In this study, various Na0.5Bi0.5TiO3:0.5 at% Ho3+ (NBT:Ho) ceramics with different Yb3+ ion doping concentrations were synthesized by a conventional solid-state reaction method. Under the irradiation of a 980 nm laser, the NBT:Ho sample exhibited four distinguished emission bands centered at 525, 548, 656, and 753 nm. By co-doping Yb3+ ions into NBT as the sensitizers, the up-conversion luminescence of Ho3+ ions was greatly enhanced. The mechanism for up-conversion luminescence was determined to be a two-photon absorption process. The DFT simulations revealed that the Ho3+ 4f orbitals pass through the Fermi level and thus f–f transitions could be highly sensitive to temperature variation. Green emissions at 525 and 548 nm were ascribed to the two thermally coupled excited states 5F4 and 5S2 transferring to the ground state 5I8, respectively. The temperature-dependent population between 5F4 and 5S2 could be interpreted by Boltzmann's distribution in the range of 167–377 K. The relative sensitivities were calculated to be 6.14% K−1 at 167 K and 1.03% K−1 at 377 K, and the corresponding absolute sensitivities were estimated to be 0.09 × 10−3 K−1 and 2.11 × 10−3 K−1, respectively. The temperature resolution was calculated to be about 0.053 K at 167 K and 0.319 K at 377 K. The excellent repeatability of the NBT:Ho3+ ceramics was demonstrated by means of successive heating–cooling cycles in the range of 167–377 K. The above investigation results demonstrate the promising application of NBT:Ho in cryogenic optical thermometers.
Hao-tian ZHU,Hai-rui GUO,Qi-jing ZHENG,Chun-yan GUAN,Li-ping ZHU,Hai-bin LI,Jin-yu YANG
Ho 3+ and Yb 3+ co-doped La 7 P 3 O 18 up-conversion phosphors were prepared by a high-temperature solid-state process. XRD results reveal that the samples are mixtures of monoclinic structure La 7 P 3 O 18 crystals with P 21/ n space group and minor LaPO 4 crystals. UV—Vis DRS results indicate that La 7 P 3 O 18 crystal is an indirect semiconductor with an optical band gap of 4.10 eV. After 980 nm laser excitation, the Ho 3+ and Yb 3+ co-doped La 7 P 3 O 18 phosphors show the characteristic blue (486 nm), green (550 nm), and red (661 nm) luminescence peaks of Ho 3+ ions. The peak at 661 nm dominates in the up-conversion luminescence spectra of samples. Meanwhile, with the increase of Ho 3+ and Yb 3+ doping content, the up-conversion luminescence intensity increases first and then decreases. By increasing the doping contents of Ho 3+ and Yb 3+ up to 1 at.% and 10 at.%, respectively, concentration quenching may appear by an electric quadrupole– electric quadrupole interaction process. The pumping power dependence of luminescence indicates that the green and red emissions of samples are excited by a two-photon absorption process. The color coordinates of Ho 3+ and Yb 3+ co-doped La 7 P 3 O 18 crystals locate in the orange—red region.
Xiaotong Zhao,Mo Liu,Niannian Xu,Shunbin Wang,Pengfei Wang
This study presents the experimental realization of a microsphere laser resonator designed to operate within the approximate wavelength range of 1.2 μm and 2.0 μm. This resonator, employing a Ho 3+ -doped fluoroaluminate glass microsphere, was stimulated by a 1150 nm laser, marking the first demonstration of its kind. The observed laser emissions at ∼1.2 μm and ∼2.0 μm were ascribed to the transitions of Ho 3+ ions, specifically 5 I 6 → 5 I 8 and 5 I 7 → 5 I 8 , respectively. The fabrication of the microsphere, possessing a characteristic diameter of approximately 50 μm, entailed the controlled melting of a fluoroaluminate glass filament through the application of a focused CO 2 laser beam. Concurrently, a tapered fiber with a waist diameter of ∼2 μm was created by subjecting a standard silica single-mode fiber to a process of controlled heating and stretching. The findings of this investigation suggest promising prospects for the development of multi-wavelength lasers utilizing fluoroaluminate glass microspheres, particularly in intricate environmental settings.
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