Wavelength converting material for a light emitting device

A wavelength converting material comprising R3-x-y-zAx+yMzSi6-w1Alw1O3x+y+w1N11-7x/3-y-w1□2-2x/3,

• the wavelength converting material comprising a crystal lattice;
• □ representing a vacancy in the crystal lattice;
• 0<x≤3;
• −3≤y<3;
• 0<z<1;
• 0≤w1≤6;
• 0≤x+y, x+y+z≤3;
• 11−7/3x−y−w1≥0;
• 3x+y+w1≤13;
• R is selected from a group trivalent La, Gd, Tb, Y, and Lu;
• A is selected from a group bivalent Ca, Mg, Sr, Ba, and Eu;
• M is selected from a group trivalent Ce, Pr and Sm;
• at least one of the vacancies □ occupied by an O atom,
• [La]>0,
• [Ca]>0,
• 0≤[Eu]≤0.01, and
• ([La]+[Ca]+[Ce]+[Eu])/[Si]≤0.52.