Broadband Near‐Infrared Down‐Shifting by Yb–O Charge‐Transfer Band in Yb3+ Singly Doped Tellurite Glasses

Yb³⁺ singly doped tellurite as‐prepared glasses and glass ceramics were synthesized by high‐temperature melt‐quenching method. The excitation and emission spectra have shown that there is an efficient near‐infrared (NIR) down‐shifting due to the sensitization of a novel Yb³⁺–O^2? charge‐transfer (CT) band. The CT band in the present host is located at around 320 nm at room temperature, which is much lower than that in other oxide hosts reported before. The possible energy‐transfer mechanism from the Yb³⁺–O^2? CT band to the ²F_5/2 multiplet of Yb³⁺ ions is discussed in detail. The concentration quenching is not observed even when the Yb³⁺‐doped concentration is increased up to 40 mol%. The excitation of this strong broad CT band causes intense NIR emission of Yb³⁺:²F_5/2→²F_7/2 from 920 to 1120 nm, making the tellurite glasses suitable for efficient photovoltaic (PV) application as a spectral conversion material for the crystalline Si (c‐Si) solar cells.     

Down-conversion from Er3+-Yb3+ codoped CaMoO4 phosphor: A spectral conversion to improve solar cell efficiency

The present paper focuses on near infrared (NIR) down-conversion photoluminescence (PL) properties by studying the energy transfer mechanism between Er³⁺ and Yb³⁺ in CaMoO₄:Er³⁺, Yb³⁺ phosphors. We have successfully synthesized a series of Er³⁺ doped and Yb³⁺ codoped CaMoO₄ phosphors by hydrothermal method. The down-conversion of Er³⁺-Yb³⁺ combination with CaMoO₄ phosphor is designed to overcome the energy losses due to spectral mismatch when a high energy photon is incident on the Si-solar cell. The XRD, FESEM, EDX, PL, UV–Vis, Lifetime measurements were carried out to characterize the prepared down-converting phosphors. The crystallinity and surface morphology were studied by X-ray diffraction (XRD) and Field Emission Scanning Electron Microscopy (FESEM) techniques. The down-conversion PL spectra have been studied using 380 nm excitation wavelength. The Er³⁺ doped phosphors exhibit hypersensitive emission at 555 nm in the visible region due to ⁴S_3/2→⁴I_15/2 transition. The addition of Yb³⁺ into Er³⁺ doped CaMoO₄ attribute an emission at 980 nm due to ²F_5/2→²F_7/2 transition. The decrease in emission intensity in visible region and increase in NIR region reveals the energy transfer from Er³⁺ to Yb³⁺ through cross relaxation. The UV–Vis–NIR spectra shows the strong absorption peak around 1000 nm due to Yb³⁺ ion. The lifetime measurement also reveals the energy transfer from Er³⁺ to Yb³⁺ ions. The maximum value of energy transfer efficiency (ETE) and corresponding theoretical internal quantum efficiency are estimated as 74% and 174% respectively.     

Molecular‐Like Ag Clusters and Eu3+ Co‐Sensitized Efficient Broadband Spectral Modification with Enhanced Yb3+ Emission

AgNO₃/EuF₃/YbF₃ tri‐doped oxyfluoride glass was prepared by a melt‐quenching method, in which a high‐efficient broadband spectral modification can be realized due to the simultaneous energy‐transfer processes of Eu³⁺→Yb³⁺, molecular‐like Ag (ML‐Ag) clusters→Yb³⁺, and ML‐Ag clusters→Eu³⁺→Yb³⁺. The spectral measurements indicated that besides the F‐center brought by the fluorides, the formation of the ML‐Ag clusters and the evolution of silver species within the glass matrix were also closely related to the introduction of Eu³⁺ and Yb³⁺ ions and which in return greatly affected the luminescence properties of these rare‐earth ions. As the UV‐visible irradiation in the wavelength region of 250–600 nm can be efficiently converted into near‐infrared emission around 1000 nm in the AgNO₃/EuF₃/YbF₃ tri‐doped glass, which thus has promising application in enhancing the photovoltaic conversion efficiency of the silicon solar cell.     

Tailorable Multicolor Up‐conversion Emissions in Tm3+/Ho3+/Yb3+ Co‐Doped LiLa(MoO4)2

Using a modified sol–gel method, LiLa(MoO₄)₂: Tm³⁺/Ho³⁺/Yb³⁺ phosphors with tailorable up‐conversion (UC) emission colors were prepared. Under the excitation of a 980 nm laser diode, up‐conversion red and green emissions in Ho³⁺/Yb³⁺ co‐doped and blue emission in Tm³⁺/Yb³⁺ co‐doped LiLa(MoO₄)₂ were observed, respectively. The intensities of the RGB (red, green, and blue) emissions could be controlled by varying concentrations of Tm³⁺ or Ho³⁺, and the optimal composition was also determined. In Tm³⁺/Ho³⁺/Yb³⁺ co‐doped LiLa(MoO₄)₂, the UC emission colors could be tuned from blue through white to yellow by adjusting the concentrations of Tm³⁺ or Ho³⁺. The UC excitation mechanisms were also investigated based on the power dependence of UC luminescence intensity.     

Near-IR Emission and upconversion luminescent properties of Tb3+/Yb3+ Co-doped HfO2/SiO2 nanoparticles

The luminescent characteristics of spherical hafnia/silica (HfO₂/SiO₂) nanoparticles (NP?s) co-doped with Tb³⁺/Yb³⁺ were analysed. These NP?s were synthesized using the spray pyrolysis technique. The addition of SiO₂ and Tb³⁺/Yb³⁺ was found to induce a cubic phase in HfO₂. The luminescent spectra presented the characteristic emission peaks for inter-electronic energy levels transitions of the Tb³⁺ and Yb³⁺ ions, with an excitation band centred at 270 nm. Under solid-state laser excitation at 980 nm an upconversion emission related to the Tb³⁺ ion was observed. The maximum emission peak in the visible region was at 543 nm, associated with ⁵D₄ → ⁷F₅ transitions of the Tb³⁺ ions and an IR emission peak at 970 nm (²F_5/2 → ²F_7/2) pertaining to Yb³⁺, with irradiation at 270 nm (UV). The energy transfer mechanism from Tb³⁺→Yb³⁺ (excitation at 270 nm), is discussed based on the time decay of the luminescence intensity analysis and the energy transfer efficiency (η_ET) and was determined to be in the range of 29.2% to40.8%.     

Emission from Mo‐O charge‐transfer state and Yb3+ emission in Eu3+‐doped and nondoped molybdates under UV excitation

Molybdates of Li⁺ and Yb³⁺ are studied to investigate the luminescence under UV excitation. LiYb(MoO₄)₂ and Eu³⁺‐doped LiYb₁‐_xEux(MoO₄)₂ (x=001–1.0) phosphors were synthesized by solid state reaction under mixing of Eu₂O₃, Yb₂O₃, Li₂CO₃ and MoO₂ in air atmosphere. Two broad absorption bands centered at 333 and 236 nm are observed in LiYb(MoO₄)₂ compound. They are attributed to the ¹A₁→¹T₁ and ¹T₂ transitions due to the O^2?→Mo⁶⁺ electron transfers in MoO₄ tetrahedron. An emission band with a peak at about 440 nm is found, which is attributed to the ³T₁→¹A₁ transition of MoO₄. Appearance of near‐infrared (NIR) Yb³⁺ emission observed under UV excitation is understood by the MoO₄→Yb³⁺ Foerster‐Type energy transfer due to spectral overlap between the low‐energy tail of the broad 440 nm emission band and the high‐energy tail of the broad Yb³⁺ absorption band and due to short Yb³⁺‐MoO₄ distance. Yb³⁺ emission observed in LiYb_1?xEu_x(MoO₄)₂ by Eu³⁺ excitation is understood by the Eu³⁺→Yb³⁺ energy transfer by cross‐relaxation (CR) process between the ⁵D₀→⁷F₆ Eu³⁺ transition and the ²F_7/2→²F_5/2 Yb³⁺ transition. The CR efficiency shows maximum efficiency of 0.24 at x=0.15 of higher acceptor Yb³⁺ concentration than donor Eu³⁺ concentration. Three Yb³⁺ emission bands with peaks at 994, 1002, and 1023 nm are observed, depending on the excitation wavelength. This is explained by less‐shielded 4f electrons of Yb³⁺ by the 5s²5p⁶ outermost electron shells, which are also responsible for unusual broadband Yb³⁺ absorption and emission. From appearance of NIR Yb³⁺ emission under excitation by not only UV light but also red light, these compounds are expected to be suitable for efficient photovoltaic application to Si‐based solar cells.     

Host sensitized near-infrared emission in Nd3+-Yb3+ Co-doped Na2GdMg2V3O12 phosphor

Yb³⁺/Nd³⁺ singly and co-doped Na₂GdMg₂V₃O₁₂ phosphors with near-infrared (NIR) emission were synthesized via sol-gel method. The phase purity and structure of samples were characterized by X-ray diffraction (XRD), the photoluminescence emission (PL) and excitation (PLE) spectra along with decay curves were also measured. Near infrared (NIR) emissions (850–1150 nm) from acceptors Yb³⁺ or Nd³⁺ matching well with the response curve of the silicon solar cell were obtained, in which VO₄³⁻ groups acted as sensitizers by capturing near ultraviolet photons which are not absorbed efficiently by silicon solar cell and transferred them to Yb³⁺/Nd³⁺ by energy transfer processes. The NIR emission intensities of the Nd³⁺-Yb³⁺co-doped samples Na₂GdMg₂V₃O₁₂ were enhanced greatly in comparison with that of Nd³⁺/Yb³⁺ singly doped samples, and the possible energy transfer processes were also discussed in detail. Results indicate that the obtained samples are potential solar spectral down-conversion (DC) convertors to enhance the conversion efficiency of the silicon solar cells.     

Eu‐, Tb‐, and Dy‐Doped Oxyfluoride Silicate Glasses for LED Applications

Luminescence glass is a potential candidate for the light‐emitting diodes (LEDs) applications. Here, we study the structural and optical properties of the Eu‐, Tb‐, and Dy‐doped oxyfluoride silicate glasses for LEDs by means of X‐ray diffraction, photoluminescence spectra, Commission Internationale de L'Eclairage (CIE) chromaticity coordinates, and correlated color temperatures (CCTs). The results show that the white light emission can be achieved in Eu/Tb/Dy codoped oxyfluoride silicate glasses under excitation by near‐ultraviolet light due to the simultaneous generation of blue, green, yellow, and red‐light wavelengths from Tb, Dy, and Eu ions. The optical performances can be tuned by varying the glass composition and excitation wavelength. Furthermore, we observed a remarkable emission spectral change for the Tb³⁺ single‐doped oxyfluoride silicate glasses. The ⁵D₃ emission of Tb³⁺ can be suppressed by introducing B₂O₃ into the glass. The conversion of Eu³⁺ to Eu²⁺ takes place in Eu single‐doped oxyfluoride aluminosilicate glasses. The creation of CaF₂ crystals enhances the conversion efficiency. In addition, energy transfers from Dy³⁺ to Tb³⁺ and Tb³⁺ to Eu³⁺ ions occurred in Eu/Tb/Dy codoped glasses, which can be confirmed by analyzing fluorescence spectra and energy level diagrams.     

REVO4‐Based Nanomaterials (RE = Y,La, Gd,and Lu) as Hosts for Yb3+/Ho3+, Yb3+/Er3+, and Yb3+/Tm3+ Ions: Structural and Up‐Conversion Luminescence Studies

Rare‐earth vanadates of the form REVO₄ (RE = Y, La, Gd, and Lu) doped by Yb³⁺/Ho³⁺, Yb³⁺/Er³⁺_, or Yb³⁺/Tm³⁺ lanthanide ions were successfully synthesized using the sol–gel method and annealing at 600°C in an air atmosphere. The structure and morphology of the prepared nanocrystals were investigated by X‐ray diffraction, thermogravimetric analysis, transmission electron microscopy, and energy‐dispersive X‐ray spectroscopy. All prepared materials were homogenous and had nanosized dimensions. Their elemental compositions were confirmed by optical emission spectrometry. Spectroscopic analysis of the materials was carried out by measuring excitation and emission spectra, luminescence decays, and dependence between the intensity of the luminescence and the laser energy. Following effective excitation by NIR radiation, Ln³⁺ co‐doped vanadate matrices exhibited a strong up‐conversion (UC) luminescence. Differences in spectroscopic properties between monoclinic LaVO₄ and tetragonal YVO₄, GdVO₄, or LuVO₄ doped by Ln³⁺ ions were observed, indicating the influence of the crystal structure on the UC emission. Drawing conclusions from these spectroscopic investigations, the UC mechanisms were proposed, including energy‐transfer processes between Yb³⁺ ions and emitting ions.     

Green Up‐Conversion Photoluminescence and Dielectric Relaxation of Ho3+/Yb3+‐Codoped Bi2Ti2O7 Pyrochlore Thin Films

Ho³⁺/Yb³⁺‐codoped Bi₂Ti₂O₇ pyrochlore thin films were prepared by a chemical solution deposition method, and their visible up‐conversion (UC) photoluminescence and dielectric relaxation were studied. Ho and Yb can be doped into Bi₂Ti₂O₇ lattice and single pyrochlore phase is maintained. Intense visible UC photoluminescence can be observed under the excitation of a 980‐nm diode laser. Two UC emission bands centered at 551 nm and 665 nm in the spectra can be assigned to ⁵F₄, ⁵S₂→⁵I₈ and ⁵F₅→⁵I₈ transitions of Ho³⁺ ions, respectively. The dependence of their UC emission intensity on pumping power indicates that both the green and red emissions of the thin films are two‐photon process. In addition, a Stokes near‐infrared emission centered at 1200 nm can be detected, which is due to ⁵I₆→⁵I₈ transition of Ho³⁺ ions. The thin films prepared on indium tin oxide–coated glass substrates exhibit a relatively high dielectric constant and a low dielectric loss as well as a good bias voltage stability. The dielectric relaxation of the thin films was also analyzed based on the temperature‐ and frequency‐dependent dielectric properties. This study suggests that Ho³⁺/Yb³⁺‐codoped Bi₂Ti₂O₇ thin films are promising materials for developing multifunctional optoelectronic thin film devices.     

Synthesis and Luminescence Properties of Blue‐Emitting Phosphor Eu2+‐Doped Zinc Fluoro‐Phosphate Zn2[PO4]F

Eu²⁺‐doped zinc fluoro‐phosphate Zn₂[PO₄]F was synthesized by the conventional high‐temperature solid‐state reaction. The phase formation was confirmed by X‐ray powder diffraction measurements and the structure refinement. The photoluminescence excitation and emission spectra, and the decay curves were measured. The natures of the Eu²⁺ emission in inorganic hosts, e.g., the emission and excitation properties, the chromaticity coordinates, the Stokes shifts, the absolute quantum efficiency, and the luminescence thermal stability were reported. Under the excitation of near‐UV light, Eu²⁺‐doped Zn₂[PO₄]F presents a narrow blue‐emitting band centered at 423 nm. The thermal stability of the blue luminescence was evaluated by the luminescence intensities as a function of temperature. The phosphor shows an excellent thermal stability on temperature quenching effects.     

Efficient dual‐mode up‐conversion and down‐shifting emission in β‐NaYF4:Yb3+,Er3+ microcrystals via ion exchange

We report efficient dual‐mode up‐conversion (UC) and down‐shifting (DS) emission in a single Yb³⁺/Er³⁺‐co‐doped β‐NaYF₄ microcrystals with controlled morphology and size via a simple Na⁺ ion‐exchange modification (IEM) method. IEM well preserves the crystal structure and monodispersed morphology of hydrothermal‐synthesized β‐NaYF₄. Meanwhile, IEM gives rise to the significant enhancement of UC emission intensity up to 3800 times and strongly enhanced DS emission intensity of Er³⁺ and Yb³⁺ by several times in β‐NaYF₄:Yb³⁺,Er³⁺ microcrystals. IEM also strongly prolongs the DS emission lifetimes of Er³⁺ and Yb³⁺ in visible and near‐infrared region. The enhanced UC and DS emission intensities and prolonged lifetimes in β‐NaYF₄:Yb³⁺,Er³⁺ are mainly ascribed to the dispersing of localized Yb³⁺ and Er³⁺ clusters during IEM.     

Microwave Sol–Gel Synthesis of CaGd2(MoO4)4:Er3+/Yb3+ Phosphors and Their Upconversion Photoluminescence Properties

CaGd₂(MoO₄)₄:Er³⁺/Yb³⁺ phosphors with the doping concentrations of Er³⁺ and Yb³⁺ (x = Er³⁺ + Yb³⁺, Er³⁺ = 0.05, 0.1, 0.2, and Yb³⁺ = 0.2, 0.45) have been successfully synthesized by the microwave sol–gel method, and the crystal structure refinement and upconversion photoluminescence properties have been investigated. The synthesized particles, being formed after heat‐treatment at 900°C for 16 h, showed a well‐crystallized morphology. Under the excitation at 980 nm, CaGd₂(MoO₄)₄:Er³⁺/Yb³⁺ particles exhibited strong 525 and 550‐nm emission bands in the green region and a weak 655‐nm emission band in the red region. The Raman spectrum of undoped CaGd₂(MoO₄)₄ revealed about 15 narrow lines. The strongest band observed at 903 cm^?1 was assigned to the ν₁ symmetric stretching vibration of MoO₄ tetrahedrons. The spectra of the samples doped with Er and Yb obtained under 514.5 nm excitation were dominated by Er³⁺ luminescence preventing the recording Raman spectra of these samples. Concentration quenching of the erbium luminescence at ²H_11/2→⁴I_15/2 and ⁴S_3/2→⁴I_15/2 transitions in the CaGd₂(MoO₄)₄:Er³⁺/Yb³⁺ crystal structure was established to be approximately at the 10 at.% doping level.     

Optical properties of PMMA doped with erbium(III) and ytterbium(III) complexes

In this article, we report the fabrication and optical/spectroscopic properties of polymethylmethacrylate (PMMA) doped with rare earth (RE) (Er³⁺ and Er³⁺/Yb³⁺) ions. Infrared spectroscopy revealed only very weak O? H stretching vibration peaks in the samples, which is important if satisfactory photoluminescence is to be observed at 1530 nm. Measurement of transmission spectra in the wavelength ranges from 300 to 700 nm for Er³⁺‐doped samples and from 900 to 1050 nm for Yb³⁺‐doped samples enabled us to observe the ⁴G_11/2 (377 nm) and ²H_11/2 (519 nm) transmission bands typical for Er³⁺‐doped samples, as well as the ²F_5/2 (975 nm) band typical for Yb³⁺‐doped samples. Under excitation at 980 nm, at room temperature, the characteristic Er³⁺ emission at 1530 nm was also observed with improving trend when the higher RE concentrations were applied. The results indicate that the PMMA reveals very low tendency to the RE clustering, which together with low cost and easy fabrication make it a material with a great potential in the active photonics devices. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

Color‐Tunable Up‐Conversion Emission and Infrared Photoluminescence and Dielectric Relaxation of Er3+/Yb3+ Co‐Doped Bi2Ti2O7 Pyrochlore Thin Films

The color‐tunable up‐conversion (UC) emission and infrared photoluminescence and dielectric relaxation of Er³⁺/Yb³⁺ co‐doped Bi₂Ti₂O₇ pyrochlore thin films prepared by a chemical solution deposition method have been investigated. The pyrochlore phase structure of Bi₂Ti₂O₇ can be stabilized by Er³⁺/Yb³⁺ co‐doping. Intense color‐tunable UC emission and infrared photoluminescence can be detected on the thin films excited by a 980 nm diode laser. Two UC emission bands centered at 548 and 660 nm in the spectra can be assigned to ²H_11/2, ⁴S_3/2 → ⁴I_15/2 and ⁴F_9/2 → ⁴I_15/2 transitions of Er³⁺ ions, respectively. A Stokes infrared emission centered at 1530 nm is due to ⁴I_13/2 → ⁴I_15/2 transition of Er³⁺ ions. The dependence of UC emission intensity on pumping power indicates that the UC emission of the thin films is a two‐photon process. The thin films also exhibit a relatively high dielectric constant and a low dissipation factor as well as a good bias voltage stability. Temperature‐ and frequency‐dependent dielectric relaxation has been confirmed. This study suggests that Er³⁺/Yb³⁺ co‐doped Bi₂Ti₂O₇ thin films can be applied to new multifunctional photoluminescence dielectric thin‐film devices.     

The absorption and emission properties of highly transparent ZrO2-doped Yb3+: Y2O3 ceramics

Ultra-highly transparent ZrO₂-doped Yb³⁺: Y₂O₃ ceramics were prepared by slip casting and vacuum pressureless sintering and the transmittance reached the highest value of 80.9% for the sample doped with 8.0 at% Yb³⁺. There are three main absorption peaks at 905, 950, and 976 nm, corresponding to the transition from the lowest level of field splitting of ²F_7/2 crystal to every splitting energy levels of ²F_5/2 crystal field. We analyzed the absorption and emission spectra of transparent Yb³⁺: Y₂O₃ from the energy level structure of Yb³⁺, and the transmission, absorption, and emission spectra were systematically studied. There are three main absorption peaks at 905, 950, and 976 nm and four emission peaks at 1076, 1031, 1013, and 977 nm, respectively. The emission peaks at 977 and 1013 nm broaden and vanish for 8.0 and 10.0 at% Yb³⁺-doped Y₂O₃, which may be related to the change of Y₂O₃ crystal field caused by high concentration.     

Effect of silica coating on the structural and luminescent properties of Sm3+/Yb3+ or Tm3+/Yb3+ co-doped TiO2 nanoparticles

The luminescent characteristics of spherical titanium dioxide (TiO₂) nanoparticles (NP's) doped with Sm³⁺/Yb³⁺ and Tm³⁺/Yb³⁺ with and without a silica coating were analyzed. These nanoparticles were synthesized using the spray pyrolysis technique and coated with silica through a wet chemical process. The Sm³⁺/Tm³⁺ and Yb³⁺ doping induces a triphasic poly-crystalline structure of rutile and anatase TiO₂ and a Sm₂Ti₂O₇/Tm₂Ti₂O₇ cubic phase. A Williamson-Hall analysis was used to monitor the tensions of the NP's crystallites at the various doping concentrations and with addition of the silica shell. The luminescent spectra presented the characteristic emission peaks for the electronic energy levels transitions of the Sm³⁺/Tm³⁺ and Yb³⁺ ions. The Sm³⁺/Yb³⁺ co-doped NP's showed a maximum emission peak in the visible region at 612 nm, associated with ⁴G_5/2 → ⁶H_7/2 transitions of the Sm³⁺ ions. The IR emission peak at 973 nm (²F_5/2 → ²F_7/2) pertaining to Yb³⁺. For the combination of Tm³⁺/Yb³⁺, two emissions associated with Tm³⁺ ions were observed at 440 nm (¹D₂ → ³F₄) and 806 nm (³H₄ → ³H₆). The emission at 973 nm (²F_5/2 → ²F_7/2) is correlated to the Yb³⁺ ions. Silica coating of the NP's resulted in luminescence emission intensity increase of about 4 times.     

Enhancement of up-conversion emission and emerging cool white light emission in co-doped Yb3+/ Er3+: Li2O-LiF-B2O3-ZnO glasses for photonic applications

A series of co-doped (Yb³⁺/Er³⁺): Li₂O-LiF-B₂O₃-ZnO glasses were prepared by standard melt quenching technique. Structural and morphological studies were carried out by XRD and FESEM. Phonon energy dynamics have been clearly elucidated by Laser Raman analysis. The pertinent absorption bands were observed in optical absorption spectra of singly doped and co-doped Yb³⁺/Er³⁺: LBZ glasses. We have been observed a strong up-conversion red emission pertaining to Er³⁺ ions at 1.0 mol% under the excitation of 980 nm. However, the up-conversion and down conversion (1.53 µm) emission intensities were remarkably enhanced with the addition of Yb³⁺ ions to Er³⁺: LBZ glasses due to energy transfer from Yb³⁺ to Er³⁺. Up-conversion emission spectra of co-doped (Yb³⁺/Er³⁺): LBZ glasses exhibits three strong emissions at 480 nm, 541 nm and 610 nm which are assigned with corresponding electronic transitions of ²H_9/2 → ⁴I_15/2, ⁴S_3/2 → ⁴I_15/2 and ⁴F_9/2 → ⁴I_15/2 respectively. Consequently, the green to red ratio values (G/R) also supports the strong up-conversion emission. The Commission International de E′clairage coordinates and correlated color temperatures (CCT) were calculated from their up-conversion emission spectra of co-doped (Yb³⁺/Er³⁺): LBZ glasses. The obtained chromaticity coordinates for optimized glass (0.332, 0.337) with CCT value at 5520 K are very close to the standard white colorimetric point in cool white region. These results could be suggested that the obtained co-doped (Yb³⁺/Er³⁺): LBZ glasses are promising candidates for w-LEDs applications.     

High Nd3+→Yb3+ energy transfer efficiency in tungsten‐tellurite glass: A promising converter for solar cells

This work reports on the energy transfer efficiency for Nd³⁺/Yb³⁺ co‐doped tellurite glasses (80TO₂‐20WO₃, in mol%,). The correlation between Yb³⁺ ion concentration and the downconversion mechanism was investigated using optical and thermal lens spectroscopies, which enabled investigation of the radiative and nonradiative processes, respectively, involved in energy transfer from neodymium to ytterbium. The Nd³⁺ near‐infrared fluorescence disappeared almost entirely when the maximum concentration of Yb³⁺ ions (4 mol%) was doped into the host. In contrast, there was a corresponding increase in the ytterbium emission at around 980 nm. When ytterbium was added, there was also a simultaneous reduction in the amount of heat generated by the sample due to a reduction in the nonradiative decay rate, corroborating the suspected high energy transfer efficiency of Nd³⁺→Yb³⁺. The results indicate that tungsten‐tellurite glasses may be of potential use in solar cells for matching the solar emission spectrum to the semiconductor cell.