Enhanced near-infrared emission in Yb3+-Cr3+ codoped KZnF3 glass ceramics excited by a solar simulator

Cr³⁺-Yb³⁺ codoped bulk glass-ceramics containing KZnF₃ nanocrystals are fabricated by thermal treatment of cast glass samples and characterized by X-ray diffraction and transmission electron microscopy. The luminescent properties of the glass and glass ceramic are investigated from the measured photoluminescence spectra and fluorescent lifetime. The measurement results demonstrate that Cr³⁺ and Yb³⁺ ions are both predominantly hosted in the KZnF₃ nanocrystals, and the energy absorbed by Cr³⁺ ions is efficiently transferred to Yb³⁺ ions when excited at 450?nm. Compared to the glass, the near-infrared emission in the Cr³⁺-Yb³⁺ codoped glass ceramics is significantly enhanced when the excitation wavelength lies in the range λ~400–800?nm of a solar simulator. Results indicate that the Cr³⁺-Yb³⁺ codoped KZnF₃ glass ceramic provides a promising material for spectral conversion from visible sunlight to near-infrared emission and a novel gain material for solar pumped fiber laser.     

Infrared to Visible Up‐Conversion Emission in Er3+/Yb3+ Codoped Fluoro–Phosphate Glass–Ceramics

Erbium Er³⁺ and ytterbium Yb³⁺ codoped fluoro‐phosphate glasses belonging to the system NaPO₃–YF₃–BaF₂–CaF₂ have been prepared by the classical melt‐quenching technique. Glasses containing up to 10 wt% of erbium and ytterbium fluorides have been obtained and characterized using differential scanning calorimetry (DSC) and UV–visible and near‐infrared spectroscopy. Transparent and homogeneous glass–ceramics have been then reproducibly synthetized by appropriate heat treatment above glass transition temperature of a selected parent glass. Structural investigations of the crystallization performed through X‐ray diffractometry (XRD) and scanning electron microscopy (SEM) have evidenced the formation of fluorite‐type cubic crystals based during the devitrification process. Finally, infrared to visible up‐conversion emission upon excitation at 975 nm has been studied on the Er³⁺ and Yb³⁺ codoped glass–ceramics as a function of thermal treatment time. A large enhancement of intensity of the up‐conversion emissions–about 150 times‐ has been observed in the glass–ceramics if compared to the parent glass one, suggesting an incorporation of the rare‐earth ions (REI) into the crystalline phase.     

An Efficient Dual‐Mode Solar Spectral Modification for c‐Si Solar Cells in Tm3+/Yb3+ Codoped Tellurite Glasses

A series of Tm³⁺/Yb³⁺ codoped tellurite glasses, which demonstrate an interesting dual‐mode solar spectral converting for c‐Si solar cells, have been successfully prepared by conventional high‐temperature melt‐quenching technique. The photoluminescence (PL), photoluminescence excitation (PLE) spectra along with the decay curves have been studied systematically. The results indicate that the transparent glasses show two distinguishable near infrared (NIR) spectral converting behaviors, that is, quantum cutting (QC) and downshifting (DS) processes, sensitized by narrow f–f transition absorption of Tm³⁺:³H₆ → ¹G₄ at 465 nm and broad absorption band due to charge‐transfer state (CTS) of Yb³⁺‐O^2? at 320 nm, respectively. The Tm³⁺/Yb³⁺ codoped tellurite glasses convert ultraviolet (240–400 nm) and blue (450–490 nm) photons into NIR (920–1100 nm) ones, which well match the optimal spectral response of silicon (Si) solar cells. The prepared tellurite glass can be potentially utilized as spectral converter to improve the photovoltaic conversion of c‐Si solar cells. The dual‐mode solar spectrum converting material might explore a novel approach to realize UV‐Vis to NIR downconversion for Si solar cells application.     

Intense 2.85 μm mid-infrared emissions in Yb3+/Ho3+ codoped and Yb3+/Er3+/Ho3+ tridoped TBLL fluorotellurite glasses and their energy transfer mechanism

Yb³⁺/Ho³⁺ codoped and Yb³⁺/Er³⁺/Ho³⁺ tridoped TeO₂–BaF₂–LaF₃–La₂O₃ (TBLL) fluorotellurite glasses with low OH^? absorption (0.026 cm^-1), high glass transition temperature (434 °C) and low phonon energy (784 cm^-1) were prepared. Their mid-infrared fluorescence properties and related energy transfer (ET) mechanism were studied under 980 nm excitation. A strong emission at 2.85 μm was realized in Yb³⁺/Ho³⁺ codoped tellurite glass, which was attributed to the high-efficiency ET from Yb³⁺ ions to Ho³⁺, and the ET efficiency was 91.1%. Further introduction of Er³⁺ ions induced stronger 2.85 μm emission, and the ET efficiency was improved to 96.2%, ascribed to the establishment of more ET channels and Er³⁺ ions playing the role of ET bridge between Yb³⁺ and Ho³⁺ ions. These results indicate that the Yb³⁺/Er³⁺/Ho³⁺ tridoped tellurite glass could be a hopeful gain medium material for the ～3 μm fiber laser.     

Near‐Infrared Quantum Cutting via Downconversion Energy Transfers in Ho3+/Yb3+ Codoped Tellurite Glass Ceramics

The different concentration of Ho³⁺/Yb³⁺ codoped tellurite glasses were prepared by high‐temperature melting‐quenching method. On excitation of Ho³⁺ ions with blue photon at 449 nm as well as ultraviolet (UV) photon at 360 nm, the near infrared emission at 977 nm from Yb³⁺ and 981, 1020 nm from Ho³⁺, which could be absorbed by silicon and enhance the efficiency of the silicon‐based solar cell, were observed. The energy‐transfer process of Ho³⁺ and Yb³⁺ ions and involved mechanism have been investigated and discussed. The first‐order energy transfer (ET) through cross relaxation and a back ET from Yb³⁺ to Ho³⁺ occurred in the near‐infrared quantum cutting (NIR QC) system are proposed and verified. The NIR quantum efficiency achieved 166% when Yb³⁺ doping concentration is 20 mol%.     

Wide‐range thermometry based on green up‐conversion luminescence of K3LuF6:Yb3+/Er3+ bulk oxyfluoride glass ceramics

Yb³⁺/Er³⁺ ions codoped bulk glass ceramics (GC) with embedded monoclinic K₃LuF₆ nanocrystals are reported for potential temperature‐sensing application by using the fluorescence intensity ratio method. Such GC with good transparency and enhanced up‐conversion were prepared by the simple conversional melt‐quenching method and subsequent annealing process. Optical, structural, and temperature‐sensing up‐conversion properties were characterized systematically. Optical spectroscopy analysis confirms the incorporation of Yb³⁺/Er³⁺ into the K₃LuF₆ crystalline lattice, resulting in enhanced up‐conversion luminescence. Compared to other Er³⁺‐doped typical systems, Er³⁺ ions in K₃LuF₆ GC present large energy gap (870 cm^?1) and high relative sensitivity (37.6 × 10^?4 K^?1 at 625 K), revealing that K₃LuF₆:Yb³⁺/Er³⁺ GC can be excellent candidates for optical thermometers.     

Optical Property of Dy3+‐and Ce3+‐Doped Si–B–Na–Sr Glasses

Novel Dy³⁺ and Ce³⁺ doped Si–B–Na–Sr (SBNS) glasses were synthesized by melt‐quenching technique. Excited by 327 nm, the 0.5Dy³⁺‐and 0.5Ce³⁺‐doped SBNS exhibits white emission with Commission Internationale de L'Eclairage coordinates of (0.308, 0.280). Basic optical characterizations have been performed by measuring the absorption and emission spectra and calculating Judd–Ofelt intensity parameters, radiative probability, luminescence branching ratio, cross sections, and effective bandwidth. The Judd–Ofelt parameters Ω₂, Ω₄, and Ω₆ indicate a high asymmetrical environment and covalent environment in the optical glass. The emission color of Ce³⁺ and Dy³⁺ codoped transparent glass can be tuned from blue to white through energy transfer from Ce³⁺ to Dy³⁺ ions. The resulting glass may have potential application in white‐light‐emitting source.     

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.     

Enhanced Luminescence of Ca14Mg2Si8O28+δN4−δ:Eu2+Phosphors by Codoping Ce3+, Mn2+ for White LEDs and Their Energy‐Transfer Mechanism

The Eu²⁺, M‐codoped(M = Ce³⁺, Mn²⁺) phosphor powders were prepared by a solid‐state reaction. The addition of Ce³⁺ in the Eu²⁺ sites in partially nitridated bredigite‐structure phosphor(CMSN) remarkably enhances the luminescent intensity by ~180% through sensitized luminescence. Dual band emission was observed for Eu, Mn‐codoped CMSN through energy transfer from Eu²⁺ to Mn²⁺. Ce³⁺–Eu²⁺ and Eu²⁺–Mn²⁺ energy‐transfer mechanism was investigated through decay profile analysis using Inokuti–Hirayama model and energy‐transfer parameters are determined. Interaction mechanism was identified as dipole–dipole interaction. In addition, phosphor in glass plates was prepared using the phosphor and its feasibility in white LED application was studied and is presented.     

Novel Er3+/Ho3+‐codoped glass‐ceramic fibers for broadband tunable mid‐infrared fiber lasers

It is well recognized that a widely wavelength‐tunable mid‐infrared (MIR) fiber laser plays an important role in the development of compact and efficient coherent sources in the MIR range. Herein, the optimizing Er/Ho ratio for enhancement of broadband tunable MIR emission covering 2.6‐2.95 μm in the Er³⁺/Ho³⁺‐codoped transparent borosilicate glass‐ceramic (GC) fibers containing NaYF₄ nanocrystals under 980 nm excitation was investigated. Specifically, the obtained GC fibers with controllable crystallization and well fsd‐maintained structures were prepared by the novel melt‐in‐tube approach. Owing to the effective energy transfer between Er³⁺ and Ho³⁺ after crystallization, the 2.7 μm MIR emission was obviously enhanced and the emission region showed a notable extension from 2.6‐2.82 μm to 2.6‐2.95 μm after the addition of Ho³⁺. Importantly, we conducted a theoretical simulation and calculation related to the MIR laser performance, signifying that the GC fiber may be a promising candidate for MIR fiber laser. Furthermore, the melt‐in‐tube approach will provide a versatile strategy for the preparation of diverse optical functional GC fibers.     

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.     

Fabrication and Characterization of Glass‐Ceramic Fiber‐Containing Cr3 + ‐Doped ZnAl2O4 Nanocrystals

Glass‐ceramic fibers containing Cr³⁺‐doped ZnAl₂O₄ nanocrystals were fabricated by the melt‐in‐tube method and successive heat treatment. The obtained fibers were characterized by electro‐probe micro‐analyzer, X‐ray diffraction, Raman spectrum and high‐resolution transmission electron microscopy. In our process, fibers were precursor at the drawing temperature where the fiber core glass was melted while the clad was softened. No obvious element interdiffusion between the core and the clad section or crystallization was observed in precursor fiber. After heat treatment, ZnAl₂O₄ nanocrystals with diameters ranging from 1.0 to 6.3 nm were precipitated in the fiber core. In comparison to precursor fiber, the glass‐ceramic fiber exhibits broadband emission from Cr³⁺ when excited at 532 nm, making Cr³⁺‐doped glass‐ceramic fiber a promising material for broadband tunable fiber laser. Furthermore, the melt‐in‐tube method demonstrated here may open a new gate toward the fabrication of novel glass‐ceramic fibers.     

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.     

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.     

Ce3+‐ and Dy3+‐Doped Oxyfluoride Borosilicate Glasses with Near White Luminescence

A series of Ce³⁺/Dy³⁺‐doped oxyfluoride borosilicate glasses prepared by melt‐quenching method are investigated for light‐emitting diodes applications. These glasses are studied via X‐ray diffraction (XRD), optical absorption, photoluminescence (PL), color coordinate, and Fourier transform infrared (FT‐IR) spectra. We find that the absorption and emission bands of Ce³⁺ ions move to the longer wavelengths with increasing Ce³⁺ concentrations and decreasing B₂O₃ and Al₂O₃ contents in the glass compositions. We also discover the emission behavior of Ce³⁺ ions is dependent on the excitation wavelengths. The glass structure variations with changing glass compositions are examined using the FT‐IR spectra. The influence of glass network structure on the luminescence of Ce³⁺/Dy³⁺ codoped glasses is studied. Furthermore, the near‐ideal white light emission (color coordinate x = 0.32, y = 0.32) from the Ce³⁺/Dy³⁺ codoped glasses excited at 350 nm UV light is realized.     

Improvement the near-infrared luminescence properties of double perovskite phosphor La(Mg0.5Sn0.5In0.5Sc0.5)0.5O3:Cr3+ via co-doping Yb3+

In recent years, the broadband near-infrared (NIR) spectroscopy technology has been widely used in the field of nondestructive testing. However, these existing NIR phosphors showed relatively short emission wavelengths, narrower half-maximum full-width (FWHM), and narrower half-peak widths, importantly, few phosphors presented the emission from 950 nm to 1100 nm. In order to solve these problems, the Yb³⁺/Cr³⁺ ions codoped La(Mg_0.5Sn_0.5In_0.5Sc_0.5)_0.5O₃ (LMSIS) was synthesized by the solid-state method, and the emission spectrum of LMSIS:Cr³⁺ can be extended to the NIR long-wave region due to the energy transfer of Yb³⁺ and Cr³⁺, and the thermal stability of the phosphor can be improved due to the inherent temperature stability of the Yb³⁺ f-f transition. The NIR phosphor converted light emitting diodes (pc-LEDs) were fabricated by combining the LMSIS:0.003Cr³⁺, 0.0015Yb³⁺ with blue LED chip, which can be expected to be used in the field of broadband near-infrared non-destructive detection.     

Optical Temperature Sensing Behavior of High‐Efficiency Upconversion: Er3+–Yb3+ Co‐Doped NaY(MoO4)2 Phosphor

A class of Yb³⁺/Er³⁺ co‐doped NaY(MoO₄)₂ upconversion (UC) phosphors have been successfully synthesized by a facile hydrothermal route with further calcination. The structural properties and the phase composition of the samples were characterized by X‐ray diffraction (XRD). The UC luminescence properties of Yb³⁺/Er³⁺ co‐doped NaY(MoO₄)₂ were investigated in detail. Concentration‐dependent studies revealed that the optimal composition was realized for a 2% Er³⁺ and 10% Yb³⁺‐doping concentration. Two‐photon excitation UC mechanism further illustrated that the green enhancement arised from a novel energy‐transfer (ET) pathway which entailed a strong ground‐state absorption of Yb³⁺ ions and the excited state absorption of Yb³⁺–MoO₄^2? dimers, followed by an effective energy transfer to the high‐energy state of Er³⁺ ions. We have also studied the thermal properties of UC emissions between 303 and 523 K for the optical thermometry behavior under a 980 nm laser diode excitation for the first time. The higher sensitivity for temperature measurement could be obtained compared to the previous reported rare‐earth ions fluorescence based optical temperature sensors. These results indicated that the present sample was a promising candidate for optical temperature sensors with high sensitivity.     

Efficient Energy Transfer and Enhanced Near‐IR Emission in Cu+/Nd3+‐Activated Aluminophosphate Glass

The development of photonic materials for efficient energy conversion and high‐power solid‐state lasers is currently pursued given the wide range of applicable technologies and the possibility to help meet global energy demands in laser fusion power plants. In this work, Cu⁺ ions successfully incorporated in aluminophosphate glass are recognized as near‐ultraviolet (UV) sensitizers of Nd³⁺ ions resulting in remarkable near‐infrared (IR) ⁴F_3/2 → ⁴I_11/2 emission at 1.06 μm. Optical absorption, solid‐state ³¹P nuclear magnetic resonance, Raman, and photoluminescence spectroscopies characterizations are employed and assessment methods for material optical and structural properties are proposed. The spectroscopic data indicates an efficient (>50%) nonradiative energy transfer where the Cu⁺ ions first absorb photons broadly around 360 nm, and subsequently transfer the energy from the Stokes‐shifted emitting states to resonant Nd³⁺ energy levels. Then, the Nd³⁺ electronic excited states decay and the upper lasing state ⁴F_3/2 is populated, leading to enhanced near‐IR emission. It is suggested that the physico‐chemically robust Cu⁺/Nd³⁺ codoped aluminophosphate glass is a suitable candidate as solid‐state laser material with enhanced pump range in the near‐UV part of the spectrum and for solar spectral conversion in photovoltaic cells.     

Influence of Crystallization on the Conversion of Sm3+→Sm2+ in SrO–Bi2O3–K2O–B2O3 Glass‐Ceramics

Sm³⁺‐doped glass 13SrO–2Bi₂O₃–5K₂O–80B₂O₃ was fabricated by the conventional melt‐quenching technique. The glass‐ceramics were obtained by heating the as‐prepared glasses in air atmosphere at selected temperatures 550°C, 600°C, 615°C, and 650°C, respectively. The luminescence spectra of both Sm³⁺ and Sm²⁺ were detected in the ceramic heated at 650°C where crystalline phase is formed. The as‐prepared glass and the ceramics heated at 550°C, 600°C, and 615°C show only the emission due to Sm³⁺. In the sample heated at 650°C in air atmosphere, however, part of Sm³⁺ ions was converted to Sm²⁺, giving rise to sharp emission lines which are characteristic of Sm²⁺ in crystalline state. It is suggested that Sm²⁺ ions are located at Sr²⁺ site in the ceramic while Sm³⁺ ions are located at Bi³⁺ sites. The Sm²⁺‐doped glass‐ceramic has a high optical stability because the fluorescence intensity decreases by only about 8% of its initial value upon excitation at 488 nm Ar⁺ laser.     

Wavelength Tailorability of Broadband Near‐Infrared Luminescence in Cr4+‐Activated Transparent Glass‐Ceramics

Four Cr⁴⁺‐activated transparent glass‐ceramics containing different species of silicate nano‐crystals (Zn₂SiO₄, Mg₂SiO₄, Li₂ZnSiO₄, and Li₂MgSiO₄) were successfully prepared. Absorption spectra, photoluminescence spectra, lifetime decay curves, and quantum yield of these transparent glass‐ceramics were measured. According to the crystal field strength of Cr⁴⁺‐incorporated tetrahedral sites, the broadband near‐infrared (NIR) luminescence of Cr⁴⁺ can be tailored from 1130 to 1350 nm and the lifetime of Cr⁴⁺ luminescence can be prolonged from 6 to 100 μs. Quantum yield in the transparent glass‐ceramics containing Li₂ZnSiO₄ nano‐crystals reached at 17%, which is the highest value of NIR luminescence in transition‐metal‐activated glass materials.