Lasers upconverting

Bhawalkar J D, Swiatkiewicz J, Pan S J, Samarabandu J K, Liou W S, He G S, Berezney R, Cheng P C and Prasad P N 1996 Three-dimensional laser scanning two-photon fluorescence confocal microscopy of polymer materials using a new, efficient upconverting fluorophore Scanning 18 562-6... 

SFG using femtosecond lasers allows all the resonances within the broad (-200 cm" ) bandwidth of the IR pulse to be probed simultaneously, without scanning the infrared source. To obtain spectral resolution in an SFG spectrum, the IR polarization is upconverted with a narrowband (-8 cm" ) visible beam, which is prepared by pulse shaping the output of a femtosecond laser. Only the frequency components of the pulse that interact resonantly with the vibrational modes are enhanced, resulting in an SFG spectrum [28, 29]. Owing to the use of femtosecond... 

Fig. 27 a Power dependence of the 480 nm blue upconverted emission intensity of Cs2NaGdCl6 Tm3+ (6, 10 and 15 mol%). b Temporal dependence of this emission (continuous line, left-hand ordinate) and of the transmitted laser beam (dotted line, right-hand ordinate) for the 10 mol% sample under high excitation power, 14.5 Pthres- (Adapted from... 

Whereas many examples of the photon avalanche phenomenon exist in the literature, only one study has been made for elpasolite systems [347], for Cs2NaGdCl6 Tm3+, where the blue upconverted emission is due to the 1G4 3H6 transition. However, the situation is rather more complex than in Fig. 24j because several other processes can occur, which also lead to emission from D2. Three features related to the 64 emission are highlighted here. First, Fig. 27a shows that a quadratic emission intensity-excitation power dependence is obtained at low excitation intensities for samples of Cs2NaGdCl6 Tm3+ doped with between 6-15 mol% Tm3+. However, a dramatic increase of the emission intensity appears above the excitation threshold value, ca. 9 kW cm 2. In Fig. 27a, the slope increases to 6 for the 10 mol% Tm3+-doped sample. Second, the time-dependence of the upconverted emission exhibits different behaviour at different excitation powers. A notable difference from other systems is that, at the threshold excitation power, Pthres, the blue emission has an almost linear rise-time which is followed by a further slower rise over several seconds. Third, at high excitation powers, the establishment of the stationary state is quicker, and the 3F4—>3G4 ESA decreases the transmitted laser light by several percent, Fig. 27b. 

Figure C3.1.13. Experimental configuration for far-UV nanosecond CD measurements using a frequeney-upconverted Ti sapphire laser as a probe source. Pj and 2 are MgF2 Roehon polarizers at eross orientations. SPj is a strained transparent plate with about 1° of linear birefringence for quasi-null ellipsometric CD deteetion. Prism PMj and the iris select the far-UV fourth harmonie of the argon laser-pumped Ti-sapphire laser s near-IR fundamental output to probe the elliptieity of the sample. A seeond laser beam at 532 nm is used to pump CD...

Optical properties of Y2O3 ceramics, doped with rare-earth ions, are of special interest for some applications, such as solid-state lasers and scintillators [95]. Luminescence properties, such as upconversions, are also of special significance. For instance, REA"b co-doped Y2O3 transparent ceramics (RE = Er, Ho, Pr and Tm), exhibited very efficient NIR-visible upconverters [96]. 

To date, primarily alkali lanthanide tetrafluorides such as NaYp4 and related crystals have been prepared by thermal decomposition. The majority of publications in this field use a method first published by Mai et al [25]. These researchers used rare-earth trifluoroacetates as reactants. The trifluoroacetates decomposit in the heat under release of fluoride and volatile by-products. Mai et al. have focussed on the synthesis of differently sized and shaped nanocrystals but did not show any upconversion data. The first upconverting NaYp4-based nanocrystals synthesised using the Mai method have been published by Boyer et al. [27, 28]. The method has been modified by Ehlert et al. to realise four different, spectroscopically distinguishable upconverting nanocrystal species [26]. Figure 3 shows the upconversion luminescence of these nanocrystals on excitation with a 980 nm laser diode. 

Fig. 3 Photographic picture of upconverting nanocrystals with four diffiaent colours (no filters or overexposwe were used). Excitation 980 mn laser diode. Reprinted with permission from [26]. Copyright 2008 American Chemical Society...

S3/2 I15/2 = 550 nm (Fig. 16.19). These emission bands match well with the absorption of c-Si. Note that the exact emission wavelength can vary by 10 nm depending on the host material. Shalav et al. in 2005 reported the application of NaYp4 20 %Er phosphors as the upconverters in a bifacial c-Si solar cell [48]. These phosphors were mixed into an optically transparent acrylic adhesive medium at a concentration of 40 wt% and then placed on the rear of a bifacial c-Si solar cell. Reflective white paint was used as a reflector on the rear of the system. An external quantum efficiency of 2.5 % was obtained for the solar cell under excitation at 1523 nm with a 5.1-mW laser. More recently, Fischer et al. also investigated the... 

---