Spectral properties and quantum efficiency of optical emission in rare earth doped crystals

Xiao-ju Wang, Shihua Huang, Jiahua Zhang, William M Yen
2006 Journal of Physics, Conference Series  
We have studied the spectral properties of Pr 3+ -doped CaAl 4 O 7 and SrAl 4 O 7 crystals at 77 and 290 K. Emissions from the 4f5d band are detected using two-photon stepwise excitation. We demonstrated a new method to conveniently measure the quantum efficiency of deep UV emission using the two-step excitation and the difference of the integrated spectral intensities. The quantum efficiencies of the emission from the lowest 4f5d state in the two systems have been estimated and are less than
more » ... % at room temperature. The effect of excited state absorption of the lowest 4f5d on the measurement of the quantum efficiency is analyzed. The actual efficiency may be higher when the effect is taken into account, especially under the condition of strong excitation. measurementdue to the excited state absorption (ESA) is discussed. The actual QEs may be higher when the ESA effect is taken into account. Experimental CAO:Pr and SAO:Pr single crystal fibers were prepared by laser heated pedestal growth method (LHPG) [6]. The concentrations of Pr 3+ is 5 at. % for CAO:Pr and 1 at. % for SAO:Pr. The trivalent rare earth ions replace divalent Ca or Sr ions in the host. 5 at. % and 1 at. % equal amount of Mg was codoped for the each sample, respectively, substituting for Al ions for charge compensation. The basic structures of both host crystals are monoclinic with space group C2/c [7]. They are transparent from 350 nm to 5 m [8]. . Experimental setup has been illustrated in Ref. 5. Pump scheme is shown in Fig. 1 . Frequency tripled YAG laser output (355 nm, 5 ns) is used to pump a three-stage dye (Coumarin 480) laser. The dye laser is tuned at 463 nm to populate 3 P 1 state, from which the electrons will quickly relax to 3 P 0 and yield strong red emissions ( 3 P 0 -3 F 2,3,4 ). Small portion of 355 nm UV output from the YAG laser is separated and optically delayed for 15 ns following the end of the dye laser pulse at the sample. The delayed UV pulses will further excite the electrons at 3 P 0 state to 4f5d band, giving strong UV emissions (4f5d-3 H J , 3 F J ) and reducing the emission intensity from 3 P 0 state. Assuming the number of electrons excited from the 3 P 0 to 4f5d band and relaxed to the lowest state of the band is n 0 and the QE of the state is 1 , the number of photons emitted from the state equals to 1 n 0 . If the QE of 3 P 0 state is 0 and branch ratios of 4f5d-3 H 4,5,6 , 3 F 2,3,4 4f5d-3 P J / 1 I 6 , and 3 P 0 -3 F 2 transitions are 1 , 1 ', and 0 , respectively, the emission intensity of 4f5d-3 H 4,5,6 , 3 F 2,3,4 , I 1 , and the decrease of 3 P 0 -3 F 2 emission due to the UV pump, I 0 , can be expressed as follows,
doi:10.1088/1742-6596/28/1/004 fatcat:xhvycvo5xra6tkmuulrkqd2ymi