Thermal Quenching Activation Energy Research Articles

Modulation and Enhancement of Red Luminescence in Ca2GdSbO6: Eu3+ Phosphor by Co-Doping with Bi3.

The double perovskite structure of Ca2GdSbO6 as a fluorescent phosphor matrix material possesses a stable structure, making it an excellent candidate for a matrix material. In this study, single-doped Ca2GdSbO6: Eu3+ fluorescent phosphors and Bi3+ sensitized Ca2GdSbO6: Eu3+, Bi3+ fluorescent phosphor materials were synthesized using the high-temperature solid-state method. The luminescence of this phosphor is based on the 5D0→4F2 transition emission of Eu3+ ions, which occurs at 612nm. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), photoluminescence (PL) spectra, high-temperature fluorescence spectra, and fluorescence decay lifetimes to study the phase structure, optical properties, crystal structure, and chemical purity of the samples. The performance of the single-doped phosphor was significantly improved by the addition of Bi3+ sensitizer. The luminescence intensity increased by nearly 100% compared to Ca2GdSbO6: Eu3+ phosphor, with a quantum efficiency increase of 124%. The thermal quenching activation energy was found to be 0.299eV, and the luminescence intensity remained at 70.3% of room temperature at 453K. These results indicate that the co-doping of Bi3+ has a modulation and enhancement effect on the luminescence of Ca2GdSbO6: Eu3+ red phosphor, showing great potential for application in near-ultraviolet-excited white LED devices.

Luminescence properties and thermal stability of Dy2O3/Sm2O3 doped glass ceramics containing NaBi(WO4)2

Dy2O3–Sm2O3 co-doped transparent glass ceramics (GCs) containing NaBi(WO4)2 crystalline phase were prepared by melt-curing-crystallization method. The optimal heat treatment condition is 580 °C/2 h. The optimum incorporation concentration of Dy2O3 is 0.4%, exceeding which a quenching phenomenon dominated by quadrupole-quadrupole interactions emerges. Meanwhile, when the concentration of Dy2O3 was fixed, the chromaticity coordinate of the sample moved the cool white light region to the warm white light region as the concentration of Sm2O3 increased. The temperature-dependent emission spectra of the 0.4% Dy2O3-0.7% Sm2O3 co-doped GC samples show that emission intensity at 575 nm at 185 °C still reaches 80% of the room temperature. The thermal quenching activation energy was 0.1537 eV and the activation energy after the addition of Mo6+ was 0.1957 eV. This study indicates that Dy2O3–Sm2O3 co-doped GCs containing NaBi(WO4)2 crystalline phase can achieve light-color tunable emission, which is potentially valuable for solid-state color rendering and illumination applications.

Regulating luminescence thermal quenching based on the synergistic effect of energy transfer and energy gap modulation.

Thermal quenching is the core challenge that hinders the application of luminescent materials. Herein, a synergistic mechanism involving energy transfer and energy gap modulation is proposed based on the local crystal field regulation around sensitizers. The substitution of coordination cation V5+/P5+ weakens the crystal field strength of the sensitizer Bi3+, and the weakening of crystal field splitting causes an increase in the 3P1 energy level, thus increasing its energy gap. Compared with the YVO4:Bi3+,Eu3+ phosphor, the thermal stability of the YV0.25P0.75O4:Bi3+,Eu3+ phosphor is significantly improved, and the relative emission intensity of Eu3+ continuously increases with heating and reaches 1.24 times the original intensity at 523 K and does not show a decreasing trend in the studied temperature range. The anti-thermal quenching performance is mainly attributed to the increasing thermal quenching activation energy (ΔE) of the sensitizer by energy gap modulation, which enhances the energy transfer to compensate thermal quenching. Based on the thermal quenching characteristics of the materials, an optical thermometer is designed. The maximum relative sensitivity (Sr) and absolute sensitivity (Sa) are as high as 1.74% K-1 and 0.59 K-1, respectively, and the minimum temperature resolution reaches 0.288 K. The synergistic effect between energy gap modulation of the sensitizer and energy transfer enables the regulation of thermal quenching. Thus, this study provides a new strategy for exploiting high-performance luminescent materials.

Preparation and characterization of SbSeI thin films

Metal chalcohalides are promising candidates for next-generation technologies that include energy conversion, information storage, and quantum computing. Among them, antimony selenoiodide (SbSeI) has received rising interest for different optoelectronic devices, including photovoltaics, due to its bandgap energy, strong optical absorption, stability, and earth abundant, low-cost, and low toxicity constituents. In this work, SbSeI thin films were prepared through a two-step process. At first, antimony selenide (Sb2Se3) thin films were deposited at 300 °C (Sb2Se3-300) and at room temperature (Sb2Se3-RT) onto molybdenum covered soda-lime glass substrates by a magnetron sputtering method. The formation of SbSeI thin films was performed by isothermally annealing the as-deposited Sb2Se3 thin films in sealed quartz ampoules in the atmosphere of antimony iodide (SbI3) with the presence of 100 Torr of argon pressure. The influence of the annealing temperature and time during the iodization of different types of substrates on the morphology and composition of SbSeI thin films was investigated. The well-oriented and dense single-phase SbSeI thin films with stoichiometric composition and single-crystal micro-columnar structures were achieved by annealing Sb2Se3-RT in SbI3 atmosphere at 250 °C for 5 min under 100 Torr of Ar pressure. The room temperature photoluminescence (RT-PL) of SbSeI exhibited a broad asymmetric PL band with a maximum at 1.67 eV. The low-temperature (T = 8 K) PL study of SbSeI showed a broad and asymmetric PL band at 1.4 eV, being quite distant from the bandgap. This PL band at 1.4 eV with obtained small thermal quenching activation energy of 12.7 meV is proposed to originate from the deep donor-deep acceptor pair (DD-DA) recombination.

Tunable luminescence properties of the Ca3-xLuxSc2-xMgxSi3O12:Ce3+ phosphor based LD lighting

In white-light laser diodes (LD) illumination, the full width at half maximum (FWHM) of the emission spectrum of blue LD is too narrow, leading to the cyan light deficiency, while the emitting color of the material limits the red component of the device. Therefore, in this paper, Ca3-xLuxSc2-xMgxSi3O12:Ce3+ (CLSMS:Ce3+, x = 0, 0.5, 1, 1.5, 2) phosphor samples were successfully prepared based on Ca3Sc2Si3O12 (CSS) cyan-green fluorescent materials with different concentrations of Lu–Mg ions introduced in the matrix instead of Ca–Sc ions. And their luminescence properties were systematically investigated. The peak of the sample was shifted from 508 nm to 590 nm as the concentration of Lu–Mg increased. The thermal stability of the series phosphors gradually deteriorated with increasing Lu–Mg concentration. At 423 K, the emission intensity of the samples was 98.11 %, 94.13 %, 92.18 %, 81.96 % and 77.60 % of that at 298 K, respectively. And the thermal quenching activation energy also gradually decreases. The CLSMS:Ce3+ fluorescent materials were prepared into LD devices and tested. It was found that the series of samples showed a gradual decrease in cyan-green light and a gradual increase in red light with increasing Lu–Mg concentration. The CSS compounded with CaLu2Mg2Si3O12 (CLMS) obtained a white LD device with color coordinates of (0.3440, 0.3455), and the cyan and red components of the samples were compensated. In summary, this study demonstrates that CLSMS:Ce3+ is a very promising fluorescent material to extend the color gamut coverage of fluorescent materials. And it has a potential reference value for the field of white-light LD lighting.

Thermally stable Dy2O3/Sm2O3 co-doped glass ceramics containing La2Sn2O7 crystal with tunable luminescence

By using the melt crystallization process, Dy2O3/Sm2O3 co-doped glass ceramics (GCs) containing La2Sn2O7(LSO) crystal were successfully prepared. By using X-ray diffraction (XRD), the sample's phase was determined, and scanning electron microscopy (SEM), the sample's morphology was examined. The optimal heat treatment condition of glass ceramics was determined to be 650 °C/1.5 h. Under 362 nm excitation, the energy transfer of Dy3+→Sm3+ was observed in Dy2O3/Sm2O3 co-doped glass ceramic samples from the emission spectrum. Electric dipole-electric dipole interaction is identified as the mechanism of energy transfer from Dy3+ to Sm3+ according to the Dexter formula for energy transfer. The emission spectra of 0.5%Dy2O3-0.4%Sm2O3 co-doped glass ceramic samples in a range from 298 K to 458 K show that the samples have high thermal stability, and the thermal quenching activation energy at 575 nm has been estimated to be 0.265 eV. According to chromaticity coordinates and correlated color temperature, warm white light emission may be achieved by co-doping Dy2O3/Sm2O3 glass ceramics. The findings demonstrate Dy2O3/Sm2O3 co-doped glass ceramics containing La2Sn2O7 crystal have a potential application prospect in warm white light-emitting diodes (w-LEDs).

Temperature/laser dependence of N3 optical centers in natural type Ia diamonds through photoluminescence spectroscopy

In this work, low-temperature photoluminescence spectroscopy was employed to investigate the N3 optical color center in natural type Ia diamond. The optical properties of the N3 center with regular changes in testing temperature and laser power were studied, and the energy level transition was also discussed. The results showed that the PL intensity of the N3 center enhanced sub-linearly with laser power increased, indicating that the electron transition of the N3 center was mainly radiative recombination with weak Auger recombination participation. In addition, the physical model was employed to analyze the change in the zero phonon line with the increase in the test temperature; it obtained thermal quenching activation energy (25.2 meV), bond softening, and strong interaction with acoustical phonons of the N3 center. The theoretical analysis of the broadening parameters revealed that the longitudinal optical phonon energy was 55.1 meV, and the electron–optic phonon coupling strength was 2.3 meV.

Regulating Luminescence Thermal Quenching of Praseodymium-Doped Niobo-Tantalate Phosphor through Intervalence Charge Transfer Band Displacement.

Pr3+-related intervalence charge transfer (IVCT) bands are a research hotspot owing to their amelioration in the luminescence thermal quenching of Pr3+-activated phosphors. Here, a typical IVCT band displacement strategy via a topological chemical scheme is reported to optimize the luminescence thermal quenching performance of praseodymium-doped niobo-tantalate. The substitution of Ta5+ ions for Nb5+ ions reduces the valence-weighted average cation optical electronegativity and increases the bond lengths of the activator (Pr3+) to the ligand cations (Nb5+ and Ta5+) via adjusting the crystal structure, leading to an increase in the IVCT energy level position from 3.521 to 4.139 eV. The increase in the IVCT energy level leads to an increase in the number of electrons located in the Pr3+ 3P0 energy level, which compensates for the emission of 1D2 during warming. Especially, the energy gap value of the IVCT band is positively correlated with the thermal quenching activation energy ΔE2. ΔE2 increases, the crossover point rises, and the nonradiative transition decreases, further enhancing the Pr3+ 1D2 emission. At 503 K, the 1D2 emission integral intensity increases from 14 to 224% relative to the 303 K original integral intensity. This IVCT band displacement strategy can be used as a scheme for designing antithermal quenching luminescence materials.

A novel red phosphor Sr3In2WO9: Eu3+ for WLEDs

A series of Sr3In2WO9: xEu3+ red phosphors were prepared using a solid-state reaction. The strongest excitation peak of Sr3In2WO9: xEu3+ appeared at 394 nm, and the strongest emission peak appeared at 612 nm. The concentration-dependent emission spectra show that the optimal doping concentration of Eu3+ ions is x = 0.30 for all Sr3In2WO9: xEu3+ samples and Eu3+ occupies the non-inverted centrosymmetric site. Analysis of the causes of concentration quenching, the dipole-quadrupole interaction in Sr3In2WO9: xEu3+ was determined to be the main cause. The thermal stability of the Sr3In2WO9: 0.30Eu3+ sample was analyzed, and it was found that the luminescence intensity of the Sr3In2WO9: 0.30Eu3+ was retained by 55.1 % at 423 K. The thermal quenching activation energy ΔE = 0.291 eV was calculated after the thermal quenching analysis. The calculated CIE chromaticity coordinate of Sr3In2WO9: 0.30Eu3+ is (0.6450, 0.3544), which are very close to the standard red light (0.667, 0.333) given by the National Television Standards Committee system. The color purity of all samples is above 95 %, and the associated color temperature is below 2400 K. The chromaticity coordinates of the encapsulated WLED point of (0.329, 0.388) with a lower correlation color temperature of 5841 K and excellent color rendering index of 88, which indicated the near-UV excited SIWO: Eu3+ red phosphor has great potential for application in the field of WLEDs devices.

Preparation, optical, and thermal stability of Tb3+‐doped glass ceramics containing Al4Ti2SiO12

AbstractThe Tb3+‐doped transparent glass ceramics containing Al4Ti2SiO12 crystal are synthesized by the melt‐solid‐crystallization method. The optimal heat treatment conditions for the glass ceramic samples are determined to be 750°C, 1.5 h based on differential scanning calorimeter, X‐ray diffractometer, scanning electron microscope, and light transmittance curve. The luminescence properties of the glass ceramics samples are characterized by a fluorescence spectrometer. The emission spectrum revealed that the dominant emission is green attributed to Tb3+, the optimal doping concentration is 0.3%. And the thermal quenching activation energy of 0.3% Tb3+‐doped glass ceramics is 0.2554 eV, while the relative sensitivity is 1.50% K−1 at 298 K and the absolute sensitivity is 2.27×10−2 K−1 at 418 K through variable temperature fluorescence spectroscopy test and a series of calculations. These findings demonstrate the excellent stability and temperature sensitivity of glass ceramics, thereby highlighting their potential for use in green lighting and temperature sensing applications.

Adjustment of Bi3+ Luminescence and Thermal Quenching Properties by B'-Site Ion Substitution Strategy in Double Perovskite CaLaMgSb/TaO6:Bi3+ Phosphor.

Thermal quenching has always been one of the most difficult issues in creating high-quality phosphor conversion light-emitting diodes (pc-LED), and a family of strategies are urgently needed to improve the luminescence performance of phosphors at high temperatures. In this contribution, a novel B'-site substitution CaLaMgSbxTa1-xO6:Bi3+ phosphor was constructed using an ion substitution strategy in the matrix with a green activator Bi3+ and a novel double perovskite material. When Sb5+ replaces Ta5+, a surprising increase in luminescence intensity occurs and the thermal quenching properties are greatly improved. The shift of the Raman characteristic peak to a smaller wavenumber and the reduction of the Bi-O bond length confirm that the crystal field environment around Bi3+ changes, which has a substantial effect on the crystal field splitting and nepheline effect of Bi3+ ions, affecting the crystal field splitting energy (Dq). This results in a corresponding increase of the band gap and the thermal quenching activation energy (ΔE) of the activator Bi3+. From the perspective of Dq, the intrinsic relationships among the activator ion band gap, bond length, and Raman characteristic peak changes were analyzed, and a mechanism for regulating luminescence thermal quenching properties was constructed, which provides an effective strategy for improving the promising new materials such as double perovskite.

Luminescence properties of Ca2GdNbO6: Sm3+, Eu3+ red phosphors with high quantum yield and excellent thermal stability for WLEDs

A series of Ca2GdNbO6: xSm3+ (0.01 ≤ x ≤ 0.15) and Ca2GdNbO6: 0.03Sm3+, yEu3+ (0.05 ≤ y ≤ 0.3) phosphors were synthesized by the traditional solid-state sintering process. XRD and the corresponding refinement results indicate that both Sm3+ and Eu3+ ions are doped successfully into the lattice of Ca2GdNbO6. The micro-morphology shows that the elements of Ca2GdNbO6: 0.03Sm3+, 0.2Eu3+ phosphor are evenly distributed in the sample, and the particle size is about 2 μm. The optical properties and fluorescence lifetime of Ca2GdNbO6: 0.03Sm3+, Eu3+ phosphors were detailedly studied. The emission peak at 5D0→7F2 (614 nm) is the strongest and emits red light under 406 nm excitation. The increase of Eu3+ concentration causes the energy transfers from Sm3+ to Eu3+ ions, and the transfer efficiency reaches 28.6%. Ca2GdNbO6: 0.03Sm3+, 0.2Eu3+ phosphor has a quantum yield of about 82.7%, and thermal quenching activation energy is of 0.312 eV. The color coordinate (0.646, 0.352) of Ca2GdNbO6: 0.03Sm3+, 0.2Eu3+ phosphors is located in the red area. The LED device fabricated based on the above phosphor emit bright white light, and CCT = 5400 K, Ra = 92.8. The results present that Ca2GdNbO6: 0.03Sm3+, Eu3+ phosphors potentially find use in the future.

Luminescence properties and thermal stability of Sm3+-doped Na2O–Y2O3–SiO2–P2O5 transparent glass-ceramics containing Na3YSi2O7 crystals

Sm3+-doped Na2O–Y2O3–SiO2–P2O5 precursor glasses were prepared by melting cooling and quenching methods. The optimal doping concentration of Sm3+ ions was determined by fluorescence spectrum. The thermodynamic parameters of precursor glass were determined by the DSC test. The transparent glass-ceramics containing Na3YSi2O7 crystals were obtained by proper heat treatment. The types and microstructures of Na3YSi2O7 crystals were characterized by XRD and SEM. The highest emission peak in the emission spectrum represents the transition of Sm3+: 6H5/2 → 4F7/2. Moreover, the emission intensity of the glass-ceramic is 3 times higher than the original. According to the calculation results of CIE chromaticity coordinates, the luminescence of the glass-ceramics and precursor glass were located in the orange light region. The high thermal stability of the glass-ceramic was discussed through the variable temperature fluorescence test. The thermal quenching activation energy was determined to be 0.27 eV. The results indicate that the transparent glass-ceramics containing Na3YSi2O7 crystals have potential applications in orange LED components.

Synthesis and photoluminescence properties of Eu3+-doped Na2YMg2V3O12: A novel red-emitting phosphor for WLEDs

The fabrication and luminescent properties of novel Na2YMg2V3O12:Eu3+ phosphors, obtained by a conventional solid-state reaction, were investigated. The self-activated emission of the Na2YMg2V3O12 host exhibits a broad emission band ranging from 400 to 700 nm with a maximum peak at 530 nm, ascribed to the d-d transition (3T2, 3T1 → 1A1) of V5+ ions in the (VO4)3− groups. On excitation with near-UV (365 nm) light, the Na2YMg2V3O12:Eu3+ phosphors emit bright red light, including both the broad emission band of the (VO4)3− groups and the sharp emission peaks of Eu3+ ions. At a quenching concentration of 0.20 mol, the Eu3+ ion emission peaks were located at 597, 613, 654 and 710 nm. The thermal stability of the as-prepared Na2YMg2V3O12:Eu3+ phosphor was studied and the thermal quenching activation energy (△E) was calculated to be 0.33 eV. Furthermore, a designed and packaged white-light-emitting diode (WLED) lamp, fabricated with the obtained phosphors, commercial (Ba, Sr)2SiO4:Eu2+ green phosphors, BaMgAl10O17:Eu2+ blue phosphors and a near-ultraviolet (n-UV) chip, emitted bright white light with a CIE coordinate of (0.3068, 0.3491), CRI of 88.20 and CCT of 4460 K. These results indicate the potential of the as-prepared Na2YMg2V3O12:Eu3+ phosphor as a red-emitting phosphor for solid-state illumination.

Nitrogen vacancy luminescence and their phonon sidebands characteristics in nitrogen-doped diamond

In this work, the nitrogen vacancy (NV) luminescence properties and their phonon sidebands in both high and low nitrogen diamonds after electron irradiation and subsequent annealing were thoroughly investigated. From the extracted results, it was demonstrated that the phonon sidebands were caused by the phonon emission behavior of the electrons located in the NV center during the induced transition process from the laser excitation. On top of that, the phonon energies of the NV0 (neutral) and NV— (negatively charged) centers were estimated at about 45 meV and 63 meV, respectively. As the measurement temperature increased, the excited electrons were more likely to return to the ground state by employing non-radiative transitions without generating phonon sidebands. As a result, the synchronous quenching of the NV luminescence and their phonon sidebands effect takes place. The complex lattice environment of the NV centers in the high nitrogen diamond leads also to a smaller thermal quenching activation energy, while the phonon process at a relatively high measurement temperature results in the manifestation of more obvious phonon sidebands of the NV centers.

Thermal Quenching Mechanism of Metal-Metal Charge Transfer State Transition Luminescence Based on Double-Band-Gap Modulation.

Bi3+-related metal-to-metal charge transfer (MMCT) transition phosphors are expected to become a new class of solid-state luminescent materials due to their unique broadband long-wavelength emission; however, the main obstacle to their application is the thermal quenching effect. In this study, one novel thermal quenching mechanism of Bi3+-MMCT transition luminescence is proposed by introducing electron-transfer potential energy (ΔET). Y0.99V1-xPxO4:0.01Bi3+ (YV1-xPxO4:Bi3+) is used as the model; when the band gap of the activator Bi3+ increases from 3.44 to 3.76 eV and the band gap of the host YV1-xPxO4 widens from 2.75 to 3.16 eV, the electron-transfer potential energy (ΔET) decreases and the thermal quenching activation energy (ΔE) increases, which result in the relative emission intensity increasing from 0.06 to 0.64 at 303-523 K. Guided by density functional calculations, the thermal quenching mechanism of the Bi3+-MMCT state transition luminescence is revealed by the double-band-gap modulation model of the activator ion and the matrix. This study improves the thermal quenching theory of different types of Bi3+ transition luminescence and offers one neo-theory guidance for the contriving and researching of high-quality luminescence materials.

Experimental and Theoretical Studies of the Site Occupancy and Luminescence of Ce3+ in LiSr4(BO3)3 for Potential X-ray Detecting Applications.

Ce3+-doped LiSr4(BO3)3 phosphors have been prepared by a high-temperature solid-state reaction method, and structural refinement of the host compound has been performed. The excitation and emission spectra in the vacuum ultraviolet-ultraviolet-visible range at cryogenic temperatures reveal that Ce3+ ions preferentially occupy eight-coordinated Sr2+ sites in LiSr4(BO3)3. Such experimental attribution is well corroborated by the calculated 4f-5d transition energies and defect formation energies of Ce3+ ions at two distinct Sr2+ sites in the first-principles framework. In addition, the doping concentration-dependent luminescence and the temperature-dependent luminescence are systematically investigated by luminescence intensity and lifetime measurements, respectively. This shows that concentration quenching does not occur in the investigated doping range, but inhomogeneous broadening exists in the concentrated samples. With the estimated thermal quenching activation energy, the discussions on the thermal quenching mechanisms suggest that the thermal-ionization process of the 5d electron is a dominant channel for thermal quenching of Ce3+ luminescence, despite the fact that thermally activated concentration quenching cannot be excluded for the highly doped samples. Finally, the X-ray excited luminescence measurement demonstrates the promising applications of the phosphors in X-ray detection.

Structure and Photoluminescence Properties of Dy3+ Doped Phosphor with Whitlockite Structure.

Whitlockite has the advantages of a low sintering temperature, high stability, and a low fabrication cost, and it is widely used as the host for luminescent material. In this study, Ca1.8Li0.6La0.6−x(PO4)2:xDy3+ phosphor was prepared by the high-temperature solid-state method, and its structure, composition, and luminescence properties were systematically studied. The results showed that a new whitlockite type matrix was prepared by replacing Ca2+ in whitlockite with monovalent and trivalent cations. The prepared phosphors belonged to a hexagonal crystal system with a particle size in the range of 5–20 μm. Under the excitation of 350 nm UV light, the samples emitted white light, and there were mainly two stronger emission peaks at 481 nm in the blue band and 573 nm in the yellow band, which correspond to the electron transitions at 4F9/2→6H15/2 and 4F9/2→6H13/2 of Dy3+, respectively. The optimal doping concentration of Dy3+ in Ca1.8Li0.6La0.6(PO4)2 matrix was 0.03 (mol%). The main mechanism of concentration quenching in the sample was dipole–dipole energy transfer. When the temperature was 130 °C, the luminescence intensity of the samples was 78.7% of that at 30 °C, and their thermal quenching activation energy was 0.25 eV. The CIE coordinates of the sample at 30 °C were (0.2750, 0.3006), and their luminescent colors do not change with temperature. All the results indicate that Ca1.8Li0.6La0.6−x(PO4)2:xDy3+ phosphor is a luminescent material with good luminescence performance and thermal stability, which shows a promising application in the field of LED display.

Indirect excitation and luminescence activation of Tb doped indium tin oxide and its impact on the host’s optical and electrical properties

The effect of adding terbium to indium tin oxide (ITO) thin films on the electrical, optical and light emission properties was investigated. The films were prepared by radio frequency dual magnetron sputtering, maintaining a high optical transmittance in the ultraviolet and visible spectral regions, and a low electrical resistivity ranging from to . Terbium-related luminescence is achieved after annealing at 470 ∘C in air at atmospheric pressure. Electrical resistivity and optical transmittance were measured after each annealing step to evaluate the compromise between the achieved light emission intensity, electrical and optical properties. Additionally, temperature dependence of Tb-related luminescence quenching was assessed by temperature-dependent photoluminescence measurements, from 83 to 533 K, under non-resonant excitation. Thermal quenching activation energies suggest an effective energy transfer mechanism from the ITO host to the rare-earth (RE) ions. This indirect excitation mechanism was modeled using a spherical potential-well and a tight-binding one-band approximation approaches, describing a short-range charge trapping process and subsequent formation of bound excitons to RE ion clusters.

Optical properties, energy transfer and thermal stability of spherical nano-phosphor YPO4:Eu3+:Sm3+

A series of phosphors of Sm3+ and Eu3+ single-doped or co-doped YPO4 matrix are synthesized by the hydrothermal method. X-ray diffractometer (XRD), scanning electron microscope (SEM), fluorescence spectrophotometer (FL), ultraviolet–visible near infrared spectrometer (UV) and Fourier transform-infrared (FI-IR) spectrophotometer are used to analyze and characterize composition, structure, morphology, luminescent properties, fluorescence lifetime and fluorescence thermal stability of the sample. The analysis results show that the phosphor has a tetragonal crystal structure, and the morphology is the nano-sphere with the diameter of 60–100 nm. Under excitation of 395 nm and 404 nm near-ultraviolet light, YPO4:Sm3+:Eu3+ emits intense red and orange red light. In the phosphor YPO4:Sm3+:Eu3+, Sm3+ and Eu3+ undergo a process of mutual energy transfer; the critical distance of energy transfer is 1.109–2.392 nm; the energy transfer mechanism is electric dipole-electric dipole interaction; the energy transfer efficiency can reach over 65%. For the optimum product YPO4:2%Sm3+:8%Eu3+, the color coordinates are X = 0.6137, Y = 0.3813; and the fluorescence lifetime is 0.219 ms. The phosphor has good thermal stability, and the thermal quenching activation energy is 0.2053 eV. The tailored yttrium orthophosphate nanoparticles significantly displayed potentiality in the field of optical displays, and also demonstrated the applicability in the biological field.