Luminescence properties and Judd-Ofelt analysis of Tb3+ doped Sr2YTaO6 double perovskite phosphors for white LED applications.

A series of Tb3+-doped Sr2YTaO6 double perovskite phosphors (SYT:Tb3+) were synthesized using a conventional solid-state reaction method. A strong green emission was observed in the SYT:Tb3+ phosphors, and the optimal doping concentration of Tb3+ was confirmed to be 5 mol%. The electric dipole-dipole interaction was ascribed to be the main mechanism for the luminescence concentration quenching. Analysis of the concentration-dependent fluorescence decay confirmed that the self-generated quenching model holds for the dynamic process of Tb3+ decays in SYT. Furthermore, the internal quantum efficiencies, non-radiative transition rates, and energy transfer rates of the 5D4 level for the SYT:Tb3+ samples were estimated, respectively. The luminescence thermal stability of the sample was also evaluated based on the Arrhenius model. The chromaticity shift of the SYT:5 mol% Tb3+ phosphor was examined to be 0.013 when the sample temperature was increased from 303 to 483 K, thus indicating excellent chromaticity shifting resistance under high temperature conditions. Moreover, the Judd-Ofelt parameters were calculated from the emission spectra of SYT:Tb3+ to be Ω2 = 0.29 × 10-20, Ω4 = 0.45 × 10-20, and Ω6 = 0.72 × 10-20 cm2, respectively. The fluorescence branching ratios and radiative transition rates for the 5D4 level were calculated based on the obtained Judd-Ofelt parameters. Finally, a white light-emitting diode (LED) prototype was assembled using a 310 nm LED chip combined with a prepared green SYT:Tb3+ phosphor and two other commercial blue and red phosphors. The obtained warm white light exhibits good chromaticity coordinates (0.32, 0.32) and a high color rendering index of 96.1. Based on the above results, it can be known that the prepared SYT:Tb3+ phosphors have a potential application as green emitting phosphors in white LEDs.

Molten Salt Synthesized CaTa4O11:Er3+/Yb3+ with Superior Upconversion Luminescence.

Low phonon tantalate-based phosphors with a layer structure are considered to have excellent upconversion luminescence (UCL) intensity, which could be reduced due to the existence of impure phase defects and inappropriate doped rare earth ions. To improve their UCL performance, we have prepared single-phase CaTa4O11:Er3+/Yb3+ samples by a molten salt synthesis (MSS) using KCl as the reaction medium and compared its UCL properties with counterparts made by a conventional solid-state reaction (SSR) in this study. We have demonstrated that the MSS samples have a much higher UCL intensity under 980 nm laser excitation than the SSR ones due to accurate replacement of Ca2+ sites by Er3+/Yb3+ in high-purity single-phase MSS samples. We have further enhanced the green UCL intensity of the MSS samples by 1.57 times via acid picking (AP). Under 980 nm laser excitation at a high powder density of 61.3 W/cm2, the green UCL intensity of the MSS-AP samples can reach 3.72 times that of the SSR-AP samples. For potential luminescence thermometry applications, the maximum absolute sensitivity (SA) of the MSS-AP samples reaches 0.01316 K-1 at 501 K based on the luminescence intensity ratio. This study shows that CaTa4O11:Er3+/Yb3+ phosphors prepared by the MSS method are single-phase samples with excellent pure green UCL as a suitable temperature sensing material.

Multicolor-emitting Er3+ and Er3+/Yb3+ doped Zn2GeO4 phosphors combining static and dynamic identifications for advanced anti-counterfeiting application.

Anti-counterfeiting labels based on luminescence materials are a newly emerging technique for protecting legal goods and intellectual property. In the anti-counterfeiting field to prevent forgery and cloning, luminescence materials with properties different from the commercialized and traditional ones are in urgent need. In this work, multicolor-emitting Er3+ single-doped and Er3+/Yb3+ co-doped Zn2GeO4 phosphors combining static and dynamic identifications were developed in order to achieve advanced anti-counterfeiting application. The variation of trap content with increasing the doping content of rare earth ions was analyzed through X - ray photoelectron spectroscopy, thermoluminescence analysis. It was found that there are two types of traps with different depth in Zn2GeO4 phosphors. The depths of the traps were experimentally confirmed to be 0.68 and 0.79 eV, respectively. The transient photocurrent response measurement confirmed the existence of charge carriers, and the mechanism for long persistent luminescence was deduced. The multicolor upconversion mechanisms under 980 and 1550 nm excitation were also discovered. Based on the multicolor steady and transient emission features, an anti-counterfeiting pattern was designed using the phosphors. Static and dynamic identification was demonstrated and presented in detail. Finally, it is indicated that the studied phosphors are excellent candidates for potential applications in luminescence anti-counterfeiting labels.

Near infrared emissions from both high efficient quantum cutting (173%) and nearly-pure-color upconversion in NaY(WO4)2:Er3+/Yb3+ with thermal management capability for silicon-based solar cells.

Raising photoelectric conversion efficiency and enhancing heat management are two critical concerns for silicon-based solar cells. In this work, efficient Yb3+ infrared emissions from both quantum cutting and upconversion were demonstrated by adjusting Er3+ and Yb3+ concentrations, and thermo-manage-applicable temperature sensing based on the luminescence intensity ratio of two super-low thermal quenching levels was discovered in an Er3+/Yb3+ co-doped tungstate system. The quantum cutting mechanism was clearly decrypted as a two-step energy transfer process from Er3+ to Yb3+. The two-step energy transfer efficiencies, the radiative and nonradiative transition rates of all interested 4 f levels of Er3+ in NaY(WO4)2 were confirmed in the framework of Föster-Dexter theory, Judd-Ofelt theory, and energy gap law, and based on these obtained efficiencies and rates the quantum cutting efficiency was furthermore determined to be as high as 173% in NaY(WO4)2: 5 mol% Er3+/50 mol% Yb3+ sample. Strong and nearly pure infrared upconversion emission of Yb3+ under 1550 nm excitation was achieved in Er3+/Yb3+ co-doped NaY(WO4)2 by adjusting Yb3+ doping concentrations. The Yb3+ induced infrared upconversion emission enhancement was attributed to the efficient energy transfer 4I11/2 (Er3+) + 2F7/2 (Yb3+) → 4I15/2 (Er3+) + 2F5/2 (Yb3+) and large nonradiative relaxation rate of 4I9/2. Analysis on the temperature sensing indicated that the NaY(WO4)2:Er3+/Yb3+ serves well the solar cells as thermos-managing material. Moreover, it was confirmed that the fluorescence thermal quenching of 2H11/2/4S3/2 was caused by the nonradiative relaxation of 4S3/2. All the obtained results suggest that NaY(WO4)2:Er3+/Yb3+ is an excellent material for silicon-based solar cells to improve photoelectric conversion efficiency and thermal management.

Lead-free double perovskite Cs2NaInCl6 nanocrystals doped with Sb3+ and Tb3+ for copper ions detection in lubricating oil.

Detecting heavy metal copper ions in lubricating oil holds immense significance for assessing mechanical wear and predicting mechanical failure. While perovskite nanocrystals offer high sensitivity in detecting copper ions, traditional lead halide perovskites suffer from lead toxicity defects. Lead-free perovskites, like Cs2NaInCl6, avoid the issue of lead toxicity but display lower luminescence intensity due to the presence of forbidden optical transitions. To address these issues, this study synthesized Cs2NaInCl6 nanocrystals (NCs) co-doped with Sb3+ and Tb3+ ions for copper ions detection in lubricating oil. The introduction of Sb3+ effectively reduced the band gap of the Cs2NaInCl6 host, creating an energy transfer pathway for Tb3+ emission via self-trapped excitations (STEs). Moreover, the doping of Tb3+ ions resulted in the suppression of STEs emission due to electron transfer from STEs to Tb3+. The emission of Tb3+ increased initially and then decreased with the increasing Tb3+ concentration, peaking at 40 %. Finally, Cs2NaInCl6: 2.5 %Sb3+, 40 %Tb3+ NCs were employed as probes for copper ions detection, exhibiting superior sensitivity and selectivity compared to similar probes. The presence of copper ions introduced competition between copper and Tb3+ for electrons from STEs, consequently leading to the quenching of multiple emission intensities associated with STEs and Tb3+. This method shows promising potential in predicting mechanical failure.

The Combination of Upconversion Nanoparticles and Perovskite Quantum Dots with Temperature-Dependent Emission Colors for Dual-Mode Anti-Counterfeiting Applications.

Novel and high-security anti-counterfeiting technology has always been the focus of attention and research. This work proposes a nanocomposite combination of upconversion nanoparticles (UCNPs) and perovskite quantum dots (PeQDs) to achieve color-adjustable dual-mode luminescence anti-counterfeiting. Firstly, a series of NaGdF4: Yb/Tm UCNPs with different sizes were synthesized, and their thermal-enhanced upconversion luminescence performances were investigated. The upconversion luminescence (UCL) intensity of the samples increases with rising temperature, and the UCL thermal enhancement factor rises as the particle size decreases. This intriguing thermal enhancement phenomenon can be attributed to the mitigation of surface luminescence quenching. Furthermore, CsPbBr3 PeQDs were well adhered to the surfaces and surroundings of the UCNPs. Leveraging energy transfer and the contrasting temperature responses of UCNPs and PeQDs, this nanocomposite was utilized as a dual-mode thermochromic anti-counterfeiting system. As the temperature increases, the color of the composite changes from green to pink under 980 nm excitation, while it displays green to non-luminescence under 365 nm excitation. This new anti-counterfeiting material, with its high security and convenience, has great potential in anti-counterfeiting applications.

Bright solid-state luminescence and high-temperature resistance of Ga-doped carbon dots with ultra-wideband white emission for light-emitting diodes.

Fluorescent CDs tend to undergo solid-state aggregation quenching in powder form. This is caused by the stacking of π-π conjugate structures and excessive resonant energy transfer. Moreover, various forms of N play an important role in white CDs suitable for LED applications. White, single-component, non-N-doped CDs have never been reported for LED application. In this study, to overcome this limitation, we developed Ga-doped CD powders containing no N element that exhibit ultra-wideband white emission in the range of 420-800 nm for LED applications and were able to resist solid-state aggregation quenching. Furthermore, the Ga-doped CD powders demonstrated excellent luminescence stability under high temperatures. Another strength of the Ga-doped CD powders is their large Stokes shift, where the peak center of white emission shifts from 550 nm to 650 nm under 365 nm excitation as the Ga doping concentration is adjusted from 0.05 to 0.6 (Ga : H2O, mass ratio). The full width at half-maximum can reach 262 nm. Additionally, the Ga-doped CD powders exhibit good luminescence stability under long-time exposure to an air atmosphere. Their luminescent intensity retained 70%-74% of the initial values even after being left in natural placement for 100 days. Moreover, the Ga-doped CDs demonstrate afterglow features.

Improving upconversion luminescence intensity of BiTa7O19:Er3+/Yb3+ by polyvalent Sb co-doping.

BiTa7O19:Er3+/Yb3+/Sb phosphors were successfully synthesized by high temperature solid sintering. X-ray diffraction (XRD), fluorescence spectrometry and X-ray photoelectron spectroscopy (XPS), were used to analyze the phase structure, upconversion luminescence (UCL) features and Sb valence state, respectively. The results suggest that polyvalent Sb with Sb3+ and Sb5+ can replace the Ta5+ sites in a BiTa7O19 host to form a pure phase. Compared with BiTa7O19:0.1Er3+/0.4Yb3+, polyvalent Sb doping further improves UCL intensity by 1.2 times under 980 nm laser stimulation with a powder density of 44.59 W cm-2. This is due to the adjustment of the local lattice structure of BiTa7O19 by the polyvalent Sb. The maximum absolute sensitivity (SA) and relative sensitivity (SR) can be estimated from the UCL variable-temperature spectra as 0.0098 K-1 at 356 K and 0.0078 K-1 at 303 K using the luminescence intensity ratio (LIR) approach. The outcomes show that host local lattice adjustment using polyvalent elements is an effective way to improve luminescence intensity, and it is possible to use BiTa7O19:Er3+/Yb3+/Sb as a temperature sensor.

Single-component full-color emitting Ca6Y2Na2(PO4)6F2:Eu2+,Tb3+,Mn2+ phosphors with superior performance: color-tunable and energy transfer study.

Highly efficient single-component full-color emitting Ca6Y2Na2(PO4)6F2 (CYNPF):Eu2+,Tb3+,Mn2+ phosphors have been synthesized by a high-temperature solid-state reaction. Coupled with the Eu2+, Tb3+, and Mn2+ emission bands centered at 455 nm, 547 nm, and 580 nm, color-tunable white light can be generated. The energy transfer (ET) process from Eu2+ to Tb3+ and Mn2+ is attributed to the resonant dipole-dipole/dipole-dipole interaction mechanism with ultra-high ET efficiency (>90%). The emission color of the phosphors can be tuned from blue to yellowish green and orange with the corresponding CIE chromaticity coordinates of (0.1719, 0.1215), (0.2852, 0.4289), and (0.4752, 0.3903), respectively. Through controlling the concentration ratio of Tb3+ and Mn2+ ions, optimal white light emission can be obtained with CIE coordinates of (0.3381, 0.3353) excited at 365 nm, which is very close to the National Television Standards Committee white (0.330, 0.330). The thermal stability of the Eu2+, Tb3+, and Mn2+ codoped CYNPF phosphors has been investigated systematically. A single-component white LED (wLED) device has been fabricated by combining the CYNPF:Eu2+,Tb3+,Mn2+ phosphor with a 365 nm near-ultraviolet (n-UV) LED chip, which exhibits a high color rendering index (Ra = 80.2) along with a low color temperature of 5207 K and CIE coordinates of (0.3212, 0.3221). The results suggest that the phosphors can be used as a candidate material for single-component white phosphors for n-UV excited full-visible-spectrum wLEDs.

Bi3+ and Tb3+ Co-doped Cs2AgInCl6 Lead-free double perovskite nanocrystals for detection of temperature and copper ions.

The content of Cu2+ in lubricating oil and lubricant temperature are important indicators predicting mechanical failure. Therefore, developing a nontoxic fluorescence probe is necessary to detect Cu2+ and temperature in lubricating oil. The lead-free inorganic double perovskite nanocrystals (NCs) Cs2AgInCl6 are potential candidates. However, the low fluorescence intensity and the high excitation energy required of Cs2AgInCl6 NCs limit their practical applications. In this study, Bi3+ and Tb3+ were successfully co-doped into Cs2AgInCl6 NCs via the hot-injection method. The doping of Bi3+ produces a broad emission originating from self-trapped excitons and reduces the excitation energy, allowing commercial LEDs as excitation sources. Tb3+ ions doping offers characteristic emission peaks (5D0-7FJ) of Tb3+ ions and improves the fluorescence intensity of Cs2AgInCl6 NCs. Furthermore, the Cs2AgInCl6: Bi3+/Tb3+ NCs have been employed as optical thermometry, which provide a temperature calibration curve with the maximum absolute and relative sensitivities of 2.15% K-1 at 350 K and 2.25% K-1 at 303 K in the temperature range of 303-423 K, respectively. Finally, the nanocrystals have been applied to detect Cu2+ in lubricating oil. The fluorescent probe shows a good detection sensitivity of 8.94 × 10-4 nM-1 and a low detection limit of 14.3 nM in the range of 10-300 nM. This work not merely offers a novel way for improving the luminescence performances of double perovskite NCs Cs2AgInCl6, but broadens their potential for detection of Cu2+ and temperature.

Intense red up-conversion luminescence and temperature sensing property of Yb3+/Er3+ co-doped BaGd2O4 phosphors.

In this study, intense red and extremely weak green up-conversion (UC) luminescence was obtained in BaGd2O4: x mol% Yb3+/y mol% Er3+ phosphors under the excitations of 980 nm and 1550 nm. The corresponding maximum integrated intensity ratios of the red to green UC emissions are 50.3 and 158.7, respectively. The UC luminescence mechanisms upon different excitations were discussed. It was confirmed that two-photon and three-photon processes were responsible for both the red and green UC emissions excited at 980 nm and 1550 nm, respectively. The energy transfer efficiency from Er3+ to Yb3+ was calculated according to the fluorescence lifetime measurement under 1550 nm excitation. Temperature sensing based upon the thermally coupled energy levels 2H11/2/4S3/2 as well as thermally coupled Stark sublevels of 4F9/2 level of Er3+ was investigated under the excitation of 980 nm. The maximum absolute sensitivities were respectively obtained to be 0.42% K-1 at 573 K and 0.18% K-1 at 298 K. Our results indicated that BaGd2O4: Yb3+/Er3+ phosphors might be a kind of promising red UC phosphors with optical temperature measurement function.

Defect-induced Ce3+ sites preferences and multilevel concentration quenching of a high-efficiency cyan phosphor for high-quality full-visible-spectrum wLED.

Currently, the efficient way to synthesize white light-emitting diodes (WLEDs) is combining a near-ultraviolet (n-UV, 380-420 nm) emitting LED chip with tricolor (red, green, and blue) emitting phosphors. However, further improving the color rendering index (CRI) for WLEDs is hindered by the absence of cyan components. Hence, a series of high-efficiency and continuously tunable Ce3+,Gd3+-doped CaScBO4 (CSBO) blue-cyan phosphors with an orthorhombic structure were successfully developed by a high-temperature solid-state reaction method. Based on density-functional theory (DFT) calculation, a vacancy was produced along with inequivalent replacement (3Ca2+ → 2Ce3+/Gd3+ + V''Ca) when just adding the trivalent cations, meanwhile causing the local environment of the lattice to relax so Ce3+/Gd3+ ions find it easier to enter into Sc3+ sites at a higher doping concentration. Under the excitation of n-UV, the emission peak position moves from 443 nm to 480 nm and two concentration quenching points appear with an increase in Ce3+ ions by defect-induced site-selective occupation. The two samples at concentration quenching points both have high quantum efficiencies of 88.6% and 86.2% and an acceptable thermal quenching performance. The property performance and internal mechanism are illuminated by the excitation and emission spectra and theoretical analysis. Finally, by combining CSBO:Ce3+, commercial green and red phosphors and an n-UV LED chip, an as-fabricated WLED with a great CRI value of 93.2 and a low CCT (4291K) was obtained. This work demonstrates the potential of CSBO:Ce3+ as a blue-cyan phosphor for use in high-quality full-visible-spectrum WLEDs in the future. The investigation of the mechanism for the defect-induced site preferences provides a reference for developing new photoluminescent materials.

Thermal enhancing effect of upconversion luminescence in Er3+/Yb3+ co-doped Cs3BiSr(P2O7)2 phosphors.

A series of Er3+/Yb3+ co-doped Cs3BiSr(P2O7)2 (CBSPO) phosphors with significant thermal enhancement were successfully prepared using the solid-state method and the thermal-enhancing effect was studied in detail. When the temperature increased from 303 to 723 K, the upconversion luminescence (UCL) emission intensities of 2H11/2 → 4I15/2 and 2H11/2 + 4S3/2 → 4I15/2 of Er3+ in CBSPO:0.1Er3+/0.2Yb3+ were enhanced 22.81 and 10.06 times under 980 nm laser excitation, respectively. Meanwhile, the UCL color of the sample obviously changed from orange to green with the increase in temperature. Furthermore, the UCL thermal enhancement mechanism was demonstrated, which originates from phonon-assisted transitions. In addition, the maximum absolute temperature sensitivity for CBSPO:0.1Er3+/0.2Yb3+ was calculated to be 0.01026 K-1 at 563 K via luminescence intensity ratio (LIR) technology. All the results show that the CBSPO:Er3+/Yb3+ phosphors can be used for safety warning and temperature measurement at high temperatures.

Net Optical Gain Coefficients of Cu+ and Tm3+ Single-Doped and Co-Doped Germanate Glasses.

Broadband tunable solid-state lasers continue to present challenges to scientists today. The gain medium is significant for realizing broadband tunable solid-state lasers. In this investigation, the optical gain performance for Tm3+ and Cu+ single-doped and co-doped germanate glasses with broadband emissions was studied via an amplified spontaneous emission (ASE) technique. It was found that the net optical gain coefficients (NOGCs) of Tm3+ single-doped glass were larger than those for Cu+ single-doped glass. When Tm3+ was introduced, the emission broadband width of Cu+-doped glass was effectively extended. Moreover, it was found that for the co-doped glass the NOGCs at the wavelengths for Tm3+ and Cu+ emissions were larger than those of Tm3+ and Cu+ single-doped glasses at the same wavelengths. In addition, the NOGC values of Tm3+ and Cu+ co-doped germanate glasses were of the same order of magnitude, and were maintained in a stable range at different wavelengths. These results indicate that the Tm3+ and Cu+ co-doped glasses studied may be a good candidate medium for broadband tunable solid-state lasers.

Engineering Er3+-sensitized nanocrystals to enhance NIR II-responsive upconversion luminescence.

An Er3+-sensitized system with a high response to 1550 nm radiation in the second near-infrared window (NIR II) has been considered for a new class of potential candidates for applications in bio-imaging and advanced anti-counterfeiting, yet the achievement of highly efficient upconversion emission still remains a challenge. Here, we constructed a novel Er3+-sensitized core-shell-shell upconversion nanostructure with a Yb3+-enriched core as the emitting layer. This designed nanostructure allows the Yb3+ emitting layer to more efficiently trap and lock excitation energy by combining the interfacial energy transfer (IET) from the shell (Er3+) to the core (Yb3+), high activator Yb3+ content, and minimized energy back-transfer. As a result, the NIR II emission at 1000 nm is remarkably enhanced with a high quantum yield (QY) of 11.5%. Based on this trap and lock-in effect of the excitation energy in the Yb3+-enriched core, highly efficient 1550 nm-responsive visible and NIR upconversion emissions are also achieved by co-doping with other activator ions (e.g., Ho3+ and Tm3+). Our research provides a new functional design for improving NIR II-responsive upconversion luminescence, which is significant for developing practical applications.

Turn-on fluorescence ferrous ions detection based on MnO2 nanosheets modified upconverion nanoparticles.

A turn on upconversion fluorescence probe based on the combination of ~32 nm NaYF4: Yb/Tm nanoparticles and MnO2 nanosheets has been established for rapid, sensitive detection of Fe2+ ions levels in aqueous solutions and serum. X-ray diffraction (XRD), transmission electron microscopy (TEM), absorption and emission spectra have been used to characterize the crystal structure, morphology and optical properties of the samples. MnO2 nanosheets on the surface of UCNPs act as a fluorescence quencher, resulting in the quenching of the blue fluorescence (with excitation/emission maximum of 980/476 nm) via fluorescence resonance energy transfer from upconversion nanoparticles to MnO2 nanosheets. With the adding of Fe2+, upconversion fluorescence of the nanocomposites recovers due to the reduction of MnO2 to Mn2+. Because of the low background of the probe offered by upconversion fluorescence, this probe can be used for detecting Fe2+ in aqueous solutions in the range of 0.1-22 µM with detection limit of 0.113 µM. The developed method has also been applied to detect 10 µM Fe2+ ions in serum with recoveries ranging from 97.6 to 105.3% for the five serum samples. Significantly, the probe shows fast response and stable signal, which is beneficial for long-time dynamic sensing. Thus, the proposed strategy holds great potential for disease diagnosis and treatment.

Photoluminescence, optical transition properties and temperature-induced shift of charge transfer band and temperature sensing property of GdNbTiO6: Sm3+ phosphors.

GdNbTiO6: Sm3+ phosphors with various Sm3+ concentrations were prepared via a high temperature solid-state reaction method. The crystal structure of the samples was characterized by means of X-ray diffraction (XRD) and the as-prepared samples were confirmed to be orthorhombic phase GdNbTiO6. Photoluminescence properties were investigated by measuring the concentration- and temperature-dependent photoluminescence spectra. Concentration-dependent luminescence quenching and luminescent thermal quenching behaviors were observed and they were respectively ascribed to the electric dipole-dipole interaction between Sm3+ ions and the cooperation of energy transfer and crossover process. The chromatic characteristics were found to be dependent on the excitation wavelength and Sm3+ concentration. In addition, temperature-induced redshift of charge transfer band of GdNbTiO6 host was found in temperature-dependent excitation spectra and the opposite variations of different excitation peaks were utilized for optical thermometry. Finally, the optical transition property was studied on the basis of the diffuse reflectance spectra and Judd-Ofelt (J-O) theory, meanwhile, its accuracy was evaluated by the result of emission spectra.

Temperature dependence of up-conversion luminescence and sensing properties of LaNbO4: Nd3+/Yb3+/Ho3+ phosphor under 808 nm excitation.

LaNbO4: Nd3+/Yb3+/Ho3+ phosphor was prepared by a conventional high temperature solid-state reaction method. The temperature dependence of up-conversion (UC) luminescence property of LaNbO4: Nd3+/Yb3+/Ho3+ phosphor under 808 nm excitation and the potential application of exploiting the red-to-green UC emission intensity ratio (IR/IG) of Ho3+ in temperature sensing were studied. Two-photon processes were confirmed to be responsible for both the green and the red UC emissions at different temperatures by analyzing the excitation power density dependent UC luminescence spectra measured at different temperatures. The energy level diagram was drawn to analyze the UC luminescence mechanism of Ho3+. In addition, it was found that the ratio IR/IG of Ho3+ was independent of the excitation power density of 808 nm laser under the current experimental condition, but it was sensitive to the temperature. And the temperature dependent UC luminescence spectra displayed that the ratio IR/IG exhibited a good linear increasing tendency with temperature rising. The obtained temperature sensing sensitivity was 2.04 × 10-3 K-1 in the temperature range of 303-693 K. The results suggest that LaNbO4: Nd3+/Yb3+/Ho3+ phosphor may be a good candidate for application in optical temperature sensors.

Fluorescence decay route of optical transition calculation for trivalent rare earth ions and its application for Er3+-doped NaYF4 phosphor.

Usually, the optical transition properties of trivalent rare earth (RE) ions in transparent hosts can be quantitatively investigated in the framework of Judd-Ofelt theory. A standard and commonly accepted calculation procedure based on the absorption spectrum has already been established. However, it is hard to assess the optical transition properties of trivalent RE ions doped in powdered and film materials owing to the difficulty in the absolute absorption spectrum measurements. In this work, we proposed a new route to calculate the Judd-Ofelt parameters of trivalent RE ion-doped materials in any morphological and shaped forms. In this method, the fluorescence decay values bridging the radiative transition rates and the Judd-Ofelt parameters were used. As an application example of the proposed Judd-Ofelt calculation method, the Judd-Ofelt parameters of Er3+ in NaYF4 were calculated via the proposed route, and it was found that the obtained results are in reasonable accordance with those derived from other routes. It was also proved that this proposed Judd-Ofelt calculation method is a practicable and effective route for evaluating optical transition properties of trivalent RE ions in non-transparent hosts as long as the fluorescence decay values can be measured.

Temperature Feedback-Controlled Photothermal/Photodynamic/Chemodynamic Combination Cancer Therapy Based on NaGdF4 :Er,Yb@NaGdF4 :Nd@Cu-BIF Nanoassemblies.

The intelligent design of multifunctional nanoplatforms is critical for cancer therapy. Herein, NaGdF4 :Er,Yb@NaGdF4 :Nd@Cu(II) boron-imidazolate frameworks (denoted as CSNPs@Cu-BIF) nanoassemblies are designed and fabricated. Upon a single 808 nm laser irradiation, the nanoassemblies not only show the outstanding photothermal conversion capacity (η = 41.7%) but also generate cytotoxic reactive oxygen species through an in situ Fenton-like reaction and fluorescence resonance energy transfer. Importantly, the nanoassemblies simultaneously introduce remarkable antitumor efficacy via photothermal/photodynamic/chemodynamic combination therapy both in vitro and in vivo. To improve the therapeutic effect of solid tumor ablation, it is highly desirable to monitor the treatment process in real-time. Multiclinical imaging modalities of ultrasonography are employed to systematically investigate the ablation mechanism of solid tumors in vivo. Furthermore, the significant difference between the eigen temperature of CSNPs@Cu-BIF nanoassemblies obtained by the temperature-sensitive emission bands signal changes and the apparent temperature recorded by the thermal imaging camera is 14.55 K at equilibrium. This current work therefore supplies an alternative strategy in temperature feedback-controlled accurate cancer therapy.