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Herein, a scheme of Sr2+/Ca2+ ion substitution was employed to simultaneously regulate the defect and intervalence charge transfer (IVCT) state of Sr2−xCaxNb2O7:Pr3+ phosphors, resulting in a dual-modulation strategy for enhancing phosphor thermal stability. [ABSTRACT FROM AUTHOR]

In our work, a totally anomalous thermal quenching phenomenon of red-shifted and enhanced charge transfer state (CTS) absorption is found for the first time in LiTaO3:xPr3+ phosphors. The crystal structure, luminescent properties and the mechanism of abnormal thermal quenching were investigated in detail. [ABSTRACT FROM AUTHOR]

Praseodymium (Pr3+) ion and the transition metal vanadium (V5+) ion with d0 electronic configuration can form an intervalence charge transfer (IVCT) band, which can function both as a compensatory channel for its red emission and as a quenching channel, thus affecting the luminescence thermal stability of the phosphors. Research studies reveal that the emission of Pr3+ in the YVO4 matrix can be quenched by the IVCT mechanism, thereby limiting the application of phosphors. As such, the present contribution is based on the solid solution replacement strategy to inhibit the constitutent of the IVCT quenching channel and thus improve thermal stability. Therefore, phosphonium (P5+) with a valence state matching V5+ and a similar ion radius was selected for the V/P substitution. It lacks a d0 electron configuration, preventing the formation of an IVCT band with Pr3+ and thereby inhibiting the construction of the quenching channels to enhance thermal stability. While the empirical formula of IVCT indicates a decrease in the IVCT energy level from 3.32438 to 3.06251 eV upon the introduction of P5+, the PLE spectra demonstrate a sharp reduction in IVCT intensity, i.e., weakening of the quenching channel. The thermal stability of the phosphors at different excitation locations was enhanced with the rise of P5+ concentration. When excited at the 3P2 level, the Y0.995PO4:0.5%Pr3+ phosphor demonstrated highly stable red emission from 303 to 523 K, with a luminescence integrated intensity ranging from 95.5% to 105.3% compared to that at 303 K. This research provides a novel approach for inhibiting the IVCT quenching channel and broadens the commercial value of YVO4:Pr3+ phosphor for various applications. [ABSTRACT FROM AUTHOR]

The synthesis conditions of most phosphors doped with lanthanide ions with d–f transition require a reducing atmosphere. The doping Bi3+ ions selected in this study perfectly avoid this requirement, and they are environmentally friendly and safe. Nevertheless, the spectral tuning of Bi3+ is a great challenge that limits its application. Herein, by regulating the value of x in the new solid solution Sr2+xLa1−xGaO5−xFx, the luminescence of Bi3+ is well promoted. Through an excitation-driven strategy, the emission peak position of Bi3+ is redshifted, and the luminescence of trivalent bismuth is successfully adjusted, which can also be applied to anti-blue lighting. In addition, we constructed a Bi3+–Eu3+ dual luminescence system, and, regardless of changes in the Bi3+/Eu3+ concentration or excitation wavelength, a single matrix white light phosphor was realized. Through calculations, the activation energy of the phosphor doped with 2.5%Eu3+ was found to be 0.257 eV, which is higher than the activation energy of some common compounds. This indicates that the phosphor has good application prospects in the field of solid-state lighting. It is worth noting that based on the different thermal response behaviors of Bi3+ and Eu3+, when the Eu3+ content is fixed at 1%, the maximum relative sensitivity of the optical thermometer based on its fluorescence intensity ratio is about 1.46% K−1 at 383 K, which is higher than that of Bi3+ and Eu3+ co-doped phosphors previously reported. We also obtained a high absolute sensitivity of 0.00139 K−1 at 403 K. Therefore, we also studied the thermal sensitivity of Bi3+ and Er3+ co-doped solid solutions. The results show that this solid-solution phosphor has far-reaching application prospects in the temperature sensing field. [ABSTRACT FROM AUTHOR]

Most praseodymium-doped red-emitting phosphors need high-temperature synthesis conditions with a reducing atmosphere. The niobate matrix selected in this work provides a sufficient electron-rich-site environment for praseodymium through charge migration, and praseodymium can be self-reduced in air atmosphere, which is safe and environmentally friendly. By building the [NbO6] group → Pr3+ energy transfer and finely modifying the doping concentration of Pr3+ ions, we constructed a dual-luminescence-system of the [NbO6] group and Pr3+. Thereby, optical temperature measurement based on fluorescence intensity ratio (FIR) technology of Pr3+ ions and [NbO6] groups was carried out using non-thermal coupling pairs, through the Boltzmann fitting and integral calculation, the maximum Sr and Sa values were 2.25% K−1 and 0.0049 K−1 at 403 K and 443 K, respectively, the Sr value is four times that obtained from the thermal coupling of Pr3+ ions, which exceeded most values previously reported for the fluorescence powder. Accordingly, we also studied the thermal sensitivity of Er3+ ions and Eu3+ ions mono-doped CaNb2O6 substrates. Results reveal that CaNb2O6:Pr3+/Er3+/Eu3+ phosphors have splendid temperature sensitivity and have far-reaching application prospects in the field of temperature measurements. [ABSTRACT FROM AUTHOR]

Currently, the unique 5D 4 energy level of terbium (Tb3+) can contribute to narrow-band green light emission, which has high application prospects. However, due to its poor thermal stability at high temperatures, how to enhance the antithermal-quenching properties of Tb-doped phosphors has become a research difficulty in the field of solid-state lighting and temperature sensing. In this contribution, the antithermal-quenching green-emitting of terbium was achieved by Nb/Ta substitution to form GdNb 1-x Ta x O 4 :Tb3+ phosphors with various components. Photoluminescence analyses reveal an increasing trend in both the optical band gap and the intervalence charge transfer (IVCT) energy level positions with substitution. Variable-temperature spectrums observed that the phosphors under different compositions presented a large discrepancy in thermal quenching performance. It is elucidated that the elevated position of the IVCT energy level (IVCT-EL) predominantly influences thermal quenching, bolstering its role as a compensatory luminescence channel of 5D 3 →5D 4 far more than functioning as a quenching luminescence channel for Tb3+5D 3 /5D 4. Delving into the perspective of IVCT-EL positioning unveils the intrinsic mechanism through which IVCT-EL positions modulate the thermal quenching properties of phosphors with varying compositions due to the substitution of Ta for Nb. This insight facilitates the realization of enhanced thermal quenching resistance in phosphors. Furthermore, the antithermal-quenching property of Tb3+ in single-phase phosphors can be effectively modulated by excitation at different wavelengths. This tuning scheme not only advances the exploration of terbium-doped antithermal-quenching phosphors but also provides a novel strategy and reference for designing green-emitting phosphors in the fields of lighting and sensing. [Display omitted] [ABSTRACT FROM AUTHOR]

• Designed dual-activators in double perovskite according to site-beneficial occupation principle. • Perovskite La 3 Li 3 W 2 O 12 matrix contains abundant sites that suitable the doping of Mn4+ and Lanthanide. • Taking advantage of diverse thermal quenching between Mn4+ and Eu3+ ions for optical thermometry. Currently, Eu3+ or Mn4+ activated red-emitting fluorescent materials are widely used for solid-state lighting and optical temperature sensing. Here, we have chosen an abundant double perovskite structure that provides not only a trivalent Eu3+ lattice but also a tetravalent Mn4+ lattice and guarantees simultaneous emission. A family of rare earth (Eu3+) and transition metal (Mn4+) co-doped La 3 Li 3 W 2 O 12 (LLWO) red-emitting phosphors were obtained by designing a site-occupation strategy. By changing the concentration of Eu3+, the coordination environment of the activator is adjusted to finally achieve the adjustable emission of the phosphor from orange to red. In addition, when the doping concentration of Eu3+ is greater than 0.05, the symmetry of the doping sites in the perovskite structure decreases leading to the luminescence performance of red color and the enhancement of luminescence intensity. Finally, optical thermometry based on fluorescence intensity ratio shows that the developed phosphor has high sensitivity. [Display omitted] [ABSTRACT FROM AUTHOR]