P. V. dos Santos

Optical temperature sensing using upconversion fluorescence emission in Er3+/Yb3+-codoped chalcogenide glass

Optical temperature sensing using upconversion fluorescence emission in Er3+/Yb3+-codoped Ga2S3:La2O3 chalcogenide glass excited at 1.06 μm is reported. Temperature measurements in the region of 20–225 °C with a resolution of approximately 0.5 °C using excitation powers of a few tens of milliwatts were obtained. The temperature sensing mechanism is independent of variations in the excitation intensity, possible fluctuations of transmission, and utilizes a simple signal detection and processing system. The results also revealed that the glass host material plays an important role in the performance of the sensing system.

Thermally induced threefold upconversion emission enhancement in nonresonant excited Er3+/Yb3+-codoped chalcogenide glass

Thermally induced threefold infrared-to-visible upconversion emission enhancement in Er3+/Yb3+-codoped Ga2S3:La2O3 chalcogenide glasses excited at 1.064 μm is reported. The times three upconversion efficiency enhancement was achieved by heating the sample in the temperature range of 23–155 °C, and is assigned to the temperature-dependent multiphonon-assisted anti-Stokes sideband excitation process of the ytterbium sensitizer. A theoretical analysis based upon rate equations considering the sensitizer absorption cross section as a function of the phonon occupation number in the host material exhibited very good agreement with experimental data.

Optical thermometry through infrared excited upconversion fluorescence emission in Er/sup 3+/- and Er/sup 3+/-Yb/sup 3+/-doped chalcogenide glasses

Optical thermometry based upon infrared excited upconversion fluorescence emission in Er/sup 3+/- and Er/sup 3+/-Yb/sup 3+/- doped Ga/sub 2/S/sub 3/-La/sub 2/O/sub 3/ chalcogenide glasses excited at 1.54 and 1.06 /spl mu/m, respectively, is presented. Temperature sensing in the region of 20/spl deg/C-220/spl deg/C with 0.3/spl deg/C accuracy using excitation powers readily obtainable from commercially available semiconductor lasers was achieved. The temperature sensing approach is independent of fluctuations in excitation intensity and transmission and requires a simple and low-cost signal detection and processing system. The results also indicate that the glassy host material plays a major role in the performance of the sensing system.

Sensitized thulium blue upconversion emission in Nd3+/Tm3+/Yb3+ triply doped lead and cadmium germanate glass excited around 800 nm

Bright blue upconversion emission by thulium ions in PbGeO3–PbF2–CdF2 glass triply doped with Nd3+–Tm3+–Yb3+ under diode laser excitation around 800 nm is reported. The results revealed that the Nd3+/Tm3+/Yb3+-codoped sample generated ten times more 475 nm blue upconversion fluorescence than the Yb3+-sensitized Tm3+-doped one, under the same excitation power. The upconversion process also showed a strong dependence upon the Yb3+ concentration. The results also indicated that the neodymium ions played a major role in the upconversion process by transfering the 800 nm excitation to thulium ions. The population of the Tm3+ ions 1G4 emitting level was accomplished through a multiion interaction involving ground-state absorption of pump photons around 800 nm by the Nd3+(4I9/2→2H9/2, 4F5/2) and Tm3+(3H6→3F4) ions followed by energy-transfer processes involving the Nd3+–Yb3+(4F3/2, 2F7/2→4I11/2, 2F5/2) and Yb3+–Tm3+(2F5/2, 3F4→2F7/2, 1G4) pairs.

Infrared-to-visible frequency upconversion in Pr3+/Yb3+- and Er3+/Yb3+-codoped tellurite glasses

Abstract Upconversion luminescence and thermal effects in Pr 3+ /Yb 3+ - and Er 3+ /Yb 3+ -codoped 60TeO 2 –10GeO 2 –10K 2 O–10Li 2 O–10Nb 2 O 5 tellurite glasses excited by CW infrared radiation at 1.064 μm is reported. Generation of intense green and red fluorescence emission in Er 3+ /Yb 3+ -codoped samples and appreciable upconversion luminescence in the wavelength region of 450–680 nm in Pr 3+ /Yb 3+ -codoped samples is observed. Temperature-induced enhancement of ×12 in the upconversion efficiency in Er 3+ /Yb 3+ - and ×10 in the Pr 3+ /Yb 3+ -doped samples is demonstrated.

Blue cooperative luminescence in Yb3+-doped tellurite glasses excited at 1.064 μm

Blue luminescence emission around 480 nm through cooperative upconversion from pairs of Yb3+ ions implanted into 60TeO2–10GeO2–10K2O–10Li2O–10Nb2O5 tellurite glasses and excited by a cw laser at 1.064 μm is demonstrated. Cooperative luminescence emission enhancement owing to the temperature dependent multiphonon-assisted anti-Stokes excitation process of the ytterbium ions is also observed. The experimental results revealed a fourfold enhancement in the cooperative luminescence emission when the sample was heated in the temperature range of 20 °C–260 °C. The thermally induced enhancement is assigned to the effective absorption cross-section for the ytterbium ions which is an increasing function of the medium temperature.

Color tunability with temperature and pump intensity in Yb3+/Tm3+ codoped aluminosilicate glass under anti-Stokes excitation

Pump and thermally induced color tunabilities were demonstrated in Yb(3+)/Tm(3+) codoped low silica calcium aluminosilicate (LSCAS) glass under anti-Stokes excitation at 1.064 microm. The effects of pump intensity and samples temperature on the upconversion emissions and mainly on the color tunabilities (from 800 to 480 nm) were investigated. The results revealed a 20- and a threefold reductions at 800/480 nm ratio as, respectively, the pump intensity and samples temperature were increased from 27 to 700 kW/cm(2) and from 296 to 577 K. These behaviors with pump intensity and temperature (a strong increase of the 480 nm emission in comparison with the 800 nm one) were attributed to the several efficient processes occurring in the LSCAS system (Yb(3+)-->Tm(3+) energy-transfer processes, easy saturations of the Yb(3+) and Tm(3+) excited states, and radiative emissions). Besides these assigns, the temperature dependence is mainly assigned to the temperature-dependent effective absorption cross section of the ytterbium sensitizer through the so-called multiphonon-assisted anti-Stokes excitation process. Theoretical analyses and fits of the experimental data provided quantitative information.

Efficient energy upconversion emission in Tm3+/Yb3+-codoped TeO2-based optical glasses excited at 1.064 μm

Efficient energy upconversion of cw radiation at 1.064 μm into blue, red, and near infrared emission in Tm3+-doped Yb3+-sensitized 60TeO2-10GeO2-10K2O-10Li2O-10Nb2O5 glasses is reported. Intense blue upconversion luminescence at 485 nm corresponding to the Tm3+ 1G4→3H6 transition with a measured absolute power of 0.1 μW for 800 mW excitation power at room temperature is observed. The experimental results also revealed a sevenfold enhancement in the upconversion efficiency when the sample was heated from room temperature to 235 °C yielding 0.7 μW of blue absolute fluorescence power for 800 mW pump power. High brightness emission around 800 nm (3F4→3H6) in addition to a less intense 655 nm (1G4→3H4 and 3F2,3→3H6) fluorescence is also recorded. The energy upconversion excitation mechanism for thulium emitting levels is assigned to multiphonon-assisted anti-Stokes excitation of the ytterbium-sensitizer followed by multiphonon-assisted sequential energy-transfer processes.

IR-visible upconversion and thermal effects in Pr3+/Yb3+-codoped Ga2O3:La2S3 chalcogenide glasses

IR-visible upconversion fluorescence spectroscopy and thermal effects in Pr3+/Yb3+-codoped Ga2O3:La2S3 chalcogenide glasses excited at 1.064 µm is reported. Intense visible upconversion emission in the wavelength region of 480-680 nm peaked around 500, 550, 620 and 660 nm is observed. Upconversion excitation of the Pr3+ excited-state visible emitting levels is achieved by a combination of phonon-assisted absorption, energy-transfer and phonon-assisted excited-state absorption processes. A threefold upconversion emission enhancement induced by thermal effects when the codoped sample was heated in the temperature range of 20-200 °C is demonstrated. The thermal-induced enhancement is attributed to a multiphonon-assisted anti-Stokes process which takes place in the excitation of the ytterbium and excited-state absorption of the praseodymium. The thermal effect is modelled by conventional rate equations considering temperature-dependent effective absorption cross-sections for the 2F7/2-2F5/2 ytterbium transition and 1G4-3P0 praseodymium excited-state absorption, and it is shown to agree very well with experimental results. Frequency upconversion in singly Pr3+-doped samples pumped at 836 nm and 1.064 µm in a two-beam configuration is also examined.

Upconversion emission enhancement induced by thermal effects in infrared excited Pr/sup 3+//Yb/sup 3+/-codoped Ga/sub 2/O/sub 3/:La/sub 2/S/sub 3/ chalcogenide glasses

Thermally induced enhancement of infrared-to-visible frequency upconversion in Pr/sup 3+//Yb/sup 3+/-codoped chalcogenide glasses excited at 1.064 /spl mu/m is demonstrated. The Pr/sup 3+//Yb/sup 3+/-codoped 70%Ga/sub 2/O/sub 3/:30%La/sub 2/S/sub 3/ glass samples were excited at 1.064 /spl mu/m, and heated in the temperature range of 20 to 200/spl deg/C. For a fixed excitation power and temperature, the upconversion emission spectrum obtained from the sample is depicted. It presents three bands centered around 500, 546, and 650 nm corresponding to the /sup 3/P/sub 1/-/sup 3/H/sub 4/, /sup 3/P/sub 1/-/sup 3/H/sub 5/, and /sup 3/P/sub 0/-/sup 3/F/sub 2/ transitions, respectively. The temperature dependence of the fluorescence intensity was studied and the results revealed an upconversion efficiency enhancement of /spl times/3.5 in the temperature range of 20-130/spl deg/C. The behavior of the system is described by conventional rate equations for the pertinent Pr/sup 3+/-Yb/sup 3+/ energy-levels, including an effective temperature dependent absorption cross-section /spl sigma//sub d/(T)=/spl sigma//sub d//sup 0/F(T) for the Yb/sup 3+/-sensitizer, where /spl sigma//sub d//sup 0/ is the cross-section at resonance and F(T)=[exp(h/spl nu//sub phonon//k/sub B/T)-1]/sup -p/. The exponent p is the number of phonons involved in the sensitizer excitation. The population of the P/sup 3+/ excited-state emitting levels was accomplished through anti-Stokes multiphonon-assisted excitation of the Yb/sup 3+/ ions and subsequent energy-transfer to and excited-state absorption from the Pr/sup 3+/ ions.