% of YAG) with CIE color coordinates of (0.33, 0.34), a superior color-rendering index of 90 and correlated color temperature of 5603 K, suitable for potential use based on 365 nm UV-InGaN chip.     

Strong luminescence and efficient energy transfer in Eu3+/Tb3+-codoped ZnO nanocrystals

Single crystalline Eu³⁺/Tb³⁺-codoped ZnO nanocrystals have been synthesized by using a simple co-precipitation method. Successful doping is realized so that strong green and red luminescence can be efficiently excited by ultraviolet and near ultraviolet radiation, demonstrating an efficient energy transfer from ZnO host to rare earth ions. The energy transfer from the ZnO host to Tb³⁺ in ZnO: Tb³⁺ samples and ZnO host to Eu³⁺ in the ZnO: Eu³⁺ samples under UV excitation are investigated. It is found that the red ⁵D₀ → ⁷F₂ emission of Eu³⁺ ions decreases with increasing temperature but the green ⁵D₄ → ⁷F₅ emission of Tb³⁺ ions increases with increasing temperature, implying a different energy transfer processes in the two samples. Moreover, energy transfer from Tb³⁺ ions to Eu³⁺ ions in ZnO nanocrystals is also observed by analyzing luminescence spectra and the decay curves. By adjusting the doping concentration, the Eu³⁺/Tb³⁺-codoped ZnO phosphors emit green and red luminescence with chromaticity coordinates near white light region, high color purity and high intensity, indicating that they are promising light-conversion materials and have potential in field emission display devices and liquid crystal display backlights.     

Fluorescence properties of Eu3+-doped alumino silicate glasses

Alumino silicate glasses of a very broad range of molar compositions doped with 1 ⋅ 10²⁰ Eu³⁺ cm⁻³ (about 0.2 mol% Eu₂O₃) were prepared. As network modifier oxides Li₂O, Na₂O, K₂O, MgO, CaO, SrO, BaO, ZnO, PbO, Y₂O₃ and La₂O₃ have been used. All glasses show relatively broad fluorescence excitation and emission spectra. For most glasses only a weak effect of the glass composition on the excitation and emission spectra is observed. Although the glasses should be structurally similar, notable differences are found for the fluorescence lifetimes. These increase steadily with decreasing mean atomic weight, decreasing refractive index and decreasing optical basicity of the glasses, which may be explained by local field effects. An exception from this rule are the strontium, barium and potassium containing glasses, which show significantly increased fluorescence lifetimes despite of their high refractive index, optical basicity and molecular weight. The non mono-exponential fluorescence decay curves as well as the fluorescence spectra indicate a massive change in the local surroundings of the doped rare earth ions for these glasses.     

Alkaline aluminum phosphate glasses for thermal ion-exchanged optical waveguide

Alkaline aluminum phosphate glasses (NMAP) with excellent chemical durability for thermal ion-exchanged optical waveguide have been designed and investigated. The transition temperature Tg (470 °C) is higher than the ion-exchange temperature (390 °C), which is favorable to sustain the stability of the glass structure for planar waveguide fabrication. The effective diffusion coefficient D_e of K⁺–Na⁺ ion exchange in NMAP glasses is 0.110 μm²/min, indicating that ion exchange can be achieved efficiently in the optical glasses. Single-mode channel waveguide has been fabricated on Er³⁺/Yb³⁺ doped NMAP glass substrate by standard micro-fabrication and K⁺–Na⁺ ion exchange. The mode field diameter is 9.6 μm in the horizontal direction and 6.0 μm in the vertical direction, respectively, indicating an excellent overlap with a standard single-mode fiber. Judd–Ofelt intensity parameter Ω₂ is 5.47 × 10⁻²⁰ cm², implying a strong asymmetrical and covalent environment around Er³⁺ in the optical glasses. The full width at half maximum and maximum stimulated emission cross section of the ⁴I_13/2 → ⁴I_15/2 are 30 nm and 6.80 × 10⁻²¹ cm², respectively, demonstrating that the phosphate glasses are potential glass candidates in developing compact optoelectronic devices. Pr³⁺, Tm³⁺ and Ho³⁺ doped NMAP glasses are promising candidates to fabricate waveguide amplifiers and lasers operating at special telecommunication windows.     

Luminescence at 1.53 μm for a new Er3+-doped transparent oxyfluoride glass ceramic

Transparent 45SiO₂25Al₂O₃5CaO10NaF15CaF₂ glass ceramics doped with different levels of Er³⁺ were prepared. The spherical CaF₂ nanocrystals with 10–20 nm in size were verified to be homogeneously embedded among the glassy matrix. Room temperature absorption and emission spectra corresponding to ⁴I_13/2 ↔ ⁴I_15/2 transitions of Er³⁺ ions in precursor glasses and glass ceramics, respectively had been measured. For glass ceramics, with increasing of Er³⁺ content from 0.1 to 2.0 mol%, the FWHM values of the emission bands increased from 42 to 71 nm; meanwhile, the lifetime of ⁴I_13/2 level slightly reduced. However, both the values of FWHM and lifetime were larger than those of precursor glasses due to the change of ligand field of Er³⁺ ions.     

Synthesis and luminescence properties of CaAl2O4:Mn4+ phosphor

CaAl_2−yO₄:yMn⁴⁺ (y = 0–1.6 mol%) phosphors are synthesized by a solid-state reaction method in air, and their crystal structure and luminescence property are investigated. To compare luminescence property, CaAl_3.99O₇:1%Mn⁴⁺ and SrAl_1.99O₄:1%Mn⁴⁺ phosphors are also synthesized at the same condition. Broad band excitation spectra are observed within the range 220–550 nm, and emission spectra cover from 600 to 720 nm with the strongest emission peak at ∼658 nm owing to the ²E → ⁴A₂ transition of Mn⁴⁺ ion. The influence of crystal field to luminous intensity is discussed, and the possible luminous mechanism of Mn⁴⁺ ion is explained by using energy level diagram of Mn⁴⁺ ion. CaAl_1.99O₄:1%Mn⁴⁺, CaAl_3.99O₇:1%Mn⁴⁺, and SrAl_1.99O₄:1%Mn⁴⁺ phosphors under excitation 325 nm light emit red light, and their CIE chromaticity coordinates are (0.7181, 0.2813), (0.7182, 0.2818), and (0.7198, 0.2801), respectively. These contents in the paper are helpful to develop novel and high-efficient Mn⁴⁺-doped phosphor for white LEDs.     

Erbium doped tellurite glasses with improved thermal properties as promising candidates for laser action and amplification

The influence of composition on the thermal stability of tellurite glasses was investigated by using differential scanning calorimetry (DSC). The studied glasses were synthesized by conventional melting quenching method. The best thermal stability and poor crystallization tendency were obtained for the glass composed of 65TeO₂–15ZnO–10Na₂O–5BaO–3La₂O₃ doped with Er₂O₃ (2 mol %). This glass will be referred, in this article, as TZNBL: Er³⁺ glass.The spectroscopic properties of the above glass are investigated based on the Judd–Ofelt and McCumber theories.The calculated intensity parameters (Ω_2,4,6) are compared to those obtained for Er³⁺ in other glasses. The radiative emission rate has been calculated for the different Er³⁺emitting levels. The high values of Ω₄ and Ω₆ confirm the results of the DSC experiment concerning the rigidity of the studied glass.Absorption, emission and gain cross section of the ⁴I_13/2 ↔ ⁴I_15/2 (Er³⁺) transition in the studied glass are reported and the results are compared to those of other glasses.The ⁴I_13/2 ↔ ⁴I_15/2 (Er³⁺) absorption and emission cross sections derived by the application of the Mc Cumber’s theory corroborate the Judd–Ofelt results.The whole of results demonstrate that the new composition leads to good thermal and mechanical properties as well efficient Er³⁺ absorption, emission cross sections, which make this glass as a promising candidate for laser action and amplification.     

Direct observation of Nd3 + and Tm3 + ion distributions in oxy-fluoride glass ceramics containing PbF2 nanocrystals

Nd^3 + and Tm^3 +, doped oxy-fluoride glasses and glass ceramics were prepared by conventional melt-quenching and subsequent heat-treatment, respectively. β-PbF₂ nanocrystals with diameter 50 –100 nm formed in the glass matrix after heat treatment. The Stark splitting in absorption peaks, enhanced photoluminescence and prolonged lifetimes that β-PbF₂ nanocrystal formation increased the luminescence of rare earth ions. Both Nd^3 + and Tm^3 + ions were incorporated into nanocrystals that were enriched in lead and fluorine, and deficient in oxygen.