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Abstract Owing to few thermal populations or spectral absence at extreme low temperature, fluorescence intensity ratio (FIR) technique based on thermal coupling levels is sometimes unpractical for low temperature sensing. Herein, using bandwidth as a sensing parameter, the low temperature sensing performances of YOF:Yb3+/Tm3+ phosphor are reported. The YOF:10%Yb3+/0.2%Tm3+ phosphor is prepared by hydrothermal and calcined methods. Under 980 nm excitation, the temperature dependent upconversion spectra are recorded in the range of 12–300 K, and the temperature sensing behaviors are investigated in detail. The phosphor exhibits a single-band near-infrared (NIR) luminescence composed of multiple narrow peaks. Thereinto, the ultranarrow bandwidths of 12,485 cm−1 (800.9 nm) and 12,580 cm−1 (794.9 nm) emission bands are only 14 cm−1 (0.9 nm) and 12 cm−1 (0.75 nm) at 12 K, respectively. Based on temperature dependent bandwidth, the maximum relative sensitivities are found to be 0.60% K−1 (12–190 K) and 0.84% K−1 (190–300 K), which enable the YOF:10%Yb3+/0.2%Tm3+ phosphor to be a promising thermometer for low temperature sensing. Graphical abstract fx1 [ABSTRACT FROM AUTHOR]

The methods of modulating emitting color are greatly important for up-conversion phosphors to broaden their applications, ranging from information storage to surface display. In this paper, the Ho 3+ /Tm 3+ /Yb 3+ tri-doped Gd 2 (MoO 4 ) 3 phosphors are synthesized by typical sol-gel method. It is found that the phosphors can radiate intense blue (475 nm), green (542 nm) and red (660 nm) up-conversion luminescence under 980 nm or 915 nm laser excitation. Especially, the emission color of the phosphors can be tuned from red to lavender by adjusting the excitation power of 980 nm or 915 nm continuous lasers. In addition, the up-conversion luminescence is also investigated under the excitation of 980 nm pulse laser. The emission color varies from green to blue and green to yellow by altering the pulse width and frequency, respectively. Combining the above methods, multi-color and white light are realized, indicating the potential application in dynamic colorful display. [ABSTRACT FROM AUTHOR]

Gd 2 (MoO 4 ) 3 :Er 3+ /Yb 3+ phosphor with respective functions of optical temperature sensing and optical heater are investigated in detail. The Gd 2 (MoO 4 ) 3 :Er 3+ /Yb 3+ film (~200 nm) and powder are successfully prepared, respectively. The crystalline structure is characterized by XRD and the relevant morphologies are analyzed by SEM and AFM, respectively. Based on fluorescence intensity ratio (FIR) technique, photo-thermal behaviors of Gd 2 (MoO 4 ) 3 :Er 3+ /Yb 3+ powder are illustrated. Under 980 nm excitation, the temperature induced by laser is calculated, which varies from 323 to 617 K as exciting power increased from 0.03 to 3.78 W. Additionally, the temperature sensing behaviors of Gd 2 (MoO 4 ) 3 :Er 3+ /Yb 3+ film are investigated. Highly accurate temperature sensing can be realized due to the negligible photo-thermal effect. This thermal sensor exhibited a high sensitivity in the range of 295–660 K, and the maximum value of relative sensitivity was determined as 13.4×10 −3 K −1 at 295 K. These results demonstrate that Gd 2 (MoO 4 ) 3 :Er 3+ /Yb 3+ phosphor can be applied in terms of temperature sensing and optical heater. [ABSTRACT FROM AUTHOR]

Although lanthanide doped luminescent materials have been extensively investigated, a quantitative analysis of how temperature affects upconversion luminescence is still incomplete. The Gd 2 (MoO 4 ) 3 :Er 3+ /Yb 3+ phosphor is synthetized by sol-gel method. Based on the absorption spectra of Er 3+ ions, J-O intensity parameters and radiative transition probabilities are computed to estimate the optical properties. In view of ion-phonon interaction, the phonon-assisted energy transfer and multiphonon relaxation are responsible for the temperature dependent luminescence. Additionally, cross relaxation probability for 4 I 11/2 + 4 I 11/2 → 4 I 15/2 + 4 F 7/2 is determined to be 240 s −1 through quantitative simulation of ion-ion interaction. These meaningful results are of vital values for the field of laser crystal and optical temperature sensing. [ABSTRACT FROM AUTHOR]

Most thermometers suffer from thermal quenching resulting in low signal to noise ratio at elevated temperature. To overcome thermal quenching, we fabricated a negative thermal expansion (NTE) thermometer based on Sc 2 Mo 3 O 12 :Nd3+/Yb3+/Er3+ phosphor. Under 808 nm excitation, the upconversion (UC) emissions of Er3+ ions show the thermal enhancement and its 524 nm emission increases 10-fold as the temperature increased from 310 to 670 K. Furthermore, the temperature sensing behaviors are investigated. It is found fluorescence intensity ratio (FIR) of 524–559 nm is linear with temperature over a wide range of 310–790 K. The maximum relative sensitivity is 0.84% K−1 at 310 K. These results indicate such phosphor not only achieves a high sensitivity, but also exhibits excellent performances at high temperature due to its thermal enhancement. [ABSTRACT FROM AUTHOR]

The emission of persistent luminescence nanoparticles (PLNPs) is in the second near infrared region (NIR-II, 1000–1700 nm), considered as ideal fluorescence imaging materials because of their special characteristic consist of no autofluorescence, weak scattering and deep tissue penetration depth in biological tissues. However, it is still a great challenge to enhance their persistent luminescence intensity. Herein, we reported a new MgGe 0.8 Ga 0.2 O 3 : Yb3+ (MGGO: Yb3+) PLNPs, which were synthesized through solvothermal liquid-solid-solution and salt microemulsion method. We found that partially replacing Ge4+ with Ga3+ ions in MgGeO 3 host can increase the density of traps, thus significantly improving the NIR-II persistent luminescence intensity of Yb3+ ions (the decay time is more than 33 min). Moreover, X-ray could be used to repeatedly stimulate the NIR-II persistent emission of MGGO: Yb3+, which is pivotal for deep tissues long term imaging. The optical penetration length of Yb3+ ions persistent luminescence was assessed to be 3.9 mm via capping tissue. The above results reveal that MGGO: Yb3+ PLNPs are promising material to be applied to deep-tissue imaging field. • A new MgGe 0.8 Ga 0.2 O 3 : Yb3+ PLNPs with a diameter of about 48 nm were synthesized. • The partially replacing Ge4+ with Ga3+ ions in MgGe 0.8 Ga 0.2 O 3 host can improve the NIR-II persistent luminescence intensity. • The optical penetration length of NIR-II persistent luminescence is about 3.9 mm. [ABSTRACT FROM AUTHOR]