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Highly efficient multi-center activated single-component white light-emitting phosphors were obtained via energy transfer.

BiTa7O19:Er3+/Yb3+/Sb phosphors were successfully synthesized by high temperature solid sintering. X-ray diffraction (XRD), fluorescence spectrometer and X-ray photoelectron spectroscopy (XPS), were used to analyze the phase structure, upconversion luminescence (UCL)...

A series of YNbO4: Bi3+ and YNbO4: Bi3+/Er3+ phosphors were prepared by a conventional high temperature solid–state reaction method. The results of XRD and Rietveld refinement confirm that monoclinic phase YNbO4 samples are achieved. The down-/up-conversion luminescence of Er3+ ions was investigated under the excitation of ultraviolet light (327 nm) and near infrared light (980 nm). Under 327 nm excitation, broad visible emission band from Bi3+ ions and characteristic green emission peaks from Er3+ ions are simultaneously observed, while only strong green emissions from Er3+ ions are detected upon excitation of 980 nm. Remarkable emission enhancement is observed in down-/up-conversion luminescence processes by introducing Bi3+ ions into Er3+-doped YNbO4 phosphors. Pumped current versus up-conversion emission intensity study shows that two-photon processes are responsible for both the green and the red up-conversion emissions of Er3+ ion. Through the study of the temperature sensing property of Er3+ ion, it is affirmed that the temperature sensitivity is sensitive to the doping concentration of Bi3+ ions. By comparing the experimental values of the radiative transition rate ratio of the two green emission levels of Er3+ ions and the theoretical values calculated by Judd-Ofelt (J-O) theory, it is concluded that the temperature sensing property of Er3+ ions is greatly affected by the energy level splitting.

Cs3BiSr(P2O7)2:Er3+/Yb3+ phosphors show excellent upconversion luminescence thermal enhancement performance under 980 nm (a) and 1550 nm (b) laser excitation, respectively.

The emission light of CSBO: Ce3+ changes from blue to broad band cyan emission with the increase of Ce3+ concentration resulted from defect-induced site selective occupation. The full-spectrum emission WLED of 93.2 color rendering index was obtained.

YVO4:Er/Yb nanowires and nanotubes phosphors were prepared by electrospinning technique following calcination at different heating rates. The obtained nanowires are of 80–200 nm in diameter and are single crystals or polycrystalline in phase. The outer diameter of the obtained nanotubes is 50–200 nm with a wall thickness of 20–30 nm. The up-conversion properties of YVO4:Er3+/Yb3+ nanowires and nanotubes were investigated. All samples were found to produce a green up-converted emission. The temperature-sensing features of YVO4:Er3+/Yb3+ nanowires and nanotubes were investigated through the fluorescence intensity ratio approach, and the sensitivity of temperature was determined over the temperature range of 30–390 °C. The temperature sensing sensitivities of the mixed YVO4:Er3+/Yb3+ nanowire samples and nanotubes exceeded the single YVO4:Er3+/Yb3+ nanowire samples because of higher Yb3+-doped concentrations. The morphology influence on optical properties was studied at a fixed doping rare earth concentration and size. The temperature sensitivities of YVO4:Er/Yb samples depended on the Yb ion concentrations rather than the morphology. The significant temperature sensitivity indicates its potential for use as an optical temperature sensing probe.

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 Ce

A series of K₁–₂ₓ–₂yBayAl₁₁O₁₇(KBAO):xEu²⁺ phosphors are designed to develop a blue phosphor with excellent thermal properties. All of the samples present similar β-Al₂O₃ structures with P63/mmc space group; the K⁺ vacancy can exist stably until the Ba²⁺ concentration exceeds around y = 0.3. KBAO:Eu²⁺ exhibits strong absorption for near-ultraviolet light and relatively standard blue emission. The mechanisms for excitation and emission spectrum variations have also been studied in detail. Based on the adjustment of K⁺ vacancy numbers in the defect structure, K₀.₆Ba₀.₁Eu₀.₁Al₁₁O₁₇ exhibits a remarkable quantum yield of around 91.2% and a terrific high-temperature characteristic. The zero-thermal quenching performance mainly results from stabilization of the flowing electron number between Eu²⁺ 5d levels and K⁺ defect e(0/–1) and e(+1/0) levels in the processes of thermal ionization and recombination. A bright fabricated white-light-emitting diode (WLED) gives a color rendering index (CRI) of Rₐ = 87 and a correlated color temperature (CCT) of 4510 K, demonstrating that KBAO:Eu²⁺ has application potential to provide a blue light component in WLED. In addition, our research is a significant attempt to achieving stable zero-thermal quenching by subjective structure design, which provides a reference value for investigating the excellent new phosphors.

In this study, intense red and extremely weak green up-conversion (UC) luminescence was obtained in BaGd

Nowadays liquid crystal display (LCD) backlighting has become an independent subject of the display field, and gradually formed an innovative and popular research area. The narrow-band emission phosphors that play an important role in LCD backlighting have been extensively investigated in recent years. Hence, a series of novel garnet structure phosphors Ca4HfGe3−ySiyO12(CHGSO):xBi3+ (0 ≤ x ≤ 0.04, 0 ≤ y ≤ 0.9) were designed and synthesized via the high temperature solid state reaction. All the samples belong to a cubic crystal system with the space group of Iad. Under the excitation of near-ultraviolet (n-UV) LED chips, Ca4HfGe3O12(CHGO):0.02Bi3+ exhibits a narrow-band blue emission with a high color purity of ∼95%, a central wavelength of 432 nm and the full-width at half maximum (FWHM) of around 36.4 nm, which is better than commercial blue phosphors (BAM: Eu2+). CHGO:0.02Bi3+ also presents an excellent quantum efficiency of 88.7%. The thermal stability is enhanced by the substitution of Si4+ for Ge4+, and the Ca4HfGe3−ySiyO12:0.02Bi3+(y = 0, 0.3, and 0.6) could remain at 51%, 58%, and 70% at 150 °C of the initial intensity at room temperature, respectively, which is related to the variation of the energy band structure. Simultaneously, our samples have the narrowest FWHM and highest color purity in the reported Bi3+-doped blue phosphors. Using K2SiF6:Mn4+ as the red phosphor, β-sialon:Eu2+ as the green phosphor, Ca4HfGe2.4Si0.6O12:0.02Bi3+ as the blue component and GaN-based chip, this optimized w-LED device shows a wide color gamut of 77% NTSC. This is comparable to the current commercial portfolio (β-sialon:Eu2+ + K2SiF6:Mn4+ + blue chip). All of the results indicate that the Bi3+-activated CHGSO phosphors have a wide application prospect in the field of advanced backlight display, which provide a reference and support for the design of near-ultraviolet excited backlight materials.

Usually, Dy3+ doped phosphors can simultaneously generate both blue and yellow emissions which can be mixed as white light if the intensities of them are closer. The aim of this work is to explore white-light generation in Dy3+ doped YNbO4 phosphors by introducing Tm3+ to compensate the lack of blue component of Dy3+. To this end, the Dy3+, Tm3+ single- and co-doped YNbO4 phosphors were synthesized via a high-temperature solid-state reaction method. Under the excitation of 354 nm, the YNbO4: Dy3+ phosphors exhibit a blue emission at 487 nm and a yellow emission at 579 nm and the results indicated that the white light cannot be obtained from Dy3+ single-doped YNbO4 phosphors owing to the deficiency of blue spectral component. To tune the emission color, Tm3+ was introduced into Dy3+ doped samples, and the energy transfer behavior between Tm3+ and Dy3+ was investigated based on the fluorescence dynamics. The chromatic property of the while light emitting phosphor was studied. High-quality white emission was obtained when Tm3+ concentration was 1.0 mol%. The color coordinates and the correlated color temperature for the concentration-optimized sample are (0.3355, 0.3345) and 5352 K, respectively.

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.

The optical transition properties of trivalent rare earth (RE3+) doped luminescent materials have received extensive attention. The Judd–Ofelt theory is an effective tool for exploring the optical transition properties for the 4f–4f transitions of lanthanides. The aim of this work is to discover the effect of Er3+ concentration and different Ln3+ ions on the Judd–Ofelt parameters in LnOCl:Er3+ (Ln = Y, La, Gd) phosphors. Oxychloride LnOCl:Er3+ (Ln = Y, La, Gd) phosphors were produced via a single displacement reaction technique. The Judd–Ofelt calculation procedure for RE3+ doped powders was modified and then adopted to obtain the Judd–Ofelt parameters of Er3+ in the studied phosphors. Meanwhile, a new route for examining the Judd–Ofelt calculation quality was proposed and used. It was found that the Er3+ doping concentration slightly affects the optical transition properties of Er3+ in YOCl and LaOCl, but greatly affects the optical transition properties in GdOCl. Moreover, it was also found that the optical transition properties of Er3+ depend also on Ln3+ (Ln = Y, La, Gd) though the crystal structure of these compounds is similar. The Judd–Ofelt parameters of Er3+ are the smallest in LaOCl:Er3+, medium in YOCl:Er3+, but the biggest in GdOCl:Er3+ when the doping concentration is the same.

Perovskite C s P b B r 3 quantum dot (QD) glasses doping C u 2 + are reported for excellent long-wavelength-pass filters. Transmittance, optical density (OD), photoluminescence (PL), PL excitation, and PL decay are used to investigate filter properties and the quenching mechanism. At low C u 2 + molar concentrations of 0%, 0.0025%, 0.005%, and 0.01%, the filters exhibit good properties in transmittance and OD. Transition wavelengths are 518, 513, 513, and 512 nm, respectively. The shape and position of transmittance and OD are almost not changed. As C u 2 + concentration increases, PL intensity is monotonously quenched. PL decay is obviously faster. The quenching mechanism is dynamic quenching, which is electron transfer from QDs to C u 2 + . In comparison with the initial intensity, the intensity decreases by factors of 7.6, 12.8, and 18.8. Oxidation and reduction atmospheres are introduced, and the dynamic quenching mechanism is further confirmed. At high C u 2 + concentrations of 0.013%–0.02%, the quenching mechanism is static quenching. Double-anion C s P b ( C l / B r ) 3 QD glasses of different C u 2 + concentrations extend the operation wavelength to the blue light region. For C u 2 + concentrations of 0%, 0.005%, and 0.01%, the transition wavelengths are 470, 472, and 473 nm for C s P b ( C l / B r ) 3 (NaCl as Cl source) QD glasses, and 430, 426, and 445 nm for C s P b ( C l / B r ) 3 ( P b C l 2 as Cl source) QD glasses, respectively.

Usually, the luminescence intensity and mechanism of rare-earth ions doped materials are dependent on both doping concentration and sample temperature. In this study, we attempt to explore the concentration effect on up-conversion (UC) luminescence and the dependence of luminescence temperature quenching on excitation wavelength in YNbO4: Ho3+/Yb3+ phosphors. The YNbO4: Ho3+/Yb3+ phosphors with various Ho3+ and Yb3+ concentrations were synthesized via a high-temperature solid-state reaction technique. Intense green UC emission peaked at 543 nm was observed, accompanying with weak red and near infrared (NIR) UC emissions centered at 659 and 745 nm. Based on the laser working current dependence of UC luminescence, two-photon processes were responsible for both the green and the red UC emissions under 980 nm excitation, which have no apparent dependence on both Ho3+ and Yb3+ concentrations. According to the Arrhenius model, crossover process was responsible for the temperature-dependent down-conversion (DC) luminescence quenching of Ho3+ under 452 nm excitation. However, the temperature quenching processes of the green and the red UC luminescence cannot be well explained by Arrhenius model. It was found that the UC luminescence intensity decayed with increasing sample temperature, which was caused by both the crossover and temperature-dependent energy transfer processes.

Novel nanoplatform with excellent photothermal conversion and temperature feedback are preferable in clinical photothermal therapy (PTT). In this work, a hybrid of NaYF4:Er3+,Yb3+@NaYF4 upconversion nanoparticles (UCNPs) conjugated with gold nanorods (GNRs) was fabricated in order to achieve effective photothermal conversion and excellent temperature detection. In this nanoplatform, the GNRs as photo-activated nano-heaters could effectively convert the 808 nm photoenergy into heat, meanwhile UCNPs as 980 nm triggered temperature probe could read the temperature in an exact microdomain where the nanocomposite was located at. The effects of excitation source, GNRs concentration and power density on photothermal conversion were investigated. In addition, the difference between eigen temperature of nanoparticles and solution temperature, and the potential for temperature feedback were analyzed under double lasers excitation. Moreover, the photothermal conversion efficiency was experimentally confirmed from thermodynamic analysis. It was found that the nanocomposite can be an excellent nanoplatform for potential application in advanced PTT.

Tunable blue–green–yellow emitting Sr3YNa(PO4)3F (SYNPF):Ce3+,Tb3+,Mn2+ phosphors have been prepared via a high-temperature solid-state reaction method. The structural and luminescent properties, energy transfer (ET) mechanism, and thermal quenching of the samples are investigated in detail. The ET from Ce3+ to Tb3+ and Mn2+ in SYNPF is identified as the interaction of the electric dipole–quadrupole with ET efficiencies of 81.6% and 69.3%, respectively. The critical distances for Ce3+/Tb3+ and Ce3+/Mn2+ are calculated through the spectral overlap method to be 9.54 and 10.92 A. Under UV excitation, high-efficiency tunable blue–green–yellow emissions from Ce3+ to Tb3+ and Mn2+ can be obtained. Moreover, white light can also be achieved by adjusting the stoichiometry of Ce3+ and Mn2+ properly in the SYNPF phosphor. In addition, the temperature-dependent luminescence spectra exhibit good thermal quenching behaviors for the as-prepared phosphors. The above results suggest that SYNPF:Ce3+,Tb3+,Mn2+ phosphors ca...

LnNbO4:Er3+ (Ln = Lu, Y, Gd) phosphors were prepared through a conventional solid-state reaction method. The phase purity of the samples was characterized by X-ray diffraction (XRD). A comparative study of spectral and temperature sensing properties of LnNbO4:Er3+ (Ln = Lu, Y, Gd) phosphors was presented. The excitation spectra of the samples show a strong band in the region of 200–350 nm coming from the NbO44−, thus indicating efficient energy transfer from the host to Er3+. From the dependence of upconversion (UC) luminescence spectra on laser diode working current, it was confirmed that 2- and 3-photon processes were respectively responsible for both the green and the red UC emissions under 980 and 1550 nm excitations. The temperature sensing properties for LnNbO4:Er3+ were compared under individual excitation of 980 and 1550 nm. It was found that the temperature sensing was independent from the excitation wavelength, but LuNbO4:Er3+ phosphors yielded the highest luminescence intensity and maximum temperature sensitivity.

In this Reply, we truthfully respond to the comments on our recent paper entitled “A universal approach for calculating the Judd–Ofelt parameters of RE3+ in powdered phosphors and its application for the β-NaYF4:Er3+/Yb3+ phosphor derived from auto-combustion-assisted fluoridation” published in Phys. Chem. Chem. Phys. [Y. Zhang, B. Chen, S. Xu, X. Li, J. Zhang, J. Sun, X. Zhang, H. Xia, R. Hua, A universal approach for calculating the Judd–Ofelt parameters of RE3+ in powdered phosphors and its application for the beta-NaYF4:Er3+/Yb3+ phosphor derived from auto-combustion-assisted fluoridation, Phys. Chem. Chem. Phys., 20, 2018, 15876–15883]. In the Comment, the authors oppugned partial calculation results we reported in our original paper, thus we redid the calculations and compared the presently obtained results with the original ones and the author provided ones. The recalculations and comparisons confirmed that our calculations are reproducible and the results are correct. In the Comment, the authors also made some comments on the Judd–Ofelt calculation approaches for powdered samples reported by other researchers. Following the authors’ train of thought we added some supplements to the comments to understand the application strategy of Judd–Ofelt theory. Furthermore, we extended some points of view regarding the fluorescence lifetime measurements the authors presented in the Comment.

Doping concentration is an important factor influencing the optical and spectroscopic properties of rare earth doped luminescence materials. In this work, the influences of Dy3+ concentration on fluorescence intensity and optical transition properties were studied. Huang’s and Uitert’s models were compared and used in discovering the fluorescence intensity quenching mechanism of Dy3+ in NaYF4 phosphors, and it was found that from these two models the fluorescence intensity quenching mechanism can be well deduced though the application manners of the models are different. The dependence of optical transition properties on Dy3+ doping concentration was studied in depth. It was found that with increasing Dy3+ concentration the Ω 2 value increases and the Ω 4 value decreases monotonically, nevertheless the Ω 6 value changes slightly. Moreover, the magnitude sequence of the Judd-Ofelt parameters changes from Ω 4 > Ω 6 > Ω 2 to Ω 2 > Ω 6 > Ω 4 when the concentrations of Dy3+ increases. Furthermore, it was found that the internal quantum efficiency of 4F9/2 decreases with increasing Dy3+ concentration.