Upconversion Photoluminescence Intensity Research Articles

Correlation between upconversion photoluminescence and dielectric response in Ba-substituted (Sr1−xBax)4(La0.85Ho0.025Yb0.125)2Ti4Nb6O30

The filled tetragonal tungsten bronze (Sr1−xBax)4(La0.85Ho0.025Yb0.125)2Ti4Nb6O30 (SBLTNx: Ho-Yb) ceramics with different Ba substitution levels (x) are prepared. The upconversion photoluminescence (UC-PL) and dielectric permittivity are investigated. The substitution of Sr2+ ions at the A2-sites by larger Ba2+ ions results in substantial variation of the UC-PL intensity as a function of substitution level x. Furthermore, the dielectric response to the substitution of Sr2+ by Ba2+ suggests a close correlation between the UC-PL intensity and dielectric permittivity. The origin for this correlation is discussed based on the random stress field (RSF) model.

Strong Influences of Melting Time and Tm3+ Concentration on Blue Up‐Conversion Photoluminescence for Tm3+/Yb3+ Co‐Doped TeO2–TlO0.5–ZnO Glass

In this study, by a conventional melt quenching method, we synthesized novel up‐conversion phosphors of 60TeO2–30TlO0.5–(9−x)ZnO–xTm2O3–1Yb2O3 (x = 0.1–0.5) glasses, whose system was recently developed in our collaborative group, and their blue up‐conversion photoluminescence (UCPL) of Tm3+ ions via three‐step energy transfer from near‐infrared (NIR) sensitizer of Yb3+ ions was observed. In particular, the substantial rate of the energy transfer <γd5> in the third step from Yb3+ to Tm3+ under excitation at 975 nm, which determined the final blue UCPL intensity, was estimated as a function of the rare‐earth concentration. With an aid of analytical methods of PL lifetime and Judd–Ofelt theory, it was revealed that the highest energy transfer rate <γd5> was achieved to be 2.07 × 10−17 cm3/s for x = 0.2, and further increasing Tm2O3 content x in the fixed Yb2O3 resulted in the decrease in the energy transfer rate <γd5>. One of the plausible causes was concentration quenching of Yb3+ ions. The other was back‐transfer from Tm3+ to Yb3+ ions. The influence of the condition of glass synthesis and the melting time on <γd5> was also discussed.

Raman investigation and glass-compositional dependence on blue up-conversion photoluminescence for Tm^3+/Yb^3+ co-doped TeO_2-TlO_05-ZnO glasses

In this study, glass-compositional dependence of Tm3+ blue up-conversion photoluminescence (UCPL), which is known to be obtained via three-steps’ energy transfers from Yb3+ to Tm3+ ions under near-infrared light excitation at ~980 nm, is investigated for Tm3+/Yb3+ co-doped TeO2-TlO0.5-ZnO glasses. The third step of energy transfer from Yb3+ to Tm3+ ions is particularly important ((Yb3+, Tm3+); (2F5/2, 3H4)→(2F7/2, 1G4)) since it determines the final blue UCPL intensity from 1G4 level compared to red and near-infrared UCPLs, and so then estimated with varied TlO0.5 and ZnO contents at the expense of TeO2 in the fixed Tm3+ and Yb3+ contents ([Yb3+]/[Tm3+] = 5). The substantial energy transfer rate (ETR) in the third step is evaluated from excitation power dependence of the blue UCPL intensity in comparison with near-infrared UCPL of Tm3+ ions with an aid of analytical method of PL lifetime and Judd-Ofelt theory. It is here revealed that the highest ETR is achieved to be 3.54 × 10−17 cm3/s for the glass composition of 70TeO2-10TlO0.5-19.4ZnO-0.1Tm2O3-0.5Yb2O3, and that the transfer rate is possibly related with the length of TeO2 glass network because a long tellurite glass network can cause segregation of rare-earth elements inducing effective Yb3+-Yb3+ energy migration and less quenching centers like dangling bonds of isolated TeO32-, resulted in the enhancement of the energy transfer for blue UCPL.

Hydrothermal synthesis of the intense green photoluminescence of hexagonal phase NaYF4:Yb3+/Er3+ microcrystals

Hexagonal phase NaYF4:Yb3+ 20mol%/Er3+ 1mol% microcrystals that exhibit intense green emission were successfully synthesized via a facile hydrothermal method. The factors including the NaF/Ln (Ln=Y+Yb+Er) molar ratio, pH value of the precursor solution, and the ethylenediaminetetraacetic acid (EDTA)/Ln molar ratio, were well studied in the influences on the crystal structures, morphologies, and sizes of final products. The experimental results indicate that the NaF/Ln ratio and pH value play key roles in crystal structure and morphology of the product. Photoluminescence measurements demonstrate that the relative up-conversion photoluminescence intensity of as-prepared products strongly depends on the crystal structures, crystallization degrees, morphologies, and sizes.

Bright dual-mode green emission from selective set of dopant ions in β-Na(Y,Gd)F4:Yb,Er/β-NaGdF4:Ce,Tb core/shell nanocrystals

Bright dual-mode green-emitting core/shell nanoparticles (NPs) were synthesized by doping selective set of lanthanide ions. Up-conversion (UC) green-emitting β-NaY0.2Gd0.6F4:Yb0.18,Er0.02 NPs (8.3 nm) were used as core material. Bright down-conversion (DC) green-emitting β-NaGd0.8F4:Ce0.15,Tb0.05 NPs showed ca. 31 times higher photoluminescence (PL) intensity than β-NaGdF4:Tb NPs and they were served as shell material with their excellent PL properties. The UC/DC core/shell NPs showed bright green light under excitations of 980 nm near infrared (NIR) light and 254 nm ultraviolet (UV) light, respectively. The UC/DC core/shell NPs showed ca. 11 times higher UC PL intensity than core UCNPs. Consequently, the core/shell NPs doped with selective set of lanthanide ions showed bright dual-mode green emission under excitations of NIR light and UV light, indicating that they are promising for application to optical imaging.

Optical Temperature Sensor Using Infrared-to-Visible-Frequency Upconversion in Er3+/Yb3+-Codoped Bi3TiNbO9 Ceramics

An optical temperature sensor based on infrared-to-visible upconversion emission in Er3+/Yb3+ co-doped Bi3TiNbO9 (BTN) ceramics is reported. The fluorescence intensity ratio of the green upconversion photoluminescence (UC-PL) around 524 nm and 545 nm depends on temperature. The operating temperature range and the maximum sensitivity of Er3+/Yb3+ co-doped Bi3TiNbO9 ceramics are 123–693 K and 0.0032 K−1, respectively. BTN:Er3+/Yb3+ ceramic has good thermal, physical and chemical stability, great UC-PL intensity and low cost fabrication. The results imply that Er3+/Yb3+ co-doped Bi3TiNbO9 ceramic is promising for applications in wide-temperature-range sensors.

Multifunctional Y<sub>2</sub>0<sub>3</sub>:Yb<sup>3+</sup>/Tm<sup>3+</sup>/Li<sup>+</sup> Nanocrystals with Enhanced Near-Infrared to Near-Infrared Upconversion Photoluminescence

Rare earth ion-doped Y2O3 nanoparticles are attractive for biological imaging applications due to their non-toxicity, resistance to photobleaching, and possibility for upconversion. Y2O3:Yb3+/Tm3+ nanocrystals display photoluminescence (PL) with a peak at ~811nm if excited at ~980nm. This Near-Infrared to Near-Infrared (NIR-to-NIR) upconversion (UC) process provides deeper light penetration into biological specimen and results in high contrast optical imaging due to absence of an autofluorescence background and decreased light scattering. Here, we report that NIR-to-NIR UC PL intensity of Y2O3:Yb3+/Tm3+ nanocrystals are enhanced by doping with different Tm3+ ions and Li+ ions concentration. When the Tm3+ ions concentration reaches 0.25 mol%, the NIR-to-NIR UC PL intensity is the strongest. And the NIR-to-NIR UC PL intensity of Y2O3:5 mol % Yb3+ ions, 0.25mol% Tm3+ ions and 5mol% Li+ ions is maximum, which is more that about 14 times than that of no doped Li+ ions. This material may show promise for use as probes for biological imaging.

Upconversion luminescence from Er-N codoped of ZnO nanowires prepared by ion implantation method

Nitrogen and erbium co-doped of ZnO nanowires (NWs) are fabricated by ion implantation and subsequent annealing in air. The incorporation of Er3+ and N+ ions is verified by energy dispersive X-ray spectroscopy (EDS) and Raman spectra. The samples exhibit upconversion photoluminescence around ∼550nm and ∼660nm under an excitation at 980nm. It is discovered that the N-doped can drastically increase the upconversion photoluminescence intensity by modifying the local structure around Er3+ in ZnO matrix. The enhancement of the PL intensity by the N-doped is caused by the formation of ErO6−xNx octahedron complexes. With the increase of the annealing temperature (Ta), the Er3+ ions diffuse towards the surface of the NWs, which benefits the red emission and evokes the variation of intensity ratio owing to the existence of some organic groups.

Enhance upconversion photoluminescence intensity by doping Li + in Ho 3+ and Yb 3+ codoped Y 2O 3 nanocrystals

Infrared-to-visible upconversion emission spectrum is investigated in Li +, Ho 3+ and Yb 3+ codoped Y 2O 3 nanocrystals. By adding Li + ion to the Y 2O 3:Ho 3+/Yb 3+ nanocrystal, the upconversion emission intensity is found being significantly enhanced comparing with that without Li + ion. The two reasons for this enhancement are discussed: one is because of the modification of the local symmetry of the Ho 3+ ion, and the other is because of the reducing number of OH groups. This indicates Li + ion would be a wonderful photoluminescence intensifier for rare-earth.