Ultraviolet luminescence of ScPO₄, AlPO₄and GaPO₄crystals

Abstract

The luminescence of self-trapped excitons (STEs) was previously observed and described for the case of tetragonal-symmetry ScPO4 single crystals. The subject band in this material is situated in the UV spectral range of ∼210 nm or ∼5.8 eV. In the present work, we are both expanding this earlier luminescence study and seeking to identify similar luminescence phenomena in other orthophosphate crystals, i.e., AlPO4 and GaPO4. These efforts have proven to be successful--in spite of the structural differences between these materials and ScPO4. Specifically we have found that for AlPO4 and GaPO4, in addition to an α-quartz-like STE, there is a UV luminescence band that is similar in position and decay properties to that of ScPO4 crystals. Potentially this represents an STE in AlPO4 and GaPO4 crystals that is analogous to the STE of ScPO4 and other orthophosphates. The decay kinetics of the UV luminescence of ScPO4 was studied over a wide temperature range from 8 to 300 K, and they exhibited some unusual decay characteristics when subjected to pulses from an F2 excimer laser (157 nm). These features could be ascribed to a triplet state of the STE that is split in a zero magnetic field. A fast decay of the STE was detected as well, and therefore, we conclude that, in addition to the slow luminescence corresponding to a transition from the triplet state, there are singlet-singlet transitions of the STE. Time-resolved spectra of the slow and fast decay exhibit a small shift (∼0.15 eV) indicating that the singlet-triplet splitting is small and the corresponding wavefunction of the STE is widely distributed over the atoms of the ScPO4 crystal where the STE is created.

Luminescence of phosphorus containing oxide materials: Crystalline SiO2‐P and 3P2O5⋅7SiO2; CaO⋅P2O5; SrO⋅P2O5 glasses

“…The triplet state of STE is split in zero magnetic fields [5,6]. The singlet-triplet splitting of STE is about 0.15 eV, small this given that corresponding wave function is spread in the space, with electron component on Sc ions and hole component on PO 4 complex [7]. Actually we had found similar properties of UV luminescence in studied objects.…”

Luminescence of phosphorus doped silica glass

“…Previously we had observed the UV band in different phosphate crystals and glasses (see e.g. [2,3]). The UV band decay kinet-ics is fast (~30 ns), whereas there is also a slower component in the μs range of time.…”

“…Analyses of literature related to the luminescence of different mate-rials with phosphorus (e.g. [2,3]. show that the common luminescence property of these materials is the observation of a UV band.…”

“…Thus, in ScPO4 zircon-type crystal the band at 5.7 eV is interpreted as self-trapped exciton (STE) of this crystal [2]. AlPO4 and GaPO4, both with structure of α-quartz, give rise to the UV bands situated at 5.83 eV and 5.65 eV respectively, and are thus interpreted as the second STE related to orthophosphate ions [2]. The first STE is similar to that of α-quartz, which band is situated in the visible range of the spectrum.…”

Luminescence in external dopant-free scandium-phosphorus vanadate solid solution: a spectroscopic and theoretical investigation

“…Besides, in principle, since the number of Sc ions in the asexpected solid solutions is fixed, a regular change of the crystal lattice cell with the larger V 5+ ions (i.e., 0.495 Å at four oxygen coordination numbers (CN)) being gradually replaced by the smaller P 5+ (i.e., 0.31 Å at CN = 4) [34][35][36] can therefore be expected further. In this case, when taken into account the emission positions of bulk ScVO 4 (i.e., 465 nm, 25,33 20.7 Â 10 3 cm À3 (blue-green) 32 ) and ScPO 4 (i.e., 430 nm (blue) under a moist atmosphere, 32 or B210 nm (UV, 5.6-5.9 eV) under dry conditions 37,38 ), varying the V/P ratios in the as-expected Sc(P x ,V 1Àx )O 4 solid solutions may lead to spectral tuning. Meanwhile, due to the lattice microenvironment modification that results from the radii matching between the V 5+ and P 5+ ions, there may exist some unexpected PL properties.…”