Upconversion emission of ZrO2 nanoparticles doped with erbium (Er3+) and ytterbium (Yb3+), synthesized by hydrothermal route

This paper reports the luminescent response upconversion of zirconium oxide (ZrO₂) nanoparticles doped with erbium (Er³⁺) and ytterbium (Yb³⁺) ions, synthesized by hydrothermal route. X ray diffraction (DRX) showed that the synthesized material presents the face centered cubic (FCC) structure. High resolution transmission electron microscopy (HRTEM) showed the presence of crystals size smaller than 10 nm. The photoluminescent analysis allowed to observe an intense upconversion luminescence emission of the samples doped with both ions Er³⁺ and Yb³⁺, when these are excited with 910 nm laser source, showing the electronic transitions ⁴F_9/2 → ⁴I_5/2; ²H_11/2 → ⁴I_5/2; ⁴S_3/2 → ⁴I_15/2 of Er³⁺. Two decay times were observed, whose behavior can be associated to the average distance between erbium ions within the nanocrystals.     

Near‐Infrared and Upconversion Luminescence in Er:Y2O3 Ceramics under 1.5 μm Excitation

Results of the spectroscopic characteristics and upconversion luminescence in Er³⁺ doped yttria (Y₂O₃) transparent ceramics prepared by a modified two‐step sintering method are presented. The near‐infrared (1.5 μm) luminescence properties were evaluated as a function of Er³⁺ concentration. Judd–Ofelt intensity parameters, radiative rates, branching ratios, and emission lifetimes were determined and compared with results reported for Er³⁺‐doped Y₂O₃ single crystal and nanocrystals. Following pumping at 1.532 μm, weak blue (~0.41 μm, ²H_9/2 → ⁴I_15/2), strong green (~0.56 μm, ²H_11/2, ⁴S_3/2 → ⁴I_15/2), and red (~0.67 μm, ⁴F_9/2 → ⁴I_15/2) emission bands were observed as well as weak near‐infrared emissions at 0.8 μm (⁴I_9/2 → ⁴I_15/2) and 0.85 μm (⁴S_3/2 → ⁴I_13/2) at room temperature. The upconversion luminescence properties under ~1.5 μm pumping were further investigated through pump power dependence and decay time studies. Sequential two‐photon absorption leads to the ⁴I_9/2 upconversion emission, whereas energy‐transfer upconversion is responsible for the emission from the higher excited states ²H_9/2, ²H_11/2, ⁴S_3/2, and ⁴F_9/2. The enhanced red emission with increasing Er³⁺ concentration most likely occurred via the cross‐relaxation process between (⁴F_7/2 → ⁴F_9/2) and (⁴I_11/2 → ⁴F_9/2) transitions, which increased the population of the ⁴F_9/2 level.     

Green and red upconversion luminescence of Er-doped K0.5Na0.5NbO3 ceramics

Er³⁺ doped K_0.5Na_0.5NbO₃ (KNN) lead-free piezoelectric ceramics were synthesized by the solid-state reaction method. The upconversion emission properties of Er³⁺ doped KNN ceramics were investigated as a function of Er³⁺ concentration and incident pumping power intensity. Bright green (~555 nm) and red (670 nm) upconversion emission bands were obtained under 980 nm excitation at room temperature, which are attributed to (²H_11/2, ⁴S_3/2)→⁴I_15/2 and ⁴F_9/2→⁴I_15/2 transitions, respectively. The upconversion emission intensity can be adjusted by changing Er³⁺ concentration, and the mechanism of upconversion processes involve not only a two-photon absorption but also a three-photon absorption. In addition to the admirable intrinsic piezoelectric properties of KNN, this kind of material may have potential application as a multifunctional device by integrating its upconversion and piezoelectric property.     

Synthesis of Li+-ion activated NaYF4: Er3+/Yb3+ phosphors via a modified solid-state process for latent fingerprint detection

Li⁺-ion codoped NaYF₄: Er³⁺/Yb³⁺ phosphors (β-NaYF₄) with a hexagonal structure were synthesized via a modified solid-state route. High-speed planetary ball milling and solid-liquid mixing were simultaneously used to overcome the drawbacks of high synthesis temperatures in conventional routes. A pure β-NaYF₄ phase was obtained through calcination at 600?°C for 3?h. Increases in the codoping content of Li⁺ ion caused a slight shift in X-ray diffraction peak positions toward high angles owing to the distortion of the local crystal field. Field emission scanning electron microscope images showed agglomerated spherical particles of approximately 0.7?µm with narrow size distribution. The upconversion properties of β-NaYF₄ codoped with Li⁺-ion were explored. Two emission bands in the green regions (520?nm and 545?nm) and one emission band in the red region (615?nm) were observed owing to the ²H_11/2→⁴I_15/2, ⁴S_3/2→⁴I_15/2, and ⁴F_9/2→⁴I_15/2 transitions of Er³⁺, respectively. Codoping with 6?mol% Li⁺ increased the upconversion intensity by three times, which was explained using the energy level diagram. The present phosphors with improved upconversion properties were utilized for latent fingerprint detection on smooth surfaces of regularly used polymer sheets, glass substrates, and compact discs. Using the present phosphors, the base elements with three-level features, such as sharp ridges, valleys, ridge flow, bifurcation, ridge shapes, and dots, were observed on all hydrophilic and hydrophobic surfaces. The prepared phosphors exhibited promising characteristics to detect the features of fingerprint impression for individual identification in forensic applications.     

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.     

Upconverting YbPO4:RE monospheres (RE=Ho,Er, Tm)

Uniform spheres of (Yb_0.98RE_0.02)PO₄ orthophosphate (RE=Ho, Er, and Tm, respectively) were synthesized via a homogeneous precipitation procedure mediated by SO₄^2? anions. The as‐precipitated and 1100°C calcined products were determined via laser‐diffraction particle sizing to have the average diameters of ~2.04 ± 0.67 and 1.80 ± 0.93 μm, respectively. The upconversion luminescence of RE³⁺ under sensitization by the host Yb³⁺ was studied for the calcination products under 978 nm laser excitation, and it was found that the emissions are dominated by a red band at ~650 nm for Ho³⁺ (⁵F₅ → ⁵I₈ transition), similarly strong green (~515‐565 nm, ²H_11/2/⁴S_3/2 → ⁴I_15/2 transition) and red (~640‐680 nm, ⁴F_9/2 → ⁴I_15/2 transition) bands for Er³⁺, and a near‐infrared band at ~800 nm for Tm³⁺ (³H₄ → ³H₆ transition). The number of laser photons needed to populate the emitting state was determined by varying the excitation power, and the possible photon reactions leading to the observed upconversion were discussed.     

Effects of temperature and electric field on upconversion luminescence in Er3+‐Yb3+ codoped Ba0.8Sr0.2TiO3 ferroelectric ceramics

Optical and electrical properties of 1%Er³⁺ and different Yb³⁺ content (1ExY) codoped Ba_0.8Sr_0.2TiO₃ (BST) ferroelectric ceramics fabricated by the solid‐phase reaction were investigated. Under 980 nm pump condition, two green emission bands at 525 and 549 nm wavelength corresponding to, ²H_11/2→⁴I_15/2 and ²S_3/2→⁴I_15/2 transitions, and two red emission bands at 655 and 668 nm wavelength attributed to ⁴F_9/2→⁴I_15/2 transition are observed. The temperature‐sensing behaviors, calculated by the intensity ratio I₅₂₅/I₅₄₉ suggested that, the maximum sensitivity of the green emission of the 1E8Y‐BST ceramics is 1.07×10^?2 K‐1 at 293 K. Furthermore, the maximum sensitivity of 1E6Y‐BST and 1E11Y‐BST ceramics were obtained around the Curie temperature. The fluorescence lifetime of 1E8Y‐BST ceramics for ²H_11/2 level and ²S_3/2 level shortened with the increase in the temperatures. Moreover, the upconversion (UC) luminescence intensity of 1E8Y‐BST decreased with the increase in the external electric field and had a mutation at the coercive electric field (E_c) of about 1.24 kV/cm, which revealed that the electric field had influence on the UC luminescence.     

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.     

Enhanced near-infrared to green upconversion from Er3+-doped oxyfluoride glass and glass ceramics containing BaGdF5 nanocrystals

In this work, effect of glass composition as well as ceramization on visible and near-infrared (NIR) luminescence properties along with their decay dynamics of Er³⁺ ions has been compared considering two different oxyfluoride glasses yielding BaF₂ and BaGdF₅ nanocrystals. Both the glass systems have exhibited an intense normal and upconversion green emission under ultraviolet (378 nm) and NIR (978 nm) excitations, respectively. A remarkable enhancement of these emission intensities is observed for gadolinium-(Gd) containing glasses. Interestingly, NIR fluorescence intensity from Er³⁺ ions at 1540 nm has showed marginal decrease in gadolinium-containing glass which is attributed to occurrence of strong excited-state absorption (ESA) due to higher fluorine content ensuing an augmentation of upconversion green emission with a concomitant decrease in NIR emission. The quadratic dependence of upconversion green emission intensity on its pump power for all the samples revealed biphotonic absorption process from ground-state ⁴I_15/2 to the excited-state ⁴I_11/2 followed by ESA of second photon to the ⁴F_7/2 level. The intense green upconversion emission as well as enhanced NIR fluorescence lifetimes indicate the suitability of these glass/glass ceramics for upconversion lasers and amplification in the third telecom window.     

Bright red upconversion luminescence from Er3+ and Yb3+ co-doped ZnO-TiO2 composite phosphor powder

ZnO-TiO₂ composites co-doped with Er³⁺ and Yb³⁺ ions were successfully synthesized by powder-solution mixing method and their upconversion (UC) luminescence was evaluated. The effect of firing temperature, ZnO/TiO₂ mixing ratio, and dopant concentration ranges on structural and UC luminescence properties was investigated. The crystal structure of the product was studied and calculated in detail by means of X-ray diffraction (XRD). Also, the site preference of Er³⁺ and Yb³⁺ ions in the host material was considered and analyzed based on XRD results and UC luminescence characteristics. Brightest UC luminescence was observed in the ZnO-TiO₂:Er³⁺,Yb³⁺ phosphor fired at 1300 °C in which the system consisted of mixed phases; Zn₂TiO₄, TiO₂, RE₂Ti₂O₇ and RE₂TiO₅ (RE = Er³⁺ and/or Yb³⁺). Under the excitation of a 980 nm laser, the two emission bands were detected in the UC emission spectrum, weak green band centered at 544 and 559 nm, and strong red band centered at 657 and 675 nm wavelengths in accordance with ²H_11/2, ⁴S_3/2 → ⁴I_15/2 and ⁴F_9/2 → ⁴I_15/2 transitions of Er³⁺ ion, respectively. The simple chemical formula equations, for explaining the site preference of Er³⁺ and Yb³⁺ ions in host crystal matrix, were generated by considering the Zn₂TiO₄ crystal structure, its crystal properties, and the effect of Er³⁺ and Yb³⁺ ions to the host crystal matrix. The UC emission intensity of the products was changed by varying ZnO/TiO₂ mixing ratios, and Er³⁺ and Yb³⁺ concentrations. The best suitable condition for emitting the brightest UC emission was 1ZnO:1TiO₂ doped with 3 mol% Er³⁺, 9 mol% Yb³⁺ fired at 1300 °C for 1 h.     

Tunable multicolor upconversion luminescence of Yb3+ sensitized Na3La(VO4)2 crystals

Multicolor upconversion luminescence materials show significantly applications in materials science. In this paper, the novel Yb³⁺-sensitized Na₃La(VO₄)₂ upconversion luminescence crystals are synthesized by the solid-state reaction method. Three primary colors upconversion luminescence are successfully achieved in Na₃La(VO₄)₂:Yb³⁺,Tm³⁺, Na₃La(VO₄)₂:Yb³⁺,Er³⁺, and Na₃La(VO₄)₂:Yb³⁺,Ho³⁺ crystals excited by the single 980 nm LD. Multicolor upconversion luminescence can be obtained by simply adjusting the combination ratios of these three samples. Luminescence mechanisms of the Yb³⁺-sensitized system are discussed in detail. In the Na₃La(VO₄)₂ host material, the Yb³⁺/Ho³⁺ codoped system exhibits unusual red upconversion luminescence based on the short decay time of Ho³⁺ ion ⁵I₆ level, which provides the possibility of three primary color luminescence under 980 nm excitation.     

Upconversion luminescence properties of NaBi(MoO4)2:Ln3+, Yb3+ (Ln = Er,Ho) nanomaterials synthesized at room temperature

Studies on lanthanide ions doped upconversion nanomaterials are increasing exponentially due to their widespread applications in various fields such as diagnosis, therapy, bio-imaging, anti-counterfeiting, photocatalysis, solar cells and sensors, etc. Here, we are reporting upconversion luminescence properties of NaBi(MoO₄)₂:Ln³⁺, Yb³⁺ (Ln = Er, Ho) nanomaterials synthesized at room temperature by simple co-precipitation method. Diffraction and spectroscopic studies revealed that these nanomaterials are effectively doped with Ln³⁺ ions in the scheelite lattice. DR UV–vis spectra of these materials exhibit two broad bands in the range of 200–350 nm correspond to MoO₄²⁻ charge transfer, s-p transition of Bi³⁺ ions and sharp peaks due to f-f transition of Ln³⁺ ions. Upconversion luminescence properties of these nanomaterials are investigated under 980 nm excitation. Doping concentration of Er³⁺ and Yb³⁺ ions is optimized to obtain best upconversion photoluminescence in NaBi(MoO₄)₂ nanomaterials and is found to be 5, 10 mol % for Er³⁺, Yb³⁺, respectively. NaBi(MoO₄)₂ nanomaterials co-doped with Er³⁺, Yb³⁺ exhibit strong green upconversion luminescence, whereas Ho³⁺, Yb³⁺ co-doped materials show strong red emission. Power dependent photoluminescence studies demonstrate that emission intensity increases with increasing pump power. Fluorescence intensity ratio (FIR) and population redistribution ability (PRA) of ²H_11/2 → ⁴I_15/2, ⁴S_3/2 → ⁴I_15/2 transitions of Er³⁺ increases with increasing the Yb³⁺ concentration. Also, these values increase linearly with increasing the pump power up to 2 W. It reveal that these thermally coupled energy levels are effectively redistributed in co-doped samples due to local heating caused by Yb³⁺.     

Temperature-dependent upconversion luminescence in ferroelectric 1.5%Pr/3%Yb:0.75Pb(Mg1/3Nb2/3)O3–0.25PbTiO3 transparent ceramics for non-contact thermometry and optical heating

Non-contact optical thermometry based upon fluorescence intensity ratio (FIR) has attracted much attention because of its excellent accuracy and sensitivity. Recently we reported the upconversion luminescence in Pr³⁺/Yb³⁺ co-doped 0.75Pb(Mg_1/3Nb_2/3)O₃–0.25PbTiO₃ transparent ceramics [Z. Lv et al., Ceramics International 45 (2019) 10924–10929]. In this article we study the temperature dependence of upconversion emissions from the 1.5%Pr/3%Yb:0.75Pb(Mg_1/3Nb_2/3)O₃–0.25PbTiO₃ transparent ceramics. The FIR between the ¹D₂-³H₄ and ³P₀–³H₄ emissions fits a thermally coupled-levels-like equation, and exhibits the maximum relative sensitivity of 1.03% K⁻¹ at the temperature 320 K. Meanwhile, the FIRs of I_Red/I_Green, I_Red/I_Blue and I_Red/I_BG show linear responses versus temperature and illustrate the high constant sensitivities of 1.09%–2.9% K⁻¹, but in a narrow temperature range of 140–240 K. The multiple temperature-sensing performances offer us chances to select distinct response functions on the basis of the practical demands. In addition, laser induced heating was observed in the transparent ceramics. The generated temperature in the ceramics can be accurately monitored and regulated from 329 to 377 K by changing the excitation power from 1.58 to 8.61 W/cm². The high heating efficiency of ~6.83 K cm²/W makes the transparent ceramics suitable for optical heater. The transparent ceramics exhibit excellent piezoelectric and ferroelectric performances, and thus they are promising candidates for multifunctional optical-electro devices besides non-contact thermometer and optical heater.     

Upconversion Luminescence and Energy‐Transfer Mechanism of NaGd(MoO4)2: Yb3+/Er3+ Microcrystals

Uniform and well‐crystallized NaGd(MoO₄)₂: Yb³⁺/Er^{3 +} microcrystals with tetragonal plate morphology were synthesized by a facile hydrothermal method. The structure and phase purity of the samples were identified by powder XRD analysis. The steady‐state and transient luminescence spectra were measured and analyzed. Under 980 nm excitation, intense green luminescence at 531 and 553 nm, and red luminescence at 657 and 670 nm were observed. The optimum doping concentrations for Yb³⁺ and Er³⁺ are determined to be 20% and 1% in NaGd(MoO₄)₂ tetragonal plate microcrystals. With increasing Yb³⁺ doping concentrations, the total integral emission intensities increase first and then decrease. The red/green intensity ratio of NaGd(MoO₄)₂: Yb³⁺/Er³⁺ microcrystals increases from 0.4 to 1.0 with the increase in Yb³⁺ concentrations. Based on the energy level diagram, the energy‐transfer mechanisms are investigated in detail according to the double logarithmic plot of upconversion intensities versus pump powers. The energy‐transfer mechanisms for green and red upconversion luminescence are ascribed to two‐photon processes at lower Yb³⁺ concentrations, and involve high‐Yb³⁺‐induced one‐photon processes at higher Yb³⁺ concentrations. For the red upconversion luminescence, energy back‐transfer process, that is, ⁴S_3/2 (Er³⁺) + ²F_7/2 (Yb³⁺) → ⁴I_13/2 (Er³⁺) + ²F_5/2 (Yb³⁺), is dominant at higher Yb³⁺ concentrations. Theoretical model of the energy‐transfer mechanisms based on rate equations is established, which agrees well with the experimental results.     

Scintillation characteristics of transparent Eu2O3–BaO–TeO2 glass-ceramics

Tellurite glass (TeG) and its glass-ceramics (TeGC435 and TeGC455), with a composition of 10Eu₂O₃–10BaO–80TeO₂, were prepared and their luminescence properties were evaluated. TeG was prepared via the melt quenching technique, while TeGC435 and TeGC455 were fabricated by heat treating TeG at 435 and 455 °C, respectively, for 5 h each. The Eu₂Te₆O₁₅ crystal phase was formed in TeGC435 and TeGC455. Both the glass and glass-ceramics showed sharp photoluminescence and scintillation peaks, attributed to the 4f→4f transitions of Eu³⁺. The highest quantum yield was obtained for TeG, whereas the highest integrated scintillation intensity was obtained for TeGC455. The scintillation intensity of TeGC455 was approximately 10% of that of the Bi₄Ge₃O₁₂ single crystal. Furthermore, typical decay times derived from the 4f→4f transitions were obtained for TeG, TeGC435, and TeGC455 during photoluminescence and scintillation.     

Observation of efficient Er3+:4I11/2→4I13/2 transition in highly Er3+ doped germanosilicate glass

Highly rare earth（RE）ions doped glass laser materials can produce efficient single frequency mid-infrared laser. In this work, a series germanosilicate glasses with various high erbium-doping concentration (up to 4?mol%) and without concentration quenching are fabricated. Spectroscopic properties and energy transfer (ET) mechanism of efficient Er³⁺:⁴I_11/2 →⁴I_13/2 transition have been investigated in detail upon a conventional 980?nm Laser Diode. The dense structure of silicate glass can be dissolved effectively by the introduction of GeO_2, which was analyzed by Raman spectra, so that the compatibility and luminous intensity of RE ions were improved. The high predicted spontaneous transition probability (A_rad =?37.65?s^?1) based on the Judd-Ofelt theory and large calculated emission cross section (8.8?×?10^?21 cm²) are obtained. The above results indicate that these glasses are promising to be the single frequency mid-infrared laser material.     

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

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

Novel Er-doped SiC/SiO2 nanocomposites: Synthesis via polymer pyrolysis and their optical characterization

Erbium activated SiC/SiO₂ nanocomposites doped with Er³⁺ concentrations ranging from 1 to 4 mol% were prepared by pyrolysis of sol–gel derived precursors. The gels were obtained from modified silicon alkoxides containing Si–CH₃ and Si–H groups. Thin discs obtained from the monolithic xerogels were pyrolyzed in an alumina tubular furnace in flowing Ar (100 ml/min) at 800, 1000, 1200 and 1300 °C. The samples were investigated by absorption and photoluminescence spectroscopies. Emission in the C-telecommunication band was observed at room temperature for all the samples upon continuous-wave excitation at 980 or 514.5 nm. The shape of the emission band corresponding to the ⁴I_13/2 → ⁴I_15/2 transition is found to be independent both on Erbium content and excitation wavelength, with a Full Width Half Maximum (FWHM) of 48 nm. By increasing the pyrolysis temperature the intensity of the luminescence increases and the electronic bandgap energy decreases.     

Multi-phase glass-ceramics containing CaF2: Er3+ and ZnAl2O4:Cr3+ nanocrystals for optical temperature sensing

Oxyfluoride transparent glass-ceramics (GC) containing CaF₂ and ZnAl₂O₄ nanocrystals have been fabricated with melt-quenching method. By carrying out the heat treatment of the precursor glass (PG), Er³⁺ and Cr³⁺ were selectively partitioned into CaF₂ and ZnAl₂O₄ nanocrystals, respectively. The obtained multi-phase GC exhibited strong upconversion (UC) fluorescence of Er³⁺ as well as intense down-conversion (DC) fluorescence of Cr³⁺. Under 980 nm excitation, the green UC fluorescence of Er³⁺ due to ²H_11/2,⁴S_3/2 → ⁴I_15/2 transition and the red DC fluorescence lifetime of Cr³⁺ due to ²E, ⁴T₂ → ⁴A₂ transition were found to be highly dependent on the temperature and makes them possibly suitable for Optical Thermometry. With least-square fitting methods, the FIR of Er³⁺ from thermally coupled energy states (²H_11/2 and ⁴S_3/2) produced maximum temperature sensing sensitivity values of 0.33% K⁻¹ at 437 K and 0.36% K⁻¹ at 267 K, respectively. Similarly, fluorescence lifetime of Cr³⁺ attributed to the parity forbidden (²E → ⁴A₂) and spin allowed (⁴T₂ → ⁴A₂) produced the maximum temperature sensor sensitivity value equal to 0.67% K⁻¹ at 535 K.     

A novel Nd3+-doped MgO-Al2O3-SiO2-based transparent glass-ceramics: Toward excellent fluorescence properties

Generally, glass-ceramics have superior properties compared to their parent glasses. Here, we prepared a novel Nd³⁺-doped MgO-Al₂O₃-SiO₂-based transparent glass-ceramics with excellent fluorescence properties. The effects of Nd₂O₃ content on the structure and properties of glass-ceramics were studied, aiming to provide a key guidance for preparing this transparent glass-ceramics. The results revealed that the glass stability increased originally and then decreased with increasing Nd₂O₃ content, so did the variation of wavenumbers in infrared spectra. And these glass-ceramics are mainly composed of cordierite with residual glassy phase. The three phenomenological intensity parameters (Ω_2,4,6) and radiative properties were estimated by Judd-Ofelt theory, and the values of Ω₂ first decreased and then increased with increasing Nd₂O₃ content. Three main emission peaks ascribed to the transitions from ⁴F_3/2 to ⁴I_9/2, ⁴I_11/2, ⁴I_13/2 at 898, 1057, 1330  nm were observed, respectively. The branching ratios for ⁴F_3/2→⁴I_11/2 transition increased as the Nd₂O₃ content raised, and the fluorescence lifetimes of the ⁴F_3/2 level were found to increase first and then decrease with Nd₂O₃ content (from 181 to 726 μs). The excellent fluorescence properties indicate that this novel glass-ceramics can be used as a potential solid-state optical functional material for 1.06 μm laser emission.