Multiphonon Relaxation Rates Research Articles

Near-pure red emission of highly thermally stable Eu3+ doped multi-component transparent oxyfluoride aluminosilicate glass-ceramic for red lasers and trichromatic WLEDs

In this paper, Eu3+ doped multi-component transparent aluminosilicate and oxyfluoride aluminosilicate glasses were fabricated by the melt-quenching procedure, and the glass-ceramics containing LiAlSi2O6 microcrystals (LAS glass-ceramics) were produced by a two-step heat treatment process. The XRD, SEM, and EDS data demonstrate that spherical single-phase LiAlSi2O6 microcrystals have precipitated from the glass matrices. The microhardness and flexural strength of the glass-ceramics vary in 6.27–6.66 GPa and 89.18–155.75 MPa, respectively. Phonon sideband analysis reveals that the phonon energies for both fluorine-containing and fluorine-free LAS glass-ceramics are approximately 971 cm−1, and the multiphonon relaxation rates (Wmp/W0) of the former are lower than those of the latter. Given its lower Wmp/W0 values, the fluorine-containing LAS glass-ceramic exhibits a higher emission intensity and a longer lifetime. Under 394 nm excitation, the fluorine-containing LAS glass-ceramic presents a warm and nearly pure red emission, characterized by a correlated color temperature of less than 3300 K and a color purity approaching 100 %. Time-resolved emission spectra support the photoluminescent stability of the Eu3+ ions. According to the Judd-Ofelt theory and spectral results, the fluorine-containing LAS glass-ceramic possesses lower Ω2/Ω4 and asymmetry ratios, leading to a more symmetrical local environment for the Eu3+ ions. Benefiting from its enhanced red emission, the 5D0→7F2 transition in the fluorine-containing LAS glass-ceramic exhibits a higher branching ratio (69.28 % > 50 %), emission cross-section (8.94 × 10−22 cm2), and gain bandwidth (12.12 × 10−28 cm3). Additionally, temperature-dependent photoluminescence spectra substantiate the excellent thermal stability of the Eu3+ doped fluorine-containing LAS glass-ceramic. Specifically, the intensity of the 5D0→7F2 transition at 150 °C remains 80 % of the initial intensity. Therefore, the Eu3+ doped multi-component transparent oxyfluoride aluminosilicate glass-ceramic has a significant competitive advantage in the field of red lasers and trichromatic WLEDs.

Revisiting the luminescence properties of Er3+, Tm3+ and Ho3+ doped Bi4Ge3O12 rod-type crystal fibers for the laser application

BGO single crystals doped with Er3+, Tm3+ and Ho3+ rare-earth ions were prepared in the form of rod-type crystal fibers via the micro-pulling down technique to perform an extensive investigation of their visible, near- and mid-infrared luminescence properties and to really decide on their interest as solid-state laser media in the various spectral domains. Revisiting and completing the absorption spectra already available in the literature led to the derivation of more reliable “effective” radiative lifetimes and branching ratios. Registration of the fluorescence decays of the most important emitting levels versus dopant concentrations led for the first time to an unambiguous determination of “intrinsic” emission lifetimes – corresponding to negligible contributions from inter-ionic energy-transfers - and non-radiative multiphonon relaxation rates. Such data also allowed for the determination of the dominant phonon energy which comes into play in the electron-phonon coupling responsible for these multiphonon relaxation processes and for its lattice vibration origin, i.e. a high phonon energy of the order of 820 cm−1 corresponding to the coupling between bending vibrations of (GeO4)4- tetrahedra and vibrations corresponding to motions of these (GeO4)4- tetrahedra against the Bi3+ ions for which the rare-earth dopant ions substitute. Using the above data and different methods for the calibration of the registered emission spectra in cross section unit and for the derivation of gain cross section curves finally show that mid-infrared emissions of Er:BGO, Tm:BGO and Ho:BGO around 1.55 μm, 1.9 μm and 2 μm, respectively, occur with comparable gain cross sections as in the most important reference mid-infrared laser materials, although over slightly shifted thus complementary spectral domains. It is shown that potentialities also exist with Tm:BGO in the blue, deep-red and near-infrared spectral domains around 470 nm, 800 nm and 1.45 μm, by pumping the crystals with conventional pump sources and using some suitable co-dopants to avoid detrimental self-terminating processes.

Effect of Nb2O5 on the ∼2.0 μm band luminescence of Ho3+/Tm3+/Ce3+ tri-doped tellurite glass

In this work, the effect of Nb2O5 oxide on the ∼2.0 μm band luminescence of Ho3+/Tm3+/Ce3+ tri-doped tellurite glass with composition of TeO2–ZnO–La2O3 was studied. The doped tellurite glass was synthesized by using the melt-quenching method. Under the pumping of 808 nm laser diode (LD), a broad and relatively flat fluorescence emission ranging from 1600 to 2200 nm with a full width at half maximum (FWHM) of 374 nm was obtained by optimizing the concentration combination of Ho3+, Tm3+ and Ce3+ ions. The observed broad luminescence was attributed to the spectral overlapping between the energy level transitions from 3F4 to 3H6 of Tm3+ at 1.82 μm and that from 5I7 to 5I8 of Ho3+ at 2.0 μm. Further, an increment by about 143% in peak intensity of 1600∼2200 nm broad luminescence was found after the introduction of Nb2O5 oxide, which is due to the enhanced energy transfer from Tm3+ to Ho3+ ions, and the increased multi-phonon relaxation (MPR) rate from higher levels to fluorescence emitting levels. It can be inferred from the results that a potential gain medium suitable for applications in optoelectronic devices operating at ∼2.0 μm band can be produced by incorporating an appropriate amount of Nb2O5 oxide into Ho3+/Tm3+/Ce3+ tri-doped tellurite glass.

Ho3+ doped low-phonon single crystals and chalcogenide glasses for mid-IR source application

A comparative study was conducted to investigate the 3.9 µm mid-IR emission properties of Ho3+ doped NaYF4 and CsCdCl3 crystals as well as Ho3+ doped Ga2Ge5S13 glass. Following optical excitation at ∼890 nm, all the studied materials exhibited broad mid-IR emissions centered at ∼3.9 µm at room temperature. The mid-IR emission at 3.9 µm, originating from the 5I5 → 5I6 transition, showed long emission lifetime values of ∼16.5 ms and ∼1.61 ms for Ho3+ doped CsCdCl3 crystal and Ga2Ge5S13 glass, respectively. Conversely, the Ho3+ doped NaYF4 crystal exhibited a relatively short lifetime of ∼120 µs. Temperature dependent decay time measurements were performed for the 5I5 excited state for all three samples. The results showed that the emission lifetimes of Ho3+:CsCdCl3 and Ho3+:Ga2Ge5S13 were nearly temperature independent over the range studied, while significant emission quenching of the 5I5 level was observed in Ho3+:NaYF4. The temperature dependence of the multi-phonon relaxation rate for 3.9 µm mid-IR emission in Ho3+:NaYF4 crystal was determined. The room temperature stimulated emission cross-sections for all three samples were calculated using the Füchtbauer-Landenburg equation. Furthermore, the results of Judd-Ofelt analysis are presented and discussed.

Tailoring multiphonon relaxation and cross relaxation energy transfer in mixed ionic-electronic 20Li2O-xBi2O3-(78-x)TeO2-1Er2O3-1Ag glasses at NIR region

A glass composed of 20Li2O-xBi2O3-(78-x)TeO2-1Er2O3-1Ag was fabricated by melt–quenching method to examine the influence of mixed ionic–electronic (MIE) effect on AC conductivity (σAC) and photoluminescence properties. The σAC decreased as the Bi2O3 content increased, until a minimum σAC at x=11 mol% attributable to the MIE effect was achieved. The photoluminescence intensity and lifetime (τmes)of the 4I13/2→4I15/2 transition were reported with a drop at x=11 mol%, coincided with the minimum σAC. Results on the analysis of the multiphonon relaxation rate (WMPR) revealed that adding low-phonon Bi2O3 concentration promoted higher photoluminescence intensity and longer τmesdue to the reduction in WMPR. However, the drop in photoluminescence intensity and τmes at x=11 mol% may be due to a blocking effect. The blocking effect may have induced nonradiative phonon-assisted Sab and cross-relaxation γ6 energy transfer, leading to a maximum WMPR and energy transfer parameter.

Optical and structural properties of Eu3+ doped MgO–Li2O–Na2O–BaO–B2O3 glasses for scintillating glass applications

The glass systems with composition of 17MgO–10Li2O-(57-X) B2O3–6BaO–10Na2O-XEu2O3 (X = 0.0(BMLNBa), 0.1(BMLNBaEu0.1), 0.3(BMLNBaEu0.3), 0.5(BMLNBaEu0.5) and 1.0(BMLNBaEu1.0) mol% were prepared and studied their optical, structural properties for scintillating applications. Density and refractive index of the glasses increases with increase in Eu2O3 content indicating close packing of glass network. IR spectra reveal signature peaks of the borate network. Photoluminescence spectra of glass systems reveals emission bands which corresponds to 5D0 →7F0 (579 nm), 5D0 →7F1 (590 nm), 5D0→7F2 (615 nm), 5D0 →7F3 (654 nm), 5D0→7F4 (700 nm) transitions. The emission and excitation intensity depends on Eu3+ ions where emission wavelength was observed at 615 nm and excited wavelength at 394 nm. The highest emission intensity was observed for BMLNBaEu0.3 glass. Asymmetry ratio (IR/O) is calculated and compared with other glasses. The phonon side-band spectra are used to calculate phonon energy of the present glass system. Judd-Ofelt analysis and radiative properties have been evaluated for BMLNBaEu0.3 glass and compared with other glass compositions. Using phonon energy, the coupling strength ‘g’, host dependent parameters (α) and multi-phonon relaxation rates (WMPR/Wo) have been evaluated. Phonon coupling strength shows 0.0054, 0.0108 and 0.0546 for BMLNBaEu0.3, BMLNBaEu0.5 and BMLNBaEu1.0 glasses respectively. The results obtained indicate the glasses are potential candidates for the scintillating material applications.

Rationalizing the structural changes and spectra of manganese and their temperature dependence in a series of garnets with first-principles calculations

Detailed first-principles calculations have been carried out to study the stabilization, excitation and luminescence mechanisms of the ion ${\mathrm{Mn}}^{3+}$ in a series of ${A}_{3}{B}_{2}{B}_{3}^{\ensuremath{'}}{\mathrm{O}}_{12}$ garnet hosts. The formation energy shows that ${\mathrm{Mn}}^{3+}$ is dominant and is situated at the octahedral $B$ site. The excited states, excitation, and emission energies of ${\mathrm{Mn}}^{3+}$ have then been calculated. The calculated energy levels of ${\mathrm{Mn}}^{3+}$ confirm that the red emission is due to the ${}^{5}{\mathrm{T}}_{2}\phantom{\rule{4pt}{0ex}}\ensuremath{\rightarrow}{\phantom{\rule{4pt}{0ex}}}^{5}{\mathrm{E}}^{\ensuremath{'}}$ transition and the near-infrared (NIR) emission arises from the ${}^{1}{\mathrm{T}}_{2}\phantom{\rule{4pt}{0ex}}\ensuremath{\rightarrow}{\phantom{\rule{4pt}{0ex}}}^{3}{\mathrm{T}}_{1}$ transition. The populations of the ${}^{5}{\mathrm{T}}_{2}$ and ${}^{1}{\mathrm{T}}_{2}$ excited states and the corresponding radiative rates lead to the temperature dependence of the red to NIR emission. Furthermore, the adiabatic potential energy surfaces along the ${A}_{1g}$ and ${E}_{g}$ moeity modes of [${\mathrm{MnO}}_{6}$] have been calculated and fitted well in the harmonic approximation. The high activation energy for ${\mathrm{Mn}}^{3+}$ indicates a low nonradiative multiphonon relaxation rate of ${}^{5}{\mathrm{T}}_{2}$ to ${}^{3}{\mathrm{T}}_{1}$. Hence, the ionization process was considered, and we show that it is responsible for the luminescence quenching of ${\mathrm{Mn}}^{3+}$, so that the luminescence has rarely been reported experimentally. This work illustrates a well-designed approach based on the density-functional theory framework to predict the optical transition properties of the transition metal ion ${\mathrm{Mn}}^{3+}$ by calculating the structural distortions due to the Jahn-Teller effect, the optical transitions, quenching processes and the influence of pressure.

Determination of radiative and multiphonon non-radiative relaxation rates of upconversion materials.

The radiative and multiphonon non-radiative relaxation rates of lanthanide ions are intrinsic parameters to characterize the optical properties, which are the basic data for the theoretical model and numerical simulation of lanthanide upconversion systems. However, there are complex energy transfer processes, such as energy migration, energy transfer upconversion, and cross-relaxation in the lanthanide-doped upconversion materials, so it is difficult to accurately measure the intrinsic radiative and multiphonon relaxation rates. Therefore, a method to determine the relaxation rates of multi-level upconversion systems is proposed based on multi-wavelength excitation and level-by-level parameter calculations in this paper. For a dilute doped multi-level luminescence system excited at low powers, a model based on the measurements of steady-state emission spectra and luminescence decay curves is established through the macroscopic rate equations at multi-wavelength excitation, which can be used for the level-by-level calculation of the multi-level radiative and multiphonon relaxation rates. With the dilute doped β-NaYF4:Er3+ six-level luminescence system as an example, the measurement method and the model are introduced in detail. Under the experimental conditions of neglecting the energy transfer effect between ions, the materials are excited by five lasers with central wavelengths of 1523 nm, 980 nm, 808 nm, 660 nm, and 520 nm to form five subsystems. The steady-state emission spectra and luminescence decay curves of the luminescence system excited by each wavelength were recorded. The intrinsic relaxation rates including 11 radiative relaxation rates and 4 multiphonon relaxation rates in the β-NaYF4:Er3+ six-level system were determined based on the established model and method, which experimentally verified the applicability of the method proposed in this paper. This work will provide basic data for the analysis and regulation of the luminescence properties of lanthanide upconversion systems.

Temperature dependence of red emission in YPO4:Pr3+ nanopowders

In order to compare spectroscopic properties between nanosized and that in single crystal form of YPO4:Pr3+, temperature-dependence of the red emission from 3P0 → 3H4 and 1D2 → 3H4 transitions of YPO4:0.1 at. % Pr3+ nanopowders has been investigated in details. The emission spectra of the sample in size of 20 nm, under selective excitation at 3P2, measured at different temperatures, T = 10, 100, 200 and 300 K have been recorded. The variation of emission intensity of each 3P0 → 3H4 and 1D2 → 3H4 against temperature has been investigated. Several spectral lines constitute 1D2 → 3H4 emission, assigned to transitions between 1D2 and 3H4 Stark levels are observed with no noticeable shifts between them and those observed at the single crystal. It is found that 1D2 → 3H4 emission intensity dominates that of 3P0 → 3H4 transition, pointing out the high efficiency of the multiphonon relaxation (MPR) process from 3P0 to 1D2. Fitting the temperature dependence of 3P0 → 3H4 emission intensity permits to estimate the phonons and their energies involved in non-radiatively transition between 3P0 and 1D2 levels, which are found different from single crystal. Also, fitting the multiphonon relaxation (MPR) rates against temperature, extracted from the measured 1D2 lifetime gives information that seven phonons can be involved to bridge the gap between 1D2 and 1G4. Furthermore, the possibility to use the YPO4: 0.1 at. % Pr3+ in the nano-thermometry application in temperature range T = 10–300 K was investigated.

Optical Transitions and Excited State Absorption Cross Sections of SrLaGaO4 Doped with Ho3+ Ions.

The spectroscopic properties of SrLaGaO4 (SLO) crystal doped with Ho3+ ions were studied in this work. Absorption, emission spectra and decay dynamics of excited states have been measured and discussed using the Judd–Ofelt model. Photoluminescence emissions were attributed to transitions from the excited 3D3, 5S2, 5F5, 5I6 and 5I7 multiplet manifolds. The experimental lifetimes for five excited states have been compared to the theoretical values, calculated using Judd–Ofelt theory, allowing for the determination of the multiphonon relaxation rates (WnR) of the respective states. The experimental data were approximately on a line expressed by WnR = W0 exp(−αΔE) with W0 = 0.5 × 107 s−1 and α = 2.6 × 10−3 cm. To discuss the excited state absorption (ESA) pathways, that originated from several excited levels, we used the Judd–Ofelt formalism allowing determination of the integrated cross section for ESA transitions.

Site occupancy and phonon sideband of trivalent europium doped calcium aluminosilicate phosphors

A series of Eu3+ doped Ca2Al2SiO7 were synthesized by the solid-state reaction method. Structural and luminescent properties of the obtained samples were investigated through X-ray diffraction, Raman and luminescence spectra. The luminescent characteristic of the 5D0 → 7F0,1 transitions from emission spectra of Eu3+ ions showed that the Eu3+ ions occupy at two different sites in Ca2Al2SiO7 lattice. The Ca2Al2SiO7:Eu3+ red phosphors have three phonon sidebands with energies ~673 cm−1, 848 cm−1 and 1443 cm−1 which have been determined via the excitation spectra of Eu3+ ions in Ca2Al2SiO7 materials. These obtained phonon energies coincided with the vibrational energies observed from Raman spectra. The multiphonon relaxation rates for the excited levels of 5D1, 5D2 and 5D3 of Eu3+ ions in Ca2Al2SiO7 were also calculated.

An energy transfer accompanied by phonon absorption in ytterbium-doped yttrium aluminum perovskite for optical refrigeration

Yttrium aluminum perovskite (YAP) is a host material that can provide a strong emission from a rare-earth dopant and it has a lower phonon energy than yttrium aluminum garnet (YAG). Therefore, YAP is a promising material for optical refrigeration and radiation balanced laser. We measured the photoluminescence (PL) spectra of ytterbium (Yb)-doped YAP and compared them with those of Yb-doped YAG. The estimated ideal laser cooling efficiencies of Yb-doped YAP and Yb-doped YAG were comparable at 300 K. Based on the temperature-dependent anti-Stokes PL, we found that the laser cooling power of Yb-doped YAP at 470 K is 14.3 times higher than that at 200 K. This enhancement at higher temperatures is 3.2 times larger than that observed for Yb-doped YAG. We attributed the higher laser cooling power of Yb-doped YAP to a lower multi-phonon relaxation rate (and/or a higher energy transfer rate) and an antenna effect caused by the energy transfer from Yb ions that are located at the Y-site to Yb ions that are surrounded by an inhomogeneous alloy structure. The calculated small signal gain of (Yb:Y)AP is 3.5 times larger than that of (Yb:Y)AG. The larger small signal gain of (Yb:Y)AP arises from its strong absorbance and small Stark splitting width.

Tunable luminescence between Stark levels of Pr3+:YPO4 nanocrystals by different crystal phase

We report time-resolved second-order fluorescence between Stark levels of 1D2 and 3H4 in Pr3+:YPO4 nanocrystals with different crystal phase. Both intensity ratios of transition peaks between Stark levels and fluorescence lifetimes are modulated by phase composition and dressing effect. We have found that the maximum excitation peak shifts from yellow to orange-red region with continuous phase transformation from hexagonal phase to tetragonal phase, which is attributed to different multi-phonon relaxation rate induced by O–H group in hexagonal phase. The fluorescence lifetimes and intensity ratios of splitting peaks in time domain have also been effectively modulated by choosing excitation frequencies to resonate with different Stark levels. Both wavelength and time tunable luminescence has potential applications in biological labeling, imaging and solid state display devices.

Role of modifier ion radius in luminescence enhancement from 5D4 level of Tb3+ ion doped alkali-alumino-telluroborate glasses

Alkali-alumino-telluroborate glasses with the different network modifier elements were prepared by melt–quenching method. Absorption, excitation, luminescence spectra as well as decay curves of 5D4 level were measured at room temperature. A phonon side band of 7F6 → 5D4 transition has been obtained from the excitation spectra of Tb3+ ion. The role of modifier ion radius in luminescence enhancement from 5D4 level of Tb3+ ion was discussed in detail. In prepared glasses, multiphonon relaxation rate from 5D3 level to 5D4 is enhanced in the host glasses containing modifier ions with large radius. This is main reason leading to the enhancement of luminescence from 5D4 level of Tb3+ ion in alkali-alumino-telluroborate glasses under excitation at 350 nm. Additionally, the Judd-Ofelt theory was used to estimate the features of ligand field and radiative properties of Tb3+ ion. The calculated results have shown that the 5D4→7F5 transition has potential applications for laser action and optical amplifier.

Excitation efficiency determines the upconversion luminescence intensity of β-NaYF4:Er3+,Yb3+ nanoparticles in magnetic fields up to 70 T.

Lanthanide-doped nanoparticles enable conversion of near-infrared photons to visible ones. This property is envisioned as a basis of a broad range of applications: from optoelectronics, via energy conversion, to bio-sensing and phototherapy. The spectrum of applications can be extended if magnetooptical properties of lanthanide dopants are well understood. However, at present, there are many conflicting reports on the influence of the magnetic field on the upconverted luminescence. In this work, we resolve this discrepancy by performing a comprehensive study of β-NaYF4:Er3+,Yb3+ nanoparticles. Crucially, we show that the magnetic field impacts the luminescence only via a Zeeman-driven detuning between the excitation laser and the absorption transition. On the other hand, the energy transfer and multiphonon relaxation rates are unaffected. We propose a phenomenological model, which qualitatively reproduces the experimental results. The presented results are expected to lead to design of novel, dual-mode opto-magnetic upconverting nanomaterials.

Luminescence behaviour and phonon sideband analysis of europium doped Bi2O3 based phosphate glasses for red emitting device applications

0.5 mol% of europium (Eu3+) doped bismuth phosphate glasses (BiP) with different contents (0, 5, 10 and 15 mol%) of bismuth and different (0.1, 0.3, 0.5, 1.0, 1.5 and 2.0) mol% of Eu3+ doped 5 mol% bismuth contained BiP glasses were made by melt-quenching technique. The structural and photoluminescence properties were analysed via FT-Raman, excitation, luminescence and decay time computations. Judd-Ofelt (J-O) parameters were evaluated from the emission spectra and also various radiative properties such as radiative transition probabilities (AR), radiative lifetimes (τrad), stimulated emission cross-sections (σe), branching ratios (β), optical gain bandwidths (σexΔλeff) and optical gain (σexτrad) values for the observed emission transitions are studied. The electron-phonon coupling constants (g), phonon energies (hω) and the multiphonon relaxation rates (WMPR) were determined. The decay curves of 5D0 level of Eu3+ in all the studied glasses exhibit single exponential nature. The lifetimes are obtained from the decay curves and reported. The CIE chromaticity co-ordinates were computed and they have fallen in red region. The characteristic red luminescence emission around 612 nm for 5D0→7F2 transition confirmed that the Eu3+ doped BiP glasses might be useful to fabricate red lasers and display devices.

Development of Eu3+ doped bismuth germanate glasses for red laser applications

The intense red-emitting Eu3+ doped bismuth germanate glasses have been prepared by melt quenching technique with the chemical composition of (100-x)(0.2Bi2O3–0.8GeO2)-xEu2O3 (x = 0.5–2 mol%). Spectroscopic analysis have been performed through FTIR, absorption, luminescence and decay time measurements to enlighten the structural and optical properties of these systems. The bonding parameter (δ) and optical band gap (Eg) of prepared glasses have been calculated from the optical absorption spectra. Phonon side band spectroscopy was used to explore the phonon energy, electron-phonon coupling strength and multiphonon relaxation rate of Eu3+ doped bismuth germanate glasses. Under near UV excitation at 393 nm enhanced red emission is observed at 611 nm (5D0 → 7F2) with rising Eu3+ content. The radiative properties including transition probability (A), branching ratio (βR), stimulated emission cross-section (σe) and decay time (τR) for different excited states have been evaluated by using Judd-Ofelt parameters determined from the emission spectra. The calculated values of asymmetric ratio (R/O) and Ω2 suggest high asymmetric environment for Eu3+ ions and high covalency for EuO bond which are also confirmed by positive values of bonding parameter. The decay curves of 5D0 → 7F2 transition were well fitted to single exponential function for all the concentrations. The slight increase in decay times with rising Eu3+ ion content is due to the increase in the asymmetry of the local environment at the Eu3+ ion site. The CIE color coordinates (x,y) of the prepared glasses are within the range of 0.637–0.648 and 0.347–0.350 and are very close to the standard red color (0.67, 0.33) suggesting pure intense red emission is achieved. The results indicate that BGEx glasses are promising materials for red laser applications.

Calibration of optical temperature sensing of Ca1-xNaxMoO4:Yb3+,Er3+ with intense green up-conversion luminescence

High luminescence intensity is crucial for realizing luminescent temperature sensing with a large signal-to-noise ratio. In this work, the temperature sensing behavior of Ca1-xNaxMoO4:Yb3+,Er3+ with intense green up-conversion luminescence was studied. It has been demonstrated that the single-band green emission was dependent on the Yb3+-MoO42- dimer sensitization as well as the low multi-phonon relaxation rate of 4S3/2 → 4F9/2. In addition, it was found that the uncorrected thermometer could not accurately measure temperature due to thermal effects. A simple method for calibration of up-conversion temperature sensing was reported. Due to high luminescence intensity and temperature sensitivity, Ca1-xNaxMoO4:Yb3+,Er3+ is a promising candidate for up-conversion temperature sensing.

Concentration dependence of visible luminescence from Pr3+-doped phosphate glasses.

To clarify the concentration dependence of visible fluorescence of Pr3+, a series of phosphate glass samples with Pr3+ concentration from 0.05 to 3.0 mol% were fabricated. Steady and dynamic spectroscopic characteristics of Pr3+-doped phosphate glasses were systematically investigated. When the Pr3+ concentration was small, only one visible fluorescence band can be observed at 596 nm, which was ascribed to the transition of 1D2 → 3H4. With increasing Pr3+ concentration from 0.05 to 0.5 mol%, since the multi-phonon relaxation rate of 3P0 was largely quicker than that of 1D2. Increasing Pr3+ concentration from 0.5 to 3 mol%, increasing two other fluorescence bands at 612 nm and 640 nm, which were assigned to the transitions of 3P0 → 3H6 and 3P0 → 3F2, respectively. It was due to the cross relaxation probability between [1D2: 1G4] and [3H4: 3F4] increased, which results in quicker decay rate of 1D2. The fluorescence lifetime of 1D2 decreased from 173 to 6 μs with increasing Pr3+ concentration from 0.1 to 3 mol%, which due to the cross relaxation probability between [1D2: 1G4] and [3H4: 3F4] increased, resulting in quicker decay rate of 1D2. Fitting the concentration dependence of fluorescence lifetime demonstrated that the cross relaxation arising from dipole-dipole interactions between Pr3+ ions.

2.7 µm Mid‐Infrared Emission in Highly Erbium‐Doped Lanthanum Gallate Glasses Prepared Via an Aerodynamic Levitation Technique

AbstractHighly Er3+‐doped La2O3–Ga2O3 glasses up to ≈5.85 × 1021 cm−3 in Er3+ concentration are synthesized by an aerodynamic levitation technique. The glasses are characterized by high glass‐transition temperatures, low OH− absorptions, and long infrared cut‐off wavelengths. Judd–Ofelt analysis reveals a large radiative transition rate and a high branching ratio of the 4I11/2 → 4I13/2 transition, e.g., 46 s−1 and 21%, respectively, at 10 mol% Er2O3. The intensity of 2.7 µm emission drastically increases with increasing Er2O3 content and reaches a maximum at 10 mol% Er2O3. By contrast, the intensity of the 1.5 µm emission decreases with increasing Er2O3 content when the Er2O3 content is greater than 1 mol%. The emission cross‐section and the gain bandwidth at 2.7 µm are as large as 9.05 × 10−21 cm2 and 9.19 × 10−26 cm3 at 10 mol% Er2O3, respectively. The upconversion spectra also indicate that the investigated glasses exhibit small multiphonon relaxation rates and large quenching concentrations.