Preparation and spectral properties of blue-to-UVB upconverting Y2O3:RE3+,Gd3+ (RE = Er, Ho) micro-/nano-phosphors

Abstract

Phototherapeutic applications gain more and more interests and require fundamental progresses in interdisciplinarity research, particularly a novel topical phototherapy using ultraviolet-B (UVB, ∼310 nm) upconverting phosphors. In this study, three synthesis methods with (out) sintering processes were implemented to obtain micro-/nano-size Y2O3:RE3+/Gd3+ (RE = Er, Ho) particles using RE oxides (RE2O3), RE-nitrates (RE (NO3)3) and RE-chlorides (RECl3) as starting materials. Pumped by an OPO laser at wavelengths of 450 and/or 490 nm, blue-to-UVB upconversion with narrowband peak at 313 nm was effectively realized for all the Y2O3:RE3+/Gd3+ powder phosphors. On basis of theoretical speculations and experimental data, a two-photon absorption process was proposed for the UVB upconversion of Y2O3:RE3+/Gd3+. Moreover, the involved energy transfer (ET) from RE3+ to Gd3+, its back ET mechanisms as well as cross-relaxation between RE3+ (RE = Er, Ho) ions were systematically treated versus the Er3+- or Ho3+-, and Gd3+-doping concentration. Note that the UVB upconversion intensity will decline severely as the particles become smaller to submicron and nanoscale, likely due to an increasing surface-to-volume ratio along with more surface defects appearance. All these results would greatly promote the development of novel blue-to-UVB upconverting materials, and their potential applications in topical phototherapy irradiated by blue light source.