Experimental and theoretical studies on NIR luminescence of titanate-germanate glasses doped with Pr3+ and Tm3+ ions

Near-infrared (NIR) luminescence of Pr³⁺ and Tm³⁺ ions in titanate-germanate glasses has been studied for laser and fiber amplifier applications. The effect of the molar ratio GeO₂:TiO₂ (from 5:1 to 1:5) on spectroscopic properties of glass systems was studied by absorption, luminescence measurements, and theoretical calculations using the Judd–Ofelt theory. It was found that independent of the TiO₂ concentration, intense NIR emissions at 1.5 and 1.8 μm were observed for glasses doped with Pr³⁺ and Tm³⁺ ions, respectively. Moreover, several spectroscopic and NIR laser parameters for Pr³⁺ and Tm³⁺ ions, such as emission bandwidth, stimulated emission cross-section, quantum efficiency, gain bandwidth, and figure of merit, were determined. The results were discussed in detail and compared to the different laser glasses. Systematic investigations indicate that Pr³⁺-doped system with GeO₂:TiO₂ = 2:1 and Tm³⁺-doped glass with GeO₂:TiO₂ = 1:2 present profit laser parameters and could be successfully applied to NIR lasers and broadband optical amplifiers.     

Multifunctional α-NaYbF4:Tm3+ nanocrystals with intense ultraviolet self-sensitized upconversion luminescence and highly efficient optical heating

Lanthanide-doped upconversion photoluminescent nanoparticles with unique anti-Stokes spectroscopic properties excel in many fields of application. Ytterbium-based self-sensitized fluorides with rich Yb³⁺ possess higher absorption efficiency of incident near infrared laser, and are more favorable for photoluminescence or optical heating applications. In this work, α-NaYbF₄:Tm³⁺ crystalline nanoparticles are synthesized, which exhibit intense ultraviolet self-sensitized upconversion photoluminescence and highly efficient optical heating capability under 980 nm laser excitation. NaYbF₄:Tm³⁺ nanocrystals emit multi-band luminescence with emission peaks located in the ultraviolet, blue and red spectral regions. The energy transfer mechanism and electronic transition pathways for the Upconversion luminescence are investigated based on the energy level scheme, and are further confirmed by luminescent dynamic analysis. Due to cross-relaxations between Tm³⁺ and energy back transfer from Tm³⁺ to Yb³⁺ processes, the NaYbF₄: 1 mol% Tm³⁺ nanoparticles possess the highest luminescence intensity. The luminescent dynamic characteristics, such as decay time and rise time, vary with Tm³⁺ doping concentrations. Highly efficient optical heating effect is observed in the NaYbF₄:Tm³⁺ nanoparticles with slope efficiency of photothermal conversion for 10 s laser irradiation is as high as 100.48 °C/W.     

The preparation of Yttrium Aluminosilicate (YAS) Glass Fiber with heavy doping of Tm3+ from Polycrystalline YAG ceramics

Yttrium aluminosilicate (YAS) glass core fibers with different doping concentration of Tm³⁺ were fabricated by a “Melt‐in‐Tube” method from YAG polycrystalline ceramics. The effect of Tm³⁺ concentration on the spectroscopy of YAG ceramics and laser performance of YAS fibers were discussed. A homemade linear all‐fiber laser based on the obtained 15% Tm³⁺‐doped YAS fiber shows an optimized slope efficiency of 12.8%. The YAS fibers have been proven to be practical to achieve extremely high Tm³⁺ doping concentration and are a promising option for the 2.0 μm laser.     

Quantitative prediction of the structure and luminescence properties of Nd3+ doped borate laser glasses

Although great advance has been made in glass science, predicting luminescence properties of laser glass poses a significant challenge for scientists due to the complex relationship between the composition, structure, and properties of the rare earth ions doped laser glasses. The development of high-performance laser glass usually relies on intuition and trial-and-error. Recently, with the proposal of the materials genome engineering, the “glass genome” has also attracted much attention. Here, the structure of the Nd³⁺ doped B₂O₃-Li₂O laser glasses was analyzed using Fourier transform infrared spectra and nuclear magnetic resonance, revealing that the glass contains similar glass-forming ion-centered coordination polyhedron structure groups to the neighbor congruent glassy compounds. The structure and properties of glass largely depend on the neighbor congruent glassy compounds. Therefore, the structure and luminescence properties of Nd³⁺ doped B₂O₃-Li₂O and B₂O₃-MgO-Li₂O laser glasses can be quantitatively predicted via the neighbor congruent glassy compounds. The predictive values are in good agreement with the experimental data, which indicates that our approach is an effective way to predict the structure and luminescence properties of Nd³⁺ doped borate laser glasses.     

Improved broadband near-infrared luminescence in Nd3+/Tm3+ co-doping tellurite glass with Ag NPs

The near-infrared (NIR) luminescence in S+E+O bands of tellurite glasses doped with Nd³⁺/Tm³⁺ and Ag nanoparticles (NPs) was investigated. The tellurite glasses were prepared by melt-quenching and heat-treated techniques. Under the excitation of 808 nm laser, Nd³⁺/Tm³⁺ doped tellurite glasses produced three NIR luminescence bands of 1.33, 1.47 and 1.85 μm, originating from Nd³⁺:⁴F_3/2→⁴I_13/2, Tm³⁺:³H₄→³F₄ and Tm³⁺:³F₄→³H₆ transitions respectively. Interestingly, a broadband luminescence spectrum ranging from 1280 to 1550 nm with the FWHM (full width at half maximum) about 201 nm was obtained due to the overlapping of the first two NIR bands. Further, the peak intensity of this broadband luminescence was increased by 75% after the introduction of Ag NPs with diameter in 10–20 nm. The analysis of fluorescence decay shows that compared with the enhanced local electric field, the energy transfer from Ag species to Nd³⁺ and Tm³⁺ ions plays a major role in luminescence enhancement. The findings in this work indicate that tellurite glass co-doped with Nd³⁺/Tm³⁺ and Ag NPs is a potential gain material applied in the S+E+O-band photonic devices.     

Quantitative prediction of the glass-forming region and luminescence properties in Tm3+-doped germanate laser glasses

Germanate laser glasses have received much attention as a promising host materials for mid-infrared fiber lasers in recent years because of the outstanding infrared transparency, low phonon energy, and high rare earth solubility of such glasses. However, the development of high-performance germanate laser glasses is usually based on intuition and a trial-and-error method, which can involve long experimental periods and high costs, and thus, this approach is highly inefficient. Recently, with proposals for materials genome engineering, the concept of the “glass genome” has grown of interest to us. Herein, the structures of Tm³⁺-doped germanate laser glasses (BaO–GeO₂ and BaO–La₂O₃–GeO₂) were investigated by Fourier transform infrared spectra (FTIR) and Raman spectra analyses, which revealed that the resulting glass contains similar structural groups to the neighboring congruently melted glassy compounds (NCMGCs) in the composition diagram. What is more, the structure and properties of the resulting laser glasses largely depend on NCMGCs. Then, the glass-forming region, physical properties, and luminescence properties were calculated via the use of NCMGCs in Tm³⁺-doped BaO–GeO₂ binary and BaO–La₂O₃–GeO₂ ternary laser glass systems. The calculated results were in good agreement with the experimental results, thus demonstrating that our approach is practical for predicting the glass-forming region, physical properties, and luminescence properties in Tm³⁺-doped BaO–GeO₂ binary and BaO–La₂O₃–GeO₂ ternary laser glass systems. This work may provide an effective method to develop Tm³⁺-doped germanate laser glasses rapidly and at low cost.     

Realization of pure red emission from energy transfer in the Er3+–Tm3+ system under 1550 nm excitation

NaY(WO₄)₂ is one of the excellent host materials for high-efficient upconversion luminescence, but it is still challenging to obtain red emission via lanthanide doping. In this work, pure red emission was achieved in the heavily-Er³⁺-doped NaY(WO₄)₂ by using a 1550 nm laser diode and introducing mediator Tm³⁺ ions in the lattice. On basis of the analysis of steady-state and transient-state luminescence properties related to dopant concentration and excitation wavelength, all possible red emission mechanisms were discussed. Finally, it has been demonstrated that the high-purity red emission was due to the several energy transfer processes between Er³⁺ and Tm³⁺. Our results provide a convenient pathway to investigate the upconversion luminescence mechanisms.     

Enhancing photovoltaic performance of dye-sensitized solar cell by rare-earth doped oxide of Lu2O3:(Tm, Yb)

In order to increase of the photocurrent, photovoltage and energy conversion efficiency of dye-sensitized solar cell (DSSC), rare-earth doped oxide of Lu₂O₃:(Tm³⁺, Yb³⁺) is prepared and introduced into the TiO₂ film in the DSSC. As a luminescence medium, Lu₂O₃:(Tm³⁺, Yb³⁺) improves incident light harvest via a conversion luminescence process and increases photocurrent; as a p-type dopant, the rare-earth ions elevate the energy level of the oxide film and increase the photovoltage. Under a simulated solar light irradiation of 100 mW cm⁻², the light-to-electric energy conversion efficiency of the DSSC with Lu₂O₃:(Tm³⁺, Yb³⁺) doping reaches 6.63%, which is increased by 11.1% compared to the DSSC without Lu₂O₃:(Tm³⁺, Yb³⁺) doping.     

Upconversion Luminescence in Yb/Ln (Ln = Er,Tm) Doped Oxyhalide Glasses Containing CsPbBr3 Perovskite Nanocrystals

Yb/Ln (Ln=Er, Tm) doped TeO₂-based glasses containing CsPbBr₃ perovskite quantum dots were successfully prepared via in-situ glass crystallization. The nanocomposites yield typical green downshifting luminescence attributing to CsPbBr₃ exciton recombination under UV excitation, and produce Er³⁺ green, Er³⁺ red and Tm³⁺ blue upconversion emissions under 980 nm laser excitation. Impressively, specific Ln³⁺ emissions will be quenched with the precipitation of CsPbBr₃ in glass, enabling to finely tune upconversion emitting color. Spectroscopic characterizations evidence that the luminescence quenching is originated from non-radiative reabsorption effect induced by the precipitation of CsPbBr₃ rather than energy transfers from Ln³⁺ to CsPbBr₃. Finally, these nanocomposites are demonstrated to exhibit superior water resistance due to the effective protecting role of dense structural glass, particularly, about 95% downshifting luminescence of CsPbBr₃ and upconversion luminescence of Er³⁺ related to pristine ones are retained after immersing the products in water up to 30 days.     

Color-tunable and white emission of Tm3+ doped transparent zinc silicate glass-ceramics embedding ZnO nanocrystals

Tm³⁺ doped zinc silicate glass-ceramics composed of SiO₂-Al₂O₃-ZnO-K₂O-Tm₂O₃ embedded with ZnO nanocrystals were successfully fabricated by melt-quenching method with subsequent heat treatment. Tm³⁺ ions and ZnO nanocrystals were introduced as blue and yellow luminescence centers, respectively. The effects of heat treatment, excitation wavelength and Tm³⁺ doping concentration on the photoluminescence behaviors of these glass-ceramics were studied. Short-time (5 minutes) heat treatment was considered as the optimal heat treatment time, which facilitates simultaneously emitting narrow blue peak located at 453 nm and a broad yellow band centered at 580 nm. Blue and yellow emissions could be attributed to the ¹D₂ → ³F₄ transition of Tm³⁺ and Zn_i/O_i-related defect emission of ZnO nanocrystals, respectively. The combination of these two emissions allows the realization of white light emitting in the glass-ceramic samples. Furthermore, tunable luminescent color and chromaticity coordinates, including yellow, white and blue, can be realized by varying the pumping wavelengths as well as the content of Tm³⁺ dopant in the glass matrix. Nearly perfect white light emission with Commission Internationale de l'Eclairage coordinate (x = 0.33, y = 0.32) was achieved for the 0.05 mol% Tm³⁺ doped glass-ceramic embedding ZnO nanocrystals by heat treatment at 750°C for 5 minutes under the excitation of 360 nm. These luminescent glass-ceramics doped with Tm³⁺ ion and ZnO nanocrystals could be a promising candidate for white light emitting devices under near-ultraviolet excitation.     

Fabrication,tunable fluorescence emission and energy transfer of Tm3+-Dy3+ co-activated P2O5–B2O3–SrO–K2O glasses

A growing demand for white light-emitting diodes (W-LEDs) gives rise to continuous exploration of functional fluorescence glasses. In this paper, Tm³⁺/Dy³⁺ single- and co-doped glasses with composition (in mol%) of 30P₂O₅–10B₂O₃–23SrO–37K₂O were synthesized using the melt-quenching method in air. The physical properties, glass structure, luminescence characteristics and energy transfer mechanism of the glasses were systematically studied. As glass network modifiers, Tm³⁺ and Dy³⁺ ions can densify the glass structure. Excitation wavelength and doping concentration of Tm³⁺/Dy³⁺ ions have a direct impact on the emission intensities of blue and orange light as well as the color coordinate of the as-prepared glasses. A white light very close to standard white light can be obtained under 354 nm excitation when the content of Tm³⁺ and Dy³⁺ is 0.2 mol% and 1.0 mol%, respectively. The results of the emission spectra and decay curves reveal the existence of energy transfer from Tm³⁺ to Dy³⁺. The analytic results based on the Inokuti-Hirayama model indicate that the electrical dipole-dipole interaction may be the main mechanism of energy transfer. Moreover, Tm³⁺/Dy³⁺ co-activated glass phosphor has good thermal stability and chrominance stability and it is a promising candidate for white LEDs and display device.     

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.     

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.     

Blue Upconversion Emission in Germanate Glass Co-Doped with Yb3+/Tm3+ Ions

In the paper, the upconversion luminescence of 70GeO₂–30[Ga₂O₃–BaO–Na₂O] glass system co-doped with Yb³⁺/Tm³⁺ ions was investigated. Strong blue emission at 478 nm corresponding to the transition ¹G₄ → ³H₆ in thulium ions was measured under the excitation of 976-nm diode laser. The dependence of the upconversion emission upon the thulium ion concentration was studied to determine the optimal conditions of energy transfer between energy levels of active dopants. The most effective energy transfer Yb³⁺ → Tm³⁺ was obtained in glass co-doped with molar ratio of dopant 0.7 Yb₂O₃/0.07 Tm₂O₃. The increase in thulium concentration more than 0.07 mol% results in the reverse energy transfer from Tm³⁺ → Yb³⁺, which leads to rapid quenching of the luminescence line at the wavelength 478 nm. In germanate glass co-doped with 0.7Yb₂O₃/0.07Tm₂O₃, the longest lifetime of ¹G₄ level equal 278 μs was achieved. The presented results indicate that elaborated germanate glass co-doped with Yb³⁺/Tm³⁺ ions is a promising material that can be used to produce fiber lasers and superluminescent fiber sources generating radiation in the visible spectrum.     

Effect of lanthanide doping on crystal phase and near-infrared to near-infrared upconversion emission of Tm doped KF–YbF3 nanocrystals

Tm³⁺ doped KF–YbF₃ nanocrystals were synthesized by a hydrothermal method using oleic acid as a stabilizing agent at 190 °C. The influence of Gd³⁺ and Sm³⁺ content on the phase structure and upconversion (UC) emission of the final products was investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM) and UC spectra. XRD analyses and TEM observations evidence that the phase and size of the as prepared Tm³⁺ doped KF–YbF₃ nanocrystals are closely related to the Gd³⁺ doping content. Without Gd³⁺ impurity, the undoped nanocrystals crystallize in orthorhombic KYb₂F₇ with an average diameter of 42 nm. When the Gd³⁺ doping is below 10 mol%, the orthorhombic KYb₂F₇ nanocrystals grow up. However, with Gd³⁺ addition beyond about 30 mol%, the complete phase transformation from orthorhombic KYb₂F₇ to cubic KGdF₄ occurs in the final products. Under the excitation of a 980 nm laser diode, the as prepared Tm³⁺ doped nanocrystals exhibit strong near-infrared UC emission at 800 nm. Particularly, the intensity of high energy UV and blue UC emissions of Tm³⁺ ions in Tm³⁺ doped KYb₂F₇ nanocrystals are selectively reduced compared to the NIR emission at 800 nm by co-doping a small amount of Sm³⁺ ions into the host matrix. Possible dynamic processes for UC emissions in Tm³⁺ doped nanocrystals are discussed in detail.     

Diffusion Properties of Tm3+ in Congruent LiNbO3 Crystal

Diffusion properties of Tm³⁺ in congruent LiNbO₃ crystal have been investigated, together with other two related issues, i.e., Tm³⁺‐doping contribution to refractive index of LiNbO₃ substrate and Li out‐diffusion. Four X‐cut and four Z‐cut congruent LiNbO₃ substrates locally coated with 15–31 nm‐thick Tm‐metal films were annealed in surrounding air under different temperatures of 1030°C–1130°C for different durations of 20–70 h. After anneal, refractive index at Tm³⁺‐doped and Tm³⁺‐free parts of crystal surface was measured at the wavelengths of 1311 and 1553 nm and surface Li₂O contents were evaluated from measured refractive index. The results show that Tm³⁺ doping has a weak effect on substrate index and a small contribution to index increment in waveguide layer in comparison with Ti⁴⁺‐ or Zn²⁺ doping. The Li₂O content at the Tm³⁺‐doped surface equals that at the Tm³⁺‐free surface. The Li out‐diffusion depends mainly on the diffusion temperature. Below 1100°C, the Li out‐diffusion is not measurable. At 1130°C, a 30‐h diffusion procedure may cause 0.2–0.3 mol% slight loss of Li₂O content. Secondary ion mass spectrometry was used to study the Tm³⁺ diffusion properties. The results show that the diffused Tm³⁺ ions in all samples follow a complementary error function profile. From measured Tm³⁺ profiles, characteristic diffusion parameters such as diffusivity, diffusion constant, activation energy, solubility, solubility constant, and heat of solution were obtained and discussed in comparison with the case of Er³⁺ diffusion. In comparison with Er³⁺ diffusion, the Tm³⁺ diffusion shows similar anisotropy and temperature dependence of solubility. In the aspect of diffusivity, under lower temperature the Tm³⁺ has a lower diffusivity than the Er³⁺, and their diffusivity difference reduces with the increased temperature and becomes null at 1130°C.     

Study on the color tunability and energy transfer mechanism in Tm3+/Dy3+ co-doped LiLaSiO4 phosphors

Many color-tunable LiLaSiO₄: αTm³⁺, βDy³⁺ phosphors were prepared using the traditional high-temperature solid-phase method. The phase composition, surface morphology, fluorescence spectrum, fluorescence lifetime, energy transfer mechanism, and color coordinates of the samples were analyzed using XRD, SEM, TEM and fluorescence spectrometer. The results show that LiLaSiO4: αTm3+ phosphor emits high intensity blue light at 460 nm and the concentration quenching point of Tm³⁺, α = 0.015 mol. In LiLaSiO₄: αTm³⁺, βDy³⁺ phosphors, as the doped Dy³⁺ doping increases, the luminescence intensity of Tm³⁺ gradually decreases, the luminescence intensity of Dy³⁺ first increases and then decreases. The concentration quenching point of Dy³⁺, β = 0.015 mol. Adjustable light-emitting color can be obtained by changing the doping molar mass of Dy³⁺ or the wavelength of the excitation light. There is an effective energy transfer between Tm³⁺→Dy³⁺. The energy transfer mechanism is the electric dipole-electric dipole interaction, and the energy transfer efficiency reaches 90.11% when β = 0.06 mol. The quantum yield of LiLaSiO₄:0.015 Tm³⁺,0.015Dy³⁺ was 39.0%. The single-matrix white light LiLaSiO₄: αTm³⁺, βDy³⁺ phosphors with excellent performance is a prospective material for of white LEDs.     

Surface modification and fabrication of white-light-emitting Tm3+/CdS quantum dots co-doped glass fibers

Due to the widely tunable band gap and broadband excitation, CdS quantum dots (QDs) show great promise for yellow-light luminescence center in white-light-emitting devices. The light intensity of the CdS QD-doped glass was enhanced by doping the Tm³⁺ ions due to the higher absorption rate. The influence of Tm³⁺ ions on the surface structure of CdS QDs was enormous according to the first-principles calculations. Doping Tm³⁺ ions change the surface state of CdS QDs, which will fix the QDs emission peaks and enhance the luminescence of CdS QDs at a lower heat-treatment temperature. White-light emission was obtained by tuning the relative concentration between Tm³⁺/CdS QDs. However, there is a fundamental challenge to fabricate QD-doped glass fibers by rod-in-tube method since uncontrollable QDs crystallization is hard to avoid. Herein, a white-light-emitting borosilicate glass fiber was fabricated by the “melt-in-tube” method using a special designed Tm³⁺/CdS QDs co-doped borosilicate glass with low-melting temperature as fiber core. After heat treatment, ideal white-light emission was observed from the fiber under excitation at single wavelength (359 nm). This finding indicates that Tm³⁺/CdS QDs co-doped glass fiber with white-light-emitting devices has potential application as gain medium of white-light-emitting sources and fiber lasers.     

Preparation and luminescence of Dy3+/Tm3+ co-doped Ca3NbGa3Si2O14 glass-ceramics for w-LED

In this work, a series of Dy³⁺ and Dy³⁺/Tm³⁺ ion activated Ca₃NbGa₃Si₂O₁₄ glass-ceramics were prepared by traditional melt crystallization method, and report on the structural, optical, and energy transfer (ET)-based photoluminescence (PL) properties of glass-ceramics co-doped Dy³⁺/Tm³⁺. The preparation of glass-ceramics was studied by DTA, XRD, SEM, and UV–vis photometer technology, phase composition, transmittance, optimum heat treatment conditions, and luminescence properties. The best heat treatment procedure for obtaining transparent and well-formed glass-ceramics is crystallization at 820 °C for 5 h. The spectra excited by Tm³⁺ and Dy³⁺ have intersections at 352 nm and 365 nm, which means that CNGS: Dy³⁺/Tm³⁺ can be effectively excited by 352 nm and 365 nm ultraviolet light. Under the excitation of 352 nm ultraviolet light, four main emission peaks corresponding to ¹D₂ →³F₄, ⁴F_9/2 → ⁶H_15/2, ⁴F_9/2 → ⁶H_13/2, ⁴F_9/2 → ⁶H_11/2 were found at 456 nm, 484 nm, 577 nm, and 663 nm, respectively. When the optimal concentration (4 at.%) of Dy³⁺ is Co-doped with a different amount of Tm³⁺, the luminous color can be adjusted by adjusting the doping amount of Tm³⁺ and changing the excitation wavelength. There is an overlapping region between the emission spectrum of Tm³⁺ doped glass and the excitation spectrum of Dy³⁺ doped glass, which indicates that there is energy transfer between Tm³⁺ and Dy³⁺. In addition, CNGS: Dy³⁺/Tm³⁺ CIE coordinates show that the color coordinates (0.3324, 0.3352) when y = 0.02 under 365 nm excitation are closest to the standard white light (0.333, 0.333), indicating that this glass has potential applications in WLED devices.     

Photoluminescence of Ag Nanoparticles and Tm3+ Ions in the Bismuth Germanate Glasses for the Blue Light‐Excited W‐LED

Materials containing rare‐earth ions and Ag nanoparticles (NPs) have been widely applied due to prior demonstration of increase in their luminescence properties. Here, Tm³⁺ ions‐doped bismuth germanate glasses were synthesized by a chemical reduction method based on the conventional melting‐quenching technique. The Ag NPs were facilely precipitated in the glass matrix by the chemical reduction method during the annealing process. TEM image shows that the Ag NPs are closely dispersed in the glass matrix. The luminescence properties and energy‐transfer mechanism were systematically investigated by means of absorption, emission, and excitation spectra. Significant enhancements of Tm³⁺ ions emission and a broad emission band centered at 568 nm caused by Ag NPs are observed upon 474‐nm excitation. Our research may illustrate the interactions between Tm³⁺ ions and Ag NPs and provide a simplified way to synthesize the high‐efficiency luminescent materials for the blue light‐excited W‐LEDs.