Low-temperature recombination luminescence of La-doped Ca2_2SnO4_4

Low-temperature ultraviolet-excited photoluminescence (PL) and recombination luminescence (RL) properties of La-doped Ca$_2$SnO$_4$ have been investigated by luminescence, electron paramagnetic resonance (EPR) and optically-detected magnetic resonance (ODMR) techniques. Two PL and RL bands at 340 nm and 450 nm have been observed. PL excitation spectra measurements with a synchrotron source showed a significant difference between the 450 nm and the 340 nm PL bands. The 450 nm band has a long-lasting hyperbolic decay, while the 350 nm band shows a fast decay. Assuming an excitonic nature of the 340 nm band, the band gap of the Ca$_2$SnO$_4$:La has been estimated to be approximately 5.5 eV. ODMR measurements suggest that the low-temperature RL band at 450 nm is caused by tunnelling recombination of electron trap and hole trap centres, and the recombination energy is transferred to Sn$^{2+}$ luminescence centres

Angular Dependence of Recombination Luminescence-Detected EPR in a ZnO Crystal

Angular dependency of electron paramagnetic resonance, optically detected by UV-excited recombination luminescence (RL-EPR), was measured for nominally pure ZnO single crystals. Observed magnetic resonances belong to the broad yellow RL band with slow decay centred at 610 nm, which is characteristic of untreated ZnO crystals. In the sample, irradiated with the 266 nm UV laser, an additional RL band centred at 740 nm appears, which has considerably faster decay time than the yellow one. This RL band is characteristic of the luminescence of Fe³⁺ ions in the ZnO crystals. It could be observed only after the UV laser treatment. No RL-EPR signal was detected for this RL band. Our spectral simulations show that the observed angular dependences of the RL-EPR spectra can be described considering a simultaneous contribution from two types of deep acceptor centres, i.e. Li<inf>Zn</inf> and a zinc vacancy, V<inf>Zn</inf>