Synthesis,structure and photoluminescence properties of Tm3+/Dy3+ co-doped borate glass for near-UV white LEDs

Tm³⁺/Dy³⁺ single and co-doped SrO–MgO–B₂O₃ (SMB) glasses were fabricated via the conventional melt-quenching technique. The thermal stability of the host glass was determined by a differential scanning calorimetry (DSC) curve. X-ray diffraction (XRD) and Fourier transform infrared (FT-IR) spectroscopy were measured to characterize the structural properties and vibration features of the as-prepared glasses, respectively. The transmittances of the studied glasses can reach about 90% in the range from 300 to 800 nm. It can be confirmed that Tm³⁺/Dy³⁺ single and co-doped SMB glasses can all be efficiently excited by near-ultraviolet (NUV) light through absorption and photoluminescence excitation spectra. Moreover, the emission spectra and fluorescence decay curves confirmed the existence of energy transfer between Tm³⁺ and Dy³⁺. The Tm³⁺/Dy³⁺ co-doped glasses can both realize tunable emission from blue light to cool white and eventually to warm white light under the excitation of 352, 362, and 365 nm. Furthermore, by using the Inokuti-Hirayama (I–H) model, the energy transfer is testified to be carried out in Tm³⁺-Dy³⁺ clusters through the dipole-dipole (d-d) interaction mechanism. More importantly, the thermal stability of Tm³⁺/Dy³⁺ co-doped SMB glass was demonstrated by temperature-dependent emission spectra. Overall, these results fully indicate that Tm³⁺/Dy³⁺ co-doped SMB glasses have great potential to be used in NUV-based white light-emitting diodes with different requirements.     

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.     

Color-tunable luminescence performance of single-component Na5Y(MoO4)4:Dy3+, Tm3+ white-emitting phosphor for white light-emitting diodes

The single-component Na₅Y(MoO₄)₄:Dy³⁺, Tm³⁺ white-emitting phosphor was prepared by the sol-combustion method, and Tm³⁺ was codoped for color-tunable white emission. The XRD patterns confirm that the as-prepared samples have a Na₅Y(MoO₄)₄ structure and do not change with Dy³⁺/Tm³⁺ codoping. Under ultraviolet excitation at 352 nm, the Na₅Y(MoO₄)₄:Dy³⁺ phosphor shows a characteristic white emission consisting of a weak peak at 485 nm and a strong peak at 577 nm. By codoping a small amount of Tm³⁺, the blue emission of phosphor is enhanced, and the chromaticity coordinates can be adjusted between (0.3663, 0.416) and (0.319, 0.3407); thus, color-tunable white emission is achieved with the synergistic effect of Dy³⁺ and Tm³⁺. The luminescence intensity of Na₅Y(MoO₄)₄:Dy³⁺, Tm³⁺ at 483 K still retains 72% of the initial intensity, showing excellent thermal stability. By combining Na₅Y(MoO₄)₄:Dy³⁺, Tm³⁺ with a 365 nm chip, the fabricated w-LED device emits bright white light for illumination. Therefore, the as-prepared Na₅Y(MoO₄)₄:Dy³⁺, Tm³⁺ has potential applications in the field of w-LEDs as white-emitting phosphors.     

Bright White‐Emitting Phosphors Ba2Gd(BO3)2Cl: Dy3+/Dy3+‐Tm3+ for Hg‐Free Lamps and White LEDs Applications

Spectroscopic properties of Ba₂Gd(BO₃)₂Cl: Dy³⁺ and Ba₂Gd(BO₃)₂Cl: Dy³⁺, Tm³⁺ under vacuum ultraviolet (VUV) and ultraviolet (UV) light excitations were investigated. Dy³⁺ single‐doped Ba₂Gd(BO₃)₂Cl showed broad absorption band in the VUV region, and bright warm white light with chromaticity coordinates (CIE) of (0.340, 0.381) upon VUV excitation at 172 nm, demonstrating this phosphor's applicability in mercury free lamps. Upon direct excitation Tm³⁺ from its ⁶F₆ level to ¹D₂ level, the decrease of emission intensity and lifetime of Tm^{3+ 1}D₂–³F₄ emission with increasing concentration of Dy³⁺ in Ba₂Gd(BO₃)₂Cl: Dy³⁺, Tm³⁺ confirmed the occurrence of energy transfer from Tm³⁺ to Dy³⁺. In addition, Ba₂Gd(BO₃)₂Cl: Dy³⁺, Tm³⁺ could be efficiently excited by 358 nm UV light and its emission color could be tuned from blue to yellow by codoping Tm³⁺. When 1% Tm³⁺ and 5% Dy³⁺ were codoped in the Ba₂Gd(BO₃)₂Cl, intensive white‐emitting light with CIE of (0.352, 0.328) and correlated color temperature of 4589 K was achieved upon 358 nm excitation, revealing the potential application of Ba₂Gd(BO₃)₂Cl: Dy³⁺, Tm³⁺ for white light‐emitting diodes (LEDs).     

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.     

Ce3+ induced broadband enhancement around 2 μm in Tm3+/Ho3+ co-doped tellurite glass

Tellurite glasses doped with Tm³⁺, Ho³⁺ and Ce³⁺ ions were prepared via melt-quenching to realise broadband and fluorescence enhancement in near-infrared (NIR) band. Under the pumping of a commercial 808 nm laser diode (LD), the emission bands at 2.0 μm, 1.85 μm, 1.47 μm, and 705 nm were observed in the Tm³⁺/Ho³⁺ co-doping glass samples, which originated from the transitions of Ho³⁺:⁵I₇→⁵I₈ and Tm³⁺:³F₄→³H₆, ³H₄→³F₄, ³F_2,3 → ³H₆, respectively. The existence of 2.0 μm band fluorescence is due to the energy transfer from the Tm³⁺:³F₄ level to the Ho³⁺:⁵I₇ level. This band overlaps with the 1.85 μm band which forms a broadband fluorescence spectrum in the range of 1600–2200 nm. In glass samples co-doped with Tm³⁺/Ho³⁺ with 0.085 mol% Ho₂O₃ and 1 mol% Tm₂O₃, the full width at half maximum (FWHM) of this broadband spectrum (1600–2200 nm) was as high as ∼370 nm. After introducing 0.6 mol% CeO₂, the emission intensity of broadband fluorescence increased by ∼50%, which was caused by the cross-relaxations between Ce³⁺ and Tm³⁺ ions. The lifetime of fluorescence decay was determined to prove the interactions among the doped rare-earth ions, the radiative parameters such as transition probability, branching ratio and radiative lifetime were calculated from the absorption spectra based on the Judd-Ofelt theory to better understand the observed luminescence phenomena. In addition, X-ray diffraction (XRD) confirmed the amorphous state structure of the synthesised glass samples, while Raman spectrum revealed the different vibrational structural units forming the glass network.     

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.     

Upconverting luminescence based dual-modal temperature sensing for Yb3+/Er3+/Tm3+: YF3 nanocrystals embedded glass ceramic

Yb³⁺/Er³⁺/Tm³⁺ doped transparent glass ceramic containing orthorhombic YF₃ nanoparticles was successfully synthesized by a melt-quenching method. After glass crystallization, tremendously enhanced (about 5000 times) upconversion luminescence, obvious Start-splitting of emission bands as well as long upconversion lifetimes of Er³⁺/Tm³⁺ confirmed the incorporation of lanthanide activators into precipitated YF₃ crystalline environment with low phonon energy. Furthermore, temperature-dependent upconversion luminescence behaviors of glass ceramic were systematically investigated to explore its possible application as optical thermometric medium. Impressively, both fluorescence intensity ratio of Er³⁺: ²H_11/2 → ⁴I_15/2 transition to Er³⁺: ⁴S_3/2 → ⁴I_15/2 one and fluorescence intensity ratio of Tm³⁺: ³F_2,3 → ³H₆ transition to the combined Tm³⁺: ¹G₄ → ³F₄/Er³⁺: ⁴F_9/2 → ⁴I_15/2 ones were demonstrated to be applicable as temperature probes, enabling dual-modal temperature sensing. Finally, the thermal effect induced by the irradiation of 980 nm laser was found to be negligible in the glass ceramic sample, being beneficial to gain intense and precise probing signal and detect temperature accurately.     

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.     

Efficient sensitization of Tb3+ emission by Dy3+ in CaMoO4 phosphors: Energy transfer,tunable emission and optical thermometry

Dy³⁺/Tb³⁺ codoped CaMoO₄ phosphors were synthesized by a simple sol–gel method and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and photoluminescence spectroscopy. The energy transfer process of Dy³⁺→Tb³⁺ was confirmed by excitation and emission spectra and luminescence decay curves, and the energy transfer efficiency was also estimated. The results verified that the efficient emission of Tb³⁺ was sensitized by Dy³⁺ under the excitation of 354 nm, realizing tunable emission in CaMoO₄ phosphors. Furthermore, optical thermometry was achieved by the fluorescence intensity ratio between Tb³⁺: ⁵D₄→⁷F₅ (~546 nm) and Dy³⁺: ⁴F_9/2→⁶H_13/2 (~575 nm). It is expected that the investigated CaMoO₄ nanograins doped with Dy³⁺/Tb³⁺ have prospective applications in display technology and optical thermometry.     

Excitation-dependent energy transfer and color tunability in Dy3+/Eu3+ co-doped multi-component borophosphate glasses

Using the melt-quench technique, potassium zinc borophosphate (KZnBP) glasses incorporated with Dy³⁺, Eu³⁺, and Dy³⁺/Eu³⁺ ions individually and combinedly were prepared, and their photoluminescence (PL)-related features were investigated. The KZnBP glass containing an optimized content of Dy³⁺ (0.5 mol%) is co-doped with Eu³⁺ in various contents, and the energy transfer (ET) process between them was studied at λ_exci = 349, 364, 387 (Dy³⁺), and 394 nm (Eu³⁺). The Dy³⁺/Eu³⁺ co-doped system, when excited with Dy³⁺ excitations has resulted in a significant decrease in the intensity of Dy³⁺ peaks observed at 480 nm (⁴F_9/2→⁶H_15/2, blue) and 574 nm (⁴F_9/2→⁶H_13/2, yellow), with simultaneous enhancement of the intensity of Eu³⁺ peaks at 591 nm (⁵D₀→⁷F₁, orange) and 617 nm (⁵D₀→⁷F₂, red). This trend is due to the efficient energy transfer from Dy³⁺ to Eu³⁺, indicating that Eu³⁺ ions were sensitized by Dy³⁺ ions. Dexter's theory and the Inokuti–Hirayama (I–H) model revealed that the dipole–dipole interaction is accountable for the energy transfer from Dy³⁺ to Eu³⁺ through energy-transfer channels [⁴F_9/2(Dy³⁺)+⁷F_1,2(Eu³⁺)→⁶H_15/2(Dy³⁺)+⁵D₂(Eu³⁺)] and [⁴F_9/2(Dy³⁺)+⁷F₀(Eu³⁺)→⁶H_13/2(Dy³⁺)+⁵D₀(Eu³⁺)]. The color coordinates of the Dy³⁺/Eu³⁺ co-doped glasses under various excitations fall within the white light emission spectrum, indicating their potential application in warm white LEDs.     

Persistent luminescence of Eu/Dy-doped Sr2MgSi2O7 glass-ceramics processed by aerodynamic levitation

Glass beads of the Sr₂MgSi₂O₇ stoichiometric composition and a non-stoichiometric composition with higher SiO₂/SrO ratio doped with Eu₂O₃/Dy₂O₃ were prepared through aerodynamic levitation coupled to CO₂ laser heating. The glass beads were subsequently treated at 1100 ºC to produce glass-ceramics with Sr₂MgSi₂O₇: Eu²⁺, Dy³⁺ as the main crystalline phase. The doped glasses exhibit red emissions; after crystallisation, the corresponding glass-ceramics emit blue light under UV excitation. The starting glass composition considerably affects the crystallisation process, resulting in Sr₂MgSi₂O₇ glass-ceramics with very different microstructures which, in turn, have a significant influence on the luminescence properties. The photoluminescence emission spectra of the glass-ceramics under UV light show a broadband emission (λ = 400–500 nm) with a main peak assigned to the typical Eu²⁺ transition under excitation at 365 nm. Both the intensity of the emission and the persistence time significatively increase on decreasing temperature. Glass-ceramics from the non-stoichimetric glass composition co-doped with 1Eu₂O₃/0.5Dy₂O₃ (mol%.) provided the longest persistence times.     

Luminescence Properties and Energy‐Transfer Behavior of a Novel and Color‐Tunable LaMgAl11O19:Tm3+, Dy3+ Phosphor for White Light‐Emitting Diodes

Novel LaMgAl₁₁O₁₉:Tm³⁺, Dy³⁺ phosphors were prepared utilizing a high‐temperature solid‐state reaction method. The phase formation, luminescence properties, energy‐transfer mechanism from the Tm³⁺ to the Dy³⁺ ions, the thermal stability, and CIE coordinates were investigated. When excited at 359 nm, the LaMgAl₁₁O₁₉: xTm³⁺ phosphors exhibit strong blue emission bands at 455 nm. After codoping with Dy³⁺ and excitation at 359 nm, the LaMgAl₁₁O₁₉:0.03Tm³⁺, yDy³⁺ phosphors emitted white light consisting of the characteristic emission peaks of Tm³⁺ and Dy³⁺. The Dy³⁺ emission intensity increased with the Dy³⁺ concentration due to the energy transfer from Tm³⁺ to Dy³⁺, and concentration quenching due to the high Dy³⁺ doping concentration (y = 0.1 mol) did not occur. The calculation of the CIE coordinates of the LaMgAl₁₁O₁₉:Tm³⁺, yDy³⁺ phosphors revealed the tunability of the emission color from blue to bluish‐white and to white by changing the excitation wavelength and the doping concentration. An energy transfer from Tm³⁺ to Dy³⁺ by dipole–dipole interaction was confirmed by the decay curve, lifetime, and energy‐transfer efficiency measurements. When excited at 359 nm, the LaMgAl₁₁O₁₉:Tm³⁺, Dy³⁺ phosphor also showed good thermal stability, suggesting that it can be used in white LEDs excited by a GaN‐based ultraviolet LED.     

Structural and Optical Properties of Tunable Warm‐White Light‐Emitting ZrO2:Dy3+–Eu3+ Nanocrystals

A series of Dy³⁺–Eu³⁺‐codoped ZrO₂ nanocrystals with tetragonal and cubic symmetry was synthesized via a wet chemical reaction. When the Eu³⁺‐doping content was fixed, the crystal structure could be stabilized from the mixed phase to single cubic phase by simply adjusting the content of Dy³⁺. The cubic ZrO₂:Dy³⁺–Eu³⁺ nanoparticles exhibited spherical and nonagglomerated morphology. The effective phonon energy of cubic ZrO₂:5%Dy³⁺–5%Eu³⁺ was calculated to be 445 cm^?1, which is lower than the previously reported results. Extensive luminescence studies of ZrO₂:Dy³⁺–Eu³⁺ as a function of Dy³⁺ content demonstrated that the dopant concentration and its site symmetry play an important role in the emissive properties. Under 352 nm excitation, the increment of Dy³⁺ concentration in ZrO₂:Dy³⁺–Eu³⁺ led to an increase in orange (590 nm) and red (610 nm) emissions of Eu³⁺ ions, which are attributed to the ⁵D₀→⁷F_J(J = 1, 2) transitions of Eu³⁺ ions. This increment is possibly due to the efficient energy transfer (ET) ⁴F_9/2:Dy³⁺→⁵D₀:Eu³⁺. The phosphors can generates light from yellow through near white and eventually to warm white by properly tuning the concentration of Dy³⁺ ions through the ET and change in site symmetry. These phosphors may be promising as warm‐white‐/yellow‐emitting phosphors.     

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.     

White‐Light and Yellow/Blue Photoluminescence Emission Based on Dy3+‐Doped SiO2–Gd2O3 Composites

This work attempts to obtain Dy³⁺‐doped SiO₂–Gd₂O₃ by sol–gel process_, with a molar ratio of 70Si⁴⁺–30Gd³⁺ and Dy³⁺ concentrations of 0.1, 0.3, 0.5, and 1 mol%. Heat treatment at temperatures of 1000°C, 1100°C, 1200°C, and 1300°C have been performed. From XRD, the Gd₂O₃ cubic phase was observed at 1000°C and 1100°C, at 1200°C also were observed Gd₂O₃ monoclinic phase, predominant at 1300°C. The band‐gap values vary between 4.4 and 5.3 eV, showing dependence on the crystalline phase. Under UV excitation, emission spectra show bands assigned to the Dy³⁺ transitions: ⁴F_9/2→⁶H_15/2 (484 nm), ⁴F_9/2→⁶H_13/2 (572 nm), and ⁴F_9/2→⁶H_11/2 (668 nm). The excitation at 275 nm has shown more effective. The ratio between the most intense emission bands (yellow/blue) show values around 0.84 and 1.63. CIE chromaticity diagrams show color coordinates at blue, yellow, and white regions, as a function of Dy³⁺ concentration and heat treatment. The lifetime values of excited state ⁴F_9/2 were around 0.20 and 0.69 ms. The morphology of particles changed from spherical to coral‐like shape as a function of heat treatment are observed. The sol–gel process showed to be an interesting route to obtain Dy³⁺‐doped binary system materials.     

Structural,optical, and spectroscopic properties of Er3+-doped TeO2–ZnO–ZnF2 glass-ceramics

Transparent fluorotellurite glass-ceramics have been obtained by heat treatment of precursor Er-doped TeO₂–ZnO–ZnF₂ glasses. ErF₃ nanocrystals nucleated in the glass-ceramics have a typical size of 45 ± 10 nm. Based on the Judd-Ofelt theory, the main radiative parameters for the ⁴I_13/2 → ⁴I_15/2 transition have been obtained. The split of the absorption and emission bands and the reduction of the Ω₂ parameter, as compared to the glass, confirm the presence of Er³⁺ ions in a crystalline environment in glass-ceramic samples. The analysis of the ⁴I_13/2 decays suggests that a fraction of Er³⁺ ions remains in a glass environment while the rest forms nanocrystals. For the glass-ceramics, intense red and green upconversion emissions were observed with an enhancement of the ⁴F_9/2 → ⁴I_15/2 red one compared to the glass sample. The temporal evolution of the red emission together with the excitation upconversion spectra suggests that energy transfer processes are responsible for the enhancement of the red emission.     

Relying on energy transfer to enhance the 2.9 μm emission by co-doped Tm3+ ions in Dy:Y2O3 transparent ceramics

2 at.% Tm, xat.% Dy:Y₂O₃ (x = 0, 0.1, 0.5 and 1) transparent ceramics were fabricated via vacuum sintering. The microstructural properties of the prepared ceramics were determined using XRD and SEM. The absorption cross-section of 2 at.% Tm, 1 at.% Dy:Y₂O₃ ceramic was 0.53 × 10^?20 cm² with the FWHM of 43.59 nm. The increased cross-section originates from a large overlapping range appearing in the absorption spectrum of the Dy³⁺:⁶H_15/2 → ⁶F_5/2 and Tm³⁺:³H₆→⁶H₄ transitions. The J-O intensity parameters Ω₂, Ω₄ and Ω₆ and the fluorescence characteristics of the pivotal luminescent level of the Dy³⁺ ions were investigated. Under 793 nm excitation, the emission cross section of the Tm,Dy:Y₂O₃ ceramic at 3094 nm was 3.63 × 10^?21 cm² with the FWHM of 355 nm. The fluorescence lifetimes of Dy³⁺:⁶H_13/2 level of 2 at.% Tm, xat.% Dy:Y₂O₃ (x = 0.1, 0.5 and 1) ceramics were fitted to be 357 μs, 282 μs and 149 μs, respectively. In order to explore the quenching mechanism of Tm³⁺:³F₄ level, the fluorescence lifetimes of Tm³⁺:³F₄ of the 2 at.% Tm, xat.% Dy:Y₂O₃ ceramics (x = 0, 0.1, 0.5 and 1) were measured to be 4.878 ms, 462 μs, 104 μs and 61 μs, respectively. The possible energy transfer mechanisms between Tm³⁺ and Dy³⁺ ions are discussed. The results show that adding Tm³⁺ ions to Dy:Y₂O₃ ceramics can effectively enhance the 2.9 μm MIR through energy transfer.     

Sensitization effect of Nd3+ ions on Yb3+/Nd3+ co-doped oxyfluoride glasses and study of their optical,fluorescence, and upconversion abilities for visible laser and NIR amplifier applications

The development of laser technology has created intense demand for optical confinement materials with high performance. Herein the authors have been investigated Yb³⁺-singly doped and Yb³⁺/Nd³⁺-codoped SiO₂-based oxyfluoride glasses in terms of their optical absorption, and their near-infrared (NIR) and up-conversion (UC) emissions including emission decay profiles. Under 808 nm laser diode (LD) excitation, four NIR emission bands were observed i.e., (Nd³⁺: ⁴F_3/2 → ⁴I_9/2, Yb³⁺: ²F_5/2 → ²F_7/2, Nd³⁺: ⁴F_3/2 → ⁴I_11/2, and Nd³⁺: ⁴F_3/2 → ⁴I_13/2) in co-doped glasses. NIR emission cross-sections [(σ_emi) stimulated, (σ^M_emi) from Mc-cumber theory] were calculated for ²F_5/2 → ²F_7/2 (～1030 nm) transition of Yb³⁺ ion. σ_emi was found to be highest (26.27 × 10^?21 cm²) for the Yb³⁺: ²F_5/2 → ²F_7/2 transition in N2 glass. UC emission spectra recorded at 980 nm LD show bands centered at 500, 536, 595 & 610, and 664 nm, attributed to ⁴G_9/2 → ⁴I_9/2, ⁴G_7/2 → ⁴I_9/2& ⁴G_7/2 → ⁴I_11/2, ⁴G_5/2 → ⁴I_9/2, and ⁴G_9/2 → ⁴I_13/2 transitions, respectively. Decay profiles were analyzed for Yb³⁺: ²F_5/2 → ²F_7/2 (～1030 nm) and Nd³⁺: ⁴F_3/2 → ⁴I_11/2 (～1057 nm) transitions at 808 nm LD. Energy transfer (ET) process from Nd³⁺ to Yb³⁺ in present glasses were detailed.     

Tunable single-phased white-emitting Sr3Y(PO4)3:Dy3+ phosphors for near-ultraviolet white light-emitting diodes

Single-component white-emitting Sr₃Y(PO₄)₃:Dy³⁺ phosphors were synthesized by a high-energy deformation process. X-ray diffraction patterns showed the resulting crystallized phase to be of cubic structure, space group I-43d (no. 220). The broad-band excitation spectra between 250 and 500 nm were observed by monitoring the emission wavelength at 576 nm, which matches well with commercial near-UV or blue LED chips. Under a 352 nm excitation, the emission peaks were observed at 483 nm (blue), 576 nm (yellow), and 666 nm (red), corresponding to the ⁴F_9/2 → ⁶H_15/2, ⁴F_9/2 → ⁶H_13/2, and ⁴F_9/2 → ⁶H_11/2 transitions of Dy³⁺ ions. The optimized doping concentration of Dy³⁺ ion was 8 mol%. By controlling the Dy³⁺ ion concentration, tunable colors from white to yellow were obtained in Sr₃Y(PO₄)₃:Dy³⁺ phosphors. These results reveal that studied materials may be a promising candidate for white LED applications.