Effective sensitization of Eu3+ ions on Eu3+/Nd3+ co-doped multicomponent borosilicate glasses for visible and NIR luminescence applications

Eu³⁺/Nd³⁺ co-doped multicomponent borosilicate glasses (ND1E: 10BaO +10ZnF₂+10K₂O +20SiO₂+(49-x) B₂O₃+1Nd₂O₃+xEu₂O₃) were prepared by conventional melting and rapid quench technique to evaluate the effect of Eu³⁺ ions in the Nd³⁺ doped glasses. Thermal stability, structural and spectroscopic characteristics of the ND1E glasses were investigated by using DSC, XRD, FTIR, Optical absorption, excitation and emission measurements. The Judd – Ofelt (JO) analysis is implemented to the absorption spectrum of the prepared glassy matrix in order to identify their potential applicability in lasing devices. Enhancement of ⁷F₀ → ⁵L₆ band (394 nm) with the increasing concentration of Eu³⁺ ion in the Nd³⁺ excitation spectra (λ_emi = 1060 nm) reveals the possibility of obtaining the characteristic fluorescence spectra of Nd³⁺ ion with the typical excitation wavelengths (Nd³⁺ = 584 nm and Eu³⁺ = 394 nm) of both rare earth ions and it is further verified from the emission spectrum. This interesting luminescence effect of showing excellent visible and NIR emission under 394 nm excitation mainly attributes the energy transfer mechanism between the RE³⁺ ions and the reason underlying this effect is discussed in detail with the help of partial energy level diagram. Energy transfer efficiency between the Eu³⁺ and Nd³⁺ ions were evaluated by using the radiative lifetimes of the prepared glasses. Also, a comparison of radiative properties and lasing characteristics of Eu³⁺/Nd³⁺ co-doped glasses with other Nd³⁺ glasses are reported. The emission intensities were characterized using CIE chromaticity diagram and the observed CIE coordinates shows a shift towards reddish – orange region with the increase in Eu³⁺ concentration. The quantum efficiency of the prepared glasses was determined experimentally. The obtained results suggest that the ND1E glassy system can be considered as a potential candidate for visible and NIR luminescence applications.     

Energy transfer and controllable colors of upconversion emission in Er3+ and Dy3+ co-doped CaF2 transparent ceramics

x at. % Er³⁺, 3 at. % Dy³⁺: CaF₂ transparent ceramics (x=1-5) with good transparency were fabricated by hot-pressed sintering. The phase composition of nanoparticles and transparent ceramics, microstructure, in-line transmittance, upconversion spectra and lifetime of transparent ceramics, as well as energy transfer mechanism between Er³⁺ and Dy³⁺ were investigated. The mean grain sizes of nanoparticles decreased from 33.0 nm to 26.2 nm with the Er³⁺ doping concentration increasing from 1 to 5 at.%. The microstructure of ceramic samples presented nearly dense microstructure and EDS analysis indicated Er³⁺ and Dy³⁺ were uniformly incorporated into CaF₂ lattice. Under 900 nm excitation, the emission intensity for ⁴F_9/2→⁶H_15/2 transition of Dy³⁺ decreased and for ⁴S_3/2→⁴I_15/2 transition of Er³⁺ increased, the lifetime for the ⁴F_9/2 level of Dy³⁺ decreased while the ⁴F_7/2 level of Er³⁺ increased with the raise of Er³⁺ doping concentration. The energy transfer mechanism was proved to be the dipole-dipole interaction. The upconversion luminescence color was tuned from orange through yellow to green by changing the Er³⁺/Dy³⁺ ratio. In addition, the Vickers hardness, fracture toughness, and the thermal conductivity of Er³⁺, Dy³⁺: CaF₂ transparent ceramics were discussed. All the results showed the Dy³⁺ could be used as a sensitizer for Er³⁺: CaF₂ transparent ceramic in the upconversion field.     

Preparation of Er3+/Yb3+ co-doped zeolite-derived silica glass and its upconversion luminescence property

A novel upconversion luminescence transparent glass has been successfully synthesized from Er³⁺/Yb³⁺ co-doped zeolite powder by Spark Plasma Sintering (SPS) method through the order–disorder transition process. XRD was used to detect the order–disorder transition process of each phase after SPS. These zeolite-derived silica glasses showed enhanced upconversion luminescence under the excitation of 980 nm diode laser, which was caused by the change of phonon energy according to the results of Raman spectrum, and the corresponding energy transfer mechanism was also discussed in detail.     

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.     

The effect of Li+ incorporation in Yb3+-Nd3+ co-doped CaF2 phosphors over the NIR photoluminescence emission excited under visible light

The structural and optical characteristics of Nd³⁺-Yb³⁺ doped CaF₂ phosphors with and without the addition of Li⁺ ions are described in this work. The phosphors synthetized by hydrothermal and co-precipitation methods showed near-infrared (NIR) luminescence emission associated with inter-electronic transition of the Yb³⁺ ion in the range of 900–1050 nm via energy transfer process from Nd³⁺ ions under visible light excitation. The addition of Li⁺ to these phosphors resulted in an improvement of the NIR luminescence intensity by a factor up to 5. The effect of the incorporation of Li⁺ ions into the CaF₂ crystallite structure, the reduction of luminescence quenching states, as well as the energy transfer mechanism involved are discussed.     

Detailed optical analysis of Dy3+ and Pr3+ co-doped alumino-borate glasses for visible lighting applications

A new glass series with nominal molar composition of 60B₂O₃ + 30NaF + 10Al₂O₃ co-doped with Dy³⁺ and Pr³⁺, synthesized by melt quench was reported. The influence of Rare Earth (RE) ratio variation on prepared glasses was investigated by using Fourier Transform Infra-Red spectroscopy, UV–Vis–NIR absorption spectroscopy, Photoluminescence, Decay curves and Density measurements. Their X-Ray Diffraction and FTIR spectra revealed the glassy nature and confirmed that AlO₆, AlO₄, BO₃ and BO₄ units are the main structural units of that matrix. A non-linear variation following the same trend for tetragonal borate units (N₄), Band gap, non-linear optical properties, Density, Molar Volume etc. was observed. Different optical parameters were obtained by UV–Vis–NIR spectroscopy. The Bonding parameter obtained from Nephelauxetic study indicated ionic nature of Dy³⁺ and covalent nature of Pr³⁺ ions. Photoluminescence excitation and emission spectra were recorded under variety of excitation wavelengths and corresponding color parameters were calculated using 1931 CIE standards. A detailed yellow to blue ratio analysis was reported as a function of RE ion concentration and excitation wavelengths. Composition DPNAB(x = 0.7) displayed the best performance with CIE coordinates (0.33, 0.37). Existence of Energy transfer from Dy³⁺ and Pr³⁺ was evidenced by the spectral overlap diagram and lifetime values obtained from fitting of Decay curves. From the obtained results, prepared glasses can be suggested for solid-state lighting devices like WLEDs and display devices.     

Tunable colors and applications of Dy3+/Eu3+ co-doped CaO-B2O3-SiO2 glasses

A series of Dy³⁺/Eu³⁺ single- and co-doped calcium borosilicate luminescent glasses were prepared by the conventional high temperature melt-quenching method. A compact glass structure is obtained by the addition of Dy³⁺/Eu³⁺ ions, which is verified by the physical properties of synthetic glasses. As network modifiers, Dy³⁺/Eu³⁺ fill in the interspaces of glass network and contribute to the conversion of [BO₃] to [BO₄]. Dy³⁺/Eu³⁺ co-doped calcium borosilicate glasses can emit white light, which consists of blue, yellow, and red light under 387 nm excitation. The emission spectra and decay curves of the white-emitting glasses have proved the existence of energy transfer. The average lifetime of Dy³⁺ decreases from 0.251 to 0.165 ms with the increasing Eu³⁺ concentration. Changing rare earth ions concentration, CIE color coordinates of Dy³⁺/Eu³⁺ co-doped glass shifts from cyan to white with increasing excitation wavelength. A white-light emission is obtained when the concentration of Dy³⁺ and Eu³⁺ equals to 4% and 2%, respectively. Moreover, the Dy³⁺/Eu³⁺ co-doped calcium borosilicate glass shows high-thermal stability and it may be applicable for high-quality white LEDs based on high power near ultraviolet (n-UV) LED chip in the future.     

Influence of Cr3+ on yellowish-green UC emission and energy transfer of Er3+/Cr3+/Yb3+ tri-doped zinc silicate glasses

In this paper, we study the influence of Cr³⁺ on yellowish-green upconversion (UC) emission and the energy transfer (ET) of Er³⁺/Cr³⁺/Yb³⁺ tri-doped in SiO₂–ZnO–Na₂O–La₂O₃ (SZNL) zinc silicate glasses under excitation of the 980 nm laser diode (LD). The influence of Cr³⁺ on enhancing the red UC emission of Er³⁺/Cr³⁺/Yb³⁺ tri-doped in SiO₂–ZnO–Na₂O–La₂O₃ zinc silicate glasses under the excitation of 980nm LD was also investigated. The ET processes between Yb³⁺, Cr^3+, and Er³⁺, together with the combination of Yb³⁺-Cr³⁺-Er³⁺, which led to the green UC emission intensity of Er³⁺/Cr³⁺/Yb³⁺ tri-doped in SiO₂–ZnO–Na₂O–La₂O₃ zinc silicate glasses bands centered at ~546 nm have been significantly enhanced. By increasing the concentration of Cr³⁺ from 0 up to 5 mol.%, we can locate the Commission Internationale de l'éclairage (CIE) 1931 (x; y) chromaticity coordinates for UC emissions of Er³⁺/Cr³⁺/Yb³⁺ tri-doped in the central position of the yellowish-green color region of CIE 1931 chromaticity diagram. Besides, the ET processes between the Yb³⁺, Cr³⁺, and Er³⁺ are also proposed and discussed.     

Energy transfer,tunable emission and optical thermometry in Tb3+/Eu3+ co-doped transparent NaCaPO4 glass ceramics

Tb³⁺/Eu³⁺ co-doped glass ceramics containing NaCaPO₄ nanocrystals were successfully synthesized via traditional melt-quenching route with further heat-treatment and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and photoluminescence spectroscopy. The energy transfer process of Tb³⁺→Eu³⁺ was confirmed by excitation and emission spectra and luminescence decay curves, and the energy transfer efficiency was also estimated. The results indicated that the efficient emission of Eu³⁺ was sensitized by Tb³⁺ under the excitation of 378 nm, realizing tunable emission in the transparent bulk glass ceramics containing NaCaPO₄ nanocrystals. Furthermore, optical thermometry was achieved by the fluorescence intensity ratio between Tb³⁺:⁵D₄→⁷F₅ (~542 nm) and Eu³⁺:⁵D₀→⁷F₂ (~612 nm). The maximum absolute sensitivity of 4.55% K⁻¹ at 293 K and the maximal relative sensitivity of 0.66% K⁻¹ at T=573 K for Tb³⁺/Eu³⁺ co-doped transparent NaCaPO₄ glass ceramic are obtained. It is expected that the investigated transparent NaCaPO₄ glass ceramics doped with Tb³⁺/Eu³⁺ have prospective applications in display technology and optical thermometry.     

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.     

Up-conversion luminescence and optical thermometry properties of transparent glass ceramics containing CaF2:Yb3+/Er3+ nanocrystals

A series of Yb³⁺/Er³⁺ codoped transparent oxyfluoride glass ceramics with various amounts of Yb³⁺ have been successfully fabricated and characterized. Under 980 nm laser prompting, the samples produce intense red, green and blue up-conversion emissions, and the emission intensities increase with Yb³⁺ concentration and heat treatment temperature. Before losing good transparency in the visible region, optimum emission intensities are obtained for the sample with 25 mol% of Yb³⁺ at a heat treatment temperature of 680 °C. A possible up-conversion mechanism is proposed from the dependence of emission intensities on pumping power. The fluorescence intensity ratio between the two thermally coupled levels ²H_11/2 versus ⁴S_3/2 was measured with the laser output power of 57 mW to avoid the possible laser induced heating effect. The fluorescence intensity ratio values in the temperature range from 295 K to 723 K can be well fitted with the equation: A exp (−∆E/k_BT), where A = 6.79 and ∆E=876 cm⁻¹. The relative temperature sensitivity at 300 K was evaluated to be 1.4% K⁻¹. All the results suggest that the Yb³⁺/Er³⁺ codoped CaF₂ glass ceramics is an efficient up-conversion material with potential in optical fiber temperature sensing.     

Enhanced up-conversion luminescence and optical thermometry characteristics of Er3+/Yb3+ co-doped Sr10(PO4)6O transparent glass-ceramics

In this paper, the Yb³⁺/Er³⁺ co-doped parent glass (PG) with composition (in mol%) of 30P₂O₅-10B₂O₃-38SrO-22K₂O and transparent glass-ceramics (GCs) containing hexagonal Sr₁₀(PO₄)₆O nanocrystals (NCs) were synthesized for the first time by melt-quenching method and subsequent heating treatment in air. Under 980 nm laser prompting, the GCs samples showed intense red and green up-conversion emissions compared to those characteristics for the PG sample. The emission intensities varied with Er³⁺ concentration and heat treatment conditions. Furthermore, in Yb³⁺/Er³⁺ co-doped GCs specimens, the optical thermometry was researched by means of fluorescence intensity ratio (FIR) of ⁴S_3/2 and ²H_11/2 levels. The GC sample heated at 620°C for 5 hours possessed a high relative temperature sensitivity (S_r) of 0.769% K⁻¹ at 303 K and the maximal absolute temperature sensitivity (S_a) of 5.951 × 10⁻³ K⁻¹ at 663 K, respectively. It is expected that the as-fabricated GC materials with Sr₁₀(PO₄)₆O NCs are promising efficient up-conversion materials for optical temperature sensor.     

Ferroelectric,upconversion emission and optical thermometric properties of color-controllable Er3+-doped Pb(Mg1/3Nb2/3)O3-PbTiO3-Pb(Yb1/2Nb1/2)O3 ferroelectrics

The (0.98-x)(0.6Pb(Mg_1/3Nb_1/3)O₃-0.4PbTiO₃)-xPb(Yb_1/3Nb_1/3)O₃-0.02Pb(Er_1/2Nb_1/2)O₃ ((0.98-x)(PMN-PT)-xPYN:Er³⁺) ceramics were prepared through a solid-state reaction method. The phase structure, piezoelectric response, ferroelectric performance and upconversion emission of the ceramics were systematically investigated. The phase structure, the electrical and optical properties are strongly related to the content of PYN. The optimized piezoelectric response and upconversion emissions of the ceramics were achieved near x = 0.12, which locates in the morphotropic phase boundary (MPB) composition. Furthermore, the temperature sensing behaviors of the resultant compounds based on the thermally coupled levels of ²H_11/2 and ⁴S_3/2 of Er³⁺ ions in the temperature range of 133–573 K were studied by utilizing the fluorescence intensity ratio technique. Additionally, the thermal effect, which is induced by the laser pump power, of the studied ceramics is also investigated and the produced temperature is enhanced from 268 to 348 K with the pump power rising from 109 to 607 mW.     

Improved photoluminescence and multi-mode optical thermometry of Er3+/Yb3+ co-doped (Ba,Sr)3Lu4O9 phosphors

Contactless optical thermometers have attracted extensive attentions for applications in scientific research and technological fields due to their apparent advantages. Herein, a novel sequence of Ba_3-xSr_xLu₄O₉ (B_3-xS_xLO):Er³⁺/Yb³⁺ phosphors were successfully prepared to investigate the temperature sensing property. By establishing energy transfer from Yb³⁺ to Er³⁺ and regulating the local lattice environment, up-conversion luminescence of Er³⁺ is dramatically improved when excited by 980 nm laser. This can effectively promote signal-noise ratio and reduce the errors in temperature detection. Furthermore, a multi-mode optical thermometry, which includes the fluorescence intensity ratio (FIR) from two thermally coupled levels of ²H_11/2/⁴S_3/2, FIR based on non-thermally coupled system of ²H_11/2/⁴F_9/2 and fluorescence lifetime of ⁴S_3/2 state of Er³⁺, was explored systematically. The fabricated samples exhibit the superior temperature measurement performances containing wide temperature-sensing range, superior signal discriminability, high sensitivity and favorable repeatability, indicative of the enormous utilization prospects of B_3-xS_xLO:Er³⁺/Yb³⁺ for thermometry.