Yanbo Qiao

Broadband conversion of visible light to near-infrared emission by Ce3+, Yb3+-codoped yttrium aluminum garnet

We show that Ce(3+) can be an efficient sensitizer for Yb(3+) in the host lattice of yttrium aluminum garnet (YAG). With blue-light excitation to induce the 4f-->5d transition of Ce(3+), characteristic near-IR emission of Yb(3+) due to transition of (2)F(5/2)-->(2)F(7/2) peaking at 1030 nm is generated as a result of energy transfer from Ce(3+) to Yb(3+). The result of spectral evolution with temperature indicates that the efficiency of energy transfer is enhanced owing to thermal effect. This evidence implies that the phonon-assisted process participates in the downconversion of YAG: Ce(3+), Yb(3+).

Cooperative downconversion in Yb 3+ –RE 3+ (RE=Tm or Pr) codoped lanthanum borogermanate glasses

We report on cooperative downconversion in Yb(3+)-RE(3+) (RE=Tm or Pr) codoped lanthanum borogermanate glasses (LBG), which are capable of splitting a visible photon absorbed by Tm(3+) or Pr(3+) ions into two near-infrared photons. The results indicate that Pr(3+)-Yb(3+) is a more efficient ion couple than Tm(3+)-Yb(3+) in terms of cooperative downconversion. We have obtained a highest quantum yield of 165% and 138% for Pr(3+)-Yb(3+) and Tm(3+)-Yb(3+) codoped LBG glasses under 468 nm excitation, respectively. However, ultraviolet light excitation to the charge transfer band of Yb(3+) does not result in quantum splitting as rapid relaxation from the charge transfer band to 4f(13) levels of Yb(3+) dominates.

BCNO-Based Long-Persistent Phosphor

A BCNO-based long-persistent phosphor prepared by a low-temperature liquid-phase route is investigated. It shows a phosphorescence peak centered at 520 nm and its afterglow decay curve fits t -0.93 . Electron paramagnetic resonance confirms the presence of a paramagnetic center, the signal of which exhibits a synchronized decay with the afterglow intensity. We assume that the phosphorescence arises from electrons that are thermally released from nitrogen vacancies and then fall into the carbon-related defects, giving the greenish emission. The BCNO material is a competitive long-persistent phosphor because it is derived from cheap raw materials.

Spectroscopic investigation on BCNO-based phosphor: photoluminescence and long persistent phosphorescence

BCNO phosphor derived from a low-temperature urea route is an efficient and environmental-friendly phosphor with emission covering the full visible and the near ultraviolet region. Systematic characterization of the BCNO phosphor was carried out by means of steady state and time-resolved spectroscopy in order to unveil the origins of different luminescence centres. Two emission bands located at 335 and 410 nm together with a changeable band located ranging from 380 to 580 nm are identified and related to the presence of carbon defects as inferred from electron paramagnetic resonance spectroscopy. The emission of the changeable band exhibits a long persistent character, which depends on the emission energy of the specimens and originates from the tunnelling recombination of electrons with the emission centres. The spectroscopic properties of the BCNO phosphor are discussed in detail and a configurational coordinate model is constructed for the explanation of the photoluminescence as well as the afterglow behaviour.

Energy transfer between Cr 3+ and Ni 2+ in transparent silicate glass ceramics containing Cr 3+ /Ni 2+ co-doped ZnAl 2 O 4 nanocrystals

The emission intensity of Ni2+ at 1200 nm in transparent ZnO-Al2O3-SiO2 glass ceramics containing ZnAl2O4 nanocrystals is improved approximately 8 times by Cr3+ codoping with 532 nm excitation. This enhanced emission could be attributed to an efficient energy transfer from Cr3+ to Ni2+, which is confirmed by time-resolved emission spectra. The energy transfer efficiency is estimated to be 57% and the energy transfer mechanism is also discussed.

Blue emission from Eu2+-doped high silica glass by near-infrared femtosecond laser irradiation

Eu2+-doped high silica glass (HSG) is fabricated by sintering porous glass which is impregnated with europium ions. Eu2+-doped HSG is revealed to yield intense blue emission excited by ultraviolet (UV) light and near-infrared femtosecond laser. The emission profile obtained by UV excitation can be well traced by near-infrared femtosecond laser. The upconversion emission excited by 800 nm femtosecond laser is considered to be related to a two-photon absorption process from the relationship between the integrated intensity and the pump power. A tentative scheme of upconverted blue emission from Eu2+-doped HSG was also proposed. The HSG materials presented herein are expected to find applications in high density optical storage and three-dimensional color displays.

Optical gain at 1550 nm from colloidal solution of Er3+-Yb3+ codoped NaYF4 nanocubes.

We demonstrated optical amplification at 1550 nm with a carbon tetrachloride solution of Er(3+)-Yb(3+) codoped NaYF(4) nanocubes synthesized with solvo-thermal route. Upon excitation with a 980 nm laser diode, the nanocube solution exhibited strong near-infrared emission by the (4)I(13/2)-->(4)I(15/2) transition of Er(3+) ions due to energy transfer from Yb(3+) ions. We obtained the highest optical gain coefficient at 1550 nm of 0.58 cm(-1) for the solution with the pumping power of 200 mW. This colloidal solution might be a promising candidate as a liquid medium for optical amplifier and laser at the optical communication wavelength.

Transparent colloid containing upconverting nanocrystals: an alternative medium for three-dimensional volumetric display

We report an alternative medium of transparent upconverting colloid containing lanthanide ion doped NaYF(4) nanocrystals for three-dimensional (3D) volumetric display. The colloids exhibit tunable upconversion luminescence with a wide spectrum of colors by adjusting the doping concentrations of the nanocrystals and the compositions of the colloids. Our preliminary experimental result indicates that an upconverting colloid-based 3D volumetric display using a convergent near infrared laser beam to induce a localized luminescent spot near the focus is technically feasible. Therefore arbitrary 3D objects can be created inside the upconverting colloid by use of computer controlled 3D scanning systems.

Enhanced broadband near-infrared luminescence from transparent Yb 3+ /Ni 2+ codoped silicate glass ceramics

The near-infrared emission intensity of Ni(2+) in Yb(3+)/Ni(2+) codoped transparent MgO-Al(2)O(3)-Ga(2)O(3)-SiO(2)-TiO(2) glass ceramics could be enhanced up to 4.4 times via energy transfer from Yb(3+) to Ni(2+) in nanocrystals. The best Yb(2)O(3) concentration was about 1.00 mol%. For the Yb(3+)/Ni(2+) codoped glass ceramic with 1.00 mol% Yb(2)O(3), a broadband near-infrared emission centered at 1265 nm with full width at half maximum of about 300 nm and lifetime of about 220 mus was observed. The energy transfer mechanism was also discussed.

Optical amplification near 1300 nm in bismuth-doped strontium germanate glass

We demonstrate the broadband optical amplification in bismuth-doped strontium germanate glass with 808 nm and 980 nm laser diodes (LDs) as excitation sources. The net optical gain has been obtained within the wavelength region of 1272 to 1348 nm with 808 nm laser diode under 0.97 W power. The maximum gain and gain coefficients are 1.23 and 1.03 cm−1 at 1315 nm, respectively. The signal increment at 1300 nm is 2.8 times with 980 nm LD, under 3 W power. The differential thermal analysis measurement reveals the good thermal stability of the studied glass. This glass could be suggested as a promising gain medium for broadband optical amplifiers.