Upconversion Emission and Dual-Mode Sensing Characteristics of NaYF4:Yb3+/Er3+ Microcrystals at High and Ultralow Temperatures

In this study, we investigate micrometer-sized NaYF4 crystals double-doped with Yb3+/Er3+ lanthanide ions, designed for temperature-sensing applications. In contrast to previous studies, which focused predominantly on the high-temperature regime, our investigation spans a comprehensive range of both high and ultralow temperatures. We explore the relationship between temperature and the upconversion luminescence (UCL) spectra in both frequency and time domains. Our findings highlight the strong dependence of these spectral characteristics of lanthanide-doped NaYF4 crystals on temperature. Furthermore, we introduce a dual-mode luminescence temperature measurement technique, leveraging the upconversion emission intensity ratio for both green and red emissions. This study also examines the correlation between temperature sensing, energy level disparities, and thermal coupling in Er3+ ions across various temperature scales. Our research contributes to advancing the understanding and application of lanthanide-doped materials, setting a foundation for future innovations in temperature sensing across diverse fields.

Voltage- and Power-Conversion Performance of Bi-functional ZrO2 : Er3+ / Yb3+ Assisted and Co-sensitized Dye Sensitized Solar Cells for Internet of Things Applications

Giant power conversion efficiency is achieved by using bifunction ZrO2  : Er3+ /Yb3+ assisted co-sensitised dye-sensitized solar cells. The evolution of the crystalline structure and its microstructure are examined by X-ray diffraction, scanning electron microscopy studies. The bi-functional behaviour of ZrO2  : Er3+ /Yb3+ as upconversion, light scattering is confirmed by emission and diffused reflectance studies. The bi-function ZrO2  : Er3+ /Yb3+ (pH=3) assisted photoanode is co-sensitized by use of N719 dye, squaraine SPSQ2 dye and is sandwiched with Platinum based counter electrode. The fabricated DSSC exhibited a giant power conversion efficiency of 12.35 % with VOC of 0.71 V, JSC of 27.06 mA/cm2 , FF of 0.63. The results, which motivated the development of a small DSSC module, gave 6.21 % and is used to drive a tiny electronic motor in indoor and outdoor lighting conditions. Small-area DSSCs connected in series have found that a VOC of 4.52 V is sufficient to power up Internet of Things (IoT) devices.

Tuning the Red-to-Green-Upconversion Luminescence Intensity Ratio of Na3ScF6: 20% Yb3+, 2% Er3+ Particles by Changes in Size

Na₃ScF₆: 20% Yb³⁺, 2% Er³⁺ samples were synthesized with different reaction times and reaction temperatures using the solvothermal method. We carried out a series of tests on Na3ScF6 crystals. The XRD patterns showed that the monoclinic phases of the Na₃ScF₆ samples could be synthesized under different reaction conditions, and doping with Yb³⁺ ions and Er³⁺ ions did not change the crystal structures. The SEM images showed that the sizes of the samples gradually increased with reaction time and reaction temperature. The fluorescence spectra showed that the emission peaks of the prepared samples under 980 nm near-infrared (NIR) excitation were centered at 520 nm/543 nm and 654 nm, corresponding to the ²H_11/2/⁴S_3/2→⁴I_15/2 and ⁴F_9/2→⁴I_15/2 transitions, respectively. With the increasing size of the samples, the emission intensities at 654 nm increased and the luminescence colors changed from green to red; at the same time, the red-to-green luminescence intensity ratios (IR/IG ratios) increased from 0.435 to 15.106-by as much as ~34.7 times. Therefore, this paper provides a scheme for tuning the IR/IG ratios of Na₃ScF₆: 20% Yb³⁺, 2% Er³⁺ samples by changing their sizes, making it possible to enhance the intensity of red upconversion, which has great potential for the study of color displays and lighting.

Tuning of the thermal quenching performance of Bi3+-doped scheelite Ca(Mo/W)O4 solid solution phosphors

The utilization of phosphor materials has always been a significant challenge in terms of improving thermal quenching performance. In this work, the thermal quenching performance tuning mechanism which establishes the band gap and thermal quenching correlation patterns is proposed. The crystal field splitting energy D_q was decreased by changing the surrounding crystal lattice environment of Bi³⁺ through a solid solution replacement, and the thermal quenching activation energy ΔE of Bi³⁺ was tuned from 0.117 eV to 0.182 eV accordingly. At 423 K, the luminous intensity increases from 0.101 to 0.396 of the preliminary intensity at 303 K with increasing substitution. In addition, the band gap value of Bi³⁺ calculated by diffuse reflectance spectroscopy increased from 4.40 eV to 4.72 eV, which corresponds to a linear positive correlation between the band gap and the thermal quenching properties. Furthermore, a monophase white-emitting phosphor with good thermal stability was prepared by constructing a Bi³⁺-Eu³⁺ co-doping system. In particular, the relative sensitivity of S_r for temperature measurement applications reached 3.17% K^-1 based on the double-luminescence fluorescence intensity ratio. Thus, this modulation scheme can be used as a reference for the design of various phosphor materials with tunable thermal quenching properties in the future.

Enhanced up-conversion luminescence and temperature-sensing of GdVO4:Ln3+ with dual-wavelength excitation

There exists a tendency in the research of up-conversion materials to shift the excitation from 980 nm to multiple excitation wavelengths. A series of GdVO4:Ln3+ with similar sizes and irregular prism morphology were successfully prepared by a co-precipitation technique. A wide multi-color emission corresponding to different Ln3+ doping was also obtained under single excitation. It is worth pointing out that among all the studied samples, only the emission intensity of GdVO4:Yb3+/Er3+ excited at two-wavelengths (980 nm + 1550 nm) simultaneously was enhanced by a factor of 1.87, compared to the sum of emission intensities excited at two single-wavelengths separately. Moreover, to further enhance the up-conversion luminescence intensity, cation ions (Lu3+/Y3+) and anion ions (PO43-) were also doped into the host, and the luminous intensity was also improved to a certain extent. A possible mechanism for energy transfer and possible transitions were also suggested and discussed in detail using an energy level diagram. In addition, not only a high record value of Sa (0.0069 K-1) but also a high Sr (1.13% K-1) is achieved for GdVO4:Yb3+/Er3+ in the physiological temperature range (273-453 K). Combining a much intensified dual-wavelength up-conversion signal and good temperature-sensing properties, this work can be extended to the surges of other lanthanide ion doped systems pumped by using multiple-wavelength lasers, and can also open new possibilities for up-conversion color displays and anti-counterfeiting applications.