Junjie Zhang

Intense multiphoton upconversion of Yb3+–Tm3+ doped β-NaYF4 individual nanocrystals by saturation excitation

Saturation excitation of individual nanocrystals represents a powerful strategy to explore unique optical characteristics of luminescent activators. Here we report the intense multiphoton upconversion of β-NaYF4: Yb3+–Tm3+ individual nanocrystals benefiting from the perfect ladder-type electron configuration of Tm3+ under saturation illumination excitation. This leads to a luminescence switching between the emissions from 2-photon upconversion and 4-photon upconversion, which exhibits significantly enhanced luminescence intensity by up to a factor of 70. Such intense multiphoton upconversion may have potential application in super-resolution imaging.

Optical spectroscopy and population behavior between I-4(11/2) and I-4(13/2) levels of erbium doped germanate glass

In this paper, mid-infrared emission properties and energy transfer mechanism were investigated in Er3+ doped germanate glass pumped by 980 nm diode laser. Spontaneous radiative transition probability and emission cross section at 2.7 μm were calculated to be as high as 36.45 s−1 and 1.61 × 10−20 cm2, respectively. Corresponding upconversion emission spectra and radiative lifetimes of 4I13/2 level were determined to elucidate the mid-infrared luminescent characteristics. Moreover, population behaviors of Er3+: 4I11/2 and 4I13/2 level were analyzed numerically via Inokuti-Hirayama model, rate equations and Dexter’s theory. In addition, DSC curves of developed samples were measured and thermal stabilities were studied to evaluate the ability of resisting thermal damage and crystallization. The results indicate that erbium activated germanate glass is a promising candidate for mid-infrared applications. This work may provide beneficial guide for investigation of population behaviors of Er3+ ions at 2.7 μm emissions.

The effect of La2O3 in Tm3+-doped germanate-tellurite glasses for ~2 μm emission

A germanate-tellurite glass (GeO2-TeO2-K2O-Nb2O5-La2O3) with thulium doping has been investigated for application as a laser material around 2.0u2005μm regions. Under the 808u2005nm laser diode pumped, intense 1.8u2005μm emission is obtained. Based on the absorption spectra, radiative properties are predicted using Judd-Ofelt theory. The maximum value of emission cross-section of Tm3+ around 1.8u2005μm can reach 1.46 × 10−20u2005cm2, which indicated that the germanate-tellurite glass may provide high gain as a good medium for efficient 1.8u2005μm laser system.

Ho 3+ /Yb 3+ -codoped germanate–tellurite glasses for 2.0 μm emission performance

2.0 μm emission property of a new germanate-tellurite (GT) glass with Ho³⁺/Yb³⁺ codoping is synthesized and analyzed. Efficient 2.0 μm emission of Ho³⁺ ions sensitized by Yb³⁺ ions from the host glass was observed under 980 nm pumping. Based on the measured absorption spectra, the Judd-Ofelt parameters were calculated and discussed. The maximum emission cross section of Ho³⁺ ions transition is 4.36×10(-21) cm2 around 2.0 μm. The energy transfer efficiency is calculated and fitted the decay signals. The good spectroscopic properties suggest that Ho³⁺/Yb³⁺-codoped GT glass may become an attractive host for developing solid state lasers operating in the mid-infrared.

The use of zinc ions to control the size of Yb/Er:KMnF3 nanocrystals with single band emission

Yb/Er co-doped KMnF3 nanocrystals (NCs) exhibit strong single band emission centered at 660 nm, which is beneficial for bio-imaging application. It is known that the bio-distribution, clearance rate, and elimination pathway of intravenously injected NCs are strongly associated with the particle size. Here, we provide a novel method to modify the size of Yb/Er:KMnF3 NCs by introducing Zn2+ in the initial solution. Through changing the concentration of Zn2+ (0–30 mol%), the size of Yb/Er:KMnF3 NCs with cubic phase KMnF3 can be easily tuned from 8 nm to 18 nm. Interestingly, the Zn2+ ions were not incorporated into the lattice structure or adhered on the surface of the final NCs; they just helped the growth of Yb/Er:KMnF3 NCs. Combined with the upconversion emission spectra results, we can provide a direct evidence for the size-dependent upconversion luminescence on account of the final NCs with different sizes having the same components, shape, crystal structure and crystallinity.

Enhancement of 1.53 μm emission in erbium/cerium-doped germanosilicate glass pumped by common 808 nm laser diode.

Erbium-doped germanosilicate glasses with various cerium ions contents have been prepared. Optical absorption and 1.53 μm emission spectra were measured to characterize the spectroscopic performances of prepared samples. A detailed study of 1.53 μm spectroscopic properties was carried out when pumped by an 808 nm laser diode. Moreover, an energy level diagram and an energy transfer mechanism between Er3+ and Ce3+ were proposed to elucidate the enhanced 1.53 μm fluorescence. It is found that the prepared samples have optimal spectroscopic properties when the Ce3+ concentration is fixed to 0.5 mol. %. High spontaneous radiative transition probability (172.66u2009u2009s(-1)), large effective emission bandwidth (74 nm), and emission cross section (9.49×10(-21)u2009u2009cm(2) indicate that 808 nm pumped Er3+/Ce3+ codoped germanosilicate glass might be a suitable material for a broadband optical amplifier.

The influence of TeO2 on thermal stability and 1.53 μm spectroscopic properties in Er3+ doped oxyfluorite glasses

In this work, the thermal and spectroscopic properties of Er(3+)-doped oxyfluorite glass based on AMCSBYT (AlF3-MgF2-CaF2-SrF2-BaF2-YF3-TeO2) system for different TeO2 concentrations from 6 to 21 mol% is reported. After adding a suitable content of TeO2, the thermal ability of glass improves significantly whose ΔT and S can reach to 118 °C and 4.47, respectively. The stimulated emission cross-section reaches to 7.80×10(-21) cm(2) and the fluorescence lifetime is 12.18 ms. At the same time, the bandwidth characteristics reach to 46.41×10(-21) cm(2) nm and the gain performance is 63.73×10(-21) cm(2) ms. These results show that the optical performances of this oxyfluorite glass are very well. Hence, AMCSBYT glass with superior performances might be a useful material for applications in optical amplifier around 1.53 μm.

The progress of single-band upconversion nanomaterials

Upconversion (UC) nanomaterials (NMs) with single-band emission properties provoke widespread interest in the bio-medical field due to their advantages over those with multi-band emissions such as for high resolution in situ multiplexed molecular mapping. Several methods have been applied in recent years to realize single-band emission with different colors. In this feature article, for the first time, we provide an overview of the recent progresses in realizing single-band UC emission through different methods and the related mechanisms. Three types of strategies, including choosing an appropriate matrix, a doping ion with suitable energy level and a coating organic dye with a certain absorption wavelength, are discussed in detail. Finally, the challenges and future perspectives for these novel NMs with single-band UC emission are stated.

Controlling red upconversion luminescence in Gd2O3:Yb3+–Er3+ nanoparticles by changing the different atmosphere

Lanthanide (Ln3+)-doped nanoparticles that produce strong red upconversion (UC) luminescence are desirable for biological applications. For nanoparticles, modification of their electronic properties and stabilization of their crystallographic phase are crucial for tuning their luminescence behaviors. Here, Yb3+–Er3+ doped Gd2O3 nanoparticles have been synthesized by calcining Gd2O2S in nitrogen (O2-free) and ambient air (∼21% O2), respectively. Various approaches including X-ray diffraction (XRD), transmission electron microscopy (TEM), Raman spectroscopy and thermo-gravimetric and differential thermal analyses (TG-DTA) were used to characterize the structure, morphology and phase formation mechanism of the nanoparticles. Upconversion luminescence properties were investigated by emission intensity vs. excitation power (double logarithmic relationship) and temperature dependent emission spectroscopy. The different splitting transition probabilities of the cubic and/or monoclinic phase, the probability of multiphonon relaxations and cross relaxations between Er3+ ions are responsible for the efficient red emission in the cubic Gd2O3 nanoparticles. More importantly, the lower phonon energy of the pure cubic sample has good thermal stability in the current detectable range of 20–100 °C. These results imply that the cubic Gd2O3 upconversion nanoparticles may have multiplexing functionality in bio-imaging.