Green Upconversion Luminescence Research Articles

Extremely intense pure green upconversion luminescence in Ho3+/Yb3+ co-doped BiTa7O19 phosphors under 980 nm laser excitation

Extremely intense pure green upconversion luminescence in Ho3+/Yb3+ co-doped BiTa7O19 phosphors under 980 nm laser excitation

Effect of vacuum annealing on the upconversion luminescence of β-Ba2ScAlO5: Yb3+, Ho3+ phosphor

Upconversion luminescence (UCL) materials with narrow emission peaks, long fluorescence lifetime, and large anti-Stokes shift have attracted considerable attention in biomedical, display, anti-counterfeiting, and solid-state lasers. This study presents a new synthesis method, combining air sintering and vacuum annealing, to obtain intense green UCL emission β-Ba2ScAlO5: 0.15 Yb3+, 0.005Ho3+ phosphor. After vacuum annealing, the green, red, and near-infrared emissions of Ho3+ are enhanced by factors of 40, 133, and 37, respectively. The diffuse reflectance spectra demonstrate that there is a defect energy band ranging from 330 to 860 nm in the air-treated samples, and it is reduced dramatically after vacuum annealing. This defect band covers the three wavelengths of Ho3+ emissions in the visible range and results in the reabsorption of UCL by the host lattice. X-ray Rietveld refinements and EPR spectra reveal the difference in the oxygen defects of the air-synthesized and vacuum-annealed phosphors and reflect that the absorption band is related to the oxygen defects. This research provides a new approach to obtain intense UCL emission of β-Ba2ScAlO5 hosted phosphors and offers an excellent green phosphor for application in anti-counterfeiting or displays.

Strong green up-conversion luminescence and optical thermometry of Ho3+/Yb3+ Co-doped AlN submicron towers

Rare-earth (RE) doped aluminum nitride (AlN) holds great promise for integrated optoelectronic devices. Here, the Ho and Yb co-doped AlN (AlN:Ho3+/Yb3+) submicron towers were prepared by a direct nitridation route. XRD, Raman, XPS and EDS studies showed successful doping of Ho and Yb ions into AlN. SEM images show that the submicron towers have an interesting layered structure by layer-by-layer stacking of hexagonal AlN nanosheets. Under excitation at 980 nm, AlN:Ho3+/Yb3+ submicron towers exhibit up-conversion (UC) luminescence at 540, 550, 659, and 762 nm, which are due to Ho3+/Yb3+ system from 5F4, 5S2→5I8, 5F5→5I8, and 5F4, 5S2→5I7 respectively. Based on the intensity ratio and decay lifetime of UC luminescence, the optical temperature sensing characteristics are investigated from 298 K to 548 K. The maximum relative sensitivities associated with the intensity ratio of I540, 550 and I659 and decay lifetime of 659 nm are as high as 2.73% K−1 and 0.43% K−1, respectively. This work broadens the optoelectronic properties of RE doped AlN.

Achieving Orthogonal Upconversion Luminescence of a Single Lanthanide Ion in Crystals for Optical Encryption.

Optical encryption shows great potential in meeting the growing demand for advanced anti-counterfeiting in the information age. The development of upconversion luminescence (UCL) materials capable of emitting different colors of light in response to different external stimuli holds great promise in this field. However, the effective realization of multicolor UCL materials usually requires complex structural designs. In this work, orthogonal UCL is achieved in crystals with a simple structure simply by introducing modulator Tm3+ ions to control the photon transition processes between different energy levels of activator Er3+ ions. The obtained crystals emit red and green UCL when excited by 980nm and 808nm lasers, respectively. The orthogonal excitation-emission properties of crystals are shown to be very suitable for high-level optical encryption, which is important for information security and anti-counterfeiting. This work provides an effective strategy for obtaining orthogonal UCL in simple structural materials, which will encourage researchers to further explore novel orthogonal UCL materials and their applications, and has important implications for the development of the frontier photonic upconversion fields.

High quenching concentration of the CaLuAlO4:Er3+ upconversion phosphor with short-range energy migration

Low activator concentration in upconversion phosphors has been a hindrance in improving luminescence performance. Herein, we report an Er3+ doping concentration as high as 30 at. % in the CaLuAlO4 upconversion host. The CaLuAlO4:Er3+ phosphors were prepared by the traditional high-temperature solid-state method. Under the excitation of a 980 nm laser, the optimal concentration of Er3+ approaches 30% according to the total integrated intensity of red and green upconversion luminescence. This quenching concentration is one order of magnitude higher than that in the traditional Er3+ doped upconversion polycrystals. The results obtained from first-principles calculations suggest that there are no in-plane or chain rare-earth ions in the cell. This increases the difficulty of propagating excitation energy to quench centers and is advantageous for high doping concentration. Our work can spark people's interest in the research and application of highly doped upconversion phosphors.

Molten Salt Synthesized CaTa4O11:Er3+/Yb3+ with Superior Upconversion Luminescence.

Low phonon tantalate-based phosphors with a layer structure are considered to have excellent upconversion luminescence (UCL) intensity, which could be reduced due to the existence of impure phase defects and inappropriate doped rare earth ions. To improve their UCL performance, we have prepared single-phase CaTa4O11:Er3+/Yb3+ samples by a molten salt synthesis (MSS) using KCl as the reaction medium and compared its UCL properties with counterparts made by a conventional solid-state reaction (SSR) in this study. We have demonstrated that the MSS samples have a much higher UCL intensity under 980 nm laser excitation than the SSR ones due to accurate replacement of Ca2+ sites by Er3+/Yb3+ in high-purity single-phase MSS samples. We have further enhanced the green UCL intensity of the MSS samples by 1.57 times via acid picking (AP). Under 980 nm laser excitation at a high powder density of 61.3 W/cm2, the green UCL intensity of the MSS-AP samples can reach 3.72 times that of the SSR-AP samples. For potential luminescence thermometry applications, the maximum absolute sensitivity (SA) of the MSS-AP samples reaches 0.01316 K-1 at 501 K based on the luminescence intensity ratio. This study shows that CaTa4O11:Er3+/Yb3+ phosphors prepared by the MSS method are single-phase samples with excellent pure green UCL as a suitable temperature sensing material.

Preparation and strong green upconversion luminescence of Ca9Y(VO4)7: Yb3+/Er3+ phosphor

Exploring novel oxysalt compounds remains significant due to their affordability and versatile applications, such as serving as laser crystals, piezoelectric crystals, frequency-doubling crystals, and luminescent materials. Specifically, this study introduces a new near-single green upconversion luminescent Ca9(VO4)7: Yb3+/Er3+ material, synthesized through high-temperature solid-phase methods. When subjected to 980 nm near-infrared laser irradiation, the Ca9(VO4)7: 0.3 Yb3+, 0.02 Er3+ phosphor demonstrates robust green luminescence at 531 nm (2H11/2 → 4I15/2) and 558 nm (4S3/2 → 4I15/2), accompanied by faint red luminescence at 665 nm (4F9/2 → 4I15/2). The optimal doping concentrations for Yb3+ and Er3+ ions, yielding the highest upconversion luminescence intensity, are determined to be 0.3 and 0.02, respectively. The investigation elucidates the upconversion luminescence mechanism through the downward shift spectrum in photoluminescence and the pumping power dependence of upconversion green-red luminescence. The primary excitation pathway identified for the upconversion process in Ca9Y(VO4)7: 0.3 Yb3+, 0.02 Er3+ involves Yb3+ (2F5/2) + Er3+ (4I11/2) → Yb3+ (2F7/2) + Er3+ (4F7/2). This research contributes to the exploration of new materials, injecting vitality into modern industries and production processes.

Anomalous thermal activation of green upconversion luminescence in Yb/Er/ZnGdO self-assembled microflowers for high-sensitivity temperature detection.

Non-contact optical temperature detection has shown a great promise in biological systems and microfluidics because of its outstanding spatial resolution, superior accuracy, and non-invasive nature. However, the thermal quenching of photoluminescence significantly hinders the practical applications of optical temperature probes. Herein, we report thermally enhanced green upconversion luminescence in Yb/Er/ZnGdO microflowers by a defect-assisted thermal distribution mechanism. A 1.6-fold enhancement in green emission was demonstrated as the temperature increased from 298 K to 558 K. Experimental results and dynamic analysis demonstrated that this behavior of thermally activating green upconversion luminescence originates from the emission loss compensation, which is attributed to thermally-induced energy transfer from defect levels to the green emitting level. In addition, the Yb/Er/ZnGdO microflowers can act as self-referenced radiometric optical thermometers. The ultrahigh absolute sensitivity of 1.61% K-1 and an excellent relative sensitivity of 15.5% K-1 based on the 4F9/2/2H11/2(2) level pair were synchronously achieved at room temperature. These findings provide a novel strategy for surmounting the thermal quenching luminescence, thereby greatly promoting the application of non-contact sensitive radiometric thermometers.

Strong green upconversion emission from submicron spindle-shaped SrMoO4:Yb3+,Er3.

Upconversion luminescence (UCL) is a fluorescence process where two or more lower-energy photons convert into a higher-energy photon. Lanthanide (Ln3+)-doped UCL materials often suffer from weak luminescence, especially when directly synthesized by a hydrothermal (HT) process due to the existing hydroxyl group and undesirable arrangement of dopants within host lattices which quench luminescence and limit energy transfer. Therefore, additional heat treatment processes are required to enhance their UCL emission, even though direct hydrothermal synthesis without further heat treatment has the advantages of low energy consumption, fast synthesis, and wide applicability to generate UCL materials. In this study, via a HT process without annealing, we have produced Yb3+ and Er3+ co-doped SrMoO4 submicron spindles with a strong green UCL emission which can be seen with the naked eye, which HT produced oxide-based UCL materials often fail to demonstrate. We have investigated different HT synthesis conditions, such as temperature, time, pH and dopant composition, which control the nucleation, growth, lattice structure arrangement, and ultimately their UCL properties through XRD, SEM, EDS and UCL measurements. The bright green UCL from the SrMoO4:Yb,Er submicron spindles is further enhanced by post-synthesis annealing within a molten NaNO3/KNO3 system to prevent particle size growth. The green UCL intensity from the annealed SrMoO4:Yb,Er submicron spindles surpasses samples produced by the solid-state method and is comparable to that from the commercial NaYF4:Yb,Er sample. We have further studied the temperature-dependent luminescence of both the HT-prepared and molten-salt annealed SrMoO4:Yb,Er submicron spindle samples. The strong UCL from our SrMoO4:Yb,Er submicron spindles could warrant their candidacy for bioimaging and anticounterfeiting applications.

Defective band enhance the single green upconversion luminescence of Ca9Y(VO4)7: Yb3+/Er3+ phosphors by doping with Ba2+ ions

The present work investigates the near-single green emission properties of Ba2+ doped Ca9Y(VO4)7: Yb3+/Er3+ upconversion luminescence. The Ba2+ doped Ca9Y(VO4)7: Yb3+/Er3+ phosphors were successfully synthesized via the high-temperature solid-phase method. XRD pattern analysis showed that Ca9Y(VO4)7: Yb3+/Er3+/Ba2+ was a single phase, and Ba2+ doping did not induce heterophase phase. Under 980 nm near-infrared laser irradiation, Ca9Y(VO4)7: Yb3+/Er3+/Ba2+ phosphors emit strong green luminescence (530 nm, 2H11/2→4I15/2, 557 nm, 4S3/2→4I15/2) and weak red luminescence (664 nm, 4F9/2→4I15/2). The upconversion green-red luminescence integral intensity ratio of Ca9Y(VO4)7: Yb3+/Er3+/Ba2+ phosphor is 32.1. This enhancement can be attributed to the presence of defect bands that facilitate excitation photon absorption and efficient energy transfer from abundant electrons into Yb3+ (2F5/2) and Er3+ (4I11/2) ions. More importantly, the maximum SA and SR of Ca9Y(VO4)7: Yb3+/Er3+/Ba2+ phosphor as a temperature sensor are 1.44 % K−1 (at 548 K) and 1.28 % K−1 (at 298 K), respectively.

Order-disorder phase transitions significantly improving the upconversion luminescence intensity of BiTa7O19:Er3+/Yb3+

BiTa7O19 (BTO) has two lattice structure, P–6C2 (188) ordered phase and P63/mcm (193) disordered phase. Ordered and disordered BTO:Er3+/Yb3+ upconversion phosphors (UCPs) were obtained by solid sintering with different temperatures. The lattice structure of all the samples was investigated by XRD, SEM and Raman spectroscopy, and upconversion luminescence (UCL) spectra were tested by spectrometers. The green integral UCL intensity of the disordered BTO:Er3+/Yb3+ UCP is 60.76 times than that of the ordered sample. By comparing Er3+/Yb3+ co-doped and Er3+ single-doped UCPs with different structures, it is found that the disordered structure enhances the energy transfer from Yb3+ to Er3+, which may be caused by the disordered structure reducing the distance between Yb3+ and Er3+. The absolute temperature sensitivity of the sample with the highest UCL intensity is 0.01005 K-1 at 352 K. All results suggest that the disordered structure of BTO host can greatly improve green UCL intensity and the disordered BTO:Er3+/Yb3+ UCPs are suitable for the application of optical temperature measurement.

Green upconversion luminescence of ZnO:Yb3+/Ho3+ nanophosphors prepared by various synthesis methods: Sol-gel and co-precipitation

ZnO: Yb3+/Ho3+ nanophosphors were synthesized using sol-gel and co-precipitation methods. The effects of co-doping and synthesis methods were investigated on the nanopowder's crystal structure, morphology, and optical properties. X-ray diffraction (XRD) confirmed the hexagonal wurtzite structure of the ZnO powder. The calculated crystallite sizes of the nanopowders are 30.4 nm and 21.3 nm for sol-gel and co-precipitation methods, respectively. Scanning electron microscopy (SEM) revealed that different synthesis methods and doping influence the morphology of the prepared nanophosphors. Energy dispersive X-ray spectrometer (EDS) confirmed the elemental composition and phase purity. Diffuse reflectance spectra (DRS) exhibited several absorption bands at 448 and 541 nm from sol-gel synthesized nanopowders and 453, 483, 536, and 641 nm from co-precipitation synthesized nanopowders. The energy band gap (Eg) was affected by the various methods and doping. DRS with the aid of Kubelka-Munk demonstrated that Eg ranges from 3.23 to 3.27 eV and 3.28–3.33 eV for samples prepared with sol-gel and co-precipitation method, respectively. The upconversion (UC) photoluminescence (PL) emission spectra upon excitation wavelength of 980 nm revealed two emission peaks located at 545 and 661 nm from ZnO:Yb3+/Ho3+ nanophosphors prepared by sol-gel method. These emission peaks can be attributed to 5S2/5F4 → 4I8 and 5F5 → 5I8 transitions of Ho3+ ions. The power dependence of the UC emission intensity of ZnO:Yb3+/Ho3+ was also examined. Power dependence revealed that a two-photon process was involved in the UC emissions and the possible UC mechanisms were discussed in detail. To investigate possible degradation, the stability of the UC was examined. In fact, there was no indication of phosphor UC degradation. Green emission, on the other hand, increased by about 10 % during the first 8 h of the experiment before stabilizing.

Effects of Er3+ and Yb3+ concentrations on upconversion luminescence and thermal sensing characteristics of Sc2O3:Er3+/Yb3+ phosphors

Sc2O3:Er3+(x mol%)/Yb3+(3 mol%) (x = 0.3, 0.5, 0.7) and Sc2O3:Er3+(0.5 mol%)/Yb3+(y mol%) (y = 1, 3, 5) phosphors were synthesized by CO2 laser zone-melting method. The upconversion luminescence (UCL) spectra of Sc2O3:Er3+/Yb3+ fluorescent materials, which were pumped by 980 nm, were measured and analyzed. The results show that the UCL intensity reaches maxima when doped with 0.5 mol% Er3+ and 3 mol% Yb3+, and the increase of Yb3+ concentration leads to reduce the ratio of green UCL to red UCL. The temperature-dependent UCL spectra of Sc2O3:Er3+/Yb3+ fluorescent materials with various Er3+ and Yb3+ concentrations were measured from 290 K to 1023 K, and the thermal sensing characteristics were revealed via the fluorescence intensity ratio (FIR) technique. The maximal relative sensitivity (SR) are almost independent of the Er3+ and Yb3+ concentration, while the maximal absolute sensitivity (SA) increases with Yb3+ concentration in the whole measurement range. Among the prepared samples, the maxima of SA and SR are achieved for the sample of Sc2O3:Er3+(0.5 mol%)/Yb3+(5 mol%)，with the values of 5.34 × 10−3 K−1 (364.1 K) and 12.5 × 10−3 K−1 (290 K), respectively. Interestingly, for Sc2O3:Er3+ (0.5 mol%)/Yb3+ (3 mol%), having the highest UCL intensity, its maximum SA and SR are 4.90 × 10−3 K−1 (371.4 K) and 11.2 × 10−3 K−1 (290 K). The wide temperature sensing range and relatively high sensitivities of the fabricated materials provide excellent potential for temperature sensing.

Upconversion Luminescence Response of a Single YVO4:Yb, Er Particle.

We present the results of the luminescence response studies of a single YVO4:Yb, Er particle of 1-µm size. Yttrium vanadate nanoparticles are well-known for their low sensitivity to surface quenchers in water solutions which makes them of special interest for biological applications. First, YVO4:Yb, Er nanoparticles (in the size range from 0.05 µm up to 2 µm), using the hydrothermal method, were synthesized. Nanoparticles deposited and dried on a glass surface exhibited bright green upconversion luminescence. By means of an atomic-force microscope, a 60 × 60 µm2 square of a glass surface was cleaned from any noticeable contaminants (more than 10 nm in size) and a single particle of 1-µm size was selected and placed in the middle. Confocal microscopy revealed a significant difference between the collective luminescent response of an ensemble of synthesized nanoparticles (in the form of a dry powder) and that of a single particle. In particular, a pronounced polarization of the upconversion luminescence from a single particle was observed. Luminescence dependences on the laser power are quite different for the single particle and the large ensemble of nanoparticles as well. These facts attest to the notion that upconversion properties of single particles are highly individual. This implies that to use an upconversion particle as a single sensor of the local parameters of a medium, the additional studying and calibration of its individual photophysical properties are essential.

Upconversion nanoparticle-based fluorescence resonance energy transfer sensing platform for the detection of cathepsin B activity in vitro and in vivo.

A simple fluorescence resonance energy transfer (FRET) sensing platform (termed as USP), comprised of upconversion nanoparticles (UCNPs) as the energy donor and Cy5 as the energy acceptor, has been synthesized for cathepsin B (CTSB) activity detection in vitro and in vivo. When Cy5-modified peptide substrate (peptide-Cy5) of CTSB is covalently linked on the surface of UCNPs, the FRET between the UCNPs (excitation: 980nm; emission: 541nm/655nm) and Cy5 (excitation: 645nm) leads to a reduction in the red upconversion luminescence (UCL) signal intensity of UCNPs. Cy5 can be liberated from UCNPs in the presence of CTSB through the cleavage of peptide-Cy5 by CTSB, leading to the recovery of the red UCL signal of UCNPs. Because the green UCL signal of UCNPs remains constant during the CTSB digestion, it can be considered as an internal reference. The findings demonstrate the ability of USP to detect CTSB with the linear detection ranges of 1 to 100ng·mL-1 in buffer and 2 × 103 to 1 × 105 cells in 0.2mL cell lysates. The limits of detection (LODs) are 0.30ng·mL-1 in buffer and 887 cells in 0.2mL of cell lysates (S/N = 3). The viability of USP to detect CTSB activity in tumor-bearing mice is hasfurtherbeen investigated using in vivo fluorescent imaging.

Experimental optimization design synthesis and up-conversion luminescence properties of YNbO4:Ho3+/Yb3+

In order to obtain the maximum green up-conversion luminescence intensity of Ho3+/Yb3+ co-doped YNbO4, a uniform design and a quadratic general rotation combination design were applied to optimize the doping concentration. The concentration of the rare earth corresponding to the strongest green luminescence intensity was determined to be 10% Ho3+/34.9% Yb3+. Maximum luminous intensity of green light tested under 980 nm excitation was 157373.266, which was close to the theoretical calculated integral intensity value of 157290.825. The variation of the up-conversion luminescence spectra at different power density of the 980 nm laser was characterized. According to the formula fitting, the up-conversion luminescence process is a two-photon process. Meanwhile, the temperature sensing characteristic of the samples has been discussed. Finally, the CIE coordinates were analyzed and calculated to be (0.297, 0.692).

Enzyme-trigger ratiometric fluorescent nanoplatform for diagnosis and imaging of oral diseases

Oral health is an essential part of overall health. Matrix metalloproteinase-2 (MMP-2) is a potential biomarker for diseases. The ability to accurately detect MMP-2 in vivo and in vitro is of great importance for the early diagnosis and prognosis, as well as the treatment evaluation, of oral diseases. In this study, cyanine 3 (Cy3) polypeptide containing the specific peptide substrate (PLGVR) of MMP-2 was modified onto SiO2-coated upconversion nanoparticles to fabricate a fluorescence resonance energy transfer (FRET)-based ratiometric fluorescent nanoplatform (UCNPs@SiO2@Cy3-pep). The green upconversion luminescence of UCNPs@SiO2 is quenched by Cy3, while its red upconversion luminescence is undisturbed. After Cy3 is cleaved at the PLGVR peptide by MMP-2, it is detached from the surface of UCNPs@SiO2, resulting in the recovery of green luminescence. Based on this principle, we applied UCNPs@SiO2@Cy3-pep to detect MMP-2 activity in different oral disease samples and models. We found that the level of MMP-2 in saliva of patients with oral cancer was 10 times higher than that of healthy individuals. In addition, the MMP-2 level in patients with periodontitis and severe dental caries also increased to varying degrees compared with that in healthy patients. Finally, in vitro and in vivo imaging experiments revealed that the nanoplatform was effective in monitoring MMP-2 level. Together, the developed nanoplatform can be an ideal tool for medical diagnosis of MMP-2-related diseases.

Ratiometric upconversion nanoprobes for turn-on fluorescent detection of hypochlorous acid

Ratiometric fluorescent nanoprobes have been developed for the detection of hypochlorous acid (HOCl) by simply mixing upconversion nanocrystals (UCNCs) with plasmocorinth B (PB) dye molecules, where UCNCs are adopted as the energy donor and dye molecules are introduced as the energy acceptor. Specifically, green upconversion luminescence (UCL) emission of UCNCs can be effectively quenched by PB, resulting from the spectral overlap between the absorption of PB and UCL emission of UCNCs in the green region. Furthermore, owing to the electrostatic repulsion between negatively charged UCNCs and PB dye molecules, the fluorescence quenching mechanism is based on the IFE process. Upon interaction with HOCl, PB dye molecules degrade, resulting in the recovery of green UCL emission through inhibition of the IFE process. The red UCL emission, however, remains unchanged. Therefore, the red UCL emission is employed as an internal reference signal for the ratiometric detection of HOCl. The detection limit of the nanoprobe for HOCl is quantified to be 1.12 µM, which is much lower than that of colorimetric detection. Moreover, the developed sensor has been successfully applied for quantitative monitoring of HOCl in tap water.

Abnormal upconversion luminescence induced by defects and Er3+–Yb3+ distance change in Cs3GdGe3O9:Er3+/Yb3+ phosphors

AbstractA series of Er3+/Yb3+ co‐doped Cs3GdGe3O9 (CGG) phosphors were prepared by solid‐phase sintering method, and the microstructure and upconversion luminescence (UCL) properties were tested by variable‐temperature X‐ray diffractometry and variable‐temperature spectrometer. Abnormal UCL phenomena were found, which include UCL intensity continuously increasing under 980 nm laser continuous irradiation and UCL thermal enhancement. After 10 min of continuous irradiation by 980 nm laser at 513 K, the UCL intensity increased 2.91 times compared with the initial UCL intensity. The phenomenon is due to the electron releasing of host defects. The green UCL intensity of CGG:0.1Er3+/0.2Yb3+ decreases at 303–423 K and increases at 423–723 K, which reaches 13.23 times compared with that at 423 K. The phenomenon is due to Er3+–Yb3+ distance change by temperature and phonon‐assisted transitions. In addition, the absolute temperature sensitivities of samples are calculated by luminescence intensity ratio technology, the maximum absolute sensitivity of CGG:0.1Er3+/0.4Yb3+ is 0.00691 K−1 at 546 K, and the maximum relative sensitivity of CGG:0.1Er3+/0.1Yb3+ is 0.01224 K−1 at 303 K. These results indicate that CGG:Er3+/Yb3+ phosphors can be used as a high‐temperature optical thermometer.

Synthesis and luminescence properties of Er3+-Yb3+ doped glass ceramics with tridymite structure

By melt annealing technique, Er3+-Yb3+ co-doped precursor glass (PG) was prepared. Glass ceramics (GCs) containing KZnPO4 crystal phase with tridymite structure were obtained by heat treatment of PG. The optimum heat treatment conditions of GCs are 670 °C for 60 min. Under these conditions, the average grain size of GC is about 205 nm, and the light transmittance in the visible region is about 80%. Through the analysis of the Rietveld refinement results of XRD, the lattice constants a and b of KZnPO4 crystal decreased from 18.155 Å to 18.109 Å, and c decreased from 8.504 Å to 8.451 Å. Therefore, it is inferred that Er3+ and Yb3+ replace the Zn2+ in the lattice. The green up-conversion luminescence of GC is about 10 times that of PG excited by 980 nm laser. The optimal doping concentrations of Er3+ and Yb3+ in GCs are 0.5% and 1.0%, respectively. The calculation results of chromaticity coordinates show that Er3+-Yb3+ co-doped GCs with KZnPO4 crystal phase is a promising green up-conversion luminescent material.