Thermally stable photoluminescence and long persistent luminescence of Ca3Ga4O9:Tb3+/Zn2+☆
Graphical abstract
(a) The temperature dependent emission spectra of the Tb3+/Zn2+ co-doped sample; (b) The lifetime curves of the Tb3+/Zn2+ co-doped sample at different temperatures after being irradiated for 15 min with UV lamp.
Introduction
As typical optical-storage materials, long persistent luminescence (LPL) phosphors can store charge carriers (electrons and holes) under the excitation at UV or sunlight and then subsequently release at room temperature (∼25–27 °C), owing to the suitable trapping depth. They have attracted extensive attention in multiple fields because of their broad applications, such as safety signage, night-vision surveillance, and decoration.1, 2, 3, 4, 5, 6, 7, 8 Especially, after the SrAl2O4:Eu2+/Dy3+ phosphor was discovered in 1996, the enthusiasm of the researchers has been greatly stimulated.9, 10 However, the process in developing excellent LPL phosphors is quite tortuous due to the lack of effective strategy. Up to now, the trial and error method is still dominant,11, 12 which leads to much consumption in the time. Hence, the use of more effective methods is necessary and meaningful. Because the LPL property is strictly dependent on the generation of suitable traps, simplifying the design with self-activated LPL phosphor as a matrix to effectively realize LPL property seems feasible and meaningful. Recently, alkaline earth metal gallate compounds have received great attention because of low synthesis temperature and high stability.13 Besides, such compounds tend to exhibit self-activated LPL behavior owing to their special structure and semiconducting properties.14 Hence, alkaline earth metal gallate compounds are definitely ideal candidates as LPL phosphor matrix.
Moreover, considering the high sensitivity of the human eye to green light,15 the development of green LPPs is exceedingly meaningful for practical applications. As a rare earth ion, Tb3+ usually presents excellent green luminescence due to the 4f inter-transition 5D4→7FJ (J = 6, 5, 4, 3).16, 17, 18 More importantly, the radius and ionization potential of Tb3+ are also appropriate for matching the alkaline earth metal ions. It implies that Tb3+ is easily introduced into the lattice to replace alkaline earth ions and create more ample traps.19, 20, 21 For alkaline earth gallate compounds, Ga3+ sites are also often replaced by doping ions with similar radii as luminescent centers or trap centers.22, 23 Zn2+ is adjacent to Ga3+ in the periodic table, which means that they have similar ion radii. And, Zn2+ has a lower ionization potential than Ga3+ ions, which also means that it may further stabilize the traps in the phosphor.
In this research, we selected an alkaline earth metal gallate compound (Ca3Ga4O9) as a matrix. As expected, the matrix shows self-activated LPL behavior related to three intrinsic lattice defects. Then, Tb3+ and Zn2+ were introduced to replace the Ca2+ and Ga3+ sites, respectively. The influence of doping ions on optical properties and traps is discussed. Because of the existence of a successive trap distribution, the thermally stable photoluminescence (PL) and high-temperature-resistance LPL are presented in Ca3Ga4O9:Tb3+/Zn2+. These results refer that this phosphor could provide potential application in a rigorous environment with a high thermal energy than the room temperature, such as in vivo-imaging.
Section snippets
Experimental
Self-activated LPL phosphor (Ca3Ga4O9) and a series of Ca3Ga4O9:Tb3+/Zn2+ phosphors were synthesized through the high-temperature solid–state reaction method. The starting materials are CaCO3 (99.99%), Ga2O3 (99.99%), Tb2O3 (99.99%), and ZnO (99.99%). The starting materials with stoichiometric amounts were mixed thoroughly in an agate mortar by grinding and subsequently sintering at 1210 °C for 10 h in air atmosphere. Finally, the samples were naturally cooled to room temperature in the
Results and discussion
Fig. 1(a) showed the X-ray diffraction patterns of the representative samples of pure Ca3Ga4O9, Ca3Ga4O9:Tb3+, Ca3Ga4O9:Zn2+, and Ca3Ga4O9:Tb3+/Zn2+, which were in good agreement with the reported Ca3Ga4O9 phase (JCPDS No. 26-178). No additional peaks were detected in the compositions, indicating that all samples are of a single phase and all doping ions are incorporated in the Ca3Ga4O9 host. As shown in Fig. 1(b), Ca3Ga4O9 possesses an orthorhombic phase with a space group Cmm2. In the Ca3Ga4O9
Conclusions
The LPL properties of the Ca3Ga4O9 host matrix were investigated, which are related to the existence of the and . When Tb3+ is doped, the dominate emission center changes from Ga3+ to Tb3+ in the PL and LPL processes, resulting in the variety of corresponding emitting color from blue to green. TL spectra show that the introduction of Tb3+ not only significantly increases the number of intrinsic , but also create a new trap (). On the other hand, Zn2+ exhibits the ability to
References (40)
- et al.
A brief review on red to near-infrared persistent luminescence in transition-metal-activated phosphors
Opt Mater
(2014) - et al.
Preparation and luminescence properties of rare-earth doped fiber with spectral blue-shift: SrAl2O4:Eu2+,Dy3+ phosphors/triarylsulfonium hexafluoroantimonate based on polypropylene substrate
J Rare Earths
(2017) - et al.
Novel flux-assisted synthesis for enhanced afterglow properties of (Ca, Zn)TiO3:Pr3+ phosphor
J Alloys Compd
(2017) - et al.
Li C, Wang XJ, Mu ZF. Recent progress in Eu2+-activated phosphate persistent phosphors
Opt Mater
(2014) - et al.
Luminescence properties and energy transfer investigations of Zn2P2O7:Ce3+,Tb3+ phosphor
J Lumin
(2015) - et al.
Photoluminescence and afterglow behavior of Tb3+ activated Li2SrSiO4 phosphor
J Lumin
(2017) - et al.
High thermal stability and quantum yields of green-emitting Sr3Gd2(Si3O9)2:Tb3+ phosphor by co-doping Ce3+
J Rare Earths
(2017) - et al.
Luminescent properties of Tb3+-doped Ca2SnO4 phosphor
J Lumin
(2013) - et al.
White-blue long persistent luminescence in Ca2Ge7O16:Tb3+ via persistent energy transfer
Ceram Int
(2015) - et al.
Effect of A-site cation nonstoichiometry on the properties of doped lanthanum gallate
Solid State Ion
(1998)
Relaxation of ultraviolet-radiation-induced structure and long-lasting phosphorescence in Eu2+-doped strontium aluminosilicate glasses
J Mater Res
Effects of oxygen vacancies on luminescent properties of green long-lasting phosphorescent (LLP) material α-Zn3(PO4)2:Mn2+,K+
J Lumin
Some properties of zinc sulfide activated with copper and cobalt
J Electrochem Soc
Persistent luminescence in Eu2+-doped compounds: a review
Materials
Persistent luminescence in non-Eu2+-doped compounds: a review
Materials
Long persistent phosphors—from fundamentals to applications
Chem Soc Rev
Ce3+/Pr3+:YAGG: a long persistent phosphor activated by blue-light
J Am Ceram Soc
Lu2CaMg2 (Si1−xGex)3O12:Ce3+ solid-solution phosphors: bandgap engineering for blue-light activated afterglow applicable to AC-LED
J Mater Chem C
Color-tunable persistent luminescence in oxyfluoride glass and glass ceramic containing Mn2+:α-Zn2SiO4 nanocrystals
J Mater Chem C
A new long phosphorescent phosphor with high brightness, SrAl2O4:Eu2+,Dy3+
J Electrochem Soc
Cited by (29)
Structural, optical, elemental and photometric properties of Sm<sup>3+</sup> activated Ca<inf>3</inf>Ga<inf>4</inf>O<inf>9</inf> oxide phosphors for WLEDs
2023, Colloids and Surfaces A: Physicochemical and Engineering Aspects
- ☆
Foundation item: Project supported by the National Natural Science Foundation of China (11774138), the Society Development Foundation of Yunnan Province (2016FA021) and the Kunming University of Science and Technology (KKSY201632046).