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The luminescence properties of Mn4+-doped β -Ga 2 O 3 are strongly affected by the surrounding crystal field within the [MnO 6 ] octahedral site, which is substitute for Ga Ⅱ site, as determined through the first-principles calculations. The crystal field strength parameters Dq, B, and C are computed, and the Tanabe-Sugano diagram is redrawn for C/B = 6.7. The temperature dependence of the optical spectra is thoroughly examined, revealing the thermal quenching mechanisms involving the thermal activation energy of 2E g and 4T 2g , which are 378 ± 26 cm−1 and 3527 ± 25 cm−1, respectively. In order to further investigate the temperature sensing characteristics, the absolute (S a) and relative (S r) sensitivities are obtained. At 303 K, the S r is determined to be 0.72 %K−1, while S a is estimated to be in the range of 10−2 (below 0.05 K-1) for the Mn4+ doped β -Ga 2 O 3 thermometers. The thermal resolution δT is demonstrated to be below 0.1 K, surpassing that of traditional Nd3+ and Er3+-doped thermometers. Moreover, a linear relationship between the energy separation ΔE of the thermally coupled 2E g -4T 2g energy levels and the crystal field strength Dq is observed in numerous materials. With this consideration, the nature of the thermometer, along with its S a and S r , can be roughly predicted and designed for various operational conditions. • The Mn4+ doped β -Ga 2 O 3 crystals was successfully grown via the optical floating zone method and their luminescence properties was first investigated in detail. • The temperature dependence of luminescence properties was further studied with the thermal quenching activation energy of 2E g and 4T 2g , respectively. • The temperature sensing properties of Mn4+ doped β -Ga 2 O 3 thermometers, whether the relative sensitivities (S r), the absolute sensitivities (S a) or the thermal resolution ΔT, is estimated to be surpassing that of traditional Nd3+ and Er3+-doped thermometers. • A linear relationship between the crystal field strength Dq and the energy separation of the thermally coupled energy levels 2E g -4T 2g was observed, which gives us a broaden idea to predict and design the nature of the thermometer for various conditions. [ABSTRACT FROM AUTHOR]

We investigated the temperature-dependence of X-ray excited luminescence of β-Ga2O3 single crystals. The recombination of free-electrons with self-trapped holes (STHs) responsible for the ultraviolet luminescence (UVL) band was observed. For the as-grown sample with a high electron concentration, the Auger recombination becomes important, which accelerates the decay dynamics and reduces the ultraviolet luminescence band. The ultraviolet luminescence band is controlled by temperature quenching due to the migration of self-trapped holes to VGa3− centers. Annealing in an oxygen environment can increase the VGa3− concentration, which contributes to the blue-green luminescence band when VGa3− captures a self-trapped hole forming a VGa2− center at rising temperature. [ABSTRACT FROM AUTHOR]

Ho-doped and Ho,Pr co-doped BaF 2 crystals were grown using the temperature gradient technique. The absorption spectra, fluorescence spectra, and fluorescence lifetimes were measured and analyzed. For Ho-doped BaF 2 , 1.0 at.% Ho:BaF 2 showed the best luminescence performance in the 3 μm band. After co-doping with Pr3+, the lower-level lifetime of Ho3+ ions in the 3 μm band was significantly reduced, while the upper laser level lifetime was minimally affected, indicating that Pr3+ ions can be effectively used as a deactivating ion of Ho3+ ions in the BaF 2 matrix. For 1.5 at.% Ho, 0.1 at.% Pr:BaF 2 , the lifetime ratio of the upper and lower levels was 0.47, effectively realizing population inversion. • Ho-doped BaF 2 , 1.0 at.% Ho:BaF 2 showed the best luminescence performance in the 3 μm band. • Pr3+ ions can be effectively used as a deactivating ion of Ho3+ ions in the BaF 2 matrix. • For 1.5 at.% Ho, 0.1 at.% Pr:BaF 2 , the lifetime ratio of the upper and lower levels was 2:7, effectively realizing population inversion. [ABSTRACT FROM AUTHOR]

High quality Pr3+ single-doped PbF 2 and Pr3+/Yb3+ co-doped PbF 2 single crystals were grown by temperature gradient technique (TGT). By co-doping Yb3+ ion as Pr3+ ions sensitizer, the visible light emission can be regulated and the largest luminescence branching ratio can be switched from red-orange to blue-green light. Besides, when Pr3+ ions doping concentration is as low as possible, the blue light self-absorption effect can be weakened, which is beneficial to high-efficiency blue laser output. Moreover, the broad band emission around 1.3 μm from 1G 4 energy level can be observed in the Pr3+/Yb3+:PbF 2 crystal with the low maximum phonon energy for the first time. Absorption, emission spectra and luminescence mechanism are well analyzed by the energy transfer process and J-O theory. The laser upper energy level lifetime of Pr3+ ions has a great increase by Yb3+ ion effect. These advantageous spectroscopic characteristics show that the Pr3+/Yb3+:PbF 2 crystal might be potential laser gain materials for blue-green and ∼1.3 μm near-IR laser operation. • By co-doping Yb3+ ion as sensitizer for Pr3+ ions, the visible light emission can be regulated and the largest luminescence component ratio can be changed from red-orange light to blue-green light. • When doping concentration of Pr3+ ion is as low as possible, the self-absorption effect of blue light can be weakened, which is beneficial to high-efficiency blue laser output. • The broad band emission around 1.3 μm from 1G 4 energy level can be observed in the Pr3+/Yb3+: PbF 2 crystal with the low maximum phonon energy for the first time. [ABSTRACT FROM AUTHOR]

Well-crystallized Bi–Te single crystals with different ratios were grown in vertical Bridgman method. Broadband emission was detected in 1900–3000 nm. Annealing treatment and XPS test revealed the emission center might be Bi clusters. The forming process and energy level transition of Bi clusters were given in this paper. [ABSTRACT FROM AUTHOR]

Abstract: Yb-doped PbClF crystals were obtained by a modified Bridgman method. Broadband emission (FWHM=58nm) with long lifetime (5.33ms) was observed in 2.0% Yb3+-doped PbClF crystals. The Stark splitting of Yb3+ 2F7/2 level was calculated to be 801cm−1 in 0.5% Yb3+-doped PbClF crystals, and the corresponding population of lower laser level is about 2.13%. All the results indicated that Yb-doped PbClF crystals should be a promising material to ultrashort pulses output at 1.0μm. [Copyright &y& Elsevier]

• A series of 0.6 at% Pr:CaF 2 -RF 3 (R= Y3+, Gd3+, Lu3+) crystals were successfully grown by the temperature gradient technique(TGT) method. • By co-doping R3+ ion (R=Y3+, Gd3+, Lu3+), the spectral performance of the crystals could be significantly improved and the function effect is also different. • The spectral performance and spectral quality factor of the crystals were systematically described and compared for the first time. • The spectral modulation effect caused by Y3+, Gd3+ and Lu3+ co-doping ion was discussed. A series of 0.6 at% Pr:CaF 2 -RF 3 (R = Y3+, Gd3+, Lu3+) crystals have been successfully grown by the temperature gradient technique(TGT). The absorption spectra, fluorescence spectra, and fluorescence decay curves were measured and analyzed at room temperature. When the R3+ concentration is higher than a certain value, the diffraction peaks of Pr:CaF 2 -RF 3 crystals were well indexed to the (Ca,Y)F 2 phase. By co-doping R3+ ion (R=Y3+, Gd3+, Lu3+), the spectral performance of the crystals could be significantly improved and the function effect is also different. For 0.6 at% Pr, 28.5 at% Y:CaF 2 crystal, the fluorescence lifetime of 3P 0 energy level was fitted to be 45.46 µs, and the emission cross sections of 3P 0 →3H 6 (605 nm), and 3P 0 →3F 2 (641 nm) were calculated to be 1.78 × 10−20 cm2, and 4.61 × 10−20 cm2 with the full width at half (FWHM) of 20.1 nm and 6.8 nm, respectively. The 0.6 at% Pr, 28.5 at% Y:CaF 2 crystal could be favorble laser medium for ultra-fast laser opreration at 605 nm and 641 nm. For 0.6 at% Pr, 18 at% Gd:CaF 2 and 0.6 at% Pr, 10 at% Lu:CaF 2 crystals, the spectral quality factors σ em• τ f of 3P 0 →3F 2 transition (642 nm) were calculated to be 614.18 × 10−20 cm2•µs and 506.36 × 10−20 cm2•µs with the FWHM of 3.7 nm and 5.3 nm. All the results show that 0.6 at% Pr, 18 at% Gd:CaF 2 and 0.6 at% Pr, 10 at% Lu:CaF 2 crystals are promising gain media for high-efficiency visible laser output at 642 nm, which would compete with commercial Pr: YLF crystal in the future. [ABSTRACT FROM AUTHOR]

Yb,Pr:CaF 2 crystals have been grown successfully by the temperature gradient technique(TGT). The absorption spectra, fluorescence spectra, fluorescence decay lifetime of Pr3+ ions in CaF 2 crystal sensitized by different Yb3+ ions concentration have been measured. The effective J-O intensity parameters were fitted to be Ω 2 =0.36 × 10−20cm2, Ω 4 =2.89 × 10−20cm2, Ω 6 =6.69 × 10−20cm2 for 0.3 at.%Pr,1.5 at.%Yb:CaF 2. And the emission cross sections of 3P 1 →3H 5 (535 nm), and 3P 0 →3F 4 (750 nm) are calculated to be 2.02 × 10−20cm2, and 2.50 × 10−20cm2 with the FWHM of 17.2 nm, and 10.5 nm, respectively. The fluorescence lifetime of 3P 0 has achieved great increasing by sensitizing of Yb3+ ion. Not only the up-conversion luminescence can be achieved, but also the broad band emission from 1D 2 energy level can be observed. The results show that Yb,Pr:CaF 2 could be a potential laser gain medium for visible and near-IR laser operation. • Not only the up-conversion luminescence can be achieved, but also the broad band emission from 1D 2 energy level can be observed by Yb3+ ion sensitizing. • Spectral properties and Judd-Ofelt parameters of Yb,Pr:CaF 2 crystal were investigated and analysed. [ABSTRACT FROM AUTHOR]