A series of Yb3+, Ho3+, Nd3+ doped Na3Y(VO4)2 phosphors are prepared by the high temperature solid reaction method. Na3Y(VO4)2: Yb3+, Ho3+ present bright yellow emission under the excitation of 980 nm. The intro-duction of Nd3+ can effectively absorb 808 nm photon energy, realizing the energy transfer process of Nd3+ (sensitizer)-> Yb3+ (energy transfer bridge)-> Ho3+ (activator) under 808 nm excitation. Up-conversion mecha-nism proves that the variable luminescence color at different concentrations Nd3+ doped samples may be attributed to back energy transfer between Ho3+ and Nd3+. Moreover, the temperature sensing behaviors are investigated by the fluorescence intensity ratio technology. The maximum temperature sensing sensitivities can be maintained as a constant of 10 x 10-3 K over the whole temperature measurement range (298-618 K), which is beneficial to achieve stable optical thermometry. The phosphors can achieve color tunable luminescence within green and yellow region by adjusting the temperature. Ho3+ activated Na3Y(VO4)2 phosphors with excellent sensitivity performance have excellent prospects in the fields of optical anti-counterfeiting and tem-perature sensing.

Efficient deep-penetrating red upconversion luminescent nanoparticles with ultra-small size are promising biological temperature probes. Herein, bright red upconversion luminescence are achieved in NaErF4@ NaYF4 core-shell nanoparticles under multi-wavelength excitation of 808 nm, 980 nm, and 1550 nm. The core-shell structure engineering is constructed to minimize energy dissipation by surface quenchers. Furthermore, the established model explains the temperature dependence of thermally coupled energy levels in detail, confirming that the non-radiative relaxation is responsible for the quenching processes. Based on the luminescence intensity ratio technique, optical temperature sensing characteristics of ther-mally coupled (2H11/2/4S3/2) and non-thermally coupled energy levels (4F9/2/4S3/2) are investigated under the excitation of a relatively safe near-infrared wavelength for 1550 nm. The thermometer can maintain a maximum sensitivity of 35 x 10-3 K-1 over the entire temperature measurement region by fitting the non-thermally coupled energy levels, which is conducive to temperature monitoring in vivo due to high sen-sitivity and relatively safe excitation wavelength.(c) 2023 Published by Elsevier B.V.

In this work,tunable white up-conversion luminescence was achieved in the Yb3+,Er3+,Tm3+,Ho3+co-doped Na3La(VO4)2 phosphors under 980 nm excitation.The emissions of three primary colors are mainly attributed to the 2H11/2/4S3/2 → 4I15/2 transitions of Er3+,1G4→3H6 transition of Tm3+,and 5F5→5I8 transition of Ho3+.White luminescence characteristics and mechanisms of up-conversion sys-tem were investigated in detail.In addition,the temperature sensing behaviors of multiple levels emission combinations for Na3La(VO4)2:Yb3+,Er3+,Tm3+,Ho3+were analyzed by employing thermally coupled and non-thermally coupled energy levels.Based on the emissions of 3F2,3/1G4 energy levels,the maximum relative and absolute sensitivities were obtained to be 2.20％/K and 0.279 K-1.The design of up-conversion luminescence materials with high-quality white luminescence and excellent sensitivity performance is critical in the field of optical applications.

In this paper, Y3Al5O12:Ce3+,Cr3+ (YAG:Ce3+,Cr3+) nano-phosphors are prepared by the co-precipitation method, the average particle size of the phosphor is similar to 100 nm. In addition, two surface treatments are introduced to improve the homogeneity of the nanoparticles. One is the addition of an appropriate amount of sodium dodecyl sulfate, and the other is coating a carbon layer on the surface of the nanoparticles by a solvothermal method using glucose as the carbon source. The optical properties and mechanisms of the synthesized YAG:Ce3+,Cr3+ nano-phosphors are detailed analyzed in the text. The CIE color coordinates (0.30, 0.36) of the nanoscale YAG: Ce3+,Cr3+ phosphor combined with the 450 nm blue chip is close to standard white light, which has potential application in white LED.

In this paper, the La2Mo2O9:Yb3+, Ho3+, Tm3+ phosphors are successfully synthesized through simple solid-state method. The white up-conversion luminescence is realized by appropriately varying the co-doped concentrations of Ho3+, Tm3+. The up-conversion luminescence characteristics and energy transfer processes of La2Mo2O9:Yb3+, Ho3+, Tm3+ are specifically analyzed upon 980 nm laser excitation. A strategy to enhance the optical temper-ature sensing performance is demonstrated via flexibly selecting diverse non-thermally coupled energy levels of dual luminescence centers with the fluorescence intensity ratio technology. The maximum values of absolute and relative sensitivity for the thermometer reach 0.2478 K-1 and 1.38% K-1 based on the non-thermally coupled energy levels of 3F2,3 (Tm3+)/5S2,5F4 (Ho3+). The luminescence color of La2Mo2O9:Yb3+, Ho3+, Tm3+ phosphors can maintain in the white region over the whole measured temperature range. These results indicate that the phosphors possess great potential in broad application prospects in the aspects of anti-counterfeiting, displays and non-contact temperature sensing.

A series of Yb 3+ , Er 3+ , Tm 3+ co-doped K 3 Gd(PO 4 ) 2 are prepared via the solid-state reaction method. Upon 980 nm excitation, the synthesized phosphors present color-tunable upconversion luminescence ranging from yellow to blue with the increment of Tm 3+ doping contents. The mechanisms of Yb 3+ , Er 3+ , Tm 3+ co-doped system are systematically investigated in detail. Varying contents of Tm 3+ can appropriately alter the upconversion emissions of blue, green and red via possible energy transfer processes. Furthermore, the thermometric performances of phosphors associated with upconversion luminescence are analyzed in the temperature region of 300-675 K. By employing non-thermally coupled energy levels ( 2 H 11/2 / 4 F 9/2 of Er 3+ ), the maximum relative and absolute sensitivity reaches 0.78% K -1 and 0.168 K -1 . Combining the sensitivity characteristic and repeatability of thermometer, the luminescence intensity ratio technology based on non-thermally coupled energy levels may be a more effective choice for optical thermometry. These excellent results will pave an avenue to K 3 Gd(PO 4 ) 2 :Yb 3+ ,Er 3+ ,Tm 3+ phosphors for the fields of color-tunable luminescence and non-contact temperature sensing.

In this paper, the Er3+,Tm3+ co-doped La2Mo2O9 up-conversion luminescence phosphors are synthesized via solid state reaction. The luminescence characteristics and up-conversion processes of La2Mo2O9:Er3+,Tm3+ phosphors under the excitation of 980 and 1550 nm are investigated in detail. Tm3+ as an important energy transfer medium is the key to effectively improve the population of red-emitting energy levels (F-4(9/2)) in the Er3+ sensitized system. Dual-color luminescence of green and red can be successfully achieved by controlling the concentration ratio of Er3+,Tm3+ co-doping under the dual-wavelength excitation. In addition, the optical temperature sensing ability of La2Mo2O9:Er3+,Tm3+ phosphors is analyzed by employing thermally coupled and non-thermally coupled energy levels. The obtained maximum absolute sensitivities are 8.33 x 10(-3) K-1 under the 1550 nm excitation for non-thermally coupled energy levels. The La2Mo2O9:Er3+,Tm3+ phosphors with dualcolor luminescence and high temperature sensing ability are the promising candidates in the fields of anticounterfeiting and non-contact temperature sensing.

A series of Er3+-doped La2Mo2O9 phosphors are prepared by the solid-state method. Up-conversion luminescence properties of La2Mo2O9:Er3+ are studied in detail under 980 and 1550 nm excitation. By inspecting the power dependent up-conversion intensity, indicating the two- and three-photon up-conversion population processes for 980 and 1550 nm excitation, respectively. The thermally coupled energy levels of H-2(11/2) and S-4(3/2) exhibit strong temperature dependence in the range of 293-533 K. Based on fluorescence intensity ratio technology, the La2Mo2O9:Er3+ phosphors present the maximum absolute sensitivity of 78.95 x 10(-4) K-1 at 493 K and high relative sensitivity of 1.16% K-1 at 293 K under relatively safe wavelength of 1550 nm excitation. The results suggest that La2Mo2O9:Er3+ phosphor can be used as excellent optical temperature sensor.

Red up-conversion luminescence with both emission and excitation peaks within the "tissue transparency window" makes for ideal fluorescent labels for deep tissue penetration and low-background biological imaging. In this work, an efficient strategy is proposed to realize bright red up-conversion luminescence based on interfacial energy transfer (IET), and the luminescence centers (Er3+ and Tm3+) and sensitizers (Yb3+) are doped in separate layers to avoid deleterious cross-relaxation. The IET process between Yb3+ and Er3+ can enable bright red photon up-conversion under 980 nm excitation via fine control and manipulation of the lanthanide ion concentration and shell thickness. By appropriately employing the fluorescence intensity ratio technique, an optical thermometer based on non-thermally coupled energy levels demonstrates a superior relative sensitivity of 2.02% K-1 across the whole temperature region. NaYF4:Er3+,Tm3+@NaYF4:Yb3+ with strong red UC luminescence and highly sensitive performance exhibits potential for application in the field of non-contact temperature sensing.