Stephan Heer

Low-temperature upconversion spectroscopy of nanosized Y2O3:Er,Yb phosphor

This work reports on the structural characterization and on the low-temperature upconversion spectroscopy of the Y2O3:2%Er,1%Yb nanophosphor prepared by thermal decomposition of a polymeric resin (Pechini’s method [U.S. Patent No. 3,330,697 (July 11 1967)]). The average particle size evaluated from transmission electron microscopy lies in the range of 05–25nm. The high-resolution upconversion luminescence spectrum at 10K in the ultraviolet to near infrared (UV-NIR) spectral regions shows narrow lines, characteristic of Er3+ transitions occupying both Y3+ sites with point symmetries C2 and C3i in the oxide cubic system. The excitation spectrum at 10K in the IR region was used to monitor the green upconversion and IR luminescences and it displayed Er and Yb lines. Power dependence measurements at 298 and 10K indicate that the main upconversion mechanism is a two-photon excitation process. The temperature dependence of the upconversion luminescence shows a decrease in the emission intensity with increasing t...

Up-conversion excitation of sharp Cr3+2E emission in YGG and YAG codoped with Cr3+ and Yb3+

The 2 E→ 4 A 2 emission of Cr 3+ in crystals and glasses is of great importance in science and technology. We found a new excitation mode for this emission in the garnets YGG and YAG codoped with Cr 3+ and Yb 3+ . It is based on an up-conversion mechanism using 2 F 5/2 of Yb 3 as an intermediate state. Excitation of the Yb 3+ in the near infrared around 1000 nm leads to visible Cr 3+ 2 E→ 4 A 2 emission around 700nm at low temperatures. The up-conversion luminescence intensity shows a strong temperature dependence due to an intrinsic loss mechanism. The up-conversion excitation spectra follow the Yb 3+2 F 7/2 → 2 F 5/2 absorptions. From its time dependence the up-conversion mechanism is found to be dominated by an energy transfer step: Two excited Yb 3 + ions simultaneously transfer their 2 F 5/2 excitation to Cr 3+ .

Upconversion excitation of Cr3+2E emission in Y3Ga5O12 codoped with Cr3+ and Yb3+

Abstract The 2 E → 4 A 2 emission of Cr3+ in crystals and glasses is of great importance in science and technology. We report a new excitation mode for this emission in Y3Ga5O12 (YGG) codoped with Cr3+ and Yb3+. It is based on an upconversion mechanism using 2 F 5/2 of Yb3+ as an intermediate state. Excitation in the near-IR at 969.6 nm leads to visible luminescence around 700 nm at low temperature. In YGG:2%Cr3+,1%Yb3+ at 15 K and for a laser power of 150 mW the efficiency of the process is 5.5%. From its time dependence the upconversion mechanism is found to be dominated by an energy transfer step: Two excited Yb3+ ions simultaneously transfer their 2 F 5/2 excitation to Cr3+.

Upconversion excitation of Cr3+ emission in YAlO3 codoped with Cr3+ and Yb3+

We report on upconversion (UC) luminescence in YAl0 3 codoped with 0.3% Cr 3+ and 6% Yb 3+ . At 10 K excitation around 10,400cm -1 leads to red Cr 3 + pair luminescence at 14,000 cm -1 . The UC excitation spectrum of the red Cr 3+ luminescence is very similar to the squared Yb 3 absorption spectrum. This demonstrates that two Yb3 2 F 7/2 2 → 2 F 5/2 excitations are involved in the UC process. From transient measurements, the UC mechanism is found to be dominated by an energy transfer step: Two excited Yb 3+ ions simultaneously transfer their excitation energy to a nearby Cr 3 -pair.

Photon upconversion emission in transparent solutions of nanocrystalline hexagonal NaGdF/sub 4/:Yb/sup 3+/, Er/sup 3+/

Photon upconversion (UC) is a nonlinear optical process in which long-wavelength (NIR) radiation is converted into short-wavelength (VIS) radiation. We have extended our synthetic and spectroscopic work towards Yb/sup 3+//Er/sup 3+/ codoped nanoparticles of NaGdF/sub 4/. The /spl beta/-NaGdF/sub 4/:Yb/sup 3+/, Er/sup 3+/ nanoparticles of roughly spherical shape and a size of about 30 nm can be transparently dissolved in DMSO. The UC emission spectra upon laser excitation of the transparent solution of /spl beta/-NaGdF/sub 4/:Yb/sup 3+/, Er/sup 3+/ nanoparticles in DMSO are observed.