Structure and optical properties of Lu <inf>2</inf>SiO <inf>5</inf>:Ce phosphor thin films

Luminescent, cerium doped Lu 2SiO 5 thin films with C2/c symmetry have been prepared by pulsed laser deposition (PLD) at temperatures much lower than the crystallization temperature (2150°C) of the corresponding bulk crystals. The PLD grown films show the typical luminescence resulting from the Ce 3+ 5d-4f transition. Maximum luminescence efficiency was observed for films prepared at an oxygen partial pressure of 200 mTorr at 600°C. These conditions reflect a balance between Ce 4+/Ce 3+ interconversion and the crystalline quality of the films. The results indicate that PLD offers a low temperature deposition technique for complex oxide phosphor materials. © 2006 American Institute of Physics

Luminescent properties and reduced dimensional behavior of hydrothermally prepared Y <inf>2</inf>SiO <inf>5</inf>: Ce nanophosphors

Hydrothermally prepared nanophosphor Y2 Si O5: Ce crystallizes in the P 21 c structure, rather than the B2b structure observed in bulk material. Relative to bulk powder, nanophosphors of particle size ∼25-100 nm diameter exhibit redshifts of the photoluminescence excitation and emission spectra, reduced self absorption, enhanced light output, and medium-dependent radiative lifetime. Photoluminescence data are consistent with reduced symmetry of the P 21 c structure and are not necessarily related to reduced dimensionality of the nanophosphor. In contrast, medium-dependent lifetime and enhanced light output are attributed to nanoscale behavior. Perturbation of the Ce ion electric field is responsible for the variable lifetime. © 2006 American Institute of Physics

Effects of ion beam irradiation on self-trapped defects in single-crystal Lu<inf>2</inf>SiO<inf>5</inf>

Ion irradiation effects on emission bands related to self-trapped defects in Czochralski-grown Lu2SiO5 (LSO) crystals has been investigated. Irradiation was carried out using 53 keV He+ and 40 keV H+ beams with doses of 1 and 2×1016 atoms/cm2, respectively, at room temperature. Post-irradiation radioluminescence measurements were carried out in the 5-300 K temperature range using Mo-target X-ray excitation. Two emission bands were observed at 256 and 315 nm and assigned to self-trapped excitons (STE) and self-trapped holes (STH), respectively. The intensity of the bands was determined by the ballistic damage induced by irradiation, and no effects due to the chemical nature of implanted species were observed. Thermal-quenching activation energies of these defects as a function of irradiation conditions were extracted by applying the Mott-Seitz two-level model. Each band presents strikingly different behavior following irradiation; activation energy of the STH increases two-fold whereas the STE decreases three-fold. The results indicate a major role of surface effects on the radioluminescence of LSO. For comparative purposes, irradiated Lu2O3 was also investigated. © 2006 Elsevier B.V. All rights reserved

The central role of oxygen on H⁺-irradiated Lu<inf>2</inf>SiO<inf>5</inf> luminescence

The behavior of self-trapped defects (STDs) in ion-beam irradiated Lu2SiO5 (LSO) crystal has been investigated via temperature-dependent radioluminescence (RL) measurements. Production of oxygen vacancies is the major effect of H+ irradiation on luminescencent properties of this phosphor. Luminescence centers for self-trapped exciton (STE) and self-trapped hole emission are assigned to oxygen vacancies and oxygen ions, respectively. Ion-induced structural damage modifies the thermal stability of the STDs and creates perturbed STEs. A striking effect of ion irradiation is the approximate factor-of-two enhancement of STE RL intensity that results from implantation of only a thin (∼250 nm) surface layer of LSO. This enhancement is attributed to ion-beam modification of a surface dead layer. © 2006 Elsevier B.V. All rights reserved