Pressure-sensitive Ce3+ photoluminescence in LiCaY5(BO3)6: high internal quantum yields and energy transfer to Tb3+

Abstract

Ce³⁺ photoluminescence (PL) has attracted attention because spin- and parity-allowed 4f-5d transition ensures brightness, and the susceptibility of the energy level of 5d electrons to the surroundings endow variable emission colors by chemical substitution or physical compression. The PL excitation spectra of LiCaY₅(BO₃)₆: xCe³⁺ (0.01 ≤ x ≤ 0.15) exhibit four typical excitation bands covering a wide range from 220 to 380 nm, and LiCa(Y_0.99Ce_0.01)₅(BO₃)₆ emits a strong blue light with an internal quantum yield (IQY) of 51%. With an efficient and probably timely energy transfer, co-doping 20% Tb³⁺ leads to an enhancement of the overall IQY to 89%. Blue and green emissions can be obtained by fabricating LiCa(Y_0.99Ce_0.01)₅(BO₃)₆ and LiCa(Y_0.79Ce_0.01Tb_0.2)₅(BO₃)₆ with a 310 nm LED chip, respectively. In situ high-temperature photoluminescence spectra for co-doped phosphors exhibit 58% in total emission intensity at 423 K. Most interestingly, the Ce³⁺ PL emission of LiCa(Y_0.99Ce_0.01)₅(BO₃)₆ is highly sensitive to applied high pressures, for example, the maximal wavelength of the emission band exhibits a linear red-shift (∼43 nm) up to 20.1 GPa, with a susceptibility dλ_max/dP = 2.05 nm/GPa. Along with the increase in high pressure, the CIE coordinate can be adjusted from (0.195, 0.124) to (0.255, 0.305) under the excitation of 375 nm. These observations suggest its potential application in an optical pressure sensor.